I. Multiple choice questions (1 Mark for each).
(20 Marks)
1. Small molecules are used as the basic units in the synthesis of large food molecules.
Which statement is correct?
A. Amino acids are basic units of carbohydrates.
B. Fatty acids are basic units of glycogen.
C. Glycerol is a basic unit of oils.
D. Simple sugar is a basic unit of protein.
2. Four different foods were tested for their composition.
The results are shown in the table.
Which food contains protein but not reducing sugar or starch?
ans.B
3. Which nutrient produces a purple colour when mixed with biuret solution?
A. fat
B. protein
C. reducing sugar
D. starch
4. The diagram shows two food tests carried out on solution X.
Which nutrients are present in solution X?
A. protein and starch
B. protein and sugar
C. starch and fat
D. starch and sugar
5. The diagram shows two food molecules before and after they have been digested by
enzymes.
What identifies the products of fat digestion?
A. P and R B. P and S C. Q and R D. Q and S
6. A student set up a test-tube containing starch, water and amylase.
How could the student test whether the amylase had digested all the starch?
A. Add Biuret solution.
B. Add dilute hydrochloric acid.
C. Add iodine solution.
D. Weigh the test-tubes and contents before and after the experiment.
6. Which pair of substances is transported in the phloem?
A. amino acids and protein
B. amino acids and sucrose
C. protein and starch
D. starch and sucrose
7. The graphs show the quantities of selected vitamins and mineral ions in four foods.
.
Which food is the richest source of the vitamin or mineral ions essential for the transport
of oxygen by the blood?
A. beans
B. egg
C. fish
D. fruit
8. When solution X is tested with iodine solution, a blue-black colour is observed.
A different solution, Y, is added to a new sample of solution X and the mixture is shaken
and left for 30 minutes at 40°C. When tested with iodine solution, an orange-brown colour
is observed. What are solutions X and Y?
ans. C
9. Which elements are contained in cellulose?
A. carbon and hydrogen only
B. carbon, hydrogen and oxygen
C. carbon, hydrogen and nitrogen
D. carbon, oxygen and nitrogen
10. Which diagram shows part of a DNA molecule? Ans.C
11. Which effect does a gradual decrease in pH from 13 to 1 have on the action of amylase?
A. slows it down only
B. slows it down then speeds it up
C. speeds it up only
D. speeds it up then slows it down
12. Which graph shows the effect of temperature between 20°C and 35°C on the activity of a
human digestive enzyme?
ans .B
13. What happens to most enzymes above 60°C?
A. They are denatured.
B. They are destroyed by white blood cells.
C. They are digested.
D. They are made more active.
14. What is a characteristic of all catalysts?
A. They are broken down in the reaction.
B. They are made of protein.
C. They are not changed by the reaction.
D. They do not change the rate of the reaction.
15. A human digestive enzyme breaks down its substrate at a fast rate at 35°C.
What would occur if the enzyme and substrate were kept at 75°C?
A .The enzyme would stop working and be denatured.
B. The reaction would continue at the same rate.
C. The reaction would take place more quickly.
D. The reaction would take place more slowly.
16. What are enzymes made of?
A. carbohydrates
B. DNA
C. fats
D. proteins
17. The diagram represents a chemical reaction.
Which diagram represents the enzyme for this reaction? Ans .D
A B C D
18. What explains why a reaction controlled by an enzyme happens more slowly as
temperature decreases?
A. The enzyme and substrate molecules have less kinetic energy.
B. The enzyme is denatured.
C. The enzyme is killed by the low temperature.
D. The substrate changes shape and cannot fit into the active site.
19. The diagram shows the action of amylase.
What is the function of the enzyme amylase?
A. breaks down the substrate into amino acids
B. changes the product into the substrate
C. increases the rate of starch breaking down into glucose
D. increases the rate of starch breaking down into maltose
20. What helps proteins to change into amino acids?
A. antibodies
B. auxins
C. enzymes
D. hormones
21. Which two substances are the products of photosynthesis?
A. carbon dioxide and glucose
B. carbon dioxide and water
C. oxygen and carbon dioxide
D. oxygen and glucose
22. Which two substances are the products of photosynthesis?
A. carbon dioxide and glucose
B. carbon dioxide and water
C. oxygen and carbon dioxide
D. oxygen and glucose
23. A plant with variegated leaves has the starch removed from its leaves by placing it in a
dark cupboard for 48 hours.
Black paper is then fixed on one leaf as shown and the plant is exposed to light.
After 24 hours, which part of the leaf contains starch? Ans. D
24. From which part of a leaf does most water evaporate during transpiration?
A. the cuticle
B. the guard cells
C. the spongy mesophyll cells
D. the xylem vessels
25. The bar chart shows the average number of chloroplasts in each of three different types of
leaf cell. Ans. A
What are the three types of cell?
26. The diagram shows a section through a leaf.
Which cell type absorbs the most carbon dioxide during the day? Ans.B
27. Which substances do root hairs take from the soil?
A. water and carbon dioxide
B. water and mineral ions
C. carbon dioxide and oxygen and mineral ions
D. carbon dioxide and oxygen and water
28. Which ions does a plant require to make amino acids from glucose?
A. calcium
B. iron
C. magnesium
D. nitrate
29. In photosynthesis, how many glucose molecules can be made from 30 carbon dioxide
molecules and 30 water molecules?
A. 5
B. 6
C. 30
D. 60
30. A student investigated the necessity of light for photosynthesis. He covered a leaf with
black paper to prevent light reaching it. What is an appropriate control for his
experiment?
A. a leaf that has been destarched
B. a leaf that is not covered with black paper
C. a leaf that is partly white and partly green
D. a leaf that has no carbon dioxide provided
II. ANSWER ALL QUESTIONS. (40 marks)
1.a. Biuret reagent is used to test for proteins. These statements about the biuret test are
incorrect. Write corrected versions of each statement.
i. To carry out the biuret test, add biuret solution to the food and heat gently. [1]
The mixture should not be heated. ; [1]
ii. If a food contains protein, biuret reagent turns from purple to blue. [1]
The colour change is from blue to purple or violet. ; [1]
b. Ethanol is used to test for fats and oils.
i. Describe how you would carry out the ethanol test. [3]
crush the food [1] ; mix with ethanol [1] ; pour some of the ethanol into distilled water [1]
ii. Describe what you would see if the test gives a positive result. [1]
a milky emulsion ; [Total=7]
2. The graph below shows how the activity of two enzymes, A and B, is affected by temperature.
a. Compare the effect of temperature on enzyme A and enzyme B. [6]
Any five from
• the optimum temperature of enzyme B is higher than enzyme A ;
• lowest temperature at which activity begins is higher for B than A ;
• highest temperature at which activity ends is higher for B than A ;
• figures quoted for both (e.g. optimum is 70 °C for B and 40 °C for A) ;
• for both, increase in temperature below optimum causes an exponential increase in
activity ;
• for both, increase in temperature above optimum causes a steeper decrease in activity ;
b. Explain the effect of temperature on enzyme B from:
i. 0 to 60 °C [3]
Any three from:
• kinetic energy of enzyme and substrate molecules increases as temperature increases ;
• so the frequency of collisions increases ;
• frequency of formation of enzyme–substrate complexes increases ;
• so, rate of reaction increases ;
ii. 70 to 90 °C [4]
Any four from:
• enzyme molecule begins to lose its shape ;
• enzyme is denatured ;
• so active site no longer complementary shape to substrate ;
• enzyme–substrate complexes cannot form ;
• so, rate of reaction decreases ; idea that increasing temperature over this range results in a
greater degree of denaturation ;
[Total: 13]
