Looking at past-paper questions (2)
Monacia Williams, Contributor

Hello again, students. I hope you have been doing well in your exams so far and that you have not had any surprises on those papers you have already done. Remember now, do not select areas to study, ensure that you revise everything.

Last week we began looking at question one from the January 2010 paper. The question gives you an idea of the type of sub-question that can be asked in this very important first question. I certainly hope you were able to provide the answers to the various parts even before I gave them to you. Remember, this is the longest question on the paper and it also carries the most marks. Let me remind you again that it is based on the practical work you would have carried out over the last two years.

Don't even begin to think that because you have handed in your lab books and the lab grades have been sent off to CXC, you have finished with labs. You will need that knowledge to answer the question one that will be on your exam paper.

Now, let us complete the question we began last week. We have already done parts (a) and (b) so we will continue with (c).

(c) Plants have mechanisms for responding to the environment.

(i) How does the response shown in Figure 2 benefit the plant? (2 marks)

Answer

In order to answer the question, you will first need to determine what the response is. What is it? Notice what is happening to the plant? It is responding to the movement of the sun. It positions itself to match the sun's position in the sky. Is this beneficial to the plant? Yes.

• In these positions the plant is able to obtain maximum sunlight as the sun is always perpendicular to it.
• This will facilitate a higher rate of photosynthesis, the process by which plants manufacture food.

(ii) Describe an experiment to determine whether a leaf on a potted plant has been photosynthesising. (3 marks)

Answer

You need to be careful here. Pay attention to the allotted marks; only three are allotted. This means you do not need to go through all the steps of the experiment, state the method and also what observation is expected.

• Boil the leaf to kill the cells
• Boil with alcohol to decolourise
• Rinse with water to soften
• Add iodine to leaf in petri dish
• If leaf becomes blue black, starch is present
• If starch is present, photosynthesis was taking place

(iii) Name TWO conditions OTHER THAN light, that are necessary for photosynthesis. (2 marks)

Answer

This might present a problem for some students because they were taught that photosynthesis had only two conditions and these were sunlight and chlorophyll. So then, what could be another? You could safely say a suitable temperature since all enzyme-controlled reactions need a suitable temperature in order to take place. Remember that photosynthesis involves a series of enzyme- controlled reactions. So the two other conditions are:

• Suitable temperature
• Chlorophyll

(d) The response to gravity shown by seedlings is due to uneven distribution of auxins. In experiments to demonstrate this response, the seedlings in the control are constantly rotated.

(i) Why is this an important step in the investigation? (2 marks)

Answer

Do you remember what happens to the auxin that is produced by the root tips and shoot tips? It diffuses unevenly away from the tips. More auxin goes to one side than the other and causes the cells on that side to elongate, causing the root tip or the stem tip to curve or bend. So, why does the control need to be constantly rotated? The answer is to prevent gravity from promoting the uneven distribution of auxin so that all the cells will receive the same amount - the same degree of elongation will take place in all cells and hence the tip will grow straight.

(ii) Explain why the response to gravity is essential for plant survival. (2 marks)

Answer

• Gravity causes the root to grow into the soil.
• Soil provides the plant with water and minerals.
• Soil provides anchorage for the plants.

I hope these answers were helpful to you and gave a boost to your confidence in approaching the biology exam. Remember that on many occasions question one has also included:

• graphs - both to draw and to interpret
• experiments to design
• food webs to draw
• simple calculations to make.

D not be intimidated. You have done it before, you can do it again! Now, have you been following all the tips I gave you? Have you covered all the required material? Are you going to get a grade one? Of course you are! You are definitely not going to let me down. It was great sharing with you all. God's blessing be with you as you write your paper!

Monacia Williams teaches at Glenmuir High School. Send questions and comments to kerry-ann.hepburn@gleanerjm.com