Total marks: 90 · Duration: 2 hours 30 minutes
Instructions to candidates
- This paper consists of SIX questions arranged in THREE sections, corresponding to the three Modules of Unit 1.
- Answer ALL SIX questions. Each question is worth 15 marks. Marks for each part are shown in brackets.
- Begin each answer on a new page and write the question number clearly in the margin.
- Where a question asks for a diagram, graph or sketch, you must draw it in your answer booklet, fully labelled, and refer to it in your written answer. No diagrams, micrographs or figures are supplied with this paper — all data you need is given in tables.
- Where calculations are required, show all working. Marks are available for method even where the final answer is incorrect.
- Silent, non-programmable calculators are permitted.
- Unit 1 covers Module 1 (Cell and Molecular Biology), Module 2 (Genetics, Variation and Natural Selection) and Module 3 (Reproductive Biology).
Paper
Section A — Module 1: Cell and Molecular Biology (answer BOTH) — 30 marks
1. (a) Distinguish between prokaryotic and eukaryotic cells with reference to THREE structural features. (6 marks)
(b) Describe the fluid mosaic model of the plasma membrane, naming FOUR components and stating the function of each. (6 marks)
(c) A student places identical cylinders of fresh potato tissue into sucrose solutions of different concentration for 40 minutes, then reweighs them. The results are shown below.
| Sucrose concentration (mol dm⁻³) | Initial mass (g) | Final mass (g) |
|---|---|---|
| 0.00 | 5.00 | 5.60 |
| 0.20 | 5.00 | 5.20 |
| 0.40 | 5.00 | 5.00 |
| 0.60 | 5.00 | 4.65 |
| 0.80 | 5.00 | 4.30 |
Calculate the percentage change in mass for the 0.80 mol dm⁻³ solution, and state, with a reason, the approximate water potential relationship between the potato tissue and the 0.40 mol dm⁻³ solution. (3 marks)
2. (a) Compare the structure of starch, glycogen and cellulose, relating each structure to its biological function. (9 marks)
(b) An enzyme-catalysed reaction is investigated at a range of temperatures. Explain the shape of the curve that would be obtained if rate of reaction were plotted against temperature between 0 °C and 60 °C. Sketch and label the expected curve. (6 marks)
Section B — Module 2: Genetics, Variation and Natural Selection (answer BOTH) — 30 marks
3. (a) Distinguish between mitosis and meiosis with reference to the number of divisions, the chromosome number of daughter cells, and genetic variation. (6 marks)
(b) Explain TWO ways in which meiosis generates genetic variation. (4 marks)
(c) In a certain plant, red flower colour (R) is dominant to white (r). A heterozygous red-flowered plant is crossed with a white-flowered plant. Using a genetic diagram, state the genotypes of the parents and gametes and give the expected phenotypic ratio of the offspring. (5 marks)
4. (a) Define natural selection and outline the conditions necessary for it to occur. (5 marks)
(b) The table shows the percentage of a Caribbean mosquito population resistant to an insecticide over six years of continuous use.
| Year | Resistant individuals (%) |
|---|---|
| 1 | 2 |
| 2 | 5 |
| 3 | 14 |
| 4 | 38 |
| 5 | 67 |
| 6 | 89 |
Explain, in terms of natural selection, how the population changed as shown, and suggest TWO measures that could slow the development of resistance. (10 marks)
Section C — Module 3: Reproductive Biology (answer BOTH) — 30 marks
5. (a) Describe the process of fertilisation in a flowering plant, from pollination to the formation of the zygote and endosperm. (8 marks)
(b) Compare wind pollination and insect pollination, referring to THREE structural adaptations of the flower in each case. (7 marks)
6. (a) Outline the roles of FSH, LH, oestrogen and progesterone in the human menstrual cycle. (8 marks)
(b) Explain how the combined oral contraceptive pill prevents pregnancy, and discuss TWO biological considerations relevant to its use. (7 marks)