8 Photosynthesis
Class Practice
8.1 How do green plants feed?
8.2 The requirements for photosynthesis
1. (a) carbon dioxide
(b) water
(c) solar energy/sunlight
(d) carbohydrates/glucose
(e) Oxygen
2.
3.
(f) mesophyll
(g) stomata
8.3 Investigations to study the requirement for photosynthesis
A. Multiple Choice Questions
1. D
2. C
B.
Structured Questions
1.
2.
(a) 1  4  3  2
(b) to soften the leaf
to extract chlorophyll/decolourise the leaf
(a) to destarch the plant
(b) (i) to show that carbon dioxide is necessary for photosynthesis
(ii) to absorb carbon dioxide
(c) (i) to show that light is necessary for photosynthesis
(ii) to exclude light / make sure the plant cannot absorb light
(d) Leaf A - blue black, leaves B and C - brown
8.4 The photosynthetic process
1. F
2. T
3. F
4. F
1.
3.
4.
The chlorophyll mainly absorbs red and blue light of the spectrum for
photosynthesis. Most of the green light is reflected.
During the light reactions, water is split into hydrogen and oxygen. Oxygen
is released immediately and hydrogen combines with carbon dioxide to
form carbohydrate in the dark reactions.
Dark reactions immediately occur after the light reactions. They both take
place in the daytime.
8.5 The effects of environmental factors on the rate of photosynthesis
(a) When the distance between the beaker and the table lamp increases, the
light intensity decreases. Therefore, the rate of photosynthesis decreases
with the increase in distance.
(b) This solution provides carbon dioxide.
(c) A large beaker can hold a greater volume of dilute sodium
hydrogencarbonate solution. This provides more carbon dioxide and
absorbs more heat energy released by the table lamp.
(d) Crops grow faster in a greenhouse because it is warmer inside. The carbon
dioxide concentration can also be increased in a greenhouse to increase the
photosynthetic rate of the crops.
8.6 The products of photosynthesis
A. 1. A
2. A
B.
1. F
2. T
3. F
4. F
5. T
6. T
1. Some of the oxygen produced during photosynthesis is used for
respiration. The rest of it diffuses out into the atmosphere.
3. Sucrose can be carried to actively growing regions where it is changed
to glucose.
4. Plants make use of glucose to make many organic substances in
addition to starch and sucrose.
8.7 Leaves-organs of photosynthesis
A. 1. B
2. A
B.
(a) i.
ii.
iii.
iv.
v.
veins
cuticle
epidermis
palisade mesophyll
spongy mesophyll
vi. xylem
vii. phloem
viii. stoma
(b) 1.
2.
3.
4.
5.
6.
Gases can diffuse into and out of the leaf easily.
Diffusion is faster and more sunlight can be absorbed.
to carry water and minerals from the soil to the leaf
to carry the product of photosynthesis away from leaf
for gaseous exchange, to allow carbon dioxide in the atmosphere
to diffuse into the leaf
to prevent excess water loss
7.
for diffusion of gases
Exam Practice
A. Multiple Choice Questions
1. B
2. D
3. A
4. B
5. B
6.
7.
8.
9.
10.
B.
C
D
D
D
B
Structured Questions
1. (a) Structure X is chloroplast.
(b) A
water
B oxygen
C carbon dioxide
D glucose/carbohydrates
M hydrogen
(c) stoma
(d) for respiration to release energy
to form chlorophyll with magnesium
to form amino acids with nitrates
2.
(e) Stage I - light reactions Stage II - dark reactions
(a) (i) variegated leaf
(ii) to remove the chlorophyll and make the results more obvious
(iii) heat the leaf in alcohol
(iv)
blue black
brown/yellow
(
b)
blue black
(i)
brown/yellow
(ii) (1) chlorophyll
(2) carbon dioxide
(3) light
C.
STS Connections
1. No. It is because green plants on the earth carry out photosynthesis which
takes up carbon dioxide and releases oxygen. Therefore, the amount of
oxygen is balanced by photosynthesis and oxygen would not be depleted.
2. (a) Glucose/carbohydrates
(b) Yes. Green plants turn solar energy to chemical energy which further
transfers to other organisms. Moreover, green plants balance the
amount of oxygen and carbon dioxide in the atmosphere to ensure
sufficient oxygen for the occurrence of respiration.
Class and Exam Practice 2
9 Respiration
Class Practice
9.1 What is respiration?
1. F
2.
3.
4.
1.
4.
5.
present.
7.
T
T
F
5. F
6. T
7. F
8. T
All living cells require energy.
The process of burning is different from that of respiration.
Burning cannot occur inside a cell even if a sufficient amount of oxygen is
The reactions of respiration are controlled by enzymes while burning does
not involve enzymes.
9.2
The use of energy released from food
9.3
The chemistry of respiration
1. F
2. T
1.
3. T
4. F
5. T
6. F
7. T
8. F
9. T
Respiration in plants occurs all the time.
9.4
4.
ATP stores energy for a short period only.
6.
8.
ATP is made inside the mitochondria.
ATP cannot be transported from cell to cell. It has to be used inside the cell
in which it is made.
Aerobic and anaerobic respiration
A. 1. (a) glucose
(b) carbon dioxide
(c) aerobic
2.
(d) glucose
(e) ethanol
(f) alcoholic fermentation
3.
(g)
(h)
1.
2.
3.
4.
5.
B.
lactic acid
lactic acid fermentation
T
F
F
F
T
2. Mitochondria are involved in aerobic respiration only.
3. Skeletal muscles carry out aerobic respiration if sufficient oxygen is
available.
4. Mitochondria are present in muscle cells.
Exam Practice
A. Multiple Choice Questions
1. C
2. B
3.
4.
5.
6.
7.
8.
9.
10.
D
C
D
B
A
D
B
C
B.
Structured Question
1.
(a) food + oxygen  carbon dioxide + water + energy
(b) oxygen
(c) The oil drop would move towards the boiling tube. The small insect
takes up oxygen during respiration and gives out carbon dioxide
which is then absorbed by the soda lime. As a result, the air pressure
inside the boiling tube becomes lower than the atmospheric pressure
and the oil drop moves towards the boiling tube.
(d) To eliminate the error caused by environmental factors such as
temperature and pressure.
(e) The oil drop moves faster towards the boiling tube because the rate of
respiration of the small insect is faster at higher temperatures.
(f) to prevent the small insect from touching the soda lime
2.
(a) The bulb of the thermometer should be immersed into the solution in
order to detect the temperature change of the yeast and glucose
solution.
The conical flask should be wrapped by cotton wool / the conical
flask should be replaced by a thermos flask so as to prevent heat loss.
(b) (i) carbon dioxide
(ii) Solution X is lime water. It turns milky.
OR Solution X is hydrogencarbonate indicator solution. It turns from
red to yellow.
(c) To prevent the solution from coming into contact with air.
(d) Boiling the glucose solution drives off any dissolved oxygen.
3.
4.
(a) The germinating seeds took up oxygen during respiration and gave
out carbon dioxide which was then absorbed by the sodium hydroxide
solution. As a result, the air pressure inside flask A became lower than
that of the atmosphere and the coloured water moved up the glass tube
X.
(M – N) R
(b) ————— cm3/h
2
(c) Oxygen had been used up and only anaerobic respiration occurred.
The sodium hydroxide solution absorbed the carbon dioxide
produced.
(a) The potassium hydroxide solution in flask A removes carbon dioxide
from the incoming air. The lime water in flask B is used to show that
the incoming air is free of carbon dioxide.
(b) The bell jar should be covered with black paper or black cloth in order
to exclude light. Otherwise, the potted plant will undergo
photosynthesis and absorb carbon dioxide.
The pot should be covered with a polythene bag to prevent the soil
micro-organisms from carrying out respiration and releasing carbon
dioxide.
(c) The lime water in flask C turns milky.
This shows that carbon dioxide has been produced by green plants in
the dark.
C.
STS Connections
(a) Aerobic exercises
(b) Glucose / carbohydrates
(c) Glucose + oxygen  carbon dioxide + water + energy (heat and ATP)
(d) Aerobic respiration is carried out and hence no lactic acid is accumulated.
10 Obtaining essentials for life in green plants
Class Practice
10.1 Nutrition
1. T
2. F
3. T
4. F
2. Green plants synthesise organic substances by using simple inorganic
substances from their surroundings. Energy is needed in this process.
4. Animals, fungi and most bacteria are heterotrophs.
10.2 The importance of minerals for proper growth in green plants
1. (a) active transport
2.
3.
4.
(b)
(c)
(d)
(e)
(f)
(g)
(h)
major elements
trace elements
proteins
nitrates
small leaves
weak stems
chlorophyll
(i)
(j)
poor growth
yellowing of leaves
10.3 Fertilizers
1. T
2. T
3. F
4. F
5. T
3.
4.
The proportion of nitrogen, phosphorus and potassium in chemical
fertilizers is not always the same.
Natural fertilizers have to undergo decay and release mineral salts slowly.
They cannot be used immediately.
10.4 Gaseous exchange in plants
A. 1. (a) stomata
(b) diffusion
2. (c) spongy
(d) air space
3. (e) cork cells
(f) lenticels
B.
1. F
2. T
1.
3. F
4. F
Green plants carry out respiration all the time.
3. The rate of respiration in plant cells is more or less constant
throughout the day.
4. At compensation point, the rates of photosynthesis and respiration are
equal.
10.5 Transpiration
A. 1. D
2.
3.
4.
B.
1.
4.
D
A
C
1. F
2. T
3. T
4. F
5. T
During transpiration, transpiration stream carries water and dissolved
mineral salts from the roots to the leaves.
The higher the temperature, the greater is the rate of transpiration
because water evaporates faster.
10.6 Absorption of water and mineral salts by the root
1. C
2. F
3. E
4.
G
5.
6.
7.
8.
H
D
A
B
10.7 Transport in flowering plants
1. F
2. F
3. T
4. T
1.
5. F
Xylem is made of vessels and each vessel is made up of many dead cells
which are joined end to end.
2. Xylem vessels run from roots, up through the stem, and finally branch out
into every leaf.
5. Sieve tubes are living cells with cytoplasm.
10.8 Support in plants
(a) turgidity — A and D
rigidity — B and C
(b) Most of the cells become flaccid because the rate of transpiration is faster
than that of water absorption. The plant will wilt.
Exam Practice
A. Multiple Choice Questions
1. C
2. A
3. C
4. D
5.
6.
7.
8.
9.
10.
B.
B
B
A
C
B
B
Structured Questions
1.
(a) (i)
Set-up C
(ii) Set-up B
(iii) Set-up A
(b) Set-up A: The leafy shoot should be cut under water to ensure the
xylem is not blocked by air. The oil must be poured onto
the water after the plant has been put into the measuring
cylinder.
Set-up B: The leaf must be fixed so it cannot slide on the needle.
Set-up C: The shoot must be cut and fitted under water to prevent
bubbles from entering the xylem of the shoot.
(c) (i) to balance the weight of the leaf
(ii) to prevent evaporation of water in the measuring cylinder
(d) No, it is not necessary because the water in the reservoir will not be
measured.
2. (a) A is root hair.
It increases the surface area for absorption of water and mineral salts.
(b) The water potential of the soil water is higher than that of the
cytoplasm and the cell sap of the root hairs. Water enters the root hairs
and epidermal cells by osmosis.
(c) Soil air supplies oxygen for the cells in the root to carry out
respiration.
3.
(d) Y is xylem vessels.
They carry water and mineral salts from roots to the leaves. They
provide mechanical support to the plant.
(a) in the daytime, warm and moving air
100
(b) —— = 25 mm/minute
4
(c) The rate of the movement of the air bubble will be much slower. It is
because the relative humidity inside the plastic bag is high / the air
inside is saturated with water vapour. Water vapour from the air space
4.
will not diffuse out easily.
(d) The transpiration stream carries dissolved mineral salts from the roots
to the leaves. Transpiration helps the absorption of water and minerals
from the soil. It also produces a cooling effect.
(a) Air should be pumped into the solution / aeration. This ensures that
the roots get enough oxygen for respiration.
The conical flask should be wrapped with aluminium foil. This
prevents algae from growing in the flask.
(b) poor growth and yellowing of leaves
B. STS Connections
(a) (i)
(ii)
(b) The thin film of moisture around mesophyll cells evaporates into the
intercellular spaces and diffuses out of the stomata into the atmosphere.
(c) Light intensity. The higher (lower) the light intensity, the larger (smaller)
are the guard cells and the wider (smaller) the stomata. More water vapour
can diffuse out. Transpiration rate increases.
11 Food requirements in humans
Class Practice
11.1 Heterotrophic nutrition
11.2 Food and food substances
1. F
2. T
3. F
4. T
5. F
1. Most heterotrophs are animals. (Some saprophytic fungi are also
heterotrophs.)
3. The food we eat every day make up our diet.
5.
As vitamins, minerals and dietary fibres are necessary for keeping us
healthy, they are called protective food substances.
11.3 Carbohydrates
A.
1. T
2. T
3. F
B.
4. F
5. T
6. F
7. T
3. In disaccharides only sucrose is non-reducing sugar.
4. Both hydrolysis and condensation require the presence of suitable
enzymes.
6. Polysaccharides do not give a sweet taste.
1. F
2.
3.
4.
5.
6.
11.4 Fats
C
D
E
B
A
11.5 Proteins
1.
2.
3.
4.
5.
6.
2.
T
F
T
F
T
F
4.
A molecule of fat is made up of three molecules of fatty acid combined
with one molecule of glycerol.
Essential amino acids cannot be made in human body.
6.
The excess amino acids are broken down in the liver by deamination.
11.6 Vitamins
1. T
2. F
3. F
4. T
5. F
6. T
7. F
2. Plants can make their own vitamins from simple substances.
3. Fat-soluble vitamins are more heat resistant than water-soluble vitamins.
5. Lack of vitamin A causes night blindness.
7. Vitamin D helps the absorption of calcium and phosphorus in the small
intestine.
11.7 Mineral salts
11.8 Dietary fibres
11.9 Water
1. C
2. A
3. C
4.
B
5.
D
11.10 Food tests
(a) Clinistix paper
(b) colour changes from pink to blue
(c) Benedict's test
(d) formation of brick-red ppt.
(e) iodine test
(f) colour changes from brown to blue black
(g)
(h)
(i)
(j)
(k)
(l)
Albustix paper
colour changes from yellow to green
spot test
formation of permanent translucent spot
DCPIP test
The blue DCPIP is decolourised
11.11 The need for a balanced diet
11.12 Food and energy
A. Q
S
R
P
B. 1. P
2. Q
C.
1.
2.
1. F
2. F
3. F
4. T
5. T
A balanced diet contains the right amount of all the food substances.
A pregnant woman needs extra food because she needs more energy
for the growth of the foetus.
3.
Energy for living comes from carbohydrates, fats and proteins.
11.13 The health problems resulting from an improper diet
1. C
2. D
3. B
4. A
Exam Practice
A. Multiple Choice Questions
1. D
2. C
3. C
4.
5.
6.
7.
8.
B.
B
A
B
B
D
Structured Questions
1. (a) 430
370
320
278
252
230
430
370
320
278
215
182
(b)
(c) 3 years of age.
Children need to maintain a higher metabolic rate in order to support
their period of greatest growth / compensate for the higher rate of heat
loss.
(d) After the age of 14, boys are more active than girls. Girls have thicker
2.
subcutaneous fat so that the rate of heat loss is lower than that of boys.
Girls require less energy than boys.
(a) The calcium requirements of group II is greater than that of group III,
because group II requires more calcium for the development of bones.
15
(b) (i) Group I: —— = 2
7.5
20
Group II: —— = 1
20
50
Group III: —— = 0.83
60
45
Group IV: —— = 0.9
50
Therefore, group I requires the greatest amount of protein per
unit weight.
(ii) Group I grows faster than other groups. Protein is important for
growth.
(c) People in group III are more active and they have thinner
subcutaneous fat.
(d) Girls lose blood every month / during menstruation. Iron is important
3.
(a)
(b)
(c)
(d)
(e)
4.
for the formation of red blood cells / haemoglobin.
B contains reducing sugar and vitamin C.
C contains protein and fat.
butter
fruit / orange / kiwi
pork / beef / fish
food sample D
The blue DCPIP becomes colourless.
In cold areas, people lose heat at a faster rate. Food sample A contains
fat which can release much more energy to compensate for the heat
loss.
(a) W — fats, X — carbohydrates, Y — water, Z — proteins
(b) Beans also contain mineral salts and vitamins which are not shown in
the table.
(c) (i) butter
(ii) cabbage
(d) Beans. Beans contain the highest percentage of carbohydrates which
can supply energy. Beans also have a relatively high percentage of
proteins for growth.
5.
(a) too much carbohydrates
too much fat
absence of dietary fibres
absence of vitamin C
(b) Eat less french fries.
Use less sugar for coffee.
}
any three
Eat fresh fruits or vegetables.
(c) Constipation — absence of dietary fibres
Scurvy — absence of vitamin C
C.
STS Connections
(a) D
B
C
(b) No, it is not a balanced diet. It does not contain any cereals or grains which
should be in the greatest amount in a balanced diet. It has too little fruits
and vegetables, and too much meat.
(c) It supplies inadequate energy for metabolism and daily activities. It contains
too little cellulose and hence would result in constipation.