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TERM 2
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world.
Revision Worksheet
Grade: 8B Subject: Biology Date:
1) Microorganisms in the soil release enzymes to digest dead leaves.
a) Explain how enzymes catalyse chemical reactions.
Ans:
substrate fits into enzyme; (shape of) substrate is complementary to, enzyme / active site;
ref to active site; substrate breaks / product(s) forms / product(s) leaves enzyme; enzyme,
free for next reaction / not used up / remains unchanged;
b) Protease and cellulase are two enzymes secreted by soil microorganisms.Protease
digests protein. Suggest what part of the dead leaf cells are digested by the enzyme
cellulase.
Ans:
(cellulose) cell wall;
2) Enzymes are necessary for many biological processes, such as the digestion of fat.
fat + water fatty acids + glycerol lipase
Explain why enzymes are necessary for biological processes
without enzymes reactions, occur too slowly ; A enzyme speed up reactions reduce,
activation energy / energy needed for a reaction ; reactions take place at lower temperature;
enzymes are catalysts
3) State the balanced chemical equation for photosynthesis.
Ans:
6CO2 + 6H2O C6H12O6 + 6O2
Multiple Choice Questions (MCQs)
1 Which graph shows the effect of temperature on the activity of an enzyme?
A B
enzyme enzyme
activity activity
0 5 100 0 5 100
temperature / C temperature / C
D
C
enzyme enzyme
activity activity
0 5 100 0 5 100
temperature / C temperature / C
2 The diagram represents enzyme action.
+ +
W X Y
What are parts W, X and Y in this chemical reaction?
enzyme Product substrate
A W Y
B X Y
C X W
D Y X
3 The table shows the conditions in four test-tubes containing equal amounts of starch and salivary
amylase.
In which test-tube is the starch broken down fastest?
temperature
pH
/ °C
A 2 27
B 2 37
C 7 27
D 7 37
4 What is true of all enzymes?
they are most effective
they are sugars
at pH7
A ✓ ✓
B ✓ C
C C ✓
D C C
5 The diagram shows the effect of an enzyme working in the human digestive system.
enzyme at pH 1.5
and temperature 37 C
protein amino acids
What would reduce the rate of production of amino acids?
A removing the amino acids as they are formed
B increasing the amount of protein
C raising the temperature to 40 C
D raising the pH to 7.5
6 Which group of compounds ensures that metabolic reactions take place effectively?
A carbohydrates
B enzymes
C fatty acids
D hormones
7 The diagram shows an experiment on the digestion of the protein in egg albumen by protease.
The protease was taken from a human stomach.
In which test-tube will the protein be digested most quickly?
A B C D
water-bath
at 37 C
egg albumen egg albumen egg albumen egg albumen
+ + + +
protease dilute dilute dilute
hydrochloric hydrochloric hydrochloric
acid acid acid
+ +
protease boiled protease
8 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
9 An enzyme in potato cells causes oxygen to be produced from hydrogen peroxide.
Cubes of potato were incubated with hydrogen peroxide at different temperatures.
The numbers of bubbles of oxygen released per minute were counted at each temperature.
The table shows the results.
The results suggest the optimum temperature for the enzyme is between which two values?
A 15 °C and 35 °C
B 35 °C and 45 °C
C 35 °C and 55 °C
D 45 °C and 55 °C
10 Which graph shows the effect of temperature between 20 °C and 35 °C on the activity of a human
digestive enzyme?
A B
rate of rate of
reaction reaction
20 20
temperature / C temperature / C
C D
rate of rate of
reaction reaction
20 20
temperature / C temperature / C
11 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.
12 Which statement is correct for all catalysts?
A They are enzymes.
B They are proteins.
C They speed up chemical reactions.
D They work in living organisms.
13 The temperature of an enzyme-controlled reaction is increased by 10 °C.
How does this affect the rate of reaction?
A It always increases the rate.
B It always decreases the rate.
C It may increase or decrease the rate.
D It has no effect on the rate.
14 Some plants digest insects and use the nutrients for growth.
What must these plants produce to digest the insects?
A acids
B alkalis
C enzymes
D hormones
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 The diagram shows the action of amylase.
amylase part of a
starch molecule
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
17 What are enzymes made of?
A carbohydrates
B DNA
C fats
D proteins
18 Which graph shows the effect of temperature on the activity of a human digestive enzyme?
A B
rate of rate of
reaction reaction
20 70 20 70
temperature / C temperature / C
C D
rate of rate of
reaction reaction
20 70 20 70
temperature / C temperature / C
19 Which substance is an enzyme?
A bile
B fibrinogen
C lipase
D maltose
20 Which are characteristics of enzymes?
A They are carbohydrates and biological catalysts.
B They are carbohydrates and chemical messengers.
C They are proteins and biological catalysts.
D They are proteins and chemical messengers.
21 The table shows whether starch was still present after four different experiments.
experiment
starch + water at 20 °C ✓ key
starch + amylase at 20 °C C ✓= starch present
C C= starch absent
starch + amylase at 30 °C
✓
starch + boiled amylase at 30 °C
What broke down the starch?
A amylase
B boiled amylase
C heat
D water
22 What helps proteins to change into amino acids?
A antibodies
B auxins
C enzymes
D hormones
23 The apparatus shown in the diagram was used for an experiment on starch digestion.
Which tube would contain most sugar after 20 minutes?
tube A tube B tube C tube D
starch starch
solution starch solution
and solution and
amylase amylase
water bath at 15 oC water bath at 37 oC
24 When a substance is added to meat, amino acids are produced.
What is this substance?
A a hormone
B an enzyme
C an oil
D water
25 The diagram shows part of a protein molecule.
What does X represent?
A amino acid
B fatty acid
C glycerol
D sugar
26 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?
Benedict’s test iodine test biuret test
A blue black purple
B bllu e brown purple
C brick red black blue
D brick red brown blue
27 What are the smaller basic units of starch and glycogen molecules?
Starch glycogen
A amino acids fatty acids and glycerol
B amino acids simple sugars
C simple sugars fatty acids and glycerol
D simple simple sugars
sugars
28 The diagram represents a protein molecule.
What do the small circles represent?
A amino acids
B fatty acids
C glycerol
D simple sugars
29 Which row shows the elements and basic units that are used in the construction of large food
molecules?
food molecules elements basic units
A Fats carbon, hydrogen, oxygen, nitrogen glucose
B Fats carbon, hydrogen, oxygen, nitrogen glycerol
C starch carbon, hydrogen, oxygen glucose
D starch carbon, hydrogen, oxygen glycerol
30 Which nutrient produces a purple colour when mixed with biuret solution?
A fat
B protein
C reducing sugar
D starch
31 Which simple molecules are the basic units of protein?
A amino acids
B fatty acids
C sugars
D vitamins
32 Which food-testing reagent shows a positive result when it turns from blue to purple?
A Benedict’s solution
B biuret reagent
C ethanol
D iodine solution
33 The diagram shows two food tests carried out on solution X.
test 1 test 2
biuret Benedict’s
solution solution
red
colour
heat
solution X purple solution X
colour
Which nutrients are present in solution X?
A protein and starch
B protein and sugar
C starch and fat
D starch and sugar
34 The data show the concentrations of sugar and starch in an onion.
total sugar including
starch
reducing sugar
/ g per 100g
/ g per 100g
3. 0.
The onion is tested with Benedict’s solution and iodine solution.
Which set of results is correct?
Benedict’s iodine
solution solution
A Bllue blue-black
B bllue brown
C brick red blue-black
D brick red brown
35 The diagram shows two food molecules before and after they have been digested by enzymes.
R
P
Q
S
before after
What identifies the products of fat digestion?
A P and R B P and S C Q and R D Q and S
36 A human cell contains a length of DNA that carries the code for making which substance?
A fat
B glycogen
C lipase
D starch
37 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.
38 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?
X Y
A
maltose
amylase
B maltose lipase
C Starch amylase
D Starch lipase
39 Which row correctly identifies the chemical elements found in proteins?
carbon hydrogen oxygen nitrogen
A ✓ ✓ ✓ ✓ key
B ✓ ✓ ✓ C ✓= present
C ✓ C ✓ C C= absent
D C ✓ C ✓
40 Nutrients are made up of smaller basic units. Nutrients can be identified by food tests.
Which nutrient is a protein?
nutrient smaller basic units food test
A amino acids Benedict’s test
B amino acids biuret test
C sugars Benedict’s test
D sugars biuret test
41 Water is a good solvent.
What does this mean?
A It dissolves well in many other substances.
B It flows easily through vessels.
C It is permeable to gases.
D Many substances dissolve well in it.
42 What does the digestion of starch produce?
A fatty acids
B glucose
C mineral salts
D water
43 Which elements do carbohydrates contain?
A carbon, hydrogen and oxygen
B carbon, hydrogen and sulphur
C carbon, nitrogen and oxygen
D carbon, nitrogen and sulphur
44 Four foods were tested for
fat (using ethanol),
protein (using the biuret test),
reducing sugar (using Benedict’s solution),starch (using iodine
solution).
Which food contains protein and starch?
colour of result of food test
blue / black purple / lilac bric-red / orange milky-white
A ✓ C ✓ C
B ✓ ✓ C C
C C C ✓ ✓
D C ✓ C ✓
Answer the following questions
1) Proteins and DNA are important nitrogen-containing compounds in cells. Describe the roles of proteins
and DNA in cells.
proteins in cells enzymes; control / catalyse, reactions e.g. respiration / photosynthesis ;
A ref. to any specific reaction(s) (part of cell) membranes ; carrier proteins / description
of role allowing movement in and out of cell ; hemoglobin ; transport of, oxygen /
carbon dioxide / gases
DNA in cells ref. to, genes / alleles / genetic information / genetic code; control
functions of the cell ; code for proteins ;e.g. a specific feature of cells / cell division /
mitosis / meiosis
2) List four chemical elements that are found in proteins.
Carbon
Nitrogen
Oxygen
Hydrog
3)
a) Photosynthesis is a very important process in the carbon cycle. Explain how the process of
photosynthesis converts carbon compounds from P to carbon compounds in Q.
Ans:
CO2 enters leaf;
CO2 diffuses to (cells);
carbon dioxide and water / CO2 + H2O;
chlorophyll / chloroplasts, traps light energy;
light energy is used to make glucose / carbohydrates;
oxygen is present;
6CO2 + 6H2O → C6H12O6 + 6O2
b) The rate of photosynthesis varies as a result of changes in environmental factors. State one
environmental factor and explain how it can affect the rate of photosynthesis.
Ans
factor: – light intensity or duration / carbon dioxide concentration / temperature;
effect of factor: – less photosynthesis, due to low light / low CO2 / non optimum
temperature
explanation: – light provides energy / CO2 substrate for photosynthesis / temperature
effects enzyme activity; ref to limiting (factor) .
c) Photosynthesis is a chemical process catalysed by enzymes. Explain this phrase
Ans:
Increases; if no enzymes then rate should increase as temperature but rate decreases,
above 30 oC / at high temperatures; enzymes are denatured; ref to active site destroyed;
substrate no longer fits into active site; reaction not catalyzed.
d) What are the factors affecting the photosynthesis?
Light
Temperature
Water
CO2
e) State three uses in a plant of the carbohydrate produced in photosynthesis.
1 Converted into starch molecules; these are an energy store for plant cells.
2 Converted into cellulose to build cell walls.
3 Glucose can be used in respiration, which releases energy for cell activities.
