CHAPTER 4 : CHEMICAL COMPOSITION OT THE CELL
Year
Quantity
2003
5
2004
4
2005
4
2006
2
2007
4
2008
3
YEAR 2003
1.
Which substances acts as the medium for chemical reactions in the cell?
A
Water
C
Fatty acid
B
Glucose
D
Amino acid
2.
Figure 5 shows the molecular structure of three food classes
Figure 5
Which food classes do X, Y and Z belong to?
X
Y
A
Carbohydrate
Protein
B
Protein
Lipid
C
Protein
Carbohydrate
D
Lipid
Carbohydrate
3
Z
Lipid
Carbohydrate
Lipid
Protein
Which of the following graphs best represents the effect of pH on the rate of reaction of
enzymes secreted by the pancreas?
A.

B
C
D
4.
Figure 15 shows how an enzyme works.
Figure 15
Which property of an enzyme is shown in Figure 15
A
Enzyme reaction is specific
B
Enzyme reaction is affected by pH
C
Enzyme reaction is affected by temperature
D
Enzyme structure changes at the end of reaction
5.
Which enzyme needs an acidic medium for its reaction?
A
Amylase
B
Trypsin
C
Pepsin
D
Erepsin
YEAR 2004
1. The table shows the substrate and optimum pH of four digestive enzymes A, B, C, and D.
Which of the enzymes A, B, C, or D is rennin?
Enzyme
2.
Substrate
Optimum pH
A
Starch
6.8
B
C
D
Protein and polypeptide
Fat
Protein
8.5
8.5
2.2
The diagram shows the action of an enzyme on a substrate.
X represents
A enzyme
B substrate
C Product of reaction
D enzyme-substrate complex
3.
Which of the following is not a polysaccharide?
A. Glycogen
B. Cellulose
C. Maltose
D. Starch
4.
The diagram shows a measuring cylinder containing albumen suspension mixed with
pepsin at 20°C. The result of the experiment was obtained after 5 minutes.
The experiment was repeated at 37°C.
Which of the following shows the result of the experiment?
A
C
B
D
YEAR 2005
1. The figure shows the breaking down of a complex molecule by an enzyme.
Which of the molecules A, B, C and D, represents the substrate?
A
BB
C
D
2. The main components of a plant cell membrane are
A.
B.
C.
D.
Lipid and carbohydrate
Protein and carbohydrate
Protein and lipid
Protein, lipid and carbohydrate
3. The information below shows four food classes and their energy content.
Which of the following represents fats?
Food
classes
A
B
C
D
Energy content/ kJ per
100g
30
3300
1700
1600
4. The graph shows the optimum pH of an enzyme Y in its reaction
Enzyme Y is
A salivary amylase
B pepsin
C
D
trypsin
rennin
YEAR 2006
1
The vitamin that functions as a coenzyme in cell respiration is
A vitamin A
B vitamin B
C vitamin C
D Vitamin K
2
Diagram 3 shows the rate of enzyme hydrolysis reaction, R and S, in the
human
Body.
Diagram 3
Which of the following is true about enzymes R and S?
A
B
C
D
Enzyme R
Secreted in the stomach
Enzyme S
Secreted into the duodenum
The active site changes at pH
more than 4
R is trypsin
The active site changes at pH
more than 7
S is lipase
Synthesized in the rough
endoplasmic reticulum
Synthesized in the smooth
endoplasmic reticulum
YEAR 2007
1. Table 1 shows the elements found in the food classes X and Y.
Food Class
X
Y
Element
C, H, O
C, H, O, N
Table 1
What are food classes X and Y
Food class X
Food class Y
A.
Carbohydrate
Lipid
B.
Lipid
Protein
Protein
Carbohydrate
Protein
Lipid
C.
D.
2. Diagram 4 shows the structures of a substrate and an enzyme.

Which of the labelled parts A, B, C and D is the active site?
3. What is the process involved in changing starch into glucose?
A Condensation
B Photolysis
C Hydrolysis
D Assimilation
4. Which of the following is true to show the relationship of the rate of reaction of
trypsin with the pH values?
C
YEAR 2008
1. Diagram 4 is a graph which shows the relationship between the rate of
reaction and
The substrate concentration when factor Y is varied.
What is factor Y?
A.
B.
C.
D.
pH
Time
Inhibitor
Enzyme concentration
2. Diagram 5 shows the mechanism of enzyme action.
Which of the following can be deduced from Diagram 5?
I
II
III
IV
Enzyme action is specific
Enzyme reaction is reversible
Enzyme is not destroyed at the end of the reaction
Optimum temperature for enzyme reaction is 40c
A. I and II
B. I and III
C. II and IV
D. III and IV
3. The following information shows starch molecules undergoing process X.
Process X
Starch
Process X
Maltose
Glucose
What is process X?
A.
B.
C.
D.
Photosynthesis
Polymerization
Condensation
Hydrolysis
CHAPTER 4 : CHEMICAL COMPOSITION OF THE CELL
2003
Section
A
B
C
-
2004
Section
A
B
C

(1)
2005
Section
A
B
C

(4)
2006
Section
A
B
C

(2)
2007
Section
A
B
-
2008
Section
A
B
-
YEAR 2004
Section A
1.
Figure 1(a) shows a reaction catalyses by lipase.
Q: fat//lipid molecule
R: fatty acid
//substrate
S: glyserol
P: lipase// enzyme
Figure 1(a)
(a) (i) Label P, Q, R and S in Figure 1(a).
(ii)
[4 marks]
State two characteristics of P.
1 -P works on specific substrate molecules// Act specifically
2 - P remains unchanged at the end of the reaction// can be reused
[2 marks]
(b) (i) State the principle of enzymic reaction as shown in Figure 1(a).
- Lock and key hypothesis
[1 mark]
(ii) What can you deduce about the enzyme lipase in Figure 1(a)?
- Lipase is an enzyme that hydrolyses lipid to fatty acid and glycerol
- Lipase is specific to its substrate/lipid
- Lipase remain unchanged at the end of the reaction/ can be used
again
[1 mark]
(c)
Enzymes are used widely in industries.
State one use of lipase in food industry.
- Ripening of cheese
- Digestion of fats in making of skin
[1 mark]
(d)
The temperature at which a lipase reaction takes place is increased to more
than 60°C.
State the effect on the quantity of the product. Explain your answer.
-
Quantity of the product decreases.
Because rate of reaction decreases.
Enzyme lipase has been destroyed/ denatured at high temperature
[2 marks]
(e)
Figure 1(b) shows a box of washing powder.
A housewife uses cold water to wash her clothes with brand X washing powder. The
cleaning is less effective.
Using the above information, explain why.
-
Cold water has a lower temperature than 40oC // 40oC is the optimum
temperature for the enzyme
The low temperature makes the enzyme inactive// rate of reaction of
enzyme is slow
[2 marks]
YEAR 2005
Section A
4. Figure 4.1 shows the organelles involved during the synthesis and secretion of an
enzyme in an animal cell.
(a)
Name the organelles labelled P and R.
P : Golgi body
R : Secretory vesicle
[2 marks]
(b)(i)
State the function of organelle S.
To generate energy / respiration
[1 mark]
(ii)
Explain the role of organelle Q in the synthesis of the enzyme.
- Q contains generic information in the DNA .
- The genetic information in the DNA is transferred to the DNA which
carries it out into the cytoplasm
[2 marks]
(c)
Enzymes are widely used in our daily life and industries
Explain how enzymes act in :
(i)
helping to cook meat.
- Protease acts on protein in meat
- Softens meat
[2 marks]
(ii) extracting agar from seaweeds.
- Cellulase acts on cellulose
- Cellulase breaks down the cell wall of seaweeds
- Release the agar
[3 marks]
(d)
Figure 4.2 shows the structure of an enzyme and three substrates W, X and Y.
YEAR 2006
Section A
2. (a) Diagram 2.1 shows human digestive system.
Structure Q in diagram 2.1 is involved in the digestion of fat
(i) Name structure Q
Ileum
[1 mark]
(ii) Name the enzyme which digests fat in Q.
Lipase
[1 mark]
(iii) Diagram 2.2 shows a mechanism of an enzyme reaction.
Draw the diagram in the spaces III and IV provided in Diagram 2.2 to complete
the mechanism of enzyme reaction.
(b)(i) Explain how starch is digested in the duodenum
- Pancreas secretes amylase into duodenum
- Digest / Hydrolyse starch to maltose
[2 marks]
(ii) A student eat too many oranges
Explain the effect of eating too many oranges on digestion of starch in the
duodenum.
- Oranges contain much acid
- Reduces the pH value / Increases acidity in the duodenum
[2 marks]
(c) In a food preparation process, a housewife carries out the following steps :
Step 1 : Marinate pieces of meat with strips of unripe papaya in a basin.
Step 2 : Immerse the basin in a container filled with water at 40°C for 30 minutes
as in diagram 2.3
Explain why the housewife carries out Step 1 and Step 2.
- Meat pieces and strips of papaya increases TSA
- to increase enzyme action (in papaya)
- to tender / soften the meat
- takes place in water at 40oC
- optimum for enzyme action
[4 marks]
CHAPTER 4 :CHEMICAL COMPOSITION OF THE CELL
2005
-
2006
 (1)
2007
-
2008
-
ANSWER
1
A group of students carried out an experiment to study the effect of the
concentration of albumen suspension on the rate of reaction of pepsin enzyme.
Diagram 1.1 shows the method used by the students.The time taken for the
change in the cloudiness of the albumen suspension is shown in Diagram 1.2.
The whole experiment in Diagram 1.1 was repeated using different
concentrations of albumen suspension.
Table 1.1 shows the results of the experiment.
(a) (i) Based on Table 1.1, state two observations on the relationship between the
quantity of albumen and time.
1 Albumen suspension which is cloudy at concentration 10%/15%/20% turns
clear after
7/10/12.5 minutes respectively.
2 When the concentration/cloudiness increases, the time taken for the
suspension to turn clear increases// or otherwise
[3 marks]
(ii) State the inference which corresponds to the observation in 1(a)(i).
1 Albumen /substrate is hydrolysed by pepsin/enzyme
2 When there are more number of albumen/substrate molecules, the rate of
reaction of enzyme is limited by enzyme molecule.
[3 marks]
(b) Using the information provided in Table 1.1, complete Table 1.2 by recording the
time taken for the albumen suspension to turn clear.
Percentage concentration
of albumen suspension
Time taken /minutes
10%
7
15%
10
20%
12.5
TABLE 1.2
[3 marks]
(c) (i) Complete Table 1.3 based on this experiment.
Variable
Manipulated variable
Concentration of albumen/substrate
Method to handle the variable
Use different
concentration of
albumen suspension
Responding variable
Time taken for the albumen to turn Record the time/Calculate the rate
clear/
of reaction
Rate of reaction of enzyme
Controlled variable
Temperature of water bath/pH value / Fix the temperature of water
concentration/volume
of bath/pH value
enzyme/volume of albumen
Fix the volume of albumen/enzyme
Fix the concentration of enzyme
TABLE 1.3
[3 marks]
(ii) The following list is part of the apparatus and material used in this experiment.
Thermometer, Stop watch, Albumen suspension, Water bath, Pepsin, Syringe
Complete Table 1.4 by matching each variable with the apparatus and material used
in this experiment.
Variables
Apparatus
Material
Manipulated
Syringe
Albumen suspension
Responding
Stop watch
Pepsin
Controlled
Thermometer
Water bath
TABLE 1.4
[3 marks]
(d) State the hypothesis for this experiment.
The higher/lower the concentration
longer/shorter time taken for reaction
of
albumen
suspension,
the
[3 marks]
(e) (i) Based on Table 1.1, construct a table and record the results of the experiment
which includes the following aspects:
• Percentage concentration of albumen suspension
• Time /min
• Rate of enzyme reaction as percentage of albumen converted per minute
Percentage concentration of
Time/min
Rate of reaction(min-1)
albumen suspension
10%
7
1.43
15%
10
1.50
20%
12.5
1.54
[3 marks]
(ii) On the graph paper provided on next page, draw the graph of rate of reaction of
pepsin against the concentration of albumen suspension.
[3 marks]
(iii) Explain the relationship between the rate of reaction of pepsin and the
concentration of albumen suspension based on the graph in 1(e)(ii).
When the concentration of albumen suspension increases, the rate of reaction
of pepsin/enzyme increases and it reaches a maximum value.
[3 marksl
(f) Based on this experiment, what can you deduce about this enzyme?
Enzyme turns the albumen suspension from cloudy to clear and the rate of
reaction of enzyme is affected by the concentration of the substrate/albumen
[3 marksj
(g) The experiment is repeated using the apparatus set up as in Diagram 1.3. The
quantities of albumen suspension and pepsin enzyme used are as shown.
The experiment is left for one hour.
P,Q,R and S are four possible observations after one hour. Choose one correct
observation and explain your choice.
S. The 1 ml of enzyme used is boiled enzyme. Hence it is denatured.and cannot act
on the substract/albumen
[3 marks]