photsynthesis exam questions

Question 1

what is needed for LDR?

Answer 1

adp, pi, water and NADP

Question 2

why line on chromatogra is drawn in pencil, not pen

Answer 2

-ink and leaf pigments would mix.

Question 3

Describe the method the student used to separate the pigments after the solution of pigments had been applied to the origin.
_________________________________________________________ (2)s

Answer 3

-solvent should be below origin line
-stop before solvent gets to the top

Question 4

The pigments in leaves are different colours. Suggest and explain the advantage of having different coloured pigments in leaves.
_____________________________________________________

Answer 4

-to absorb different wavelengts of light for photosynthesis.

Question 5

Heat stress is a condition that often occurs in plants exposed to high temperatures for a prolonged period of time. Heat stress is a major factor in limiting the rate of photosynthesis.
(a) Heat stress decreases the light-dependent reaction of photosynthesis.
Explain why this leads to a decrease in the light-independent reaction (2)

Answer 5

-less ATP
-less NADP

Question 6

Another effect of heat stress is a decrease in the activity of the enzyme rubisco. A decrease in the activity of an enzyme means that the rate of the reaction it catalyses becomes slower.
A decrease in the activity of the enzyme rubisco would limit the rate of photosynthesis.
Explain why.
___________________________________________________________

Answer 6

-less carbon dioxide reacts with RuBP
less GP produced

Question 7

Scientists investigated the effect of temperature on the activity of two enzymes isolated from the leaf cells of cotton plants.
• Rubisco
• Rubisco activase – an enzyme that activates rubisco
Figure 1 and Figure 2 show their results.
(d) The scientists concluded that heat stress reduces the activity of rubisco in plant leaves by affecting rubisco activase
use all the information to evaluate their conclusion. (4)

Answer 7

-no statistical test
-rubisco activity increases with temperature.
-only for cotton plant
-graph suggests that rubisco activase does not affect rubisco activity.

Question 8

explain how chemicals which inibit the decolourisation of DCPIP couldto slow the growth of weeds

Answer 8

-less ATP produced
-less reduced NADP produced
-less GP reduced to TP.

Question 9

The scientists suggested that mutant plants producing more chlorophyll b
would grow faster than normal plants in all light intensities.
Explain how these data support this suggestion (4)

Answer 9

at all light intensities, chloroplasts from mutant plants have
-faster production of ATP and reduced NADP.
-faster light independent reaction
-more sugars produced to use in respiration.
-more energy for growth.

Question 10

The scientists suggested that mutant plants producing more chlorophyll b
would grow faster than normal plants in all light intensities.
Explain how these data support this suggestion (2)

Answer 10

-stirrer distributes heat energy
-water has high specific heat capacity.

Question 11

Plants and algae produce fuels called biofuels. Scientists have used Chlorella to
produce biofuel. Chlorella is a genus of single-celled photosynthetic alga.
Chlorella can be grown in open ponds and fermenters.
(c) In natural ecosystems, most of the light falling on producers is not used in
photosynthesis.
Suggest two reasons why (2)

Answer 11

-carbon dioxide concentration is a limiting factor
-light is wrong wavelength
-light reflected.

Question 12

Atrazine binds to proteins in the electron transfer chain in chloroplasts of
weeds, reducing the transfer of electrons down the chain.
Explain how this reduces the rate of photosynthesis in weeds (4)

Answer 12

-fewer protons transferred across thylakoid membranes
-less ATP produced
-less reduced NADP produced
-prevents light independent reaction.

Question 13

When treated with Atrazine, weeds have been shown to give off small
amounts of heat.
Suggest an explanation for this observation (1)

Answer 13

-heat energy released from excited electrons.

Question 14

In both Treatment 1 and Treatment 2, the uptake of carbon dioxide falls to
zero when the light is turned off.
Explain why. (2)

Answer 14

-no use of carbon dioxide for photosynthesis
-concentration gradient for carbon dioxide out of the leaf.

Question 15

Suggest and explain why the rate of photosynthesis was low between 525 nm and
575 nm wavelengths of light. (2)

Answer 15

-light not absorbed
-light needed for LDR.

Question 16

Explain why CO2 uptake is a measure of net productivity. (1)

Answer 16

-shows photosynthesis

Question 17

Use the information in the figure to explain how the shade plant is better
adapted than the sun plant to growing at low light intensities. (2)

Answer 17

shaded plant has lower respiration rate
so higher net productivity.

Question 18

process of LDR (6 marks)

Answer 18

-light energy absorbed by chlorophyll
-excites electrons
-moves through electron transport carrier chain
-ADP and Pi form ATP using energy
-photolysis of water produces hydrogen ions, electrons and oxygen
-NADP reduced by electrons

Question 19

process of LIR (6)

Answer 19

-CO2 reacts with RuBP
-to produce 2 molecules of GP
-GP reduced to TP
-using reduced NADP
-using energy from ATP.
-in calvin cycle
-TP converted to other useful organic substances.

Question 20

the scientists carried out a similar experiment but increased the carbon dioxide concentration for 1 to 2%. The relative amounts of GP and RuBP remained the same. Suggest two reasons why. (2)

Answer 20

-limiting factors- light
-temperature
-rubisco enzyme

Question 21

explain why the increase in the dry mass of the plant over 12 months is less than the mass of hexose produced over the same period. (3)

Answer 21

-some hexose used in respiration
-carbon dioxide lost to the air
- some parts of plant eaten

Question 22

how is light energy converted to chemical energy during the LDR. (3)

Answer 22

-electrons are excited- transported via electron transport carrier chain
-hydrogen ions pass through co enzyme ATP synthase, which leads to the production of ATP from ADP +Pi

Question 23

explain why between 0 and 300 seconds, the concentration of radioactive GP remained constant. (3)

Answer 23

-GP is being produced at the same rate it is being used
-GP is reduced to TP with the release of ATP and reduced NADP.

Question 24

explain why there is twice the amount of GP than RuBP when CO2 concentration is high (1)

Answer 24

CO2 reacts with RuBP to form 2 molecules of GP.

Question 25

Explain the rise in the amount of ribulose bisphosphate after the carbon dioxide
concentration is reduced. (1)

Answer 25

-less RuBP added to CO2 so less RuBP used to form GP.

Question 26

Explain how lack of light caused the amount of radioactively labelled glycerate
3-phosphate to rise (2)

Answer 26

-ATP and reduced NADP not formed
-less GP reforms RuBP

Question 27

Use the data from Figure 2 for plants that do not produce GB to explain the effect of
temperature on changes in dry mass of the plants shown in Figure 1. (4)

Answer 27

as temperature increases, enzyme denatured
less photosynthesis- less sugars produced
less respiration- less ATP produced
-less ATP for active transport of mineral ions so reduced growth.

Question 28

Rubisco activase is an enzyme found in chloroplasts. It activates the light-independent reaction
of photosynthesis.

The scientists discovered that, as temperature increased from 25°C to 45°C, rubisco activase
began attaching to thylakoid membranes in chloroplasts and this stopped it working.

(c) Rubisco activase stops working when it attaches to a thylakoid.

Use your knowledge of protein structure to explain why. (2)

Answer 28

-alters tertiary structure
-prevents enzyme substrate complexes forming.

Question 29

Few species of plant can live below large trees in a forest.
Use the information in Figure 1 and Figure 2 to suggest why. (4)

Answer 29

-less light reaches the ground
-reduced range of wavelengths absorbed
-less light absorbed by chlorophyll
-not enough photosynthesis.