AQA GCSE Combined Science: Trilogy Biology Paper 2 (Foundation), 2021: Question 1

10 marks · Standard Demand difficulty · Short Answer

Identify chromosome numbers, define genetic terms, and complete a Punnett square to determine the probability of inheriting a specific trait.

Practise this question

Question

A biology exam paper featuring seven sub-questions about genetics. It starts with a multiple-choice question about the number of chromosomes in a human sperm cell. This is followed by a matching task where students must link the terms 'Gene', 'Genome', and 'Nucleus' to their definitions. The final section describes the inheritance of the ability to taste PTC, featuring a Punnett square for two heterozygous parents (Tt) and questions on genotype identification and phenotype probability.
Question text

01 A human body cell contains 46 chromosomes.

01.1 How many chromosomes does a human sperm cell contain?

[1 mark]

Tick ( ) one box.

22 23 46

01.2 Draw one line from each word to the meaning of that word.

[3 marks]

Word Meaning

A small ring of DNA in the

cytoplasm

Gene

All the genetic material of

an organism

Genome

A small section of DNA

which codes for a protein

Nucleus

A structure which

4 contains chromosomes

Some plants contain a harmful chemical called PTC.

Some people can taste PTC.

01.3 Suggest one advantage of being able to taste PTC.

*03* [1 mark]

Only people with a dominant allele T can taste PTC.

People with only the allele t cannot taste PTC.

01.4 A person has the genotype Tt.

What word describes the person’s genotype?

[1 mark]

Tick ( ) one box.

Heterozygous

Phenotype

Recessive

01.5 Give the genotype of a person who cannot taste PTC.

[1 mark]

01.6 A woman and a man plan to have a child.

The woman and the man both have the genotype Tt.

Complete Figure 1 to show the possible genotypes of the child.

[2 marks]

*04* Figure 1

Woman

T t

T T T

Man

t

01.7 What is the chance of the child being able to taste PTC?

Use Figure 1.

[1 mark]

Tick ( ) one box.

25% 50% 75% 100%

Mark scheme

Show the mark scheme The mark scheme for the genetics questions. It lists '23' as the correct chromosome count for 01.1. For 01.2, it shows lines connecting Gene to 'A small section of DNA...', Genome to 'All the genetic material...', and Nucleus to 'A structure which contains chromosomes'. It provides 'heterozygous' for 01.4, 'tt' for 01.5, a completed Punnett square for 01.6 with genotypes Tt, Tt, and tt, and '75%' for the probability in 01.7.

AO /

Question Answers Extra information Mark

Spec. Ref.

01.1 23 1 AO1

4.6.1.2

01.2 AO1

4.6.1.4

4.6.1.3

additional line from a box on the left negates the mark for that box

01.3 any one from: 1 AO2

• to survive allow to protect them 4.7.1.4

• so you do not eat the plants

• to stop you being harmed /

poisoned allow stop you getting ill / dying

01.4 heterozygous 1 AO2

4.6.1.4

01.5 tt allow homozygous recessive 1 AO2

4.6.1.4

01.6 allow 1 or 2 genotypes correct 2 AO2

Woman

for 1 mark 4.6.1.4

T t

T T T Tt

Man

t Tt tt

01.7 75% allow only a probability 1 AO3

consistent with student’s 4.6.1.4

derivation

if no answer to question 01.6

allow 75%

Total 10

How to answer it

Genetics, Inheritance, and the PTC Tasting Gene

What this question tests

This question assesses your understanding of basic genetic terminology, the difference between body cells and gametes, and your ability to use Punnett squares to predict the probability of offspring inheriting specific traits.

Part 01.1

Chromosome Numbers

Correct Answer

23

Key Knowledge

  • Human body cells contain 46 chromosomes (23 pairs).
  • Gametes (sperm and egg cells) contain half that number: 23 chromosomes.

Exam Technique

Always look for the word "sperm" or "egg". If you see these, you must divide the normal body cell number by 2. This is because when they join during fertilisation, they restore the full number (23 + 23 = 46).

Part 01.2

Genetic Definitions

Correct Matching

  • Gene: A small section of DNA which codes for a protein.
  • Genome: All the genetic material of an organism.
  • Nucleus: A structure which contains chromosomes.

Common Errors

Students often confuse "Gene" with "Genome". Remember: Genome = The Whole Home (everything), while a Gene = One Instruction.

⚠️ Examiner Tip: Drawing two lines from one word will cancel out the mark for that word, even if one of the lines is correct!

Part 01.3

Survival Advantages

Correct Answer

To survive / To stop you being poisoned / To stop you eating harmful plants.

Exam Technique

When asked for an "advantage" in biology, think about survival. If a chemical is "harmful," being able to taste it means you won't eat it, which keeps you alive.

Parts 01.4 & 01.5

Genotypes and Phenotypes

Correct Answers

01.4: Heterozygous

01.5: tt (or homozygous recessive)

Key Knowledge

  • Heterozygous: Two different alleles (e.g., Tt).
  • Homozygous: Two of the same alleles (e.g., TT or tt).
  • Dominant (T): Only needs one copy to show the trait.
  • Recessive (t): Needs two copies to show the trait.
Part 01.6

The Punnett Square

Step-by-Step Calculation

To complete the grid for two parents with genotype Tt:

  1. Combine the top letter and side letter for each empty box.
  2. Always write the capital letter first if there is one.
T t
T TT Tt
t Tt tt

Award 1 mark for 1 or 2 correct genotypes; 2 marks for all 3 correct.

Part 01.7

Calculating Probability

Correct Answer

75%

How to work it out

  • The question asks for the chance of being able to taste PTC.
  • Tasters need at least one dominant allele (T).
  • Looking at our grid: TT, Tt, and Tt are all tasters.
  • That is 3 out of 4 boxes.
  • 3/4 = 75%

Common Trap

Don't confuse the genotype (the letters) with the phenotype (the physical ability). Even though Tt and TT look different in the grid, they both result in the same "Taster" ability.

Topics

Biology · B6: Inheritance, Variation and Evolution · B7: Ecology

Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Biology Paper 2 (Foundation), 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.