Photosynthesis (A Level only) (AQA A Level Biology)

Exam Questions

2 hours15 questions
1a3 marks

Figure 1 below shows a diagram of a chloroplast. 

Figure 1

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Identify the parts of a chloroplast labelled A-C in Figure 1.

1b1 mark

The part of the chloroplast labelled B in Figure 1 contains various photosynthetic pigments. 

Suggest why chloroplasts contain more than one different photosynthetic pigment. 

1c2 marks

The pigments in a chloroplast can be separated and identified using a technique called thin layer chromatography. After extracting pigments from a spinach leaf, a student carried out thin layer chromatography.

Some of their results can be seen in Figure 2 below.

Figure 2

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Use the equation provided to calculate the Rf values for pigments X and Y in Figure 2.

                                      R subscript f equals fraction numerator D i s tan c e space m o v e d space b y space p i g m e n t over denominator D i s tan c e space m o v e d space b y space s o l v e n t end fraction

1d2 marks

Table 1 contains value ranges for the Rf values of common photosynthetic pigments. 

Table 1

Pigment Rf value range
Carotene 0.89-0.95
Neoxanthin 0.05-0.11
Chlorophyll a 0.64-0.69
Chlorophyll b 0.53-0.62
Pheophytin a 0.78-0.86

Use your answers to part c) to identify pigments X and Y from Figure 2

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2a1 mark

Figure 1 below shows a representation of some of the reactions taking place during the light dependent reactions of photosynthesis. 

Figure 1

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State the exact location of the reactions shown in Figure 1 within a plant cell.

2b2 marks

Name and describe the process labelled A in Figure 1.

2c2 marks

State the products made at the positions marked B and C on Figure 1.

2d2 marks

Figure 1 shows the loss of electrons from photosystem 2, but does not show how these electrons are replaced. 

State and explain the source of the electrons that replace those lost at stage A in Figure 1

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3a1 mark

Figure 1 below shows the reactions of the Calvin cycle. 

Figure 1

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Name the enzyme marked enzyme X in Figure 1.  

3b2 marks

Name the molecules required at the positions marked Y and Z to convert GP into TP.

3c2 marks

One of the products produced from TP is hexose sugars. Give two uses for hexose sugars inside plant cells.

3d2 marks

Name one other product that is made during the Calvin cycle, and state its role inside plant cells.

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4a2 marks

Carbon dioxide concentration is a limiting factor in photosynthesis. 

State why this is the case.

4b2 marks

Figure 1 below shows the relationship between carbon dioxide concentration and the rate of photosynthesis.

Figure 1

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Describe the relationship between carbon dioxide concentration and rate of photosynthesis shown in Figure 1

4c1 mark

Identify a possible limiting factor at the point labelled X in Figure 1.

4d3 marks

Sketch a graph of the rate of photosynthesis against temperature and explain the shape you have drawn.

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5a1 mark

A student wanted to investigate the effect of light intensity on the rate of photosynthesis. They set up an investigation as shown in Figure 1, and altered the light intensity by changing the distance between the lamp and the pondweed. 

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Name the variable measured here to assess the rate of photosynthesis. 

5b2 marks

State two variables that need to be controlled in the investigation shown in Figure 1

5c2 marks

Figure 2 below shows the student’s results.

Figure 2

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Using Figure 2, calculate the percentage decrease in the rate of photosynthesis that takes place when the distance from the lamp is 10 cm compared to when it is 90 cm. 

5d2 marks

Explain why lower light intensity leads to a reduced rate of photosynthesis, as shown in Figure 2.

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1a5 marks

Crops absorb and use light energy for the production of photosynthetic products. Describe how light energy is used by crop plants during the light-dependent reaction.

1b2 marks

An experiment using radioactive carbon was carried out by scientists to investigate the Calvin Cycle. Multiple leaves of a plant were enclosed within a sealed bag containing radioactive carbon for different lengths of time. The leaves were removed and analysed for radioactive compounds. Figure 1 below shows the results.

Figure 1

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Use Figure 1 to explain the changes in the amount of radioactive substances in the dark.

1c5 marks

Figure 2 below depicts the light-independent reactions of photosynthesis.

Figure 2

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Describe the mechanism of these reactions and explain how they allow for the continuous synthesis of 6-carbon sugars.

1d3 marks

Describe how plants can use compound P shown in Figure 2.

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2a2 marks

Lab technicians wanted to determine the effects of light intensity and temperature on the rate of photosynthesis in Rhododendrons. They recorded the effect of different temperatures on the net rate of photosynthesis at various light intensities. Their experiment also recorded the rate of respiration at the different temperatures. Figure 1 below shows the results from their experiment.

         Figure 1

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Name the limiting factor of the rate photosynthesis between A and B. Justify your answer.

2b1 mark

Use information in Figure 1 to calculate the gross rate of photosynthesis at 25°C and low light intensity.

2c3 marks

Rhododendrons have been found in several alpine regions. Ecologists noted that in one of the plant's natural habitats the average summer temperature rose from 21°C to 24°C, while the cloud cover increased. 

Describe and explain how these changes would impactthe growth of Rhododendrons.

2d2 marks

Name two other variables that could act as limiting factors for the rate of photosynthesis. 

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3a2 marks

Plants possess a collection of photosynthetic pigments that allow for the absorption of light energy. This group of pigments includes two types of chlorophyll and multiple carotenoids. Different species of plants possess different quantities of each pigment. The combination and quantity of each pigment that each plant species possess is an adaptation to their habitat and behaviour. Figure 1 demonstrates how different wavelengths of light are absorbed by chlorophyll a, chlorophyll b and carotenoids from a particular plant species.

Figure 1

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Describe the absorption of light at different wavelengths by pigment chlorophyll b.

3b2 marks

Suggest why it is beneficial for plants to possess multiple photosynthetic pigments such as chlorophyll a, chlorophyll b and carotenoids.

3c4 marks

A researcher wanted to investigate the energy of different wavelengths of light that hit the ground in a woodland area. He measured the energy from direct sunlight and sunlight that had passed through the tree canopy. Figure 2 shows his results.

Figure 2

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Only a small number of plant species are found on the ground below tall trees in woodland areas. Use Figure 1 and Figure 2 to suggest why this is.

3d1 mark

Suggest a practical method that could be used to determine the different photosynthetic pigments present in a plant species.

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4a1 mark

Herbicides are chemicals used in agriculture to reduce the growth of competing weeds. Research was carried out to determine how the use of a new herbicide “Weed Wonder” would affect the yield of corn. Some fields in different farms were treated with “Weed Wonder” and the other fields were not. Figure 1 below shows the results from the study. 

   Figure 1

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Calculate the percentage increase in yield caused by the use of “Weed Wonder” in farm Q.

4b2 marks

A scientist reviewing the data stated that no definite conclusions could be made when comparing the mean values between farms in Figure 1.

Suggest why the scientist made this statement.

4c6 marks

“Weed Wonder” works in a very specific way. It inhibits particular proteins within the electron transport chain in the chloroplasts of weeds. 

Explain how this would affect the growth of weeds.

4d2 marks

DCPIP is sometimes used in experiments to compare the effectiveness of different weed killers. DCPIP solution is blue when oxidised and colourless when reduced. The weed killers are measured by their ability to prevent the decolourisation of DCPIP in chloroplast suspensions.

Different concentrations of three different weed killers were added to illuminated chloroplast suspensions containing DCPIP. The  IC50 was then calculated for each weedkiller. The IC50 is the concentration of a chemical which prevents the decolourisation of DCPIP by 50%.

Table 1 below shows the results for the three different weed killers. Suggest and explain which weed killer would be the best choice for a farmer.

Table 1 

Weed Killer IC50 (kg dm3)
Weed Wonder 1.5
Chemical B 0.8
Chemical C 1.1

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5a2 marks

When plants are exposed to extreme high or cold temperatures for a continued period of time they are put under a lot of stress. This stress greatly impacts the rate of photosynthesis, in particular the light-dependent reaction of photosynthesis.

Explain why extreme cold leads to a decrease in the light-independent reaction.

5b1 mark

State where the light-independent reactions take place in photosynthetic plants.

5c2 marks

Extreme cold can also cause a decrease in rubisco activity that can limit the rate of photosynthesis.

Explain why.

5d4 marks

Lab technicians isolated two enzymes from the leaf cells of tomato plants: rubisco and rubisco activase. Rubisco activase is an enzyme that activates rubisco. They investigated the effect of temperature on the two enzymes. Figure 1 shows their results.

Figure 1

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The lab technicians concluded that extreme heat reduces the activity of rubisco in plant leaves by affecting rubisco activase. Use the information given in Figure 1 to evaluate this conclusion.

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1a2 marks

Explain why the light-independent stage of photosynthesis stops in the absence of light.

1b6 marks

Figure 1 shows the effect of light intensity, carbon dioxide and temperature on the rate of photosynthesis.  

Figure 1

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A - 0.04% carbon dioxide at 15°C

B - 0.04% carbon dioxide at 25°C

C - 0.04% carbon dioxide at 35°C

D - 0.1% carbon dioxide at 25°C

State two dependent variables that could be measured to estimate the rate of photosynthesis in this experiment. In each case, outline a method that could provide accurate data.  

1c2 marks

A commercial farmer growing peppers keeps her greenhouses at 25°C and circulates air around the greenhouses. Air has a CO2 concentration of 0.04% and the ambient light intensity is 4,000 lux. Use Figure 1 to predict whether the farmer would be more likely to achieve higher pepper yields by raising the carbon dioxide concentration to 0.1% or by raising the temperature to 35°C.

Explain your answer.  

1d3 marks

Explain why, at 25°C, raising the level of carbon dioxide from 0.04% to 0.1% increases the amount of glucose produced. 

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2a5 marks

In the light-dependent stage of photosynthesis, explain the role of protons in supplying intermediate products to the light-dependent stage. 

2b5 marks

Figure 1 shows the experimental set-up of a study of the effect of ammonium hydroxide on chloroplasts extracted from spinach leaves.  All five tubes were then placed in a water bath at 20°C and illuminated from all sides during the subsequent reaction. 

Figure 1

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For each tube in Figure 1, explain the rationale for setting the tubes’ contents in the way shown. 

2c2 marks

Referring to the experiment depicted in Figure 1, state the role of the compound DCPIP and outline the molecule that it replaces in this experiment. 

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3a1 mark

State the exact location within a palisade cell that the light-independent stages of photosynthesis takes place.

3b1 mark

A team of researchers investigated the effect of changing the carbon dioxide concentration on the levels of glycerate-3-phosphate (GP) and ribulose bisphosphate (RuBP) in photosynthesising cells.

Table 1 shows the results obtained when the carbon dioxide concentration was reduced.

Table 1

Photosynthetic
intermediate

Level before
experiment /
arbitrary units

Level after experiment / arbitrary units
1.0% CO2 0.003% CO2
RuBP 18 18 37
GP 36 36 17

         

Explain the decrease in the level of GP at the lower carbon dioxide concentration.

3c3 marks

The researchers carried out a similar experiment but increased the carbon dioxide concentration from 1% to 2%. The relative levels of GP and RuBP remained the same both before and after the experiment.

Suggest three reasons why. 

3d3 marks

Some primitive species of bacteria that live on the ocean floor do not have access to light for photosynthesis. Instead, they use the process of chemosynthesis to make food (glucose) using the energy stored in chemicals such as methane, hydrogen sulfide (H2S) and carbon dioxide. A simplified equation of one of these reactions is shown below:

carbon dioxide + water + hydrogen sulfide → glucose + sulfur + sulfur compounds

Use your knowledge of photosynthesis to suggest what the hydrogen sulfide is used for in chemosynthesis in these bacteria.

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4a2 marks

There are two types of chlorophyll in chloroplasts, chlorophyll A and chlorophyll B. Researchers created a genetically-modified (GM) vine plant with an allele that caused them to synthesise higher levels of chlorophyll B than wild-type vine plants. They investigated the effect of this new allele on the rate of plant growth.

The researchers grew wild-type and GM vines. They grew some of each in low light intensity and grew others in high light intensity. They extracted chloroplasts from mature plants of both types. Finally, they measured oxygen production at different light intensities by the chloroplasts they had extracted from the plants.

Figure 1 shows the researchers’ results.

Figure 1

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Explain the purpose of measuring oxygen production.

4b2 marks

Calculate the percentage improvement in oxygen production caused by the genetic modification for vines grown at high light intensity at an experimental light intensity of 20 mmol photons m-2 min-1. Give your answer to 3 significant figures. 

4c4 marks

The researchers suggested that GM plants producing more chlorophyll B would grow faster than wild-type plants in all light intensities.

Explain how these data support this suggestion.

4d5 marks

In a woodland, the concentrations of carbon dioxide in the air at different heights above ground change during a 24-hour period. 

Use your knowledge of photosynthesis to describe and explain these changes. Assume that there is no air movement caused by wind throughout the 24-hour period. 

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5a1 mark

A research student investigated the uptake of radioactively labelled carbon dioxide in chloroplasts. He used three tubes, each containing different components of chloroplasts.

He illuminated all three tubes and after 20 minutes, measured the uptake of carbon dioxide in each of these tubes.

His results are shown in Table 1.

Table 1

Tube

Tube contents

Absorption of radioactively
labelled CO2

 / counts per minute

X grana, stroma 9600
Y ATP, reduced NADP,
stroma

9800

Z stroma 400



Name the substance which combines with carbon dioxide in a chloroplast.

5b3 marks

Use the information in Table 1 to predict the level of absorption of radioactively labelled carbon dioxide in each tube if they were placed in the dark for 20 minutes. Explain your answer.

5c3 marks

Certain weed killers act by inhibiting electron transfer during photosynthesis. The addition of such a weedkiller to tube X decreased the uptake of carbon dioxide.

Explain why.

5d3 marks

Describe the exact role of ribulose bisphosphate (RuBP) in the Calvin cycle.

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