Photosynthesis (A Level only) (AQA A Level Biology): Exam Questions

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.

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. The leaves were removed and analysed for radioactive compounds.

Figure 1 below shows the results.

Figure 1

Explain the changes in the amount of radioactive substances that occur in Figure 1 when environmental conditions change from light to dark.

When the Calvin cycle progresses normally in the presence of light, hexose sugars are produced

Describe how plants can use these hexose sugars.

Lab technicians wanted to determine the effects of light intensity and temperature on rate of photosynthesis in Rhododendron plants. 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

Name the limiting factor between points A and B. Justify your answer.

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

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 impact the growth of Rhododendrons.

Name two environmental variables, other than light intensity and temperature, that could affect the rate of photosynthesis. 

Plants contain 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, and the combination and quantity of each pigment that each plant contains 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

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

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

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 from sunlight that had passed through the tree canopy.

Figure 2 shows his results.

Figure 2

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 the case.

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

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

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

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

Justify the scientist's statement.

“Weed Wonder” inhibits proteins within the electron transport chain in the chloroplasts of weeds. 

Explain how this would affect the growth of weeds.

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

When plants are exposed to extreme temperatures for a continued period of time they are put under a lot of stress. This stress greatly impacts the rate of photosynthesis.

Explain why extreme cold leads to a decrease in the rate of photosynthesis.

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. Note that the two enzymes were investigated separately.

Figure 1 shows their results.

Figure 1

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.

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

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

• 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

Figure 1

 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.  

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 light intensity is 4000 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.

Explain why, at 25°C, raising the level of carbon dioxide from 0.04% to 0.1% will increase glucose production.

Explain the role of protons in supplying products to the light-dependent stage. of photosynthesis.

Figure 1 shows the experimental set-up of a study looking at the effect of ammonium hydroxide on chloroplasts extracted from spinach leaves. 

All five tubes were placed in a water bath at 20 °C and illuminated from all sides and any changes were observed.

Figure 1

For each tube in Figure 1, explain the contents.

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

State the exact location within a palisade cell in which the light-independent stages of photosynthesis occur.

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

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

The researchers carried out a similar experiment but increased the carbon dioxide concentration from 1.0% to 2.0%. The relative levels of GP and RuBP remained the same both before and after the experiment.

Suggest how this result could be explained.

Some 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 for one of these reactions is shown below:

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

Use your knowledge of photosynthesis to suggest the role of hydrogen sulfide in chemosynthesis.

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 photosynthesis.

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

Figure 1 shows the researchers’ results.

Figure 1

Explain why oxygen production is measured here.

Calculate the percentage increase in oxygen production in GM vines compared to wild-type 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. 

Explain how this increase in growth rate in GM vines could have occurred.

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 explain these changes. Assume that there is no air movement caused by wind throughout the 24-hour period. 

A research student investigated the uptake of radioactively labelled carbon dioxide in chloroplasts.

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

The student used three tubes, each containing different components of chloroplasts.

All three tubes were illuminated, and after 20 minutes the uptake of carbon dioxide in each of these tubes was measured.

The results are shown in Table 1.

Table 1

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 answers.