Photosynthesis (Edexcel GCSE Biology: Combined Science)

Figure 1 shows a food chain. 

Figure 2 show the rate of photosynthesis in a field containing small plants, during a 12 hour period. 

Figure 2

Higher Tier only

A scientist investigated the effect of light intensity on the rate of photosynthesis of the aquatic Cabomba plant. 

A lamp was used as a source of light. The lamp was placed at different distances (d) from the Cabomba plant, and the number of bubbles produced in 60 seconds was used to calculate the rate of photosynthesis. 

The light intensity was then calculated using the inverse square law .

Figure 1 shows the scientist's results. 

Figure 1

(2)

(2)

(2)

The student repeats the experiment, changing the lightbulb to allow for a higher light intensity to be achieved. The student found that despite the higher light intensity that the rate of reaction did not increase any further.

Explain why the rate of photosynthesis did not increase when the light intensity increased. 

Figure 1 shows a cross section through a leaf. 

Figure 1

Describe the process that takes place in a leaf to produce oxygen. 

Some of the oxygen does not leave the leaf and instead is used for another reaction within the leaf. 

(1)

(2)

The concentration of carbon dioxide in two areas of a rainforest was measured. Each measurement was taken three times. The results are shown in Figure 1.

Area A was full of large trees and area B was an area with a small number of small trees, as it was just recovering from some recent deforestation. 

Figure 1

Calculate the mean carbon dioxide concentration in area B. 

(2)

Explain why all the carbon dioxide concentration readings for area B are higher than for area A. 

(2)

The experiment was repeated in a high altitude area.

Suggest how the results would vary in the high altitude area compared to the data in Figure 2, and explain how this would affect the biomass of the trees in this area. 

A student placed some balls made of algae into each of four small glass bottles containing hydrogencarbonate indicator. 

Three of the bottles were sealed with a lid and placed at different distances from a light source. 

The fourth bottle was wrapped in opaque foil in order for the algae to be kept in the dark.

Hydrogencarbonate indicator changes colour due to the amount of carbon dioxide in the solution. 

The investigation was left for 50 minutes and the colour of hydrogencarbonate solution was recorded. 

Figure 1 shows this investigation.

Figure 1

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At the start of the investigation the hydrogencarbonate indicator was red in colour.

Figure 2 shows the colour of the hydrogencarbonate indicator in the four bottles at the end of the investigation. 

Figure 2

Explain why the hydrogencarbonate indicator in the bottle nearest to the light source turned purple. 

Figure 1 shows the effect of temperature on the rate of photosynthesis. 

Figure 1

Describe and explain the effect of temperature on the rate of photosynthesis

Figure 3 shows how light intensity changed during one day.

Use the information in Figure 3 to explain why oxygen moved out of the leaf between 9 am and midday.

Figure 4 shows an enzyme and three substrates found in plant cells.

The enzyme will only break down one of these substrates.

State the name of this enzyme.

Higher Tier Only

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

Figure 1

(2)

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Higher Tier Only

A student measured the rate of photosynthesis using algal balls in a laboratory.

The tube of algal balls was kept at a temperature of 25 °C and was moved to different distances from a light source.

The results of this investigation showed that the rate of photosynthesis is

Explain how substances are moved through a plant by transpiration and translocation.

Figure 1 shows an area of woodland with some small plants growing in the ground between the trees.

Colin Smith, CC BY-SA 2.0 <https://creativecommons.org/licenses/by-sa/2.0>, via Wikimedia Commons

Figure 1

The leaves of the small plants are green.

Describe how these plants make glucose.

Name a group of organisms that break down the dead leaves and release mineral ions into the soil.

The mineral ions are absorbed from the soil into the roots of plants.

Describe how these mineral ions are transported from the roots to the leaves of the plants.

A scientist recorded the mean light intensity and the mean number of small plants per m² for six 25m² areas of the woodland.

Figure 2 shows the results.

Figure 2

Explain the effect of light intensity on the number of small plants per m²

(2)

(ii)

State one variable the scientist should have controlled to make sure the light intensity measurements could be compared.

(1)

The scientist selects an area near the edge of the woodland where many stinging nettles are growing.

This area is partly shaded by the trees.

Describe how the scientist should use a belt transect to investigate how light intensity affects the growth of stinging nettles.