Total marks: 100 · Duration: 2 hours 30 minutes
Instructions to candidates
- This paper consists of SIX questions in TWO sections. Answer ALL questions.
- Section A has a compulsory data analysis question and two structured questions. Write your answers in the spaces provided.
- Section B has three extended response questions. Write your answers in the spaces provided at the end of each question.
- Where appropriate, answers should be illustrated by diagrams.
- You may use a silent, non-programmable calculator.
- Where a question describes apparatus, a graph or a structure in words, you may find it helpful to sketch it.
Information
- The total mark for this paper is 100. Section A carries 55 marks and Section B carries 45 marks.
- The marks for each question and part question are shown in brackets.
- This paper covers the CSEC Biology syllabus: living organisms in the environment; life processes and disease; and continuity and variation.
Paper
Section A — Data Analysis and Structured Questions (55 marks)
Question 1 — Data analysis: respiration in yeast (25 marks)
A student investigated the effect of glucose concentration on the rate of respiration in yeast. She set up six test tubes, each containing 10 cm³ of yeast suspension and 10 cm³ of glucose solution of a different concentration. Each tube was fitted with a delivery tube leading into water, and kept in a water bath at 30 °C. After 10 minutes, she counted the bubbles of gas released in one minute.
| Glucose concentration (%) | 0 | 2 | 4 | 6 | 8 | 10 |
|---|---|---|---|---|---|---|
| Bubbles per minute | 2 | 14 | 26 | 35 | 38 | 38 |
(a) (i) Plot a line graph of the results, with glucose concentration on the x-axis. [5 marks]
(ii) Describe the trend shown by the results. [2 marks]
(iii) Explain why the rate of bubbling does not increase above 8% glucose. [2 marks]
(b) (i) Identify the independent variable and the dependent variable in this investigation. [2 marks]
(ii) State two variables that the student kept constant. [2 marks]
(iii) Explain why the test tubes were kept in a water bath. [1 mark]
(iv) The student set up a seventh tube with 20% glucose solution but no yeast. Explain the purpose of this tube. [2 marks]
(c) (i) Write a word equation for anaerobic respiration in yeast. [2 marks]
(ii) Name one Caribbean industry that depends on this process. [1 mark]
(d) Describe how the student could show that the gas released is carbon dioxide. [2 marks]
(e) Calculate the percentage increase in the rate of bubbling when the glucose concentration is increased from 2% to 6%. [2 marks]
(f) Suggest one source of error in counting bubbles, and one way of improving the method. [2 marks]
Question 2 — Living organisms in the environment (15 marks)
In a coral reef, phytoplankton and seaweed are eaten by zooplankton and parrotfish. Damselfish feed on zooplankton. Barracuda feed on damselfish and parrotfish.
(a) (i) Construct a food chain of four organisms from this information. [2 marks]
(ii) Name one primary consumer in this food web. [1 mark]
(iii) Explain why food chains rarely have more than five trophic levels. [2 marks]
(b) In this reef, the primary consumers receive 2000 kJ/m² per year and the secondary consumers receive 180 kJ/m² per year. Calculate the percentage efficiency of energy transfer between these levels. [2 marks]
(c) Describe the roles of nitrogen-fixing, nitrifying and denitrifying bacteria in the nitrogen cycle. [3 marks]
(d) Untreated sewage is released into the sea near the reef. Explain how this can lead to the death of fish and coral. [3 marks]
(e) Suggest two measures that could help to conserve coral reefs in the Caribbean. [2 marks]
Question 3 — Continuity and variation (15 marks)
(a) Give three differences between mitosis and meiosis. [3 marks]
(b) Albinism is caused by a recessive allele, a. The dominant allele, A, produces normal pigmentation. Two parents with normal pigmentation have a child with albinism.
(i) State the genotypes of the parents. [1 mark]
(ii) Draw a genetic diagram to show the possible genotypes and phenotypes of their children. [2 marks]
(iii) State the probability that their next child will have albinism. [1 mark]
(c) Haemophilia is caused by a recessive allele on the X chromosome. A woman who is a carrier has children with a man who does not have haemophilia. State the probability that a son of this couple will have haemophilia. Explain your answer. [2 marks]
(d) Distinguish between continuous and discontinuous variation, giving one example of each. [2 marks]
(e) Sugar cane is grown from stem cuttings (setts). Give one advantage and one disadvantage of growing crops by asexual reproduction. [2 marks]
(f) Give one benefit and one concern about the use of genetic engineering in agriculture. [2 marks]
Section B — Extended Response (45 marks)
Question 4 — Nutrition (15 marks)
(a) A student eats a meal of rice, chicken and butter. Describe how each of the three main nutrients in this meal is digested. In your answer, name the enzymes involved, where they act and the products formed. [8 marks]
(b) Explain how the small intestine is adapted for the absorption of digested food. [4 marks]
(c) Explain why a diet high in saturated fat and salt increases the risk of heart disease. [3 marks]
Question 5 — Gaseous exchange, transport and respiration (15 marks)
(a) Describe the mechanism of breathing in (inhalation) in humans. [5 marks]
(b) Explain how the structure of red blood cells and of capillaries suits each for its function. [4 marks]
(c) Give three differences between aerobic and anaerobic respiration. [3 marks]
(d) Explain how cigarette smoking damages the respiratory system. [3 marks]
Question 6 — Disease and immunity (15 marks)
(a) Dengue fever is common in the Caribbean. Explain how dengue is transmitted, and describe three methods of controlling its spread. [6 marks]
(b) Describe how the body defends itself against pathogens that enter the blood, and explain how vaccination gives long-term protection. [5 marks]
(c) Explain why antibiotics should not be prescribed for viral infections, and why the overuse of antibiotics is a problem. [4 marks]