CSEC BIOLOGY · SECTION C · SECTION TEST

Section C Test: Continuity and Variation

Twenty multiple-choice items and three structured questions covering DNA, cell division, inheritance, sex linkage, variation, natural selection and genetic engineering.

Continuity and Variation20 MCQ31 structured marks≈ 45 min
Before you start

How to take this test

  1. Take it after you have worked through the lessons below — it checks the whole section, not one lesson.
  2. Work under exam conditions: about 45 minutes, no notes. Every question here is new; none is repeated from the lessons.
  3. Part 1: answer every multiple-choice item, then check. Items you get wrong tell you which lesson to revisit.
  4. Part 2: write full answers, then reveal each mark scheme and self-mark strictly.
  5. Your test score (multiple choice 50% + structured 50%) counts towards your section and paper readiness.

Lessons covered: C1 DNA, Genes, Chromosomes and Mitosis, C2 Meiosis and Gamete Formation, C3 Inheritance: Genetic Crosses, C4 Sex Determination and Sex-Linked Inheritance, C5 Genetic Variation, C6 Species, Speciation and Natural Selection, C7 Genetic Engineering

Part 1 · Multiple choice

Multiple choice

20 items covering the whole section. Choose the best answer for each, then check.

C1 · SO C1.1

1. A section of DNA that codes for a particular protein is a

Answer: B. A gene is a length of DNA coding for one protein; a chromosome carries many genes.
C1 · SO C1.1

2. A sample of DNA contains 15% thymine. What percentage of the bases are cytosine?

Answer: A. Adenine pairs with thymine, so each is 15% (30% together). Cytosine and guanine share the other 70% equally: 35% each.
C1 · SO C2.2

3. Mitosis produces

Answer: D. Mitosis keeps the chromosome number and produces identical cells.
C1 · SO C2.3

4. Which of the following is NOT a role of mitosis?

Answer: B. Gametes are produced by meiosis.
C2 · SO C2.4

5. How many chromosomes are in a human egg cell?

Answer: A. Gametes are haploid: half of 46.
C2 · SO C2.5

6. Which event in meiosis increases genetic variation?

Answer: C. Crossing over exchanges sections between paired chromosomes, making new combinations.
C2 · SO C2.6

7. In a flowering plant, meiosis takes place in the

Answer: B. Meiosis happens in the reproductive organs — anthers and ovules.
C3 · SO C2.8

8. A heterozygous tall plant (Tt) is crossed with a short plant (tt). What ratio of offspring is expected?

Answer: A. Tt × tt gives 2 Tt : 2 tt = 1 tall : 1 short.
C3 · SO C2.7

9. An organism with two identical alleles for a gene is

Answer: B. Homo- = same: e.g. TT or tt.
C3 · SO C2.9

10. Flower colour in snapdragons shows codominance (CᴿCᴿ red, CᴿCᵂ pink, CᵂCᵂ white). What fraction of offspring from pink × pink will be white?

Answer: B. CᴿCᵂ × CᴿCᵂ gives 1 red : 2 pink : 1 white.
C3 · SO C2.7

11. The term “phenotype” means

Answer: C. Phenotype is what you see; genotype is the alleles.
C4 · SO C2.10

12. A couple already has two sons. What is the probability that their next child will be a girl?

Answer: A. Each pregnancy is independent; half the sperm carry X.
C4 · SO C2.10

13. A man with haemophilia (XʰY) has children with a woman who is not a carrier (XᴴXᴴ). Their daughters will

Answer: A. Every daughter receives the father’s Xʰ and the mother’s Xᴴ: XᴴXʰ.
C4 · SO C2.10

14. Sex-linked conditions such as colour blindness are more common in males because males

Answer: D. With one X, a single recessive allele is expressed.
C5 · SO C3.3

15. Which is an example of DISCONTINUOUS variation?

Answer: C. Blood groups fall into distinct categories with no in-betweens.
C5 · SO C3.1

16. The original source of new alleles in a population is

Answer: D. Mutation creates new alleles; meiosis and fertilisation shuffle existing ones.
C6 · SO C4.1

17. Two populations are considered separate species when they

Answer: C. The species test is the ability to produce fertile offspring.
C6 · SO C5.1

18. Antibiotic-resistant bacteria become more common in a hospital because

Answer: C. Antibiotics select bacteria that already carry resistance.
C7 · SO C6.1

19. Which enzyme is used to cut DNA at specific sequences in genetic engineering?

Answer: D. Restriction enzymes cut; ligase joins.
C7 · SO C6.2

20. One difference between genetic engineering and artificial selection is that genetic engineering

Answer: D. Genetic engineering can move a gene from one species into another, quickly.
Part 2 · Structured questions

Structured questions

3 Paper 2 style questions (31 marks). Write your answers first, then reveal the mark scheme and tick the points you earned.

C3 · Original · SO C2.7, C2.8, C2.10

Question 1 [11 marks]

In cattle, the allele for hornless (polled) (H) is dominant to the allele for horns (h).

(a) Define the terms “dominant” and “recessive”. [2]

MARK SCHEME — (a) (max 2)

(b) A farmer crosses a hornless bull with several horned cows. About half the calves have horns. Use a full genetic diagram to explain this result. [5]

MARK SCHEME — (b) (max 5)

(c) Suggest how the farmer could ensure that all future calves are hornless. [2]

MARK SCHEME — (c) (max 2)

(d) Explain why a colour-blind father cannot pass colour blindness to his son. [2]

MARK SCHEME — (d) (max 2)

C2 · Original · SO C2.2, C2.5, C3.1, C3.3

Question 2 [10 marks]

Cell division and variation.

(a) State THREE differences between mitosis and meiosis. [3]

MARK SCHEME — (a) (max 3)

(b) Explain how meiosis and fertilisation produce variation among offspring. [3]

MARK SCHEME — (b) (max 3)

(c) Distinguish between continuous and discontinuous variation, giving ONE example of each. [4]

MARK SCHEME — (c) (max 4)

C6 · Original · SO C4.1, C5.1, C6.1, C6.2

Question 3 [10 marks]

Warfarin is a poison once widely used to kill rats. In some areas, rats are now resistant to it.

(a) Using the theory of natural selection, explain how a warfarin-resistant rat population developed. [4]

MARK SCHEME — (a) (max 4)

(b) Define the term “species”. [1]

MARK SCHEME — (b) (max 1)

(c) Outline how bacteria can be genetically engineered to produce human insulin. [3]

MARK SCHEME — (c) (max 3)

(d) State TWO concerns people have about growing genetically modified crops. [2]

MARK SCHEME — (d) (max 2)

Your result

Test score

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Multiple choice (50%)0%
Structured (50%)0%