Photosynthesis Exam Questions

Question 1

The products of the light dependent stage are used in the light independent stage of photosynthesis. What are these products uses for?

Answer 1

To incorporate Caron dioxide to make sugars

Question 2

Tomato growers have increased the yield of fruit from 100 to 400 tonnes per hectare by growing the tomato plants in automatically healed glasshouses and enhancing the carbon dioxide concentration.
Tomato fruits have a high percentage of water. Growers can reduce the water content of the fruit by adding sodium chloride to the nutrient solution.
Explain how adding sodium chloride can reduce the water content of the fruit ( 2marks)

Answer 2

Lowers the water potential of nutrient solution

Less water absorbed into roots by osmosis

Question 3

Maintaining a high temperature in a glasshouse in winter, when the light intensity is low may reduce the yield. Explain how ( 2marks )

Answer 3

Increased temperature increases the rate of respiration

Rate of photosynthesis too low to replace respiratory loss

Question 4

Explain how enhancing the co2 concentration helps to increase the yield

Answer 4

Rate of photosynthesis is increased since the normal atmospheric concentration is a limiting factor

Question 5

Chloroplasts contain chlorophyll a and chlorophyll b. Scientists found tobacco plants with a mutation that caused them to make more chlorophyll b than normal tobacco plants. They investigated the effect of this mutation on the rate of photosynthesis. Scientists grew normal and mutating tobacco plants. They grew some of each in low light intensity and grew others in high light intensity.
They isolated samples of chloroplasts from mature plants of both types
Finally they measured oxygen production by the chloroplasts they had isolated from the plants
Explain why the scientists measured the rate of production of oxygen in this investigation ( 2 marks )

Answer 5

Oxygen is produced in the light dependent reaction

The faster oxygen is produced, the faster the light dependent reaction

Question 6

Some bacteria use hydrogen sulfide to produce organic compounds. The hydrogen sulfide has a similar role to that of water in photosynthesis
Suggest what the hydrogen sulfide is used for in these bacteria ( 2 marks )

Answer 6

Provides hydrogen/ protons/ H+ and electrons for reduction

So a source of electrons for the electron transport chain

Question 7

Crops use light energy to produce photosynthetic products.

Describe how crop plants use light energy during the light dependent reaction ( 5 marks )

Answer 7

Excites electrons so the leave the chlorophyll
Electrons move down the electron transport chain
This energy is used to join adp and pi to form atp
The electrons are used in the photolysis of water
And NADP is reduced by electrons

Question 8

Explain why co2 uptake is a measure of net productivity ( 1 mark )

Answer 8

Shows the rate of photosynthesis , more carbon dioxide used in photosynthesis than produced in respiration

Question 9

During the light independent reaction of reaction of photosynthesis, carbon dioxide is converted into useful organic substances. Describe how ( 6marks)

Answer 9

Carbon dioxide combines with 5 carbon ribulose bisphopshate. The 6 carbon molecule then splits into two glycerate 3- phosphates.
These 2 molecules are then reduced to triose phosphate using nadph and energy from atp
Triose phosphate can be converted into hexose sugars or regenerated back to RuBP

Question 10

The scientists suggested that the rise in the mean rate of photosynthesis was the cause of the rise in the mean rate of respiration in the soil under trees.
Suggest how the rise in the mean rate of photosynthesis could lead to the rise in the mean rate of respiration in the soil under trees ( 2 marks )

Answer 10

Photosynthesis produces sugars which are moved to the roots to be taken up for respiration

Question 11

Scientists investigated the effect of iron deficiency on the production of triose phosphate in sugar beet plants. They grew the plants under the same conditions with their roots in a liquid growth medium containing all the necessary nutrients. Ten days before the experiments, they transferred half the plants to a liquid growth medium contains no iron. The scientist measured the concentration of triose phosphate in these plants and in the control plants : at end of 6 hours in the dark, then 16 hours in the light.
The plants were left for 6 hours in the dark before the experiment. Explain why ( 1 mark)

Answer 11

This is so the amount of triose phosphate will be low at the start

Question 12

Iron deficiency reduces electron transport. Use this information and your knowledge of photosynthesis to explain the decrease in production of triose phosphate in the iron deficient plants ( 4 marks)

Answer 12

If the electron transport is reduced then less atp is formed and reduced NADP which is used in the light independent reaction to reduce gp into tp

Question 13

Iron deficiency results in a decrease in the uptake of co2. Explain why ( 2 marks )

Answer 13

Less triose phosphate produced so less will be regenerated into RuBP which accepts co2

Question 14

In the leaves at the top of trees in a forest, carbon dioxide is often the limiting factor for photosynthesis,
Use your knowledge to suggest and explain one reason why

Answer 14

Light intensity isn’t a limiting factor at the top of trees so the light dependent reaction is fast

Question 15

Describe what happens during the light dependent reaction ( 5 marks )

Answer 15

Chlorophyll absorbs energy which excites the electrons
So the electrons leave the chlorophyll and travel down the ETC
They lose energy whcih is used to join adp and pi to form atp
The photolysis of water produces protons, electrons and oxygen
The electrons reduce NADP

Question 16

DCMU is used as a weed killer, it inhibits electron transfer during photosynthesis. The addition of DCMU to a tube a decreased the uptake of carbon. Explain why ( 2 marks)

Answer 16

Less atp and reduced NADP produced in the light dependent reaction

Question 17

An investigation was carried out in bright light. Explain why reducing the light intensity would affect the amount of oxygen released by the seaweeds ( 3 marks )

Answer 17

Light intensity is a limiting factor which would mean less electrons are released from the chlorophyll for the photolysis of water

Question 18

ATP is useful in many biological processes . Explain why ( 4 marks)

Answer 18

Releases energy in small manageable amounts
Broken down in a single reaction
Lowers the activation energy
Can be reformed

Question 19

Creeping azalea is a plant which grows on mountains. Scientists predict that in the area where this plant grows. The mean summer temperatures is likely to rise three degrees and become more cloudier
Describe and explain how these changes are likely to affect the growth of creeping azalea ( 3 marks )

Answer 19

Growth will decrease

Rate of respiration will increase at higher temperature but photosynthesis will decreased as there is less light

Question 20

Explain why the increase in the dry mass of a plant over twelve months is less than the mass of hexose produced over the same period ( 3 Marks )

Answer 20

Some hexose is used in respiration
Co2 is produced
Some parts of the plant are eaten

Question 21

An investigation was carried out to find the effect of increasing carbon dioxide concentration on the rate of photosynthesis in a particular type of plant.
Suggest suitable units for measuring the tate of photosynthesis in this investigation

Answer 21

Co2 produced per unit of time

Question 22

In which part of a chloroplasts do the light dependent reactions occur

Answer 22

Thylakoids

Question 23

Explain the role of chlorophyll in photolysis ( 3marks)

Answer 23

The chlorophyll absorbs light energy whcih means the electrons leave the chlorophyll which is replaced by the photolysis of water

Question 24

ATP and reduced NADP are two products of the light dependent reactions. Describe one function of each of these substances in the light independent reactions ( 2marks )

Answer 24

ATP provides energy for the reduction of GP to TP

Reduced NADP provides electrons for the reduction of GP to TP

Question 25

The red seaweed lives under water at a depth of 2 metres. Suggest an advantage to the red seaweed having other pigments in addition to chlorophyll a

Answer 25

More wavelengths absorbed so more efficient photosynthesis can occur at these depths

Question 26

Lowering the temperature has very little effect in the light dependent reaction, but it slows the light independent reaction. Explain why

Answer 26

Enzymes are only involved in the light independent which will slow the rate meaning less frequent collisions

Question 27

A suspension of chloroplasts was isolated from an aquatic plant and a reagent was added. The reagent is blue when oxidised and is colourless when reduced.
Another suspension of chloroplasts was set up before. Small quantities of adp and phosphate ions were added and then the tube was exposed to light. The blue colour disappeared more quickly. Explain why ( 2 marks)

Answer 27

Adp and phosphate is needed to produce atp

So adp levels were a limiting factor