Exam Qs

Question 1

Plants photosynthesise and respire. Fig. 18.1 shows the rate of production of carbohydrate in photosynthesis and the rate of use of carbohydrate by respiration.
Explain the shape of the curve for the rate of photosynthesis in Fig. 18.1.

Answer 1

increased photosynthetic activity during daylight (1)
as light intensity increases there is increased activity of the light dependent reaction (1)

Question 2

Explain the shape of the curve for the rate of plant respiration in Fig. 18.1.

Answer 2

daytime temperatures generally higher than night time (1)
rate of respiration increases with increased temperature as its enzymes are temperature-dependent (1)

Question 3

What is happening at the points indicated by the letter L?

Answer 3

compensation point(s) / carbohydrate produced by photosynthesis equal to carbohydrate used in respiration (1)

Question 4

Plants grow successfully in temperatures that are suited to their metabolism. Some plants are adapted for growth in cool climates while others can grow well in warm climates.
Plants also vary in their photosynthetic metabolism. Many plants produce a 3-carbon compound as the first product of carbon fixation and so are referred to as C3 plants. Another group of plants produces a 4-carbon compound as the first product and so are referred to as C4 plants. C3 plants include barley, lentil, rice, soya, sunflower and wheat. C4 plants include maize, millet, sorghum and sugar cane.
Fig. 18.2 shows the assimilation of carbon dioxide by four different crops at different temperatures.
(i) With reference to Fig. 18.2, what is the general relationship between increasing temperature and the assimilation of carbon dioxide?

Answer 4

for all crops
initial increase in assimilation with increasing temperature (1)
at higher temperatures the assimilation decreases (1)

Question 5

With reference to Fig. 18.2, suggest which curve corresponds to each of the following crops:

Answer 5

Sugar cane
C4 crop 2 (1)
Barley
C3 crop 1 (1)

Question 6

Suggest two ways in which the ultrastructure of the chloroplast can be altered by high temperatures.
For each suggestion, explain the effect that it will have on photosynthesis.

Answer 6

four from
damage to chlorophyll / reduction in
pigment (1)
which will reduce the light dependent stage (1)
damage to membranes in chloroplast / reduction in sites for light capture (1)
which will reduce the light dependent stage (1)
damage to membranes in chloroplast / reduction in reaction sites for electron transfer (1)
which will reduce, photophosphorylation / ATP production in the light dependent stage (1)
damage to membrane around chloroplast / release of enzymes (1)
which will reduce, light independent stage / Calvin cycle (1)

Question 7

During the light-independent stage of photosynthesis, triose phosphate (TP) is synthesised in the chloroplasts of plant cells.
(i) State two possible uses of this molecule within the plant. 1

Answer 7

synthesis of:
(named) carbohydrate (1) hexose sugars (1)
amino acids (1)
lipids (1)

Question 8

From which molecule is TP synthesised during the light-independent stage?

Answer 8

GP / glycerate-3-phosphate

Question 9

Heliamphora, shown in Fig. 18.1, is a genus of carnivorous plant. Its leaves are adapted to form water-filled traps for insects. The insects are attracted by nectar, then fall into the traps and drown. The plants digest the insects and absorb the mineral ions produced. This allows Heliamphora to survive in soils with low mineral content.
Four pigments, A, B, C and D, were extracted from a Heliamphora plant. Thin layer chromatography (TLC) was carried out on the pigments. The results of the TLC are shown in Fig. 18.3.Using Fig. 18.3, what can you conclude about the composition of pigments A to D?

Answer 9

pigment A contains 2, components / molecules (1)
pigments B and D contain 1, component / molecule (1)
pigment C contains 3, components / molecules (1)
idea that pigments A and C share 2, components / molecules (1)
idea that pigments A and D
OR pigments B and C OR pigments C and D
share 1, component / molecule (1) all pigments are soluble (in liquid phase) (1)

Question 10

Much biological knowledge is obtained and verified through observation. A biologist has a small pond containing goldfish in her garden.
On a sunny day, more pondweed is at the surface of the water but on a cloudy day, less pondweed is at the surface.
Suggest an explanation for this observation.

Answer 10

1 greater light intensity on a sunny day /
less light intensity on a cloudy day;
2 oxygen produced during, photosynthesis / photolysis / light dependent stage;
3 (more) oxygen trapped within weed increases buoyancy;

Question 11

Describe the effect on the rate of photosynthesis of increasing leaf temperature.

Answer 11

1 rate of photosynthesis increases (reaches peak)
and then decreases;
2 peak / optimum, for 0.04% CO2, between 20°C and 30°C / at 25°C;
3 peak / optimum, for 0.19% CO2, between 30°C and 40°C / at 35°C;
4 ref to zero rate / no result / no photosynthesis,
at 40°C and 45°C / from 40°C / above 35°C,
with 0.04% CO2

Question 12

Use the information in the table to state one other effect of an increased concentration of carbon dioxide on
the rate of photosynthesis.

Answer 12

idea that increases the optimum temperature (for photosynthesis)
or
maximum rate of photosynthesis at higher temperature
or
can photosynthesise at higher temperatures
or
maximum rate of photosynthesis is higher or
rate of photosynthesis starts to decrease at a higher temperature
or
the rate of photosynthesis increased, at a higher rate / faster

Question 13

Suggest why there are no results for 0.04% CO2 at 40 °C and 45 °C.

Answer 13

1 no, photosynthesis / Calvin cycle / carbon fixation
or
rate too low to be recorded;
2 CO2 is limiting
or
idea that the level of CO2 is too low to compensate for the high temperature; 3 rubisco is binding to O2 (instead);
4 decreased enzyme activity;
5 (high temperature has) distorted rubisco active site;

Question 14

Explain the effect that the levels of rubisco would have on the rate of photosynthesis as the age of the leaf increases beyond the line labelled X.

Answer 14

1 rate of photosynthesis would decrease;
2 little rubisco being synthesised and the rubisco present being broken down
or
more rubisco is being broken down than being synthesised;
3 less / no, enzyme / rubisco, available to fix, carbon dioxide / CO2;
4 less / no, Calvin cycle / light independent stage, can take place;
5 rubisco becomes limiting (factor

Question 15

State the advantage to the plant of having a range of accessory pigments in photosystems.

Answer 15

able to, absorb / use,
a range of / different / more / other,
(light) wavelengths /

Question 16

Describe two ways in which the structure of part C is adapted to its function

Answer 16

1 contain, (named) pigment (molecules) / photosystems;
2
3
contain, (named) electron carriers / ETC / ATP synth(et)ase;
idea that has a large surface area (in a small volume) for, light absorption / light dependent reaction(s) / light dependent stage / electron transport;

Question 17

Fig. 1.2 shows the theoretical and actual relationship between light intensity and the rate of photosynthesis.
With reference to the biochemistry of photosynthesis, explain why the theoretical rate of photosynthesis is not achieved at higher light intensities.

Answer 17

1
at high light intensity
other (named) factor becomes a limiting factor;
idea that temperature becomes limiting as, Calvin cycle / light independent reaction, involves enzymes / relies on kinetic energy of molecules;
idea that CO2 (concentration) becomes limiting as it is required for, Calvin cycle / light independent reaction / formation of (named) Calvin cycle compound / reaction with RuBP / fixation by Rubisco

Question 18

Plants are usually adapted to living in conditions of different light intensities.
The rate of photosynthesis at different light intensities for two different species of plant was investigated. The results are shown in Fig. 1.3 Using the information in Fig. 1.3, explain which of the two species, D or E, is better adapted to living in shady conditions

Answer 18

species E because

E starts photosynthesising at low(er) light intensity;
E reaches its maximum rate at low(er) light intensity;
E steep(er) increase in rate of photosynthesis (with small increase in light intensity);
E has a, higher / greater / faster, rate of photosynthesis (than D)
at low light intensities;

Question 19

The leaf of a plant that is adapted to living in shade will differ from the leaf of a plant that is adapted to living in sunlight.
Suggest one way in which the structure of these leaves will differ.

Answer 19

shade leaf will have
large(r) / more, chloroplast(s) / (palisade) mesophyll;
more, grana / thylakoids (in chloroplast);
large(r) surface area (of leaves)

Question 20

Plants are autotrophs. Most other organisms are heterotrophs.
Outline the ways in which heterotrophic organisms are dependent on plants.

Answer 20

animals / heterotrophs (need to), eat / obtain organic material from / AW, plants / autotrophs;
(plants / autotrophs) produce (named) organic molecules during, photosynthesis / Calvin cycle / light independent stage;
(plants / autotrophs) produce oxygen during, photosynthesis / photolysis / light dependent stageglucose / carbohydrate / oxygen, (produced in photosynthesis) are used in respiration by, animals / heterotrophs;

Question 21

Palisade mesophyll cells are an example of a specialised plant cell. These cells are the main site of photosynthesis in plants.
A team of scientists investigated the effect of shining light on the upper and lower surfaces of a leaf on the rate of photosynthesis.
The results are shown in Fig. 3.2What conclusions can you draw from the data in Fig. 3.2 about the effects of light and the internal structure of a leaf? Explain your answer.

Answer 21

idea that at low light levels, photosynthetic rate is greater when light is shone on the
upper surface ✓
palisade cells are, nearer / AW, upper surface ✓
idea that chloroplasts also present in cells at lower surface ✓
(little difference because) leaf is thin ✓
idea that light can pass through the leaf from the lower surface to reach palisade cells ✓
no difference (in rate) at high(er) light intensity ✓
(at high light intensity) carbon dioxide (concentration) is limiting factor / number of stomata limit carbon dioxide uptake ✓
figures to support, with units