Photosynthesis & Leaf Structure (CIE IGCSE Biology: Co-ordinated Sciences (Double Award))

Fig. 1 is a diagram of a variegated leaf from a plant. The plant was exposed to sunlight so that it could photosynthesise.

Fig. 1

A student tested the leaf for starch and found that:

• Starch was present in the green part of the leaf
• There was no starch in the white part of the leaf.

Explain the results of this test.

Explain the following steps of testing a leaf for the presence of starch:

       Boiling the leaf at the start of the procedure.

[1]

Heating ethanol in a water bath.

[1]

Extended Tier Only

The results of the investigation described in parts a and b showed that photosynthesis had occurred in certain parts of the leaf.

Give the balanced chemical equation for photosynthesis.

Extended Tier Only

Energy is converted from one form to another during the process of photosynthesis.

Describe this energy conversion.

In an investigation the carbon dioxide concentration in the air above a crop of maize plants was measured for 24 hours.

There was no wind blowing during the 24 hours of the investigation.

The results of this investigation are shown in Fig. 1.

Fig. 1

State the two times, on Fig. 1, at which the carbon dioxide concentration in the air was 37 arbitrary units.

[1]

(ii)

Calculate the difference in the carbon dioxide concentration in the air between 04:00 (sunrise) and 12:00 (midday) on Fig. 1. Give your answer in arbitrary units.

[1]

(iii)

Explain why the concentration of carbon dioxide decreases between 04:00 and 09:00.

[3]

State two environmental factors that would affect the results of this investigation.

Extended Tier Only

Describe and explain the concentration of carbon dioxide between 16:00 and sunset in Fig. 1.

Extended Tier Only

The concentration of carbon dioxide was highest at sunrise.

Suggest a reason for this.

Fig. 1 shows a diagram of a leaf.

Fig. 1

• The part of the leaf labelled G contains no chlorophyll and is a white colour.
• The part of the leaf labelled H contains chlorophyll and is a green colour.

Glucose produced during photosynthesis is stored in the leaf as starch.

The leaf was boiled in ethanol to remove the chlorophyll. The leaf was then tested for the presence of starch with iodine solution. 

Predict the colour of the part of the leaf labelled G after iodine solution has been added.

[1]

Predict the colour of the part of the leaf labelled H after iodine solution has been added. 

State a conclusion about chlorophyll from this investigation.

[1]

A similar leaf was kept in the dark for 24 hours and then tested for the presence of starch.

The leaf contained no starch.

Explain why the leaf contained no starch.

Extended Tier Only

Glucose is converted into insoluble starch for storage.

Use your knowledge of osmosis to explain why plant cells do not use glucose as a storage molecule.

A student modified the experiment from part (a) in order to investigate if light is needed for photosynthesis. Before carrying out the experiment, the student had to include an important step to ensure they obtain accurate results.

Describe this step.

[1]

Explain the importance of the step described at part (i).

[2]

A group of students used an aquatic plant to investigate the effect of temperature on the rate of photosynthesis.

Fig. 1 shows the apparatus the students used.

Fig. 1

The students counted the number of bubbles of gas the aquatic plant produced, in two minutes, at different temperatures.

Fig. 2 shows a graph of their results.

Fig. 2

State the temperature at which the aquatic plant produced the most bubbles of gas in two minutes.

Give your answer in °C.

[1]

Use Fig. 2 to find the number of bubbles of gas produced by the aquatic plant, in two minutes, at 15 °C and at 25 °C. 

Use your answer to (a)(ii) to calculate the percentage increase in the number of bubbles of gas produced by the aquatic plant at 15 °C and at 25 °C.

Show your working. 

Describe the results shown in Fig. 2.

Extended Tier Only

Use your knowledge on enzymes to suggest an explanation for the results obtained between 30 °C and 40 °C in Fig. 2.

The students added sodium hydrogen carbonate (NaHCO₃) to the water in the beaker in Fig.1.

State the purpose of this.

Fig. 1 is a scanning electron micrograph of a vertical section through part of the leaf of a broad bean plant, Vicia faba.

Fig. 1

State the names of the tissues labelled A and B.

[2]

The cells in regions B and C in Fig. 1 have a large surface area.

Explain why this is necessary for the functioning of the leaf cells.

[3]

Explain why there are many interconnecting air spaces within the leaf.

[2]

Extended Tier Only

Stomata are found on the lower surface of broad bean leaves.

Describe the function of stomata.

Extended Tier Only

Plants growing in soils lacking magnesium ions struggle to photosynthesise and therefore do not grow to their full potential.

Suggest why.

The rate of photosynthesis of terrestrial plants can be determined by measuring the uptake of carbon dioxide.

Explain why plants take up carbon dioxide during photosynthesis.

Extended Tier Only

The rate of photosynthesis of parts of individual leaves can be measured using a hand-held device as shown in Fig. 1.

Fig. 1

This apparatus allows air to flow through the transparent chamber that encloses part of the leaf. The apparatus measures the carbon dioxide concentration of the air entering and leaving the chamber.

Explain how the results from the apparatus can be used to calculate the rate of photosynthesis.

Extended Tier Only

A student used the apparatus shown in Fig. 1 to investigate the effect of temperature on the rate of photosynthesis of the leaves of Chinese plantain, Plantago asiatica, at two different concentrations of carbon dioxide, A and B.

Fig. 2 shows the results of the investigation.

Fig. 2

State one environmental factor that should have been kept constant in this investigation.

[1]

Describe the effect of temperature on the rate of photosynthesis when carbon dioxide concentration A was supplied.

Use the data from Fig. 2 in your answer.

[3]

Calculate the percentage increase in the rate of photosynthesis at 30 °C when the carbon dioxide concentration was increased from A to B as shown in Fig. 2.

Show your working and give your answer to the nearest whole number.

[2]

Explain the effect of increasing temperature on the rate of photosynthesis for carbon dioxide concentration B.

[3]

Extended Tier Only

A similar investigation was carried out on Arizona honeysweet, Tidestromia oblongifolia, that grows in Death Valley in California where the highest temperatures may be greater than 45 °C.

The results are shown in Fig. 3.

Fig. 3

Predict and explain what would happen to the rate of photosynthesis if the investigation is continued at temperatures higher than 45 °C.

The apparatus shown in Fig. 1 was used to investigate the effects of different conditions on the rate of photosynthesis in an aquatic plant.

Fig. 1

A student investigated the effects of light and carbon dioxide on the rate of photosynthesis.

The number of bubbles of oxygen produced in one minute was counted in four different conditions.

Table 1 shows the results.

Table 1

State two conclusions about the conditions needed for photosynthesis using the information in Table 1.

The investigation was carried out at 15 °C. It was repeated at 25 °C.

Suggest and explain the effect this had on the results of test 2 and test 3.

Carbon dioxide enters plant cells by diffusion.

The word diffusion on the left can be joined to two boxes on the right to make two correct statements about diffusion. 

Draw two straight lines from diffusion to the boxes to complete the two statements.  

Table 2 shows the volume of water absorbed, as well as the water usage by a plant over a period of 24 hours.

Table 2

Show your working and give your answer to two decimal places.

[2]

An investigation was carried out to test the effect of temperature on the rate of photosynthesis of pondweed.

The volume of oxygen produced per hour was measured. The results can be seen in Table 1.

Table 1

Calculate the mean rate of photosynthesis per hour when the temperature was 45 °C.

Plot the results from Table 1 onto an appropriate graph using the graph paper in Fig. 1.

Fig. 1

Describe and explain the results shown in the graph.

A farmer growing strawberries in his greenhouse used the results in Table 1 to decide on the best temperature for his greenhouse. He decided to heat the greenhouse to 30 °C.

When the farmer measured the rate of photosynthesis of his plants, he found the rate to be 11.5% slower than the data suggested.

Calculate the rate of photosynthesis that the farmer actually achieved at 30 °C.

Extended Tier Only

A student carried out an investigation into the effect of soil magnesium on plant growth.

In this investigation, the student set up two different environments as follows:

1. One plant was grown in sterile soil, provided with distilled water and placed in bright light.
2. One plant was grown in sterile soil, provided with magnesium dissolved in distilled water and placed in bright light.

Predict what the student will observe after two weeks of growing in these conditions.

Extended Tier Only

Explain your prediction from part (a).

When selecting the plants for the investigation in part (a), the student made sure that they picked plants with the same number of leaves.

Explain why this was necessary.

One method that can be used to show that photosynthesis has occurred is to test the leaves with iodine.

Explain how this shows that photosynthesis has occurred.