Examination questions and answers
Joanna George-Johnson, Contributor

Exam papers are passed based on the candidate's knowledge and exam techniques. Be sure to read all instructions for each paper that you do. For each question, try not to focus only on a single topic, but on the subject area; because knowledge on many topics may be needed to answer a single question.

Here are a few examples with the answers:

1. Figure 1A shows a vertical section through a pair of guard cells and through some epidermal cells as they appear in a leaf in the dark. Figure 1B shows a simple drawing of the same guard cells seen in surface view.

Figure 1A

Figure 1B

(a) (i) On Figure 1A, clearly label a cell wall, cytoplasm and a vacuole. (3 marks)

N.B. Since the question did not specify that the labels were to be on the guard cell, then they could be placed on any of the cells present.

(ii) In the space below, redraw Figure 1B to show the cells as they appear in the daylight. (2 marks)

Drawing should show the guard cells curved out like two sausages facing each other. Therefore, the 'stoma' will be clearly visible. Make sure to label the diagram showing the stoma and guard cells. (labels help, especially when the drawing skills are poor)

(b) Name the gases which pass into and out of a leaf in daylight. (2 marks)

All the gases found in air may be mentioned: O2, N2 and CO2

(C) Explain the possible advantages to a plant of the stomata being closed at night. (3 marks)

Oxygen generated during photosynthesis may be used for respiration at night.

Figure 2A

Figure 2B

2. Figure 2A shows the appearance of droplets of fat in the human stomach. Figure 2B shows how the same fat appears farther along the alimentary canal.

(a) Where in the alimentary canal would fat droplets, similar to those in figure 2B, be found?

Duodenum (Small intestines) may be written also. (1 mark)

(b) (i) Name the process that caused the change in appearance of the fat, and explain how this change has been brought about.

Name of process - emulsification

Explanation: Type of mechanical digestion that breaks the fat pieces into smaller droplets, thus increasing its surface area. (3 marks)

(ii) Explain the importance of this process in fat digestion.

Increasing the surface area of the fat increases the rate at which the enzyme lipase can work on chemically breaking down the fat into its molecular form. (4 marks)

3. Figure 3A below is a pie chart which shows the relative proportion of certain organisms in a particular community.

Figure 3A

(a) Select two herbivores from figure 3A, and based on the information in the pie chart, give a reason for your selections.

Herbivores - butterfly & grasshopper

Reason: They have the largest part of the pie chart, and the relative numbers tend to increase as you ascend the trophic levels. (3 marks)

(b) In the space below, construct a food web using the seven species given in figure 3A. You must show three trophic levels.

Please note the direction of the arrows. Students often miss getting maximum marks from questions like this one by not putting the arrows in the right direction or not putting them at all, so be careful.

(c) What should be included to make the food web complete?

Plant (a primary producer) (1 mark)

Explain your answer

Food webs are about energy transfer; this energy ultimately comes from the sun, which is trapped by plants to be made available to living things. (1 mark)

(d) What two factors, other than food supply, determine the numbers of a species in a particular community?

Availability of space; predators; diseases, etc. (2 marks)

(e) State how it is possible for different species, having similar numbers, to live in the same environment.

They are not prey or predators of each other; both adapted to the climatic conditions, etc. (One mark, one answer is needed here.)

Figure 4

Joanna George-Johnson teaches at Ardenne High School.
Email: Masterbio@gmail.com.