Edexcel Combined Science: Biology — Recall & Retrieval

1.1 Explain how the sub-cellular structures of eukaryotic and prokaryotic cells are related to their functions, including: a animal cells – nucleus, cell membrane, mitochondria and ribosomes b plant cells – nucleus, cell membrane, cell wall, chloroplasts, mitochondria, vacuole and ribosomes c bacteria – chromosomal DNA, plasmid DNA, cell membrane, ribosomes and flagella

1.

How does the nucleus control the activities of an animal or plant cell?

The nucleus contains genetic material that controls the activities of the cell.

2.

How are mitochondria adapted for their role in releasing energy by aerobic respiration?

Mitochondria are adapted for aerobic respiration, providing a large surface area for the reactions that release energy.

3.

How do ribosomes contribute to the function of animal, plant and bacterial cells?

Ribosomes are the site of protein synthesis.

4.

How are chloroplasts adapted for photosynthesis in plant cells?

Chloroplasts contain chlorophyll, which absorbs light energy for photosynthesis.

5.

How do the cell wall and vacuole help a plant cell maintain its shape?

The cell wall supports the cell, while the vacuole contains cell sap and helps maintain turgor pressure.

6.

How do chromosomal DNA, plasmid DNA, the cell membrane, ribosomes and flagella contribute to the functions of a bacterial cell?

Chromosomal DNA contains the main genetic information; plasmid DNA contains additional genes; the cell membrane controls movement of substances; ribosomes synthesise proteins; flagella allow movement.

1.2 Describe how specialised cells are adapted to their function, including: a sperm cells – acrosome, haploid nucleus, mitochondria and tail b egg cells – nutrients in the cytoplasm, haploid nucleus and changes in the cell membrane after fertilisation c ciliated epithelial cells

1.

How is the acrosome of a sperm cell adapted for fertilisation?

The acrosome contains enzymes that digest the egg cell membrane, allowing the sperm to enter.

2.

Why does a sperm cell contain a haploid nucleus?

A sperm cell contains a haploid nucleus so that fertilisation restores the diploid chromosome number.

3.

How are the mitochondria and tail of a sperm cell adapted for reaching an egg cell?

Mitochondria provide energy for movement, while the tail propels the sperm towards the egg.

4.

How are nutrients in the cytoplasm and the haploid nucleus of an egg cell adapted for its function?

Nutrients provide an energy source for the developing embryo, while the haploid nucleus contains half the genetic information needed by the offspring.

5.

How does the cell membrane of an egg cell change after fertilisation?

The membrane changes so that no more sperm cells can enter the egg.

6.

How are ciliated epithelial cells adapted to move substances along the surface of tissues?

Ciliated epithelial cells have cilia that beat to move substances such as mucus along the surface of tissues.

1.3 Explain how changes in microscope technology, including electron microscopy, have enabled us to see cell structures and organelles with more clarity and detail than in the past and increased our understanding of the role of sub-cellular structures

1.

How has microscope technology improved our ability to study cells?

Improvements in microscope technology have increased magnification and resolution, allowing smaller structures to be observed in greater detail.

2.

Why can electron microscopes show greater detail than light microscopes?

Electron microscopes have a much higher resolution than light microscopes.

3.

How has electron microscopy increased our understanding of sub-cellular structures?

Electron microscopy has allowed scientists to observe smaller sub-cellular structures and understand their functions in greater detail.

4.

Why can electron microscopes be used to observe structures that are too small to resolve clearly with a light microscope?

Electron microscopes have a higher resolution, allowing structures that are close together to be distinguished.

5.

How has increased resolution helped scientists understand the functions of cell organelles?

Increased resolution has allowed scientists to identify the detailed structures of organelles and relate their structures to their functions.

6.

What is the relationship between the resolution of a microscope and the detail that can be observed in cells?

Higher resolution allows smaller structures and greater detail to be observed.

1.4 Demonstrate an understanding of number, size and scale, including the use of estimations and explain when they should be used

1.

Why are estimations useful when measuring biological structures?

Estimations are useful when an exact measurement is difficult or unnecessary.

2.

When should an estimate be used instead of an exact measurement in biology?

An estimate should be used when an exact measurement cannot be obtained reliably or when an approximate value is sufficient.

3.

How can the size of a biological structure be estimated from a microscope image?

The scale of the image can be used to compare the structure with a known size and estimate its actual size.

4.

Why is it important to consider the scale of a biological structure when interpreting an image?

The scale allows the actual size of the structure to be interpreted correctly.

5.

How can an order-of-magnitude estimate be used to check whether a calculated biological measurement is reasonable?

An order-of-magnitude estimate gives an approximate power of ten and can be compared with the calculated value.

6.

Why should calculated values for biological structures be checked against their expected size?

Checking against the expected size can identify errors in calculations or unit conversions.

1.5 Demonstrate an understanding of the relationship between quantitative units in relation to cells, including: a milli (10−3) b micro (10−6) c nano (10−9) d pico (10−12) e calculations with numbers written in standard form

1.

What does the prefix milli mean in powers of ten?

Milli represents 10−3.

2.

What does the prefix micro mean in powers of ten?

Micro represents 10−6.

3.

What does the prefix nano mean in powers of ten?

Nano represents 10−9.

4.

What does the prefix pico mean in powers of ten?

Pico represents 10−12.

5.

How many micrometres are there in one millimetre?

There are 1000 micrometres in one millimetre.

6.

How can numbers written in standard form be multiplied or divided when calculating biological measurements?

Multiply or divide the numbers and separately apply the powers of ten.

1.6 Core Practical: Investigate biological specimens using microscopes, including magnification calculations and labelled scientific drawings from observations

1.

How is the magnification of a biological specimen calculated from its image size and actual size?

Magnification = image size ÷ actual size.

2.

What equation is used to calculate magnification when the image size and actual size are known?

Magnification = image size ÷ actual size.

3.

Why must the units of image size and actual size be the same when calculating magnification?

The units must be the same so that the ratio between image size and actual size is correct.

4.

What features should be included in a labelled scientific drawing of a biological specimen?

A scientific drawing should show clear outlines, accurate proportions, appropriate detail and labels with straight label lines.

5.

Why should scientific drawings use clear single lines rather than artistic shading?

Clear single lines show the observed structures accurately without adding features that were not observed.

6.

How can observations from a microscope be used to produce an accurate labelled scientific drawing?

Observe the specimen carefully, draw the structures using clear lines and accurate proportions, and add appropriate labels.

1.7 Explain the mechanism of enzyme action including the active site and enzyme specificity

1.

What is the active site of an enzyme?

The active site is the region of an enzyme where the substrate binds.

2.

How does a substrate interact with the active site of an enzyme?

The substrate binds to the active site and forms an enzyme-substrate complex.

3.

Why is an enzyme specific to a particular substrate?

An enzyme is specific because its active site has a particular shape that is complementary to its substrate.

4.

How does the shape of an enzyme's active site determine which substrate can bind?

Only a substrate with a complementary shape can bind effectively to the active site.

5.

What happens when an enzyme-substrate complex forms?

An enzyme-substrate complex forms when the substrate binds to the active site.

6.

How does enzyme specificity allow enzymes to catalyse particular reactions?

Enzyme specificity ensures that enzymes only catalyse particular reactions involving complementary substrates.

1.8 Explain how enzymes can be denatured due to changes in the shape of the active site

1.

What does it mean when an enzyme is denatured?

A denatured enzyme has had its active-site shape changed so that it can no longer function effectively.

2.

How can a change in temperature cause an enzyme to become denatured?

High temperatures can break bonds holding the enzyme's structure together, changing the shape of the active site.

3.

How can an extreme pH cause an enzyme to become denatured?

Extreme pH can alter bonds in the enzyme, changing the shape of the active site.

4.

What happens to the active site when an enzyme is denatured?

The active site changes shape.

5.

Why can a denatured enzyme no longer bind effectively to its substrate?

The substrate is no longer complementary to the active site and cannot bind effectively.

6.

Why is enzyme denaturation usually irreversible?

The changes to the enzyme's structure are usually permanent, so the original active-site shape cannot be restored.

1.9 Explain the effects of temperature, substrate concentration and pH on enzyme activity

1.

How does increasing temperature affect enzyme activity up to the optimum temperature?

Enzyme activity increases as temperature increases up to the optimum because particles have more kinetic energy and collide more frequently.

2.

Why does enzyme activity decrease rapidly above the optimum temperature?

High temperatures denature the enzyme, changing the shape of its active site.

3.

How does increasing substrate concentration affect enzyme activity when enzyme concentration is fixed?

Increasing substrate concentration increases the rate because more enzyme-substrate complexes can form, until the enzymes become saturated.

4.

Why does enzyme activity eventually stop increasing when substrate concentration continues to increase?

All active sites become occupied, so increasing substrate concentration further cannot increase the rate.

5.

How does pH affect the activity of an enzyme?

Changes in pH can alter the shape of an enzyme's active site and therefore affect its activity.

6.

Why does each enzyme have an optimum pH?

Different enzymes have different structures and therefore different pH conditions at which their active sites work most effectively.

1.10 Core Practical: Investigate the effect of pH on enzyme activity

1.

How can the effect of pH on enzyme activity be investigated experimentally?

Use the same concentration and volume of enzyme and substrate, vary the pH using buffer solutions, and measure the rate of reaction at each pH.

2.

What variable should be changed when investigating the effect of pH on enzyme activity?

The pH should be changed.

3.

What measurements could be taken to determine the rate of an enzyme-controlled reaction?

Temperature, enzyme concentration, substrate concentration and volumes should be controlled.

4.

Which variables should be controlled when investigating the effect of pH on enzyme activity?

Measure the amount of product formed in a fixed time or the time taken to produce a fixed amount of product.

5.

Why should the same concentration of enzyme and substrate be used at each pH?

This ensures that differences in reaction rate are due to pH rather than changes in enzyme or substrate concentration.

6.

How can results from an investigation of pH and enzyme activity be used to determine the optimum pH?

The pH giving the highest rate of reaction is the optimum pH.

1.11 Demonstrate an understanding of rate calculations for enzyme activity

1.

How is the rate of an enzyme-controlled reaction calculated?

Rate = change in quantity ÷ time.

2.

What equation can be used to calculate rate from the change in product concentration and time?

Rate = change in product concentration ÷ time.

3.

What units could be used for the rate of an enzyme-controlled reaction?

Units could include cm³ s−1, cm³ min−1 or concentration per unit time.

4.

How would the rate change if the same amount of product were produced in half the time?

The rate would double.

5.

How can a graph of product formed against time be used to determine enzyme activity?

Calculate the gradient of the graph; a greater gradient represents a greater rate of enzyme activity.

6.

What does a steeper gradient on a product-against-time graph indicate about enzyme activity?

A steeper gradient indicates a faster reaction and therefore greater enzyme activity.

1.12 Explain the importance of enzymes as biological catalysts in the synthesis of carbohydrates, proteins and lipids and their breakdown into sugars, amino acids and fatty acids and glycerol

1.

Why are enzymes important in the synthesis and breakdown of biological molecules?

Enzymes increase the rate of reactions involved in building up and breaking down biological molecules.

2.

Which smaller molecules are produced when carbohydrates are broken down by enzymes?

Carbohydrates are broken down into sugars.

3.

Which smaller molecules are produced when proteins are broken down by enzymes?

Proteins are broken down into amino acids.

4.

Which smaller molecules are produced when lipids are broken down by enzymes?

Lipids are broken down into fatty acids and glycerol.

5.

How do enzymes act as biological catalysts in the synthesis of carbohydrates, proteins and lipids?

Enzymes lower the activation energy of reactions, allowing synthesis and breakdown to occur rapidly under suitable biological conditions.

6.

Why would the synthesis and breakdown of biological molecules be too slow without enzymes?

Without enzymes, these reactions would occur too slowly to support normal biological processes.

1.15 Explain how substances are transported into and out of cells, including by diffusion, osmosis and active transport

1.

What is diffusion and how does it transport substances into or out of cells?

Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration.

2.

How does the concentration gradient affect the net movement of particles by diffusion?

A steeper concentration gradient increases the net rate of diffusion.

3.

What is osmosis?

Osmosis is the net movement of water molecules from a dilute solution to a more concentrated solution through a partially permeable membrane.

4.

How does osmosis differ from diffusion?

Osmosis involves the movement of water through a partially permeable membrane, whereas diffusion can involve different types of particles and does not necessarily require a membrane.

5.

What is active transport and how does it differ from diffusion?

Active transport moves substances against their concentration gradient using energy, whereas diffusion moves substances down their concentration gradient without energy.

6.

Why does active transport require energy from respiration?

Active transport requires energy released by respiration to move substances against their concentration gradient.

1.16 Core Practical: Investigate osmosis in potatoes

1.

How can potato cylinders be used to investigate osmosis experimentally?

Place potato cylinders in solutions of different concentrations and measure their masses before and after the investigation.

2.

What should be measured before and after placing potato cylinders in different concentrations of solution?

The mass should be measured before and after.

3.

Why should potato cylinders be cut to the same size when investigating osmosis?

This ensures that differences in mass change are due to solution concentration rather than differences in the size of the potato cylinders.

4.

Which variable should be changed when investigating the effect of solution concentration on osmosis in potato tissue?

Solution concentration should be changed.

5.

Which variables should be controlled when investigating osmosis using potato cylinders?

Temperature, volume and concentration of solutions, size of potato cylinders and time should be controlled.

6.

How can the results of a potato osmosis experiment be used to determine the concentration at which there is no net movement of water?

Plot percentage change in mass against solution concentration. The concentration where there is no change in mass represents no net movement of water.

1.17 Calculate percentage gain and loss of mass in osmosis

1.

What equation is used to calculate the percentage change in mass of a potato cylinder during osmosis?

Percentage change = (change in mass ÷ initial mass) × 100.

2.

How is percentage gain in mass calculated when the final mass is greater than the initial mass?

Percentage gain = ((final mass − initial mass) ÷ initial mass) × 100.

3.

How is percentage loss in mass calculated when the final mass is less than the initial mass?

Percentage loss = ((initial mass − final mass) ÷ initial mass) × 100.

4.

A potato cylinder increases in mass from 4.0 g to 5.0 g. What is its percentage gain in mass?

Percentage gain = ((5.0 − 4.0) ÷ 4.0) × 100 = 25%.

5.

A potato cylinder decreases in mass from 5.0 g to 4.0 g. What is its percentage loss in mass?

Percentage loss = ((5.0 − 4.0) ÷ 5.0) × 100 = 20%.

6.

Why is percentage change in mass useful when comparing osmosis results from potato cylinders of different starting masses?

Percentage change allows mass changes to be compared fairly when the starting masses are different.

2.1 Describe mitosis as part of the cell cycle, including the stages interphase, prophase, metaphase, anaphase and telophase and cytokinesis

1.

What happens during interphase before a cell undergoes mitosis?

During interphase, the cell grows, carries out normal functions and replicates its DNA.

2.

What happens to the chromosomes during prophase?

During prophase, chromosomes condense and become visible.

3.

What happens to the chromosomes during metaphase?

During metaphase, chromosomes line up at the centre of the cell.

4.

What happens to the chromosomes during anaphase?

During anaphase, sister chromatids separate and move to opposite poles of the cell.

5.

What happens to the chromosomes during telophase?

During telophase, chromosomes reach opposite poles and new nuclei form around them.

6.

What is cytokinesis, and when does it occur in the cell cycle?

Cytokinesis is the division of the cytoplasm to form two separate daughter cells.

2.2 Describe the importance of mitosis in growth, repair and asexual reproduction

1.

How does mitosis allow a multicellular organism to increase in size?

Mitosis produces new cells, increasing the number of cells in an organism.

2.

How does mitosis allow damaged tissues to be repaired?

Mitosis produces replacement cells that can replace damaged or dead cells.

3.

Why is mitosis important in asexual reproduction?

Mitosis allows asexual reproduction because one parent can produce genetically identical offspring.

4.

Why are the cells produced by mitosis suitable for growth and tissue repair?

The genetically identical cells produced by mitosis retain the same genetic information and chromosome number as the parent cell.

5.

How does mitosis allow a single parent organism to produce genetically identical offspring by asexual reproduction?

Repeated mitotic divisions produce genetically identical offspring from a single parent.

6.

Why must mitosis occur repeatedly during the growth of a multicellular organism?

Repeated cell division increases the number of cells required as the organism grows.

2.3 Describe the division of a cell by mitosis as the production of two daughter cells, each with identical sets of chromosomes in the nucleus to the parent cell, and that this results in the formation of two genetically identical diploid body cells

1.

How many daughter cells are produced when one diploid body cell undergoes mitosis?

Two daughter cells are produced.

2.

How does the chromosome number of each daughter cell produced by mitosis compare with the parent cell?

Each daughter cell has the same chromosome number as the parent cell.

3.

Why are the daughter cells produced by mitosis genetically identical to each other?

The daughter cells receive identical sets of chromosomes.

4.

Why are the daughter cells produced by mitosis genetically identical to the parent cell?

Each daughter cell contains the same genetic information as the parent cell.

5.

What does the term diploid mean when describing body cells produced by mitosis?

Diploid means having two sets of chromosomes.

6.

What must happen to the DNA before a diploid cell can divide by mitosis?

The DNA must be replicated so that each daughter cell receives an identical set of chromosomes.

2.4 Describe cancer as the result of changes in cells that lead to uncontrolled cell division

1.

What is cancer?

Cancer is a disease caused by changes in cells that result in uncontrolled cell division.

2.

What happens to cell division when a cell becomes cancerous?

Cell division becomes uncontrolled.

3.

How can changes in cells lead to uncontrolled cell division?

Changes in genes controlling cell division can cause cells to divide uncontrollably.

4.

How can uncontrolled cell division result in the formation of a tumour?

Uncontrolled cell division can produce a mass of abnormal cells called a tumour.

5.

Why is uncontrolled cell division harmful to the body?

Uncontrolled cell division can disrupt the normal functioning of tissues and organs.

6.

How does uncontrolled cell division in cancer differ from normal cell division?

Normal cell division is controlled, whereas cancer involves uncontrolled cell division.

2.5 Describe growth in organisms, including: a cell division and differentiation in animals b cell division, elongation and differentiation in plants

1.

Which two processes contribute to growth in animals?

Cell division and cell differentiation contribute to growth in animals.

2.

How does cell division contribute to growth in animals?

Cell division increases the number of cells in the organism.

3.

How does cell differentiation contribute to growth in animals?

Cell differentiation causes cells to become specialised for particular functions.

4.

Which three processes contribute to growth in plants?

Cell division, cell elongation and cell differentiation contribute to growth in plants.

5.

How does cell elongation contribute to growth in plants?

Cell elongation increases the size of plant cells, contributing to the growth of the plant.

6.

How does cell differentiation contribute to growth in plants?

Cell differentiation produces specialised plant cells with particular functions.

2.6 Explain the importance of cell differentiation in the development of specialised cells

1.

What is cell differentiation?

Cell differentiation is the process by which cells become specialised.

2.

Why is cell differentiation important in multicellular organisms?

It allows multicellular organisms to develop different types of specialised cells.

3.

How does cell differentiation allow cells to become specialised?

Different genes are expressed in different cells, causing them to develop different structures and functions.

4.

Why do different cells need to become specialised for different functions?

Specialised cells are adapted to perform particular functions efficiently.

5.

How does differentiation contribute to the development of tissues and organs?

Differentiation allows specialised cells to form tissues and organs with specific functions.

6.

What would happen to the development of a multicellular organism if cells could not differentiate?

Without differentiation, cells would not become specialised and the organism could not develop normal tissues and organs.

2.7 Demonstrate an understanding of the use of percentiles charts to monitor growth

1.

What information can a percentile chart provide when monitoring the growth of a child?

A percentile chart shows how a measurement compares with measurements from other individuals of the same age and sex.

2.

How can a child's height be monitored using a percentile chart?

Record the child's height and plot it against their age on the appropriate percentile chart.

3.

How can a child's mass be monitored using a percentile chart?

Record the child's mass and plot it against their age on the appropriate percentile chart.

4.

What does it mean if a child's measurement follows approximately the same percentile over time?

It suggests that the child's growth is following a consistent pattern relative to others of the same age and sex.

5.

What might a significant change in a child's position on a percentile chart indicate?

It may indicate an unusual change in the child's growth pattern.

6.

How can percentile charts be used to identify unusual patterns of growth?

Tracking measurements over time can identify whether growth is following an expected pattern or changing significantly.

2.8 Describe the function of embryonic stem cells, stem cells in animals and meristems in plants

1.

What are embryonic stem cells?

Embryonic stem cells are unspecialised cells found in early embryos.

2.

What is the function of embryonic stem cells?

They can differentiate into many different types of specialised cells.

3.

What is the function of stem cells found in animals after birth?

Animal stem cells can divide and differentiate to produce specialised cells for growth and repair.

4.

Why can animal stem cells produce different types of specialised cells?

Animal stem cells can differentiate into different cell types because they are not fully specialised.

5.

What are meristems in plants?

Meristems are regions of actively dividing unspecialised cells in plants.

6.

How do meristems allow plants to produce new cells for growth?

Meristems produce new cells that can divide, elongate and differentiate for plant growth.

2.9 Discuss the potential benefits and risks associated with the use of stem cells in medicine

1.

What is one potential medical benefit of using stem cells?

Stem cells could replace damaged or diseased cells and help treat some conditions.

2.

How could stem cells be used to replace damaged or diseased cells?

They could differentiate into replacement cells for damaged tissues.

3.

Why could embryonic stem cells be useful in treating human diseases?

Embryonic stem cells can differentiate into many different specialised cell types, making them potentially useful for treating disease.

4.

What is one ethical concern associated with obtaining embryonic stem cells?

One ethical concern is that obtaining embryonic stem cells involves the destruction of an embryo.

5.

What is one medical risk associated with using stem cells in patients?

Stem cell treatments may carry risks such as uncontrolled cell division or immune rejection.

6.

Why might stem cell treatments require careful control to reduce the risk of unwanted cell division?

Careful control is needed because uncontrolled division of transplanted stem cells could result in tumour formation.

2.13 Explain the structure and function of sensory receptors, sensory neurones, relay neurones in the CNS, motor neurones and synapses in the transmission of electrical impulses, including the axon, dendron, myelin sheath and the role of neurotransmitters

1.

What is the function of a sensory receptor in the nervous system?

Sensory receptors detect stimuli and convert them into electrical impulses.

2.

What is the function of a sensory neurone?

Sensory neurones carry electrical impulses from sensory receptors to the central nervous system.

3.

What is the function of a relay neurone, and where is it found?

Relay neurones connect sensory and motor neurones within the central nervous system.

4.

What is the function of a motor neurone?

Motor neurones carry electrical impulses from the central nervous system to effectors.

5.

What are the functions of the axon, dendron and myelin sheath in a neurone?

The axon carries impulses away from the cell body, the dendron carries impulses towards the cell body, and the myelin sheath insulates the neurone and increases the speed of impulse transmission.

6.

How do neurotransmitters allow an electrical impulse to pass across a synapse?

Neurotransmitters are released from one neurone and diffuse across the synapse, where they bind to receptors on the next neurone and initiate an electrical impulse.

2.14 Explain the structure and function of a reflex arc including sensory, relay and motor neurones

1.

What is a reflex action?

A reflex action is a rapid, automatic response to a stimulus.

2.

What is the correct pathway of a nerve impulse through a reflex arc?

Receptor → sensory neurone → relay neurone → motor neurone → effector.

3.

What is the role of the sensory neurone in a reflex arc?

The sensory neurone carries the impulse from the receptor to the central nervous system.

4.

What is the role of the relay neurone in a reflex arc?

The relay neurone passes the impulse between the sensory and motor neurones within the central nervous system.

5.

What is the role of the motor neurone in a reflex arc?

The motor neurone carries the impulse from the central nervous system to the effector.

6.

Why do reflex arcs allow responses to occur rapidly without conscious thought?

Reflex arcs use a short pathway through the central nervous system and do not require conscious processing before the response occurs.

3.3 Explain the role of meiotic cell division, including the production of four daughter cells, each with half the number of chromosomes, and that this results in the formation of genetically different haploid gametes. The stages of meiosis are not required

1.

What is the role of meiotic cell division in sexual reproduction?

Meiosis produces gametes for sexual reproduction.

2.

How many daughter cells are produced from one cell during meiosis?

Four daughter cells are produced.

3.

How does the chromosome number of each daughter cell produced by meiosis compare with the original cell?

Each daughter cell has half the number of chromosomes of the original cell.

4.

What is a haploid gamete?

A haploid gamete contains one set of chromosomes.

5.

Why are the four gametes produced by meiosis genetically different from each other?

The gametes are genetically different because of the random assortment of chromosomes and genetic variation.

6.

How does meiosis produce gametes with half the normal chromosome number?

Meiosis involves two divisions following DNA replication, producing four cells with half the original chromosome number.

3.4 Describe DNA as a polymer made up of: a two strands coiled to form a double helix b strands linked by a series of complementary base pairs joined together by weak hydrogen bonds c nucleotides that consist of a sugar and phosphate group with one of the four different bases attached to the sugar

1.

What is the overall structure of a DNA molecule?

DNA consists of two strands coiled together to form a double helix.

2.

How are the two strands of DNA held together?

The two strands are held together by weak hydrogen bonds between complementary bases.

3.

What is meant by complementary base pairing in DNA?

Complementary base pairing means that each base pairs with a specific other base.

4.

Which bases are complementary in DNA?

Adenine pairs with thymine, and cytosine pairs with guanine.

5.

What three components make up a DNA nucleotide?

A nucleotide consists of a sugar, a phosphate group and one of four bases.

6.

How are nucleotides arranged to form a DNA molecule?

Nucleotides join together to form each DNA strand, with complementary bases linking the two strands.

3.5 Describe the genome as the entire DNA of an organism and a gene as a section of a DNA molecule that codes for a specific protein

1.

What is meant by the genome of an organism?

The genome is the entire DNA of an organism.

2.

What is a gene?

A gene is a section of DNA that codes for a specific protein.

3.

How is a gene related to a protein?

A gene contains the genetic information needed to produce a specific protein.

4.

How does a gene differ from the entire genome?

The genome contains all of an organism's DNA, whereas a gene is only a section of DNA.

5.

Where are genes found?

Genes are found on chromosomes.

6.

Why can different sections of DNA code for different proteins?

Different sections of DNA contain different sequences of bases, which can code for different proteins.

3.6 Explain how DNA can be extracted from fruit

1.

How can DNA be extracted from fruit?

Mash the fruit, add detergent and salt, filter the mixture, then add cold ethanol or propanone to precipitate the DNA.

2.

Why is the fruit mashed or blended when extracting DNA?

Mashing or blending breaks up the fruit tissue and cells, releasing their contents.

3.

Why is detergent added when extracting DNA from fruit?

Detergent breaks down the cell membranes and nuclear membranes, releasing DNA.

4.

Why is salt added when extracting DNA from fruit?

Salt helps separate DNA from proteins and other cell components.

5.

Why is the fruit mixture filtered during DNA extraction?

Filtering removes solid pieces of fruit and other insoluble material.

6.

Why is cold ethanol or propanone added to the filtered fruit extract?

Cold ethanol or propanone causes the DNA to precipitate, making it visible.

3.12 Explain why there are differences in the inherited characteristics as a result of alleles

1.

What is an allele?

An allele is an alternative form of a gene.

2.

Why can different alleles of the same gene produce differences in inherited characteristics?

Different alleles have different DNA base sequences, which can result in different proteins and characteristics.

3.

How can two individuals inherit different alleles for the same gene?

Individuals can inherit different alleles from their parents.

4.

How can different combinations of alleles cause variation in inherited characteristics?

Different combinations of alleles can result in different inherited characteristics.

5.

Why can offspring inherit different combinations of alleles from their parents?

Each parent contributes one allele for a gene, so offspring can receive different combinations.

6.

How do alleles contribute to genetic variation within a population?

Alleles create different versions of genes, producing genetic variation within a population.

3.13 Explain the terms: chromosome, gene, allele, dominant, recessive, homozygous, heterozygous, genotype, phenotype, gamete and zygote

1.

What is a chromosome?

A chromosome is a long, coiled DNA molecule containing many genes.

2.

What is a gene?

A gene is a section of DNA that codes for a specific protein.

3.

What is an allele?

An allele is an alternative form of a gene.

4.

What is meant by a dominant allele?

A dominant allele is expressed in the phenotype when present in either a homozygous or heterozygous genotype.

5.

What is meant by a recessive allele?

A recessive allele is expressed in the phenotype only when two copies are present.

6.

What is a homozygous genotype?

A homozygous genotype has two identical alleles for a gene.

7.

What is a heterozygous genotype?

A heterozygous genotype has two different alleles for a gene.

8.

What is meant by genotype?

A genotype is the combination of alleles an organism has.

9.

What is meant by phenotype?

A phenotype is the observable characteristics of an organism.

10.

What is a gamete?

A gamete is a haploid sex cell containing one set of chromosomes.

11.

What is a zygote?

A zygote is the diploid cell formed when two gametes fuse during fertilisation.

12.

How does a zygote differ from a gamete?

A zygote is diploid and contains two sets of chromosomes, whereas a gamete is haploid and contains one set.

3.14 Explain monohybrid inheritance using genetic diagrams, Punnett squares and family pedigrees

1.

What is a monohybrid cross?

A monohybrid cross investigates the inheritance of one characteristic controlled by a single gene.

2.

How can a Punnett square be used to predict the genotypes of offspring?

A Punnett square shows the possible combinations of alleles in offspring.

3.

How can a genetic diagram be used to show the inheritance of a single characteristic?

A genetic diagram shows the parental genotypes, gametes and possible offspring genotypes and phenotypes.

4.

How can a family pedigree be used to show the inheritance of a characteristic?

A family pedigree uses symbols to show how a characteristic is inherited through generations of a family.

5.

How can a dominant allele affect the phenotype of a heterozygous individual?

A dominant allele is expressed in a heterozygous individual.

6.

How can a recessive phenotype be inherited from two heterozygous parents?

Two heterozygous parents can each pass on the recessive allele, producing a 25% probability of a homozygous recessive offspring.

3.15 Describe how the sex of offspring is determined at fertilisation, using genetic diagrams

1.

Which sex chromosomes are present in a human female?

A human female has two X chromosomes (XX).

2.

Which sex chromosomes are present in a human male?

A human male has one X chromosome and one Y chromosome (XY).

3.

Which sex chromosomes can a human female's eggs contain?

All eggs contain an X chromosome.

4.

Which sex chromosomes can a human male's sperm contain?

Sperm can contain either an X chromosome or a Y chromosome.

5.

How is the sex of a human offspring determined at fertilisation?

An X-bearing sperm produces an XX female offspring, while a Y-bearing sperm produces an XY male offspring.

6.

What is the probability that a human offspring will be male or female?

The probability is 50% male and 50% female.

3.16 Calculate and analyse outcomes (using probabilities, ratios and percentages) from monohybrid crosses and pedigree analysis for dominant and recessive traits

1.

How can probabilities be calculated from a monohybrid Punnett square?

Count the number of relevant outcomes in the Punnett square and divide by the total number of possible outcomes.

2.

How can the expected genotype ratio of offspring be determined from a genetic cross?

Compare the possible offspring genotypes to determine the expected genotype ratio.

3.

How can the expected phenotype ratio of offspring be determined from a genetic cross?

Compare the possible offspring phenotypes to determine the expected phenotype ratio.

4.

How can the probability of inheriting a recessive phenotype be calculated from a genetic cross?

Count the outcomes with the homozygous recessive genotype and divide by the total number of possible outcomes.

5.

How can percentages be used to express the expected outcomes of a monohybrid cross?

Multiply the probability by 100 to express it as a percentage.

6.

How can a pedigree be analysed to determine whether a characteristic is dominant or recessive?

A characteristic appearing in every generation is likely to be dominant, whereas a recessive characteristic can skip generations.

3.19 State that most phenotypic features are the result of multiple genes rather than single gene inheritance

1.

What does polygenic inheritance mean?

Polygenic inheritance occurs when a characteristic is influenced by multiple genes.

2.

Why are most phenotypic features not controlled by a single gene?

Most phenotypic features are influenced by several genes rather than a single gene.

3.

How can multiple genes contribute to a single phenotypic feature?

Different genes can each contribute to the development of the same characteristic.

4.

Why can polygenic characteristics show a wide range of phenotypes?

Different combinations of alleles at several genes can produce a wide range of phenotypes.

5.

Give one example of a human characteristic that is influenced by multiple genes.

Examples include height and skin colour.

6.

How does polygenic inheritance differ from single-gene inheritance?

Single-gene inheritance involves one gene, whereas polygenic inheritance involves multiple genes.

3.20 Describe the causes of variation that influence phenotype, including: a genetic variation – different characteristics as a result of mutation and sexual reproduction b environmental variation – different characteristics caused by an organism's environment (acquired characteristics)

1.

What is meant by variation within a population?

Variation is the differences in characteristics between individuals of the same species.

2.

How can mutations cause genetic variation?

Mutations can create new alleles, producing genetic variation.

3.

How can sexual reproduction produce genetic variation?

Sexual reproduction produces genetic variation because offspring inherit different combinations of alleles from their parents.

4.

How can environmental factors cause variation in phenotype?

Environmental factors such as diet, temperature and lifestyle can affect phenotype.

5.

What is an acquired characteristic?

An acquired characteristic is a characteristic that develops during an organism's lifetime due to environmental factors.

6.

What is the difference between genetic variation and environmental variation?

Genetic variation is caused by differences in genes or alleles, whereas environmental variation is caused by differences in an organism's environment.

3.21 Discuss the outcomes of the Human Genome Project and its potential applications within medicine

1.

What was the main aim of the Human Genome Project?

The main aim was to determine the sequence of bases in the human genome and identify the genes it contains.

2.

What did the Human Genome Project determine about human DNA?

It determined the sequence of bases in human DNA and helped identify genes within the genome.

3.

How could information from the Human Genome Project improve the diagnosis of inherited diseases?

It can help identify genetic mutations associated with inherited diseases, improving diagnosis.

4.

How could the Human Genome Project contribute to the development of personalised medicine?

It could allow treatments to be tailored to an individual's genetic information.

5.

How could knowledge of the human genome help identify genes associated with disease?

Comparing genomes can help identify genes associated with particular diseases.

6.

What are potential limitations or ethical concerns associated with using information from the human genome?

Concerns include genetic privacy, discrimination and the possibility of misuse of genetic information.

3.22 State that there is usually extensive genetic variation within a population of a species and that these arise through mutations

1.

What is genetic variation?

Genetic variation is differences in the genes or alleles between individuals in a population.

2.

Why is there usually extensive genetic variation within a population of a species?

Mutations create new alleles, resulting in genetic variation.

3.

How do mutations create new alleles?

Mutations can change the DNA base sequence and create new alleles.

4.

Why can mutations increase the genetic variation within a population?

New alleles increase the number of different genetic forms present in a population.

5.

How can sexual reproduction contribute to the variation produced by mutations?

Sexual reproduction produces different combinations of alleles, increasing variation between individuals.

6.

Why does genetic variation mean that individuals of the same species can have different genotypes?

Individuals of the same species can inherit different alleles and therefore have different genotypes.

3.23 State that most genetic mutations have no effect on the phenotype, some mutations have a small effect on the phenotype and, rarely, a single mutation will significantly affect the phenotype

1.

What effect do most genetic mutations have on an organism's phenotype?

Most genetic mutations have no effect on phenotype.

2.

Why might a genetic mutation have no effect on the phenotype?

A mutation may occur in a non-coding section of DNA or may not alter the resulting protein sufficiently to affect phenotype.

3.

What effect can some genetic mutations have on an organism's phenotype?

Some mutations have a small effect on phenotype.

4.

How can a mutation have a small effect on phenotype?

A mutation may slightly alter the structure or function of a protein, causing a small change in phenotype.

5.

Why can a single mutation rarely have a significant effect on phenotype?

A mutation can rarely cause a major change in the structure or function of an important protein, significantly affecting phenotype.

6.

Why do genetic mutations not always result in noticeable changes to an organism's characteristics?

Mutations do not always alter the protein or its function enough to produce a noticeable change in characteristics.

4.2 Explain Charles Darwin's theory of evolution by natural selection

1.

What is meant by evolution by natural selection?

Evolution by natural selection is the change in inherited characteristics of a population over generations due to differences in survival and reproduction.

2.

Why is there variation between individuals within a population?

Variation can arise from genetic differences, including mutations and sexual reproduction.

3.

How does competition for limited resources affect individuals within a population?

Individuals compete for limited resources such as food, water and mates.

4.

How does natural selection cause individuals with advantageous characteristics to survive and reproduce more successfully?

Individuals with advantageous characteristics are more likely to survive and reproduce, passing their alleles to offspring.

5.

How can advantageous alleles become more common in a population over many generations?

The advantageous alleles are inherited by offspring and become more common in the population over generations.

6.

How does Darwin's theory of natural selection explain how species can change over time?

Natural selection causes populations to change as advantageous inherited characteristics become more common over time.

4.3 Explain how the emergence of resistant organisms supports Charles Darwin's theory of evolution including antibiotic resistance in bacteria

1.

How can antibiotic resistance arise in a population of bacteria?

A mutation can produce an allele that gives a bacterium resistance to an antibiotic.

2.

Why does an antibiotic kill susceptible bacteria but allow resistant bacteria to survive?

The antibiotic kills susceptible bacteria, while resistant bacteria survive.

3.

How does natural selection increase the proportion of antibiotic-resistant bacteria in a population?

Resistant bacteria survive and reproduce, increasing the proportion of resistant bacteria in the population.

4.

Why does the use of antibiotics create a selection pressure on bacterial populations?

Antibiotics act as a selection pressure because they favour bacteria with resistance.

5.

How does the emergence of antibiotic-resistant bacteria provide evidence supporting Darwin's theory of evolution?

Resistant bacteria surviving and reproducing demonstrates natural selection and evolution.

6.

Why can an antibiotic-resistant bacterial population become more common after repeated antibiotic use?

Repeated antibiotic use kills susceptible bacteria and allows resistant bacteria to reproduce, making the resistant population more common.

4.4 Describe the evidence for human evolution, based on fossils, including: a Ardi from 4.4 million years ago b Lucy from 3.2 million years ago c Richard Leakey's discovery of fossils from 1.6 million years ago

1.

What is a fossil?

A fossil is the preserved remains or traces of an organism from the past.

2.

How can fossils provide evidence for human evolution?

Fossils from different time periods can show changes in the characteristics of organisms over time.

3.

What does the fossil evidence from Ardi, dating from about 4.4 million years ago, contribute to our understanding of human evolution?

Ardi provides evidence about early human ancestors and their characteristics around 4.4 million years ago.

4.

What does the fossil evidence from Lucy, dating from about 3.2 million years ago, contribute to our understanding of human evolution?

Lucy provides evidence about human ancestors and their characteristics around 3.2 million years ago.

5.

What did Richard Leakey's discovery of fossils from about 1.6 million years ago contribute to the evidence for human evolution?

Richard Leakey's fossils from about 1.6 million years ago provide further evidence of human ancestors and their changing characteristics.

6.

Why does a sequence of fossils from different time periods provide evidence for changes in human characteristics over time?

Fossils from different periods can be compared to identify changes in human characteristics over millions of years.

4.5 Describe the evidence for human evolution based on stone tools, including: a the development of stone tools over time b how these can be dated from their environment

1.

How can stone tools provide evidence for human evolution?

Stone tools provide evidence of changes in the abilities and behaviour of human ancestors.

2.

How did the design and complexity of stone tools change over time?

Stone tools became more complex and sophisticated over time.

3.

What can increasingly sophisticated stone tools suggest about the development of human abilities?

Increasingly sophisticated tools suggest increasing technological ability and development of human intelligence and behaviour.

4.

How can the development of stone tools be used to provide evidence for human evolution?

Changes in stone tools over time provide evidence of changes in human ancestors.

5.

How can the environment surrounding a stone tool be used to determine its age?

The age of stone tools can be estimated by dating materials and rocks in the surrounding environment.

6.

Why is dating stone tools important when using them as evidence for human evolution?

Dating allows the development of tools to be placed in chronological order and compared with other evidence of human evolution.

4.7 Describe how genetic analysis has led to the suggestion of the three domains rather than the five kingdoms classification method

1.

What is meant by classification in biology?

Classification is the organisation of organisms into groups based on their similarities and differences.

2.

What are the three domains used to classify organisms?

The three domains are Bacteria, Archaea and Eukarya.

3.

What evidence from genetic analysis led scientists to propose the three-domain system?

Genetic analysis revealed significant differences in DNA and ribosomal RNA between groups of organisms.

4.

How did genetic analysis challenge the traditional five-kingdom classification system?

Genetic evidence showed that some organisms previously grouped together were not as closely related as previously thought.

5.

Why is genetic information useful when determining evolutionary relationships between organisms?

Genetic information can be compared to identify evolutionary relationships between organisms.

6.

How does the three-domain system differ from the five-kingdom classification system?

The three-domain system divides organisms into Bacteria, Archaea and Eukarya, whereas the five-kingdom system uses five kingdoms.

4.8 Explain selective breeding and its impact on food plants and domesticated animals

1.

What is selective breeding?

Selective breeding is the process of choosing parents with desirable characteristics and breeding them to produce offspring with those characteristics.

2.

What steps are involved in selectively breeding organisms with desirable characteristics?

Select parents with the desired characteristic, breed them, select offspring with the characteristic and repeat the process over many generations.

3.

How can selective breeding produce food plants with desirable characteristics?

Food plants can be bred for characteristics such as increased yield, disease resistance or larger fruits.

4.

How can selective breeding produce domesticated animals with desirable characteristics?

Domesticated animals can be bred for characteristics such as increased meat or milk production.

5.

Why can selective breeding increase the frequency of desirable alleles in a population?

Repeated selection increases the frequency of alleles associated with desirable characteristics.

6.

What are potential disadvantages of selective breeding, including reduced genetic variation and inherited health problems?

Selective breeding can reduce genetic variation and increase the risk of inherited genetic disorders.

4.10 Describe genetic engineering as a process which involves modifying the genome of an organism to introduce desirable characteristics

1.

What is genetic engineering?

Genetic engineering is the process of modifying an organism's genome to introduce a desirable characteristic.

2.

What is modified during genetic engineering?

The organism's genome is modified.

3.

Why is a gene introduced into an organism during genetic engineering?

A desired gene is introduced so that the organism develops the characteristic coded for by that gene.

4.

How can genetic engineering introduce a desirable characteristic into an organism?

A gene coding for the desirable characteristic is transferred into the organism's genome.

5.

How does genetic engineering differ from selective breeding?

Genetic engineering directly introduces specific genes, whereas selective breeding involves choosing organisms with desirable characteristics to reproduce.

6.

Give one example of a desirable characteristic that could be introduced using genetic engineering.

A gene for insect resistance could be introduced into a crop plant.

4.11 Describe the main stages of genetic engineering including the use of: a restriction enzymes b ligase c sticky ends d vectors

1.

What is the role of a restriction enzyme in genetic engineering?

Restriction enzymes cut DNA at specific base sequences.

2.

What are sticky ends and why are they useful in genetic engineering?

Sticky ends are short sections of unpaired bases produced by restriction enzymes that can form complementary base pairs with another DNA fragment.

3.

What is the role of DNA ligase in genetic engineering?

DNA ligase joins the sugar-phosphate backbones of DNA fragments.

4.

What is a vector and why is it used in genetic engineering?

A vector carries the desired gene into a target cell.

5.

What are the main stages involved in transferring a desired gene into an organism using genetic engineering?

Isolate the desired gene, cut the gene and vector using the same restriction enzyme, join them using DNA ligase, then introduce the recombinant vector into the target organism.

6.

How do restriction enzymes, sticky ends, ligase and vectors work together during genetic engineering?

Restriction enzymes produce matching sticky ends, allowing the desired gene to bind to the vector, and ligase joins the DNA fragments together.

4.14 Evaluate the benefits and risks of genetic engineering and selective breeding in modern agriculture and medicine, including practical and ethical implications

1.

What is one benefit of genetic engineering in modern agriculture?

Genetic engineering can introduce desirable characteristics such as pest resistance or increased nutritional value into crops.

2.

What is one potential risk of genetic engineering in agriculture?

Risks include possible effects on ecosystems, unintended effects and concerns about the long-term consequences of modifying organisms.

3.

What is one medical benefit of genetic engineering?

Genetic engineering can be used to produce useful medicines such as human insulin.

4.

What is one potential practical or ethical concern associated with genetic engineering?

Concerns can include ethical objections to genetic modification, possible environmental effects and practical difficulties.

5.

What are the benefits and risks of selective breeding in agriculture?

Selective breeding can increase food production and desirable characteristics, but can reduce genetic variation and increase inherited health problems.

6.

How should practical, environmental and ethical factors be considered when evaluating genetic engineering and selective breeding?

Evaluation should consider benefits, risks, effectiveness, environmental effects, cost and ethical concerns.

5.1 Describe health as a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity, as defined by the World Health Organization (WHO)

1.

How does the World Health Organization define health?

Health is a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity.

2.

What three aspects of well-being are included in the WHO definition of health?

Physical, mental and social well-being.

3.

Why does being free from disease not necessarily mean that a person is healthy?

A person can be free from disease but still have poor physical, mental or social well-being.

4.

What is meant by physical well-being?

Physical well-being relates to the healthy functioning of the body.

5.

What is meant by mental and social well-being?

Mental well-being relates to psychological health, while social well-being relates to a person's ability to interact and function within society.

6.

Why is health considered more than simply the absence of disease or infirmity?

Health includes overall physical, mental and social well-being rather than simply being free from disease.

5.2 Describe the difference between communicable and non-communicable diseases

1.

What is a communicable disease?

A communicable disease is a disease caused by a pathogen that can be transmitted between organisms.

2.

What is a non-communicable disease?

A non-communicable disease cannot be transmitted between organisms.

3.

How are communicable diseases different from non-communicable diseases?

Communicable diseases can spread between individuals, whereas non-communicable diseases do not spread between individuals.

4.

Why can communicable diseases be transmitted between individuals?

Pathogens can be transferred between individuals through routes such as air, water, direct contact or vectors.

5.

Give one example of a communicable disease and one example of a non-communicable disease.

Cholera is communicable; cardiovascular disease is non-communicable.

6.

Why are non-communicable diseases not spread from person to person?

Non-communicable diseases are not caused by pathogens that are transmitted between individuals.

5.3 Explain why the presence of one disease can lead to a higher susceptibility to other diseases

1.

Why can having one disease increase a person's susceptibility to another disease?

One disease can weaken the immune system, making the person more susceptible to other diseases.

2.

How can one disease weaken the immune system?

A disease can damage or reduce the effectiveness of immune cells.

3.

Why can damage caused by one disease make it easier for another pathogen to cause disease?

Damage caused by one disease can make it easier for another pathogen to enter or infect the body.

4.

How can HIV infection increase susceptibility to other diseases?

HIV destroys white blood cells, weakening the immune system and increasing susceptibility to other diseases.

5.

Why are people with weakened immune systems more likely to develop infections?

A weakened immune system is less effective at recognising and destroying pathogens.

6.

How does the presence of one disease affect the body's ability to defend itself against other diseases?

A disease can reduce the body's ability to defend itself, allowing other pathogens to cause infection more easily.

5.4 Describe a pathogen as a disease-causing organism, including viruses, bacteria, fungi and protists

1.

What is a pathogen?

A pathogen is a disease-causing organism.

2.

Which four types of pathogen are included in the Edexcel specification?

Viruses, bacteria, fungi and protists.

3.

How do pathogens cause disease?

Pathogens cause disease by entering the body, reproducing or growing and damaging cells or tissues.

4.

How are viruses different from bacteria as pathogens?

Viruses reproduce inside host cells, whereas bacteria are living cells that can reproduce independently.

5.

How can fungi cause disease?

Fungi can grow on or within organisms and cause tissue damage.

6.

How can protists cause disease?

Protists can infect organisms and damage cells or tissues.

5.5 Describe some common infections, including: a cholera (bacteria) causes diarrhoea b tuberculosis (bacteria) causes lung damage c Chalara ash dieback (fungi) causes leaf loss and bark lesions d malaria (protists) causes damage to blood and liver e HIV (virus) destroys white blood cells, leading to the onset of AIDS

1.

Which type of pathogen causes cholera and what symptom does cholera cause?

Cholera is caused by bacteria and causes diarrhoea.

2.

Which type of pathogen causes tuberculosis and what damage can tuberculosis cause?

Tuberculosis is caused by bacteria and can cause lung damage.

3.

Which type of pathogen causes Chalara ash dieback and what symptoms does it cause in ash trees?

Chalara ash dieback is caused by fungi and causes leaf loss and bark lesions.

4.

Which type of pathogen causes malaria and what tissues can malaria damage?

Malaria is caused by protists and causes damage to blood and liver.

5.

Which type of pathogen causes HIV and what cells does HIV destroy?

HIV is caused by a virus and destroys white blood cells.

6.

How can destruction of white blood cells by HIV lead to the onset of AIDS?

Destruction of white blood cells weakens the immune system, leading to the onset of AIDS.

5.6 Explain how pathogens are spread and how this spread can be reduced or prevented, including: a cholera (bacteria) – water b tuberculosis (bacteria) – airborne c Chalara ash dieback (fungi) – airborne d malaria (protists) – animal vectors

1.

How is cholera transmitted and how can its spread be reduced?

Cholera is spread through contaminated water; providing clean water and good sanitation reduces its spread.

2.

How is tuberculosis transmitted and how can its spread be reduced?

Tuberculosis is spread through airborne droplets; reducing contact with infected people and improving ventilation can reduce its spread.

3.

How is Chalara ash dieback transmitted and how can its spread be reduced?

Chalara ash dieback can be spread through airborne fungal spores; controlling movement of infected material can reduce its spread.

4.

How is malaria transmitted and what type of organism acts as its vector?

Malaria is transmitted by animal vectors, particularly mosquitoes.

5.

What is meant by an animal vector in the transmission of disease?

An animal vector is an animal that carries a pathogen from one organism to another.

6.

How do clean water, reducing airborne transmission and controlling vectors help prevent the spread of pathogens?

Clean water prevents waterborne transmission, reducing airborne transmission limits spread through droplets or spores, and vector control reduces transmission by animals.

5.8 Explain how sexually transmitted infections (STIs) are spread and how this spread can be reduced or prevented, including: a Chlamydia (bacteria) b HIV (virus)

1.

What is a sexually transmitted infection?

A sexually transmitted infection is an infection that can be transmitted through sexual contact.

2.

How is Chlamydia transmitted?

Chlamydia is transmitted through sexual contact with an infected person.

3.

How is HIV transmitted as a sexually transmitted infection?

HIV can be transmitted through sexual contact with an infected person.

4.

How can the spread of Chlamydia be reduced or prevented?

Using barrier contraception, testing and treating infected individuals can reduce the spread of Chlamydia.

5.

How can the sexual transmission of HIV be reduced or prevented?

Barrier contraception, testing, treatment and avoiding contact with infected blood or bodily fluids can reduce sexual transmission of HIV.

6.

Why can barrier contraception reduce the transmission of some sexually transmitted infections?

Barrier contraception reduces direct contact with infected bodily fluids, reducing the likelihood of transmission.

5.12 Describe how the physical barriers and chemical defences of the human body provide protection from pathogens, including: a physical barriers, including mucus, cilia and skin b chemical defence, including lysozymes and hydrochloric acid

1.

How does the skin act as a physical barrier against pathogens?

The skin forms a physical barrier that prevents pathogens entering the body.

2.

How does mucus help protect the body from pathogens?

Mucus traps pathogens and prevents them from reaching deeper tissues.

3.

How do cilia help prevent pathogens from reaching the lungs?

Cilia move mucus and trapped pathogens out of the airways.

4.

How does hydrochloric acid protect the body from pathogens?

Hydrochloric acid in the stomach provides a very acidic environment that kills many pathogens.

5.

What are lysozymes and how do they help defend the body against pathogens?

Lysozymes are enzymes that break down bacterial cell structures.

6.

How do physical barriers and chemical defences work together to prevent pathogens entering and surviving in the body?

Physical barriers prevent pathogens entering, while chemical defences destroy or inhibit pathogens that enter the body.

5.13 Explain the role of the specific immune system of the human body in defence against disease, including: a exposure to pathogen b the antigens trigger an immune response which causes the production of antibodies c the antigens also trigger production of memory lymphocytes d the role of memory lymphocytes in the secondary response to the antigen

1.

What happens when the body is exposed to a pathogen for the first time?

The immune system recognises the pathogen and mounts a specific immune response.

2.

What are antigens and how do they trigger an immune response?

Antigens on the pathogen are recognised by lymphocytes, triggering an immune response.

3.

How do lymphocytes respond to antigens on a pathogen?

Lymphocytes produce antibodies that are complementary to the pathogen's antigens.

4.

What are memory lymphocytes?

Memory lymphocytes are long-lasting cells produced during the primary immune response.

5.

How do memory lymphocytes produce a faster secondary immune response?

Memory lymphocytes recognise the antigen quickly during a second exposure and trigger a rapid production of antibodies.

6.

Why does the secondary response usually produce antibodies more quickly than the primary response?

The secondary response is faster and produces more antibodies, providing a stronger defence against the pathogen.

5.14 Explain the body's response to immunisation using an inactive form of a pathogen

1.

What is immunisation?

Immunisation involves introducing an inactive form of a pathogen into the body.

2.

Why is an inactive form of a pathogen used during immunisation?

The inactive pathogen cannot cause the disease but retains antigens that stimulate an immune response.

3.

How does an inactive pathogen stimulate an immune response?

The antigens trigger lymphocytes to produce specific antibodies.

4.

How does immunisation lead to the production of memory lymphocytes?

Memory lymphocytes are produced during the immune response.

5.

Why can a person respond more rapidly to the real pathogen after immunisation?

On later exposure to the real pathogen, memory lymphocytes produce a rapid secondary immune response.

6.

How does immunisation help protect an individual from developing a disease?

The rapid secondary response can destroy the pathogen before the person develops symptoms or becomes seriously ill.

5.16 Explain that antibiotics can only be used to treat bacterial infections because they inhibit cell processes in the bacterium but not the host organism

1.

Why are antibiotics used to treat bacterial infections?

Antibiotics treat bacterial infections by inhibiting processes in bacterial cells.

2.

Why are antibiotics not effective against viral infections?

Antibiotics do not work against viruses because viruses do not carry out the bacterial cell processes targeted by antibiotics.

3.

How do antibiotics affect processes in bacterial cells?

Antibiotics inhibit essential bacterial cell processes, preventing bacteria from surviving or reproducing.

4.

Why can antibiotics inhibit bacterial cell processes without normally damaging human cells?

Antibiotics target processes or structures specific to bacteria and therefore do not normally affect human cells.

5.

Why would taking antibiotics to treat a viral infection be ineffective?

Taking antibiotics for a viral infection will not kill the viruses or treat the infection.

6.

How does the difference between bacterial and human cells allow antibiotics to treat bacterial infections?

Bacterial cells have cellular processes that can be targeted by antibiotics, whereas viruses rely on host cells to reproduce.

5.20 Describe that the process of developing new medicines, including antibiotics, has many stages, including discovery, development, preclinical and clinical testing

1.

What are the main stages involved in developing a new medicine?

Discovery, development, preclinical testing and clinical testing.

2.

What happens during the discovery stage of medicine development?

Potential medicines are identified or discovered.

3.

What is meant by the development stage of medicine development?

A promising substance is developed into a suitable medicine for further testing.

4.

What is the purpose of preclinical testing when developing a new medicine?

Preclinical testing investigates safety and effectiveness before testing in humans, using laboratory tests and animals where appropriate.

5.

What is the purpose of clinical testing when developing a new medicine?

Clinical testing investigates safety, dosage and effectiveness in human participants.

6.

Why must a new medicine undergo several stages of testing before it can be widely used?

The stages identify medicines that are effective and safe enough for use while reducing risks to patients.

5.23 Describe that many non-communicable human diseases are caused by the interaction of a number of factors, including cardiovascular diseases, many forms of cancer, some lung and liver diseases and diseases influenced by nutrition

1.

What is a non-communicable disease?

A non-communicable disease is a disease that cannot be transmitted between individuals.

2.

Why are many non-communicable diseases caused by several interacting factors?

Different genetic, lifestyle and environmental factors can interact to increase disease risk.

3.

Which types of disease can be influenced by multiple risk factors?

Cardiovascular diseases, many forms of cancer, some lung and liver diseases and diseases influenced by nutrition.

4.

How can cardiovascular disease be influenced by several different factors?

Cardiovascular disease can be influenced by factors such as diet, exercise, smoking and genetics.

5.

How can lifestyle and environmental factors interact to increase the risk of cancer?

Cancer risk can be influenced by factors such as genetics, smoking, diet and environmental exposure.

6.

Why is it difficult to identify one single cause for many non-communicable diseases?

Several interacting factors contribute to many non-communicable diseases, making a single cause difficult to identify.

5.24 Explain the effect of lifestyle factors on non-communicable diseases at local, national and global levels, including: a exercise and diet on obesity and malnutrition, including BMI and waist : hip calculations, using the BMI equation: mass (kg) / height (m)² b alcohol on liver diseases c smoking on cardiovascular diseases

1.

How can exercise and diet affect the risk of obesity?

Regular exercise and a balanced diet can reduce the risk of obesity, while excessive energy intake and insufficient exercise can increase it.

2.

How can inadequate nutrition lead to malnutrition?

Inadequate or unbalanced nutrition can cause malnutrition.

3.

How is BMI calculated?

BMI = mass (kg) ÷ height (m)².

4.

How can waist-to-hip ratio be used when assessing health risks?

Waist-to-hip ratio = waist circumference ÷ hip circumference; it can be used to assess the distribution of body fat and associated health risks.

5.

How can excessive alcohol consumption increase the risk of liver disease?

Excessive alcohol consumption can damage the liver and increase the risk of liver disease.

6.

How can smoking increase the risk of cardiovascular disease?

Smoking damages blood vessels and increases the risk of cardiovascular disease.

5.25 Evaluate some different treatments for cardiovascular disease, including: a life-long medication b surgical procedures c lifestyle changes

1.

What are the potential benefits of using lifelong medication to treat cardiovascular disease?

Lifelong medication can control risk factors or symptoms and reduce the risk of cardiovascular events.

2.

What are the potential disadvantages of lifelong medication for cardiovascular disease?

Disadvantages can include side effects, the need for long-term adherence and the possibility that medication does not remove the underlying cause.

3.

What are the potential benefits and risks of surgical procedures for cardiovascular disease?

Surgery can provide rapid or effective treatment, but it carries risks such as complications and may require recovery time.

4.

How can lifestyle changes help prevent or manage cardiovascular disease?

Lifestyle changes such as improved diet, regular exercise and stopping smoking can reduce risk factors and improve cardiovascular health.

5.

Why might lifestyle changes be preferred to some medical treatments for cardiovascular disease?

Lifestyle changes can reduce disease risk without the risks or side effects associated with some medical treatments.

6.

How should the advantages and disadvantages of medication, surgery and lifestyle changes be evaluated when treating cardiovascular disease?

Treatment should be evaluated by considering effectiveness, risks, side effects, cost, long-term suitability and the individual's circumstances.

6.1 Describe photosynthetic organisms as the main producers of food and therefore biomass

1.

What are photosynthetic organisms?

Photosynthetic organisms are organisms that use light energy to make food by photosynthesis.

2.

Why are photosynthetic organisms described as producers?

They are described as producers because they produce organic food from carbon dioxide and water.

3.

Why are photosynthetic organisms the main producers of food in ecosystems?

They are the main producers because they convert light energy into chemical energy stored in glucose.

4.

How do photosynthetic organisms produce biomass?

They produce biomass by using glucose made during photosynthesis to make organic substances and build new cells and tissues.

5.

Why is photosynthesis important for providing food for other organisms?

Photosynthetic organisms provide food that supplies energy and biomass for other organisms.

6.

How does the production of biomass by photosynthetic organisms support food chains?

They form the base of food chains, providing biomass that is transferred to consumers.

6.2 Describe photosynthesis in plants and algae as an endothermic reaction that uses light energy to react carbon dioxide and water to produce glucose and oxygen

1.

What is photosynthesis?

Photosynthesis is an endothermic reaction in which plants and algae use light energy to convert carbon dioxide and water into glucose and oxygen.

2.

Which two raw materials are required for photosynthesis?

Carbon dioxide and water.

3.

What products are produced during photosynthesis?

Glucose and oxygen.

4.

Why is photosynthesis described as an endothermic reaction?

It is endothermic because it takes in energy from the surroundings.

5.

What form of energy is required for photosynthesis?

Light energy.

6.

Where do plants obtain the carbon dioxide and water required for photosynthesis?

Carbon dioxide enters through the stomata in leaves, while water is absorbed from the soil by the roots.

6.3 Explain the effect of temperature, light intensity and carbon dioxide concentration as limiting factors on the rate of photosynthesis

1.

What is meant by a limiting factor in photosynthesis?

A limiting factor is a factor that limits the rate of photosynthesis when it is in short supply.

2.

How does light intensity affect the rate of photosynthesis when light is a limiting factor?

Increasing light intensity increases the rate of photosynthesis until another factor becomes limiting.

3.

How does carbon dioxide concentration affect the rate of photosynthesis when carbon dioxide is a limiting factor?

Increasing carbon dioxide concentration increases the rate of photosynthesis until another factor becomes limiting.

4.

How does temperature affect the rate of photosynthesis?

Increasing temperature increases the rate up to an optimum temperature; above this, the rate decreases.

5.

Why does increasing one limiting factor eventually stop increasing the rate of photosynthesis?

Another factor becomes the limiting factor, so increasing the original factor no longer increases the rate.

6.

How can temperature, light intensity and carbon dioxide concentration each limit the rate of photosynthesis?

Low light intensity, low carbon dioxide concentration or an unsuitable temperature can each limit the rate of photosynthesis.

6.4 Explain the interactions of temperature, light intensity and carbon dioxide concentration in limiting the rate of photosynthesis

1.

Why can more than one factor limit the rate of photosynthesis at the same time?

The rate of photosynthesis depends on several environmental factors, so more than one can limit the rate at different times.

2.

How does the effect of increasing light intensity depend on the availability of carbon dioxide?

Increasing light intensity increases the rate only while carbon dioxide is available in sufficient concentration; otherwise carbon dioxide becomes limiting.

3.

How does the effect of increasing carbon dioxide concentration depend on light intensity?

Increasing carbon dioxide concentration increases the rate only if there is sufficient light; otherwise light intensity remains limiting.

4.

Why does increasing temperature only increase the rate of photosynthesis within a suitable temperature range?

Increasing temperature increases the rate only up to an optimum because photosynthesis involves enzyme-controlled reactions.

5.

How can changing one environmental factor reveal another limiting factor?

Increasing one factor until the rate stops increasing shows that another factor has become limiting.

6.

How do temperature, light intensity and carbon dioxide concentration interact to determine the rate of photosynthesis?

The rate of photosynthesis is determined by whichever of temperature, light intensity or carbon dioxide concentration is most limiting at that time.

6.5 Core Practical: Investigate the effect of light intensity on the rate of photosynthesis

1.

How could you investigate the effect of light intensity on the rate of photosynthesis in a plant?

Place an aquatic plant at different distances from a lamp and measure the rate of photosynthesis at each distance, for example by measuring oxygen produced in a fixed time.

2.

What variable should be changed when investigating the effect of light intensity on photosynthesis?

Light intensity.

3.

What measurement could be used to determine the rate of photosynthesis in an aquatic plant?

The volume or number of bubbles of oxygen produced in a given time.

4.

Which variables should be controlled when investigating the effect of light intensity on photosynthesis?

Temperature, carbon dioxide concentration, type and size of plant, volume of water and time allowed for each measurement.

5.

Why should the temperature and carbon dioxide concentration be kept constant when investigating light intensity?

To ensure that changes in the rate of photosynthesis are caused by light intensity rather than other limiting factors.

6.

How could repeated measurements improve the reliability of an investigation into the effect of light intensity on photosynthesis?

Repeat each measurement and calculate a mean, identifying and investigating any anomalous results.

6.6 Explain how the rate of photosynthesis is directly proportional to light intensity and inversely proportional to the distance from a light source, including the use of the inverse square law calculation

1.

How does the rate of photosynthesis change when light intensity increases, if light intensity is the limiting factor?

The rate of photosynthesis increases in direct proportion to light intensity while light intensity is the limiting factor.

2.

What does it mean for the rate of photosynthesis to be directly proportional to light intensity?

It means that if light intensity increases by a certain factor, the rate of photosynthesis increases by the same factor, provided other factors are not limiting.

3.

How does the intensity of light change as the distance from a light source increases?

Light intensity decreases as the distance from the light source increases.

4.

What does it mean for light intensity to be inversely proportional to the square of the distance from a light source?

It means light intensity is proportional to 1/distance².

5.

A plant is moved from 20 cm to 40 cm from a light source. By what factor does the light intensity change?

The distance doubles, so the light intensity decreases by a factor of 4.

6.

How can the inverse square law be used to calculate changes in light intensity when the distance from a light source changes?

Use the inverse square relationship: new light intensity / original light intensity = (original distance / new distance)².

6.7 Explain how the structure of the root hair cells is adapted to absorb water and mineral ions

1.

What is the function of a root hair cell?

Root hair cells absorb water and mineral ions from the soil.

2.

How does the long extension of a root hair cell help it absorb water and mineral ions?

The long extension provides a large surface area for absorption.

3.

How does the large surface area of root hair cells help water uptake?

The large surface area increases the area available for water to enter the cell.

4.

How does the thin cell wall of a root hair cell help water enter the cell?

The thin cell wall provides a short distance for water to diffuse through.

5.

How are mineral ions absorbed by root hair cells when their concentration is lower in the soil than inside the cell?

Mineral ions are absorbed by active transport, using energy to move ions against their concentration gradient.

6.

How is the structure of a root hair cell adapted for efficient absorption of water and mineral ions?

Root hair cells have long extensions, a large surface area and thin cell walls, and contain adaptations for active transport of mineral ions.

6.8 Explain how the structures of the xylem and phloem are adapted to their function in the plant, including: a lignified dead cells in xylem transporting water and minerals through the plant b living cells in phloem using energy to transport sucrose around the plant

1.

What is the function of xylem tissue?

Xylem transports water and mineral ions from the roots through the plant.

2.

How are xylem vessels adapted to transport water and mineral ions?

Xylem vessels are long, continuous tubes of dead cells with no end walls and lignified walls.

3.

Why does lignin strengthen xylem vessels?

Lignin strengthens the vessels and prevents them collapsing when water is transported under tension.

4.

What is the function of phloem tissue?

Phloem transports sucrose around the plant.

5.

Why do phloem cells require energy to transport sucrose?

Energy is required for the active transport involved in loading sucrose into phloem.

6.

How do the structures of xylem and phloem differ in relation to their functions?

Xylem consists of lignified dead cells adapted for transporting water and minerals, whereas phloem consists of living cells adapted for transporting sucrose using energy.

6.9 Explain how water and mineral ions are transported through the plant by transpiration, including the structure and function of the stomata

1.

What is transpiration?

Transpiration is the loss of water vapour from a plant, mainly through the stomata in leaves.

2.

How does water loss from leaves contribute to the movement of water through a plant?

Water evaporating from the leaves creates a pull that draws more water up through the xylem.

3.

How are mineral ions transported through a plant with water?

Mineral ions dissolved in water are carried upwards through the xylem.

4.

What are stomata?

Stomata are pores in the surface of leaves that allow gases and water vapour to move into and out of the leaf.

5.

How do stomata control the movement of gases and water vapour into and out of a leaf?

Guard cells open and close the stomata, controlling gas exchange and water vapour loss.

6.

How does transpiration result in water and mineral ions being transported from the roots to the leaves?

Water evaporates from the leaves during transpiration, creating a transpiration stream that pulls water and dissolved mineral ions from the roots to the leaves through the xylem.

6.10 Describe how sucrose is transported around the plant by translocation

1.

What is translocation?

Translocation is the transport of dissolved sucrose around a plant.

2.

Which substance is transported around a plant by translocation?

Sucrose.

3.

Which plant tissue transports sucrose by translocation?

Phloem.

4.

Why does a plant need to transport sucrose from its leaves to other parts of the plant?

Sucrose is transported to parts of the plant where it is needed for respiration, growth or storage.

5.

How can sucrose be transported from a source to a sink in a plant?

Sucrose is transported through the phloem from sources, such as leaves, to sinks, such as roots, fruits or growing tissues.

6.

How does translocation differ from the transport of water and mineral ions in plants?

Translocation transports sucrose through the phloem, whereas water and mineral ions are transported through the xylem.

6.12 Explain the effect of environmental factors on the rate of water uptake by a plant, to include light intensity, air movement and temperature

1.

How does increasing light intensity affect the rate of water uptake by a plant?

Increasing light intensity generally increases the rate of water uptake.

2.

Why can increased light intensity increase the rate of water uptake by a plant?

Greater light intensity causes stomata to open more, increasing transpiration and therefore water uptake.

3.

How does increased air movement affect the rate of water uptake by a plant?

Increased air movement generally increases the rate of water uptake.

4.

Why can increased air movement increase the rate of water uptake by a plant?

Air movement removes water vapour from around the leaf, maintaining a steep concentration gradient for diffusion.

5.

How does temperature affect the rate of water uptake by a plant?

Increasing temperature generally increases water uptake because it increases the rate of evaporation and diffusion of water vapour, up to suitable conditions.

6.

How do light intensity, air movement and temperature affect water uptake through their effects on transpiration?

Increased light intensity, air movement and temperature generally increase transpiration, which increases the rate of water uptake.

6.13 Demonstrate an understanding of rate calculations for transpiration

1.

How is the rate of transpiration calculated from a change in mass over a given time?

Rate of transpiration = change in mass ÷ time.

2.

A plant loses 6 g of water in 30 minutes. What is its average rate of water loss in g/min?

6 ÷ 30 = 0.2 g/min.

3.

A plant loses 12 g of water over 2 hours. Calculate its average rate of water loss in g/hour.

12 ÷ 2 = 6 g/hour.

4.

A plant loses 0.8 g of water in 20 minutes. Calculate its rate of water loss in g/min.

0.8 ÷ 20 = 0.04 g/min.

5.

A plant loses 9 g of water in 3 hours. Calculate its average rate of water loss in g/hour.

9 ÷ 3 = 3 g/hour.

6.

Why is calculating the rate of water loss more useful than simply measuring the total mass of water lost when comparing transpiration in different plants?

Rate allows fair comparison between plants or conditions even when different amounts of time have been used.

7.1 Describe where hormones are produced and how they are transported from endocrine glands to their target organs, including the pituitary gland, thyroid gland, pancreas, adrenal glands, ovaries and testes

1.

What is a hormone, and how are hormones transported from endocrine glands to their target organs?

A hormone is a chemical messenger released by an endocrine gland and transported in the blood to a target organ.

2.

Where is the pituitary gland located, and what is its role as an endocrine gland?

The pituitary gland is located at the base of the brain and releases hormones that control other endocrine glands and body processes.

3.

Which hormone-producing gland is located in the neck, and what is its main hormone?

The thyroid gland is located in the neck and produces thyroxine.

4.

Which hormones are produced by the pancreas, and what process do they regulate?

The pancreas produces insulin and glucagon, which regulate blood glucose concentration.

5.

Where are the adrenal glands located, and what hormone associated with the fight-or-flight response do they produce?

The adrenal glands are located above the kidneys and produce adrenalin.

6.

Which hormones are produced by the ovaries and testes?

The ovaries produce oestrogen and progesterone; the testes produce testosterone.

7.2 Explain that adrenalin is produced by the adrenal glands to prepare the body for fight or flight, including: a increased heart rate b increased blood pressure c increased blood flow to the muscles d raised blood sugar levels by stimulating the liver to change glycogen into glucose

1.

Which glands produce adrenalin, and why is adrenalin released during a fight-or-flight response?

The adrenal glands produce adrenalin, which prepares the body for rapid physical activity in a fight-or-flight situation.

2.

How does adrenalin affect heart rate and blood pressure during a fight-or-flight response?

Adrenalin increases heart rate and blood pressure, increasing the delivery of blood to tissues.

3.

How does adrenalin increase blood flow to the muscles during a fight-or-flight response?

It increases blood flow to the muscles, providing them with more oxygen and glucose for respiration.

4.

How does adrenalin increase blood glucose concentration during a fight-or-flight response?

Adrenalin stimulates the liver to break down glycogen into glucose, increasing blood glucose concentration.

5.

What substance stored in the liver is converted into glucose when adrenalin raises blood glucose concentration?

Glycogen.

6.

Explain how the effects of adrenalin prepare the body for vigorous physical activity.

Adrenalin increases heart rate, blood pressure, blood flow to muscles and blood glucose concentration, providing muscles with more oxygen and glucose for increased respiration and activity.

7.3 Explain how thyroxine controls metabolic rate as an example of negative feedback, including: a low levels of thyroxine stimulates production of TRH in hypothalamus b this causes release of TSH from the pituitary gland c TSH acts on the thyroid to produce thyroxine d when thyroxine levels are normal thyroxine inhibits the release of TRH and the production of TSH

1.

What is the role of thyroxine in controlling metabolic rate?

Thyroxine controls the body's metabolic rate.

2.

What happens to TRH production when thyroxine levels in the blood are low?

Low thyroxine levels stimulate the hypothalamus to produce TRH.

3.

How does TRH cause the production of thyroxine to increase?

TRH stimulates the pituitary gland to release TSH.

4.

What is the role of TSH in controlling thyroxine production?

TSH stimulates the thyroid gland to produce thyroxine.

5.

What happens to TRH and TSH production when thyroxine levels return to normal?

Normal thyroxine levels inhibit the release of TRH and the production of TSH.

6.

Explain how thyroxine provides an example of negative feedback.

When thyroxine levels fall, TRH and TSH production increase, stimulating thyroxine production. When thyroxine levels return to normal, thyroxine inhibits TRH and TSH production, reducing further thyroxine production.

7.4 Describe the stages of the menstrual cycle, including the roles of the hormones oestrogen and progesterone, in the control of the menstrual cycle

1.

What happens to the uterus lining during menstruation?

The uterus lining breaks down and is lost from the body as menstrual blood.

2.

What happens to the uterus lining during the part of the menstrual cycle when it is repaired and thickened?

The uterus lining is repaired and thickened in preparation for possible implantation.

3.

What is ovulation, and approximately when does it occur during the menstrual cycle?

Ovulation is the release of an egg from an ovary and occurs approximately halfway through the menstrual cycle, around day 14 of a 28-day cycle.

4.

What is the role of oestrogen in the menstrual cycle?

Oestrogen stimulates the repair and thickening of the uterus lining.

5.

What is the role of progesterone in the menstrual cycle?

Progesterone maintains the uterus lining after ovulation.

6.

What causes the uterus lining to break down during menstruation?

The uterus lining breaks down when progesterone levels fall.

7.5 Explain the interactions of oestrogen, progesterone, FSH and LH in the control of the menstrual cycle, including the repair and maintenance of the uterus wall, ovulation and menstruation

1.

What is the role of FSH in the menstrual cycle?

FSH stimulates the development of an egg-containing follicle and stimulates the production of oestrogen.

2.

How does FSH stimulate the production of oestrogen during the menstrual cycle?

FSH stimulates the development of a follicle, which produces oestrogen.

3.

How does oestrogen affect FSH production and the uterus lining?

Oestrogen stimulates the repair and thickening of the uterus lining and inhibits FSH production; high oestrogen levels contribute to the LH surge.

4.

What is the role of LH in causing ovulation?

LH causes ovulation.

5.

How does progesterone maintain the uterus lining after ovulation?

Progesterone maintains the uterus lining after ovulation.

6.

Explain how changes in oestrogen, progesterone, FSH and LH control the menstrual cycle.

FSH stimulates follicle development and oestrogen production; oestrogen repairs the uterus lining and influences FSH and LH; LH causes ovulation; progesterone maintains the lining, and falling progesterone leads to menstruation.

7.6 Explain how hormonal contraception influences the menstrual cycle and prevents pregnancy

1.

How does hormonal contraception prevent pregnancy?

Hormonal contraception uses hormones to prevent ovulation and therefore reduces the chance of fertilisation.

2.

How can hormonal contraceptives containing oestrogen and progesterone prevent ovulation?

Oestrogen and progesterone maintain relatively high hormone levels, inhibiting FSH and LH and preventing ovulation.

3.

How does hormonal contraception affect FSH and LH levels?

Hormonal contraception inhibits the release of FSH and LH.

4.

How can hormonal contraception make it more difficult for sperm to reach an egg?

Some hormonal contraceptives increase the thickness of cervical mucus, making it more difficult for sperm to reach an egg.

5.

How can hormonal contraception affect the uterus lining?

Hormonal contraception can alter the uterus lining, reducing the likelihood of implantation.

6.

Explain how hormonal contraception reduces the probability of fertilisation and pregnancy.

It reduces the probability of ovulation, fertilisation and implantation, thereby reducing the chance of pregnancy.

7.7 Evaluate hormonal and barrier methods of contraception

1.

What is a hormonal method of contraception, and how does it prevent pregnancy?

Hormonal contraception uses hormones to prevent ovulation and may also thicken cervical mucus or alter the uterus lining.

2.

What is a barrier method of contraception, and how does it prevent pregnancy?

Barrier contraception physically prevents sperm from reaching an egg.

3.

What are the advantages of hormonal contraception compared with barrier contraception?

Hormonal contraception is generally more effective at preventing pregnancy when used correctly and does not require use during every act of intercourse.

4.

What are the disadvantages of hormonal contraception compared with barrier contraception?

Hormonal contraception can cause side effects and does not generally protect against STIs.

5.

Which type of contraception can also reduce the risk of sexually transmitted infections?

Barrier methods such as condoms can reduce the risk of sexually transmitted infections.

6.

How should the effectiveness, side effects, convenience and protection against STIs be considered when evaluating contraceptive methods?

Consider effectiveness, reliability, side effects, ease of use, convenience, cost and protection against STIs when evaluating methods.

7.8 Explain the use of hormones in Assisted Reproductive Technology (ART) including IVF and clomifene therapy

1.

What is assisted reproductive technology (ART), and why may hormones be used during ART?

ART includes treatments that assist fertilisation or pregnancy; hormones can stimulate egg production or ovulation.

2.

How are hormones used during IVF to stimulate the development of multiple eggs?

Hormones can stimulate the ovaries to develop and mature multiple eggs during IVF.

3.

What happens to an egg and sperm during IVF before the resulting embryo is transferred to the uterus?

Eggs are collected and fertilised with sperm in a laboratory; the resulting embryo develops before being transferred to the uterus.

4.

What is the purpose of transferring an embryo into the uterus during IVF?

The embryo is transferred to the uterus so that it can implant in the uterus lining and develop into a pregnancy.

5.

How does clomifene therapy increase the chance of ovulation?

Clomifene stimulates the release of hormones that promote ovulation, increasing the chance of an egg being released.

6.

Explain how hormones can be used in IVF and clomifene therapy to increase the chance of pregnancy.

During IVF, hormones stimulate the development of multiple eggs before fertilisation and embryo transfer; clomifene stimulates ovulation to increase the chance of pregnancy.

7.9 Explain the importance of maintaining a constant internal environment in response to internal and external change

1.

What is meant by maintaining a constant internal environment?

Maintaining a constant internal environment means keeping conditions inside the body within suitable limits.

2.

Why must organisms maintain a constant internal environment?

Cells require stable conditions for their metabolic reactions to occur effectively.

3.

Which internal conditions are commonly regulated to maintain a constant internal environment?

Conditions such as temperature, blood glucose concentration and water content are regulated.

4.

How can changes in the external environment affect the internal conditions of an organism?

Changes in the external environment can alter internal conditions, such as body temperature or water balance.

5.

What is homeostasis?

Homeostasis is the regulation of the internal conditions of an organism to maintain a stable internal environment.

6.

Explain why homeostasis is important for the correct functioning of cells and enzymes.

Homeostasis keeps conditions suitable for enzyme activity and cellular processes, allowing cells to function correctly.

7.13 Explain how the hormone insulin controls blood glucose concentration

1.

What causes the pancreas to release insulin?

The pancreas releases insulin when blood glucose concentration is too high.

2.

What effect does insulin have on blood glucose concentration?

Insulin lowers blood glucose concentration.

3.

How does insulin cause body cells to take up more glucose from the blood?

Insulin causes body cells to take up more glucose from the blood.

4.

How does insulin affect the conversion of glucose into glycogen in the liver and muscles?

Insulin stimulates the liver and muscles to convert glucose into glycogen for storage.

5.

What happens to blood glucose concentration when insulin is released?

Blood glucose concentration decreases.

6.

Explain how insulin helps return a high blood glucose concentration to a normal level.

When blood glucose concentration rises, the pancreas releases insulin. Insulin increases glucose uptake by cells and conversion of glucose to glycogen, reducing blood glucose concentration towards normal.

7.14 Explain how blood glucose concentration is regulated by glucagon

1.

What causes the pancreas to release glucagon?

The pancreas releases glucagon when blood glucose concentration is too low.

2.

What effect does glucagon have on blood glucose concentration?

Glucagon increases blood glucose concentration.

3.

How does glucagon affect glycogen stored in the liver?

Glucagon stimulates the breakdown of glycogen stored in the liver into glucose.

4.

What happens to blood glucose concentration when glucagon is released?

Blood glucose concentration increases.

5.

How do insulin and glucagon have opposite effects on blood glucose concentration?

Insulin lowers blood glucose concentration, whereas glucagon increases it.

6.

Explain how glucagon helps return a low blood glucose concentration to a normal level.

When blood glucose concentration falls, the pancreas releases glucagon, which stimulates glycogen to be converted to glucose in the liver, raising blood glucose concentration towards normal.

7.15 Explain the cause of type 1 diabetes and how it is controlled

1.

What causes type 1 diabetes?

Type 1 diabetes occurs when the immune system attacks and destroys the insulin-producing cells of the pancreas.

2.

Why can a person with type 1 diabetes have a high blood glucose concentration?

There is insufficient insulin to cause cells to take up glucose and for glucose to be converted into glycogen, so blood glucose concentration remains high.

3.

Why does the immune system cause a lack of insulin in type 1 diabetes?

The immune system mistakenly attacks the body's insulin-producing cells.

4.

How is type 1 diabetes controlled using insulin?

It is controlled by administering insulin, usually by injection or an insulin pump.

5.

How can a person with type 1 diabetes adjust insulin treatment to help control blood glucose concentration?

Insulin doses can be adjusted according to food intake, exercise and blood glucose concentration.

6.

Explain why people with type 1 diabetes require insulin to regulate their blood glucose concentration.

People with type 1 diabetes produce little or no insulin, so insulin must be supplied to lower and regulate blood glucose concentration.

7.16 Explain the cause of type 2 diabetes and how it is controlled

1.

What is the main cause of type 2 diabetes?

Type 2 diabetes is mainly caused by body cells becoming resistant to insulin; being overweight is an important risk factor.

2.

What is meant by insulin resistance in type 2 diabetes?

Insulin resistance means body cells respond less effectively to insulin.

3.

Why can blood glucose concentration remain high in a person with type 2 diabetes?

Cells take up less glucose in response to insulin, so blood glucose concentration remains higher than normal.

4.

How can changes to diet and exercise help control type 2 diabetes?

A healthier diet, weight management and regular exercise can improve insulin sensitivity and help control blood glucose concentration.

5.

What medicines may be used to help control type 2 diabetes?

Medicines such as metformin may be used to help control blood glucose concentration.

6.

Explain how type 2 diabetes can be controlled through lifestyle changes and, when necessary, medication.

Type 2 diabetes can be controlled through diet, exercise and weight management, with medication used when necessary.

7.17 Evaluate the correlation between body mass and type 2 diabetes including waist:hip calculations and BMI, using the BMI equation

1.

What does BMI measure, and how is BMI calculated from body mass and height?

BMI = mass (kg) ÷ height (m)².

2.

A person has a mass of 80 kg and a height of 1.60 m. Calculate their BMI.

BMI = 80 ÷ 1.60² = 80 ÷ 2.56 = 31.25 kg/m².

3.

A person has a mass of 72 kg and a height of 1.80 m. Calculate their BMI.

BMI = 72 ÷ 1.80² = 72 ÷ 3.24 = 22.22 kg/m².

4.

How can waist-to-hip ratio be calculated?

Waist-to-hip ratio = waist circumference ÷ hip circumference.

5.

Why can a higher body mass or waist-to-hip ratio be associated with an increased risk of type 2 diabetes?

Higher body mass, particularly excess body fat around the waist, is associated with a higher risk of type 2 diabetes.

6.

Explain why a correlation between body mass and type 2 diabetes does not necessarily prove that body mass alone causes the disease.

A correlation shows that two variables are associated, but it does not prove that one directly causes the other because other factors may influence the relationship.

8.1 Describe the need to transport substances into and out of a range of organisms, including oxygen, carbon dioxide, water, dissolved food molecules, mineral ions and urea

1.

Why do multicellular organisms need transport systems to move substances around their bodies?

Multicellular organisms need transport systems to move substances between exchange surfaces and cells throughout the body.

2.

Which gas must be transported to cells for aerobic respiration?

Oxygen.

3.

Which waste gas produced by aerobic respiration must be transported away from cells?

Carbon dioxide.

4.

Why must water and dissolved food molecules be transported to cells?

Water and dissolved food molecules are needed by cells for metabolic reactions, growth and other cellular processes.

5.

Why do organisms need to transport mineral ions to their cells?

Mineral ions are needed for processes such as making proteins and maintaining healthy cells.

6.

Why must urea be transported away from cells?

Urea is a waste product that must be transported to the kidneys for excretion.

8.2 Explain the need for exchange surfaces and a transport system in multicellular organisms including the calculation of surface area : volume ratio

1.

Why do multicellular organisms require specialised exchange surfaces for efficient movement of substances?

Specialised exchange surfaces provide a large area for substances to move into and out of the organism efficiently.

2.

Why does a small surface area to volume ratio make exchange by diffusion less efficient in a multicellular organism?

A small surface area to volume ratio means there is less surface area available for exchange relative to the volume of cells requiring substances.

3.

Calculate the surface area : volume ratio of a cube with a surface area of 150 cm² and a volume of 125 cm³.

Surface area : volume = 150 : 125 = 1.2 : 1.

4.

Calculate the surface area : volume ratio of a cube with a surface area of 600 mm² and a volume of 1000 mm³.

Surface area : volume = 600 : 1000 = 0.6 : 1.

5.

Why does increasing the size of an organism generally decrease its surface area to volume ratio?

Volume increases more rapidly than surface area as an organism becomes larger.

6.

Why do multicellular organisms require transport systems in addition to exchange surfaces?

Exchange surfaces alone cannot supply substances quickly enough to cells that are far from the surface, so a transport system is required.

8.3 Explain how alveoli are adapted for gas exchange by diffusion between air in the lungs and blood in capillaries

1.

How does the large surface area of the alveoli increase the rate of gas exchange?

The large surface area provides more area for diffusion, increasing the rate of gas exchange.

2.

How does the thin wall of an alveolus increase the rate of diffusion between the air and blood?

The thin alveolar wall gives a short diffusion distance, increasing the rate of diffusion.

3.

Why does the extensive blood supply surrounding the alveoli help maintain a concentration gradient for oxygen?

The extensive blood supply continually brings deoxygenated blood to the alveoli, maintaining a steep concentration gradient for oxygen.

4.

How does ventilation of the lungs help maintain a concentration gradient between alveolar air and the blood?

Ventilation continually replaces air in the alveoli, maintaining concentration gradients for oxygen and carbon dioxide.

5.

In which direction does oxygen diffuse between the alveoli and surrounding capillaries, and why?

Oxygen diffuses from the alveoli into the blood because the oxygen concentration is higher in the alveoli than in the blood.

6.

In which direction does carbon dioxide diffuse between the blood and alveoli, and why?

Carbon dioxide diffuses from the blood into the alveoli because its concentration is higher in the blood.

8.6 Explain how the structure of the blood is related to its function: a red blood cells (erythrocytes) b white blood cells (phagocytes and lymphocytes) c plasma d platelets

1.

How is the biconcave shape of a red blood cell adapted for transporting oxygen?

Their biconcave shape provides a large surface area and short diffusion distance for oxygen.

2.

How does the absence of a nucleus in a red blood cell increase its ability to transport oxygen?

It provides more space for haemoglobin, allowing more oxygen to be transported.

3.

What are the roles of phagocytes and lymphocytes in defending the body against pathogens?

Phagocytes engulf and digest pathogens; lymphocytes produce antibodies.

4.

How are phagocytes adapted to engulf and destroy pathogens?

They can change shape and surround pathogens before engulfing them.

5.

What substances are transported in blood plasma?

Plasma transports substances including glucose, amino acids, carbon dioxide, urea, hormones, mineral ions and heat.

6.

How are platelets adapted to their role in blood clotting?

Platelets are small cell fragments that help form blood clots, preventing excessive blood loss and entry of pathogens.

8.7 Explain how the structure of the blood vessels is related to their function

1.

How is the thick muscular wall of an artery adapted to withstand high blood pressure?

The thick muscular and elastic wall withstands and maintains the high pressure of blood leaving the heart.

2.

How does the narrow lumen of an artery help maintain high blood pressure?

The narrow lumen helps maintain high blood pressure.

3.

How is the thin wall of a capillary adapted for efficient exchange of substances with tissues?

The thin wall provides a short diffusion distance for exchange between blood and tissues.

4.

Why are capillaries arranged as extensive networks around body tissues?

Networks provide a large surface area and ensure most cells are close to a blood supply.

5.

How are veins adapted to carry blood back to the heart at relatively low pressure?

Veins have thinner walls, wider lumens and valves to return blood to the heart at low pressure.

6.

What is the function of valves in veins, and why are they necessary?

Valves prevent the backflow of blood, ensuring blood flows towards the heart.

8.8 Explain how the structure of the heart and circulatory system is related to its function, including the role of the major blood vessels, the valves and the relative thickness of chamber walls

1.

Why is the wall of the left ventricle thicker than the wall of the right ventricle?

The left ventricle pumps blood around the whole body, so it needs a thicker muscular wall to generate higher pressure.

2.

What is the function of the valves in the heart?

Valves prevent the backflow of blood and ensure it flows in the correct direction.

3.

What is the function of the septum separating the left and right sides of the heart?

The septum prevents oxygenated and deoxygenated blood from mixing.

4.

Which major blood vessel carries oxygenated blood from the heart to the body, and which chamber pumps this blood?

The aorta carries oxygenated blood to the body, and the left ventricle pumps this blood.

5.

Which major blood vessel carries deoxygenated blood from the body to the heart?

The vena cava carries deoxygenated blood from the body to the heart.

6.

Why does the circulatory system transport blood through the lungs before it reaches the rest of the body?

Blood is transported through the lungs to pick up oxygen and remove carbon dioxide before being pumped to the rest of the body.

8.9 Describe cellular respiration as an exothermic reaction which occurs continuously in living cells to release energy for metabolic processes, including aerobic and anaerobic respiration

1.

Why is cellular respiration described as an exothermic reaction?

It releases energy to the surroundings.

2.

Where does cellular respiration occur in living cells?

Cellular respiration occurs continuously in living cells, with aerobic respiration occurring mainly in mitochondria.

3.

Why must cellular respiration occur continuously in living cells?

Cells continuously require energy for metabolic processes.

4.

What is the main purpose of the energy released during cellular respiration?

The energy is used for metabolic processes such as active transport, movement, growth and synthesis of substances.

5.

What substances are used and produced during aerobic respiration?

Aerobic respiration uses glucose and oxygen and produces carbon dioxide and water.

6.

What is the difference between aerobic and anaerobic respiration in terms of oxygen availability?

Aerobic respiration uses oxygen; anaerobic respiration occurs without oxygen.

8.10 Compare the process of aerobic respiration with the process of anaerobic respiration

1.

What are the reactants and products of aerobic respiration?

Glucose + oxygen → carbon dioxide + water.

2.

What is the product of anaerobic respiration in human muscle cells?

Lactic acid.

3.

Why does anaerobic respiration release less energy than aerobic respiration?

Glucose is only partially broken down, so less energy is released.

4.

What is produced during anaerobic respiration in yeast?

Ethanol and carbon dioxide.

5.

Why may muscle cells use anaerobic respiration during vigorous exercise?

Oxygen supply may not meet the energy demand of muscles during vigorous exercise.

6.

What is the main difference between aerobic and anaerobic respiration regarding the use of oxygen?

Aerobic respiration requires oxygen, whereas anaerobic respiration does not.

8.11 Core Practical: Investigate the rate of respiration in living organisms

1.

How could you investigate the rate of respiration in germinating seeds by measuring the uptake of oxygen?

Place germinating seeds in a sealed respirometer and measure the decrease in gas volume or movement of a marker as oxygen is taken up over time.

2.

Why could a respirometer be used to investigate the rate of respiration in germinating seeds?

A respirometer allows changes in gas volume caused by oxygen uptake during respiration to be measured.

3.

What variable could be changed to investigate its effect on the rate of respiration in a respirometer?

Temperature, or another suitable independent variable such as the mass of seeds.

4.

Why should a control be included when investigating the rate of respiration in living organisms?

A control allows changes caused by respiration to be distinguished from changes caused by other factors.

5.

How could the rate of respiration be calculated from measurements of oxygen uptake over time?

Rate of respiration = volume of oxygen taken up ÷ time.

6.

Why should temperature be controlled when investigating the rate of respiration in living organisms?

Temperature affects the rate of enzyme-controlled reactions involved in respiration, so it must be kept constant for a fair test.

8.12 Calculate heart rate, stroke volume and cardiac output, using the equation cardiac output = stroke volume × heart rate

1.

A person's heart beats 72 times per minute. Calculate their heart rate in beats per minute.

72 beats/min.

2.

A person's heart pumps 70 cm³ of blood per beat at a heart rate of 75 beats per minute. Calculate their cardiac output in cm³ per minute.

Cardiac output = 70 × 75 = 5250 cm³/min.

3.

A person's cardiac output is 5,600 cm³ per minute and their heart rate is 80 beats per minute. Calculate their stroke volume.

Stroke volume = 5600 ÷ 80 = 70 cm³/beat.

4.

A person's stroke volume is 90 cm³ and their heart rate is 65 beats per minute. Calculate their cardiac output in cm³ per minute.

Cardiac output = 90 × 65 = 5850 cm³/min.

5.

A person's cardiac output is 7,200 cm³ per minute and their stroke volume is 80 cm³ per beat. Calculate their heart rate.

Heart rate = 7200 ÷ 80 = 90 beats/min.

6.

An athlete has a stroke volume of 120 cm³ and a heart rate of 150 beats per minute during exercise. Calculate their cardiac output in dm³ per minute.

Cardiac output = 120 × 150 = 18 000 cm³/min = 18 dm³/min.

9.1 Describe the different levels of organisation from individual organisms, populations, communities, to the whole ecosystem

1.

What is an organism in an ecosystem?

An organism is an individual living thing.

2.

What is a population?

A population is all the organisms of one species living in a particular area.

3.

What is a community?

A community is all the populations of different species living and interacting in an area.

4.

What is an ecosystem?

An ecosystem is a community of organisms and the non-living components of their environment.

5.

What is the difference between a population and a community?

A population consists of one species, whereas a community contains populations of different species.

6.

What is the correct order of ecological organisation from the smallest level to the largest: organism, population, community and ecosystem?

Organism → population → community → ecosystem.

9.2 Explain how communities can be affected by abiotic and biotic factors, including: a temperature, light, water, pollutants b competition, predation

1.

What is an abiotic factor, and how can temperature affect the organisms in a community?

An abiotic factor is a non-living factor; temperature affects enzyme activity and therefore the survival and distribution of organisms.

2.

How can light intensity affect the distribution and abundance of organisms in a community?

Light intensity affects photosynthesis and therefore can affect the growth, distribution and abundance of plants and organisms that depend on them.

3.

How can water availability affect the distribution and abundance of organisms in a community?

Water availability affects the survival, growth and distribution of organisms.

4.

How can pollutants affect the organisms within a community?

Pollutants can harm organisms, reduce population sizes and disrupt ecosystems.

5.

How can competition between organisms affect the size of populations within a community?

Competition for resources can reduce population sizes and limit the distribution of organisms.

6.

How can predation affect the population sizes of predator and prey species within a community?

Predation reduces prey numbers and provides food for predators, so changes in prey numbers can affect predator populations.

9.3 Describe the importance of interdependence in a community

1.

What is meant by interdependence between organisms in a community?

Interdependence means organisms depend on other organisms for resources or survival.

2.

Why are organisms in a community often dependent on other species for their survival?

Organisms may depend on other species for food, shelter, pollination or other resources.

3.

How can a reduction in the population of one species affect other species in the same community?

A reduction in one species can reduce food or resources available to other species, changing their population sizes.

4.

How can changes in prey abundance affect a predator population?

A decrease in prey abundance can reduce the size of a predator population.

5.

Why can the removal of one species have effects throughout a community?

Removing one species can affect organisms that depend on it for food or other resources, causing changes throughout the community.

6.

How does interdependence contribute to the stability of a community?

Interdependence means changes to one population can affect others, contributing to interactions that influence community stability.

9.4 Describe how the survival of some organisms is dependent on other species, including parasitism and mutualism

1.

What is parasitism?

Parasitism is a relationship in which one organism benefits while the host is harmed.

2.

How does a parasite benefit from its relationship with a host?

A parasite obtains resources such as nutrients from its host.

3.

How can parasitism negatively affect the survival of the host organism?

The parasite can damage the host, reducing its health or ability to survive and reproduce.

4.

What is mutualism?

Mutualism is a relationship in which both organisms benefit.

5.

How do both organisms benefit from a mutualistic relationship?

Both organisms gain an advantage from the relationship.

6.

Why can the survival of some organisms depend on maintaining a mutualistic relationship with another species?

Each organism may depend on the benefits provided by the other for survival or successful reproduction.

9.5 Core Practical: Investigate the relationship between organisms and their environment using field-work techniques, including quadrats and belt transects

1.

How can a quadrat be used to investigate the distribution of organisms in a habitat?

Place quadrats in different areas and record the number or percentage cover of the organism within each quadrat.

2.

Why should quadrats be placed randomly when investigating the distribution of plants in a habitat?

Random placement reduces bias and makes the sample more representative of the habitat.

3.

How can a belt transect be used to investigate how the distribution of organisms changes across a habitat?

Place quadrats at regular intervals along a line through the habitat and record organisms at each position.

4.

Why should several quadrats be used when investigating the abundance of organisms in a habitat?

Several quadrats provide more data and give a more representative estimate of abundance.

5.

How could you investigate the effect of distance from a river on the distribution of a plant species using a belt transect?

Place a belt transect from the river away from it, position quadrats at regular intervals and record the abundance of the plant species in each quadrat.

6.

What measurements could be recorded in quadrats placed along a belt transect to investigate the relationship between an organism and its environment?

Record the number of organisms, percentage cover or frequency of the species in each quadrat and compare these measurements with distance along the transect.

9.6 Explain how to determine the number of organisms in a given area using raw data from field-work techniques, including quadrats and belt transects

1.

How can the mean number of organisms per quadrat be calculated from raw quadrat data?

Add the numbers of organisms in all quadrats and divide by the number of quadrats.

2.

A researcher counts 8, 12, 10, 14 and 6 daisies in five quadrats. Calculate the mean number of daisies per quadrat.

Mean = (8 + 12 + 10 + 14 + 6) ÷ 5 = 10 daisies per quadrat.

3.

A researcher records an average of 15 plants per 1 m² quadrat. Estimate the number of plants in a 200 m² field.

Estimated number = 15 × 200 = 3000 plants.

4.

Why is the total area sampled important when estimating the population size of organisms?

The sampled area is used to calculate population density and extrapolate the number of organisms to the whole habitat.

5.

A researcher counts 24 organisms in ten 0.5 m² quadrats. Estimate the number of organisms in a 100 m² habitat.

Total organisms = 24 ÷ (10 × 0.5) × 100 = 480 organisms.

6.

How can data from quadrats placed along a belt transect be used to determine how the number of organisms changes across a habitat?

Compare the number or abundance of organisms in quadrats at different positions along the transect to identify changes across the habitat.

9.9 Explain the positive and negative human interactions within ecosystems and their impacts on biodiversity, including: a fish farming b introduction of non-indigenous species c eutrophication

1.

How can fish farming have positive effects on human food supplies and reduce pressure on wild fish populations?

Fish farming produces a reliable supply of fish and can reduce fishing pressure on wild populations.

2.

How can fish farming negatively affect biodiversity in aquatic ecosystems?

Fish farms can release waste, nutrients, chemicals or escaped fish that may disrupt ecosystems and reduce biodiversity.

3.

Why can introducing a non-indigenous species reduce biodiversity in an ecosystem?

A non-indigenous species may compete with native species, prey on them or introduce diseases.

4.

How can a non-indigenous species affect native species through competition or predation?

It can reduce native populations through competition for resources or predation.

5.

How can fertilisers containing nitrates and phosphates cause eutrophication?

Fertilisers can enter water and increase nitrate and phosphate concentrations, causing excessive algal growth.

6.

How can eutrophication lead to the death of aquatic organisms and a reduction in biodiversity?

Algal blooms block light and eventually die; microorganisms decompose them and use up oxygen, causing aquatic organisms to die.

9.10 Explain the benefits of maintaining local and global biodiversity, including the conservation of animal species and the impact of reforestation

1.

What is biodiversity?

Biodiversity is the variety of different species of organisms in an area.

2.

Why is maintaining biodiversity important for the stability of ecosystems?

Greater biodiversity can make ecosystems more stable and resilient to environmental changes.

3.

How can conserving endangered animal species help maintain biodiversity?

Conservation prevents species from becoming extinct and maintains the variety of species within ecosystems.

4.

How can reforestation increase biodiversity?

Reforestation creates habitats and increases the number of plant and animal species that can live in an area.

5.

How can maintaining biodiversity provide resources that are useful to humans?

Biodiversity provides resources such as food, medicines, timber and genetic resources.

6.

Why can reforestation have benefits for both biodiversity and the environment?

Reforestation provides habitats, increases biodiversity, stores carbon and can help improve soil and water quality.

9.12 Describe how different materials cycle through the abiotic and biotic components of an ecosystem

1.

What is meant by a material cycle in an ecosystem?

A material cycle is the continuous movement and recycling of materials between living organisms and the non-living environment.

2.

What are the biotic components of an ecosystem?

The biotic components are the living organisms in an ecosystem.

3.

What are the abiotic components of an ecosystem?

The abiotic components are the non-living parts of an ecosystem, such as air, water and soil.

4.

How do materials move between organisms and the non-living environment?

Organisms take materials from the environment and return them through processes such as respiration, excretion and decomposition.

5.

Why must materials such as carbon, water and nitrogen be continually recycled through ecosystems?

Materials are limited resources, so recycling makes them available for repeated use by organisms.

6.

How do decomposers contribute to the cycling of materials between biotic and abiotic components of an ecosystem?

Decomposers break down dead organisms and waste, releasing substances back into the environment for reuse.

9.13 Explain the importance of the carbon cycle, including the processes involved and the role of microorganisms as decomposers

1.

Why is the carbon cycle important to living organisms?

Carbon is needed to make carbohydrates, proteins, lipids and other biological molecules.

2.

How does photosynthesis transfer carbon dioxide from the atmosphere into living organisms?

Plants and algae absorb carbon dioxide during photosynthesis and convert the carbon into organic compounds.

3.

How does respiration return carbon dioxide to the atmosphere?

Respiration releases carbon dioxide back into the atmosphere.

4.

How does combustion of fossil fuels transfer carbon from fossil fuels into atmospheric carbon dioxide?

Combustion releases carbon stored in fossil fuels as carbon dioxide into the atmosphere.

5.

How do microorganisms act as decomposers in the carbon cycle?

Microorganisms decompose dead organisms and waste materials, releasing carbon dioxide through respiration.

6.

How does decomposition return carbon from dead organisms and waste materials to the atmosphere?

Decomposers break down dead material and waste; the microorganisms respire and release carbon dioxide into the atmosphere.

9.14 Explain the importance of the water cycle, including the processes involved and the production of potable water in areas of drought including desalination

1.

Why is the water cycle important to living organisms and ecosystems?

Water is essential for living organisms and is continually recycled through ecosystems and the environment.

2.

What processes transfer water from the Earth's surface into the atmosphere during the water cycle?

Evaporation and transpiration transfer water into the atmosphere as water vapour.

3.

How does water return from the atmosphere to the Earth's surface?

Water returns to the Earth's surface by precipitation.

4.

How can water from the environment be treated to produce potable water?

Water can be treated by filtration and sterilisation to remove particles and microorganisms and produce potable water.

5.

Why can desalination be used to produce potable water in areas affected by drought?

Desalination can provide potable water from seawater when freshwater supplies are limited by drought.

6.

How does desalination remove dissolved salts from seawater to produce potable water?

Desalination removes dissolved salts from seawater, commonly by distillation or reverse osmosis.

9.15 Explain how nitrates are made available for plant uptake, including the use of fertilisers, crop rotation and the role of bacteria in the nitrogen cycle

1.

Why do plants need nitrate ions?

Plants need nitrate ions to make amino acids and proteins.

2.

How do nitrogen-fixing bacteria contribute to making nitrogen compounds available in soil?

Nitrogen-fixing bacteria convert atmospheric nitrogen into nitrogen compounds that can enter the nitrogen cycle and become available to plants.

3.

How do nitrifying bacteria help make nitrate ions available for plant uptake?

Nitrifying bacteria convert ammonium compounds into nitrites and then nitrates.

4.

How can fertilisers increase the availability of nitrate ions for plants?

Fertilisers add nitrate ions or compounds containing nitrogen to the soil, increasing nitrate availability.

5.

How does crop rotation with leguminous plants increase the nitrate content of soil?

Leguminous plants contain nitrogen-fixing bacteria in root nodules; growing them during crop rotation increases nitrogen compounds in the soil.

6.

Why are bacteria essential for making nitrogen compounds available to plants in the nitrogen cycle?

Bacteria carry out key conversions in the nitrogen cycle that make nitrogen compounds, including nitrates, available for plant uptake.

Biology

Edexcel GCSE Combined Science: Biology

Topic 1 – Key concepts in biology