AQA A LEVEL BIOLOGY PAPER 2 (2026) STUDY
OUTLINE & MARK SCHEME REVIEW GUIDE (7402/2)
|| NEW UPDATED VERSION
Topic 1: Inheritance (17 Questions)
1. What is the difference between a gene and an allele?
✓ A gene is a sequence of DNA bases that codes for a polypeptide. An allele is a
specific, alternative form of a gene.
2. What is meant by codominance?
✓ Both alleles are expressed in the phenotype, neither one is recessive.
3. A person with blood group AB is an example of what genetic inheritance pattern?
✓ Codominance.
4. What is a mutation?
✓ A change in the sequence of DNA bases.
5. What is a frameshift mutation and why is it often more severe than a substitution?
✓ The insertion or deletion of bases, which changes every subsequent triplet code
(codon) downstream, altering the entire amino acid sequence.
6. What is meant by the term 'multiple alleles'?
✓ A gene that has more than two possible allele forms (e.g., the gene for human blood
group).
7. Describe the difference between genetic diversity and phenotypic variation.
✓ Genetic diversity is the number of different alleles in a population. Phenotypic
variation is the difference in observable characteristics, caused by both genetic and
environmental factors.
8. What is the role of meiosis in generating genetic variation?
✓ It produces genetically unique haploid gametes through the processes of crossing
over (prophase I) and independent assortment (metaphase I).
9. What is the chi-squared (χ²) test used for in genetics?
✓ To determine if there is a significant difference between observed and expected
results, testing the validity of a null hypothesis.
, 10. If the calculated χ² value is greater than the critical value, what do you conclude?
✓ Reject the null hypothesis; there is a significant difference between observed and
expected, meaning the results are not due to chance alone.
11. What is the difference between interspecific and intraspecific competition?
✓ Interspecific is between different species. Intraspecific is between individuals of the
same species.
12. Define stabilising selection.
✓ A type of natural selection that favours the average phenotypes and selects against
the extreme phenotypes, reducing variation.
13. Define directional selection.
✓ A type of natural selection that favours one extreme phenotype, causing the
population mean to shift in one direction.
14. What is the Hardy-Weinberg principle?
✓ A mathematical model that predicts that allele frequencies in a population will
remain constant from generation to generation, assuming no evolutionary influences
are acting.
15. State the two Hardy-Weinberg equations.
✓ p² + 2pq + q² = 1 and p + q = 1 (where p = frequency of dominant allele, q = frequency
of recessive allele).
16. In a population, 16% show the recessive phenotype (tt). Calculate the frequency of the
heterozygous genotype (Tt).
✓ q² = 0.16, so q = 0.4. p = 1 - 0.4 = 0.6. 2pq = 2 * 0.6 * 0.4 = 0.48 (48%).
17. What are the conditions required for the Hardy-Weinberg principle to hold true?
✓ No mutations, no natural selection, a large population, random mating, and no
migration (isolated population).
Topic 2: Populations and Evolution (14 Questions)
18. What is a species?
✓ A group of similar organisms that can interbreed to produce fertile, viable offspring.
19. What is a population?
✓ A group of individuals of the same species that live in the same habitat and can
interbreed.
,20. What is the biological definition of a gene pool?
✓ The complete set of alleles present in a population at a given time.
21. What is allopatric speciation?
✓ The formation of a new species due to geographical isolation, which prevents
interbreeding and leads to genetic divergence.
22. What is sympatric speciation?
✓ The formation of a new species without geographical isolation, often due to genetic
or behavioural differences (e.g., polyploidy in plants).
23. What is genetic drift?
✓ A change in allele frequency in a small population due to chance, not natural
selection.
24. Why does genetic drift have a greater effect in smaller populations?
✓ Because chance events have a larger proportional impact on the gene pool.
25. What is the founder effect?
✓ A type of genetic drift where a small group breaks away from a main population to
found a new colony, with a gene pool that is not representative of the source
population.
26. What is a phylogenetic tree?
✓ A diagram that shows the evolutionary relationships between different species.
27. What is the role of a courtship ritual in species classification?
✓ It is species-specific, allowing individuals to recognise members of their own species
to mate with, preventing interbreeding. It can be used to classify species based on
behavioural similarities.
28. How can DNA sequencing be used to classify organisms?
✓ The more similar the DNA base sequence, the more closely related the species are
assumed to be.
29. What is the definition of biodiversity?
✓ The variety of living organisms in an area. It includes species diversity, genetic
diversity, and ecosystem diversity.
30. What is the formula for an index of diversity (d)?
✓ d = N(N-1) / Σn(n-1) (where N = total number of organisms, n = number of individuals
of each species).
, 31. Why is a high index of diversity important for an ecosystem?
✓ It often leads to greater stability, as the ecosystem is more resilient to
environmental changes.
Topic 3: Homeostasis and Response (20 Questions)
32. What is homeostasis?
✓ The maintenance of a stable internal environment despite changes in external or
internal conditions.
33. What is negative feedback?
✓ A process that reverses a deviation from the normal level, bringing the system back
to its set point.
34. What is positive feedback?
✓ A process that amplifies a change from the normal level, leading to an even greater
deviation (e.g., oxytocin during childbirth).
35. Outline the role of the pancreas in blood glucose regulation.
✓ It detects blood glucose levels and secretes the hormones insulin (from β-cells) and
glucagon (from α-cells).
36. Describe how insulin lowers blood glucose concentration.
✓ It binds to receptors on target cells (e.g., liver/muscle), increasing their permeability
to glucose. It also stimulates glycogenesis (conversion of glucose to glycogen).
37. Describe how glucagon raises blood glucose concentration.
✓ It binds to receptors on liver cells, stimulating glycogenolysis (breakdown of
glycogen to glucose) and gluconeogenesis (production of glucose from non-
carbohydrates).
38. What is the second messenger model of hormone action?
✓ A hormone (1st messenger, e.g., adrenaline/glucagon) binds to a receptor on the cell
surface membrane, activating a G-protein which activates adenylate cyclase. This
converts ATP to cyclic AMP (cAMP, the 2nd messenger), which then triggers a cascade
of intracellular effects.
39. What is the difference between Type 1 and Type 2 diabetes?
✓ Type 1 is an autoimmune disease where the body attacks its own β-cells, leading to
an inability to produce insulin. Type 2 is where the body's cells become resistant to
insulin, often linked to obesity.
OUTLINE & MARK SCHEME REVIEW GUIDE (7402/2)
|| NEW UPDATED VERSION
Topic 1: Inheritance (17 Questions)
1. What is the difference between a gene and an allele?
✓ A gene is a sequence of DNA bases that codes for a polypeptide. An allele is a
specific, alternative form of a gene.
2. What is meant by codominance?
✓ Both alleles are expressed in the phenotype, neither one is recessive.
3. A person with blood group AB is an example of what genetic inheritance pattern?
✓ Codominance.
4. What is a mutation?
✓ A change in the sequence of DNA bases.
5. What is a frameshift mutation and why is it often more severe than a substitution?
✓ The insertion or deletion of bases, which changes every subsequent triplet code
(codon) downstream, altering the entire amino acid sequence.
6. What is meant by the term 'multiple alleles'?
✓ A gene that has more than two possible allele forms (e.g., the gene for human blood
group).
7. Describe the difference between genetic diversity and phenotypic variation.
✓ Genetic diversity is the number of different alleles in a population. Phenotypic
variation is the difference in observable characteristics, caused by both genetic and
environmental factors.
8. What is the role of meiosis in generating genetic variation?
✓ It produces genetically unique haploid gametes through the processes of crossing
over (prophase I) and independent assortment (metaphase I).
9. What is the chi-squared (χ²) test used for in genetics?
✓ To determine if there is a significant difference between observed and expected
results, testing the validity of a null hypothesis.
, 10. If the calculated χ² value is greater than the critical value, what do you conclude?
✓ Reject the null hypothesis; there is a significant difference between observed and
expected, meaning the results are not due to chance alone.
11. What is the difference between interspecific and intraspecific competition?
✓ Interspecific is between different species. Intraspecific is between individuals of the
same species.
12. Define stabilising selection.
✓ A type of natural selection that favours the average phenotypes and selects against
the extreme phenotypes, reducing variation.
13. Define directional selection.
✓ A type of natural selection that favours one extreme phenotype, causing the
population mean to shift in one direction.
14. What is the Hardy-Weinberg principle?
✓ A mathematical model that predicts that allele frequencies in a population will
remain constant from generation to generation, assuming no evolutionary influences
are acting.
15. State the two Hardy-Weinberg equations.
✓ p² + 2pq + q² = 1 and p + q = 1 (where p = frequency of dominant allele, q = frequency
of recessive allele).
16. In a population, 16% show the recessive phenotype (tt). Calculate the frequency of the
heterozygous genotype (Tt).
✓ q² = 0.16, so q = 0.4. p = 1 - 0.4 = 0.6. 2pq = 2 * 0.6 * 0.4 = 0.48 (48%).
17. What are the conditions required for the Hardy-Weinberg principle to hold true?
✓ No mutations, no natural selection, a large population, random mating, and no
migration (isolated population).
Topic 2: Populations and Evolution (14 Questions)
18. What is a species?
✓ A group of similar organisms that can interbreed to produce fertile, viable offspring.
19. What is a population?
✓ A group of individuals of the same species that live in the same habitat and can
interbreed.
,20. What is the biological definition of a gene pool?
✓ The complete set of alleles present in a population at a given time.
21. What is allopatric speciation?
✓ The formation of a new species due to geographical isolation, which prevents
interbreeding and leads to genetic divergence.
22. What is sympatric speciation?
✓ The formation of a new species without geographical isolation, often due to genetic
or behavioural differences (e.g., polyploidy in plants).
23. What is genetic drift?
✓ A change in allele frequency in a small population due to chance, not natural
selection.
24. Why does genetic drift have a greater effect in smaller populations?
✓ Because chance events have a larger proportional impact on the gene pool.
25. What is the founder effect?
✓ A type of genetic drift where a small group breaks away from a main population to
found a new colony, with a gene pool that is not representative of the source
population.
26. What is a phylogenetic tree?
✓ A diagram that shows the evolutionary relationships between different species.
27. What is the role of a courtship ritual in species classification?
✓ It is species-specific, allowing individuals to recognise members of their own species
to mate with, preventing interbreeding. It can be used to classify species based on
behavioural similarities.
28. How can DNA sequencing be used to classify organisms?
✓ The more similar the DNA base sequence, the more closely related the species are
assumed to be.
29. What is the definition of biodiversity?
✓ The variety of living organisms in an area. It includes species diversity, genetic
diversity, and ecosystem diversity.
30. What is the formula for an index of diversity (d)?
✓ d = N(N-1) / Σn(n-1) (where N = total number of organisms, n = number of individuals
of each species).
, 31. Why is a high index of diversity important for an ecosystem?
✓ It often leads to greater stability, as the ecosystem is more resilient to
environmental changes.
Topic 3: Homeostasis and Response (20 Questions)
32. What is homeostasis?
✓ The maintenance of a stable internal environment despite changes in external or
internal conditions.
33. What is negative feedback?
✓ A process that reverses a deviation from the normal level, bringing the system back
to its set point.
34. What is positive feedback?
✓ A process that amplifies a change from the normal level, leading to an even greater
deviation (e.g., oxytocin during childbirth).
35. Outline the role of the pancreas in blood glucose regulation.
✓ It detects blood glucose levels and secretes the hormones insulin (from β-cells) and
glucagon (from α-cells).
36. Describe how insulin lowers blood glucose concentration.
✓ It binds to receptors on target cells (e.g., liver/muscle), increasing their permeability
to glucose. It also stimulates glycogenesis (conversion of glucose to glycogen).
37. Describe how glucagon raises blood glucose concentration.
✓ It binds to receptors on liver cells, stimulating glycogenolysis (breakdown of
glycogen to glucose) and gluconeogenesis (production of glucose from non-
carbohydrates).
38. What is the second messenger model of hormone action?
✓ A hormone (1st messenger, e.g., adrenaline/glucagon) binds to a receptor on the cell
surface membrane, activating a G-protein which activates adenylate cyclase. This
converts ATP to cyclic AMP (cAMP, the 2nd messenger), which then triggers a cascade
of intracellular effects.
39. What is the difference between Type 1 and Type 2 diabetes?
✓ Type 1 is an autoimmune disease where the body attacks its own β-cells, leading to
an inability to produce insulin. Type 2 is where the body's cells become resistant to
insulin, often linked to obesity.
