Plants & Photosynthesis (WJEC GCSE Science (Double Award): Biology): Exam Questions

Write the word equation for photosynthesis.

The diagram shows leaves from two varieties of geranium A and B of the genus Pelargonium. Light energy falling on the two leaves and the light energy reflected from each leaf, during a period of one hour is also shown.

Calculate the percentage of light energy falling on leaf B that is reflected.

Write your answer in the diagram.

The graph shows the rate of photosynthesis in the two plants between 06.00 hours and 18.00 hours.

Use the diagram opposite and the graph above to explain why the mass of variety A is likely to increase at a faster rate than the mass of variety B.

State one resource oak trees need for growth.

..........

Describe how you would investigate the effect of light intensity on the rate of photosynthesis using only the apparatus shown in Image 3.

Image 3

[6 QER]

It is possible to determine if photosynthesis is taking place by testing a leaf for the presence of starch using iodine solution. Explain why this test is not suitable for determining the rate of photosynthesis.

Plant leaves absorb light for photosynthesis.

State the source of the light absorbed by the leaves.

Image 1.1 shows a violet plant (Viola riviniana).

Image 1.1

Gareth calculated the area of a leaf from one of the violet plants. This is what he did:

Step 1. He drew an outline of a leaf on a grid as shown in Image 1.2.

Image 1.2

Step 2. He counted the number of whole squares inside the outline.

Step 3. He multiplied the total number of whole squares by the area of one square.

(i) Count the number of whole squares inside the outline.

[1]

Number of whole squares inside the outline = ..........................................

(ii) Each square has an area of 0.25 cm².

Use the formula below to calculate the outline area.

[1]

Outline area = 0.25 × number of whole squares inside the outline.

Outline area = .......................................... cm²

(iii) Counting only the whole squares gave an outline area which was much lower than the actual leaf area.

I. Explain why.

[1]

II. Suggest one improvement to step 2 to get an answer closer to the true value.

[1]

(iv) Gareth decided to test the following hypothesis:

"The leaf area of violet plants in the shade will be greater than that of violet plants in bright light".

He picked one violet plant growing in shade and one growing in bright light.

Gareth used his method to calculate the leaf areas of 10 leaves from each plant.

The mean results are shown in Table 1.3.

Table 1.3

I. Calculate the difference in mean leaf area between the two plants.

[1]

Difference = .......................................... cm²

II. Complete the following sentence by underlining the correct word.

[1]

The results show that Gareth's hypothesis is:

invalid / rejected / supported.

Explain the advantage of a large leaf area for plants growing in shade.

State the word equation for photosynthesis.

Students used a computer simulation to investigate how the limiting factors of photosynthesis affect its rate. A screenshot from the simulation is shown in Image 4.1.

Image 4.1

The simulation allowed the students to carry out investigations into the rate of photosynthesis by adjusting the temperature, light intensity and carbon dioxide concentration the plant received. The rate of photosynthesis was then calculated by measuring the volume of oxygen produced by the plant per hour. The computer then produced a graph of the results as shown in Graph 4.2.

Graph 4.2

(i) With reference to limiting factors, explain why the rate of photosynthesis is:

I. lower in investigation C than in investigation A;

[2]

II. higher in investigation C than in investigation D.

[2]

(ii) Suggest how you could increase the rate of photosynthesis in investigation A.

[1]

(iii) State the limiting factor which is controlling the rate of photosynthesis at point X on Graph 4.2.

...................................................................................................

[1]

(iv) The levels were adjusted to the following:

• light intensity to bright daylight levels

• CO₂ concentration to 0.04%

• temperature to 80 °C.

I. Suggest how a temperature of 80 °C would affect the rate of photosynthesis and explain your answer.

[2]

II. Suggest why a CO₂ concentration of 0.04% was chosen.

[1]

Explain why the volume of oxygen produced by the plant per hour can be used as a measurement of the rate of photosynthesis.

Tradescantia is a plant whose leaves have green and white areas.

In the experiment below, a Tradescantia plant is used in an investigation to demonstrate three factors, A, B and C, needed for photosynthesis.

(i) State the factor needed for photosynthesis, which is being demonstrated in each of the following:

A ........................................................................................

B ........................................................................................

C ........................................................................................

[3]

(ii) How could the experiment in flasks B and B1 be improved? Explain your answer.

[2]

(iii) Before the apparatus was set up, the Tradescantia plant was kept in a dark cupboard for 48 hours. Explain the reason for this.

[2]

The diagram below shows the stages in testing a leaf for starch.

Name the liquids 1, 2, 3 and 4 shown in the diagram.

1 ........................................................................................

2 ........................................................................................

3 ........................................................................................

4 ........................................................................................

An incomplete diagram of a plant leaf cell is shown in Image 1.1.

Image 1.1

(i) Complete Image 1.1 by drawing the cell wall.

[1]

(ii) Structure X contains chlorophyll and absorbs light.

I. Complete the following sentence by underlining the correct term in the brackets.

Structure X is a (vacuole / chloroplast / mitochondrion).

[1]

II. State the name of the process that uses the light absorbed by structure X.

..................................................................................

[1]

Seaweeds (marine algae) contain large amounts of iodine in their tissues. The iodine is obtained from the seawater in which they live and is needed to maintain healthy growth of the plant. The iodine content of seawater is about 0.055 mg / kg. Some of the largest seaweeds are the kelps that live in kelp ‘forests’ in shallow seas and oceans where light can penetrate. Some kelp species are over 80 m in length and can grow 0.5 m in a day.

State the reason why kelp only grows in seawater where sunlight can penetrate.

In a classroom exercise some students used a computer simulation to investigate the factors affecting the rate of photosynthesis. A well-watered plant was placed inside a transparent sealed container with a high intensity lamp above the plant. The air in the airtight container was continually monitored in order to measure the rate of O₂ production.

• The light intensity of the lamp could be varied between 0–100%.

• The CO₂ concentration of the air inside the sealed container could be varied between 0–1000 ppm.

• The temperature inside the sealed container could be varied between 0–50 °C.

The table below shows the results obtained by one of the students.

Explain how oxygen production can be used as a measure of the rate of photosynthesis.

Explain why oxygen production remains at 3.1 cm³/h for readings 2, 3 and 4.

Identify the limiting factor for readings 6, 7, 8 and 9 and explain your answer.

State why the container must be sealed.

Sian and Dafydd are students who carried out the computer simulation. Sian suggested that they try to set up a 'live version' of the apparatus in the laboratory. Dafydd said that if they did this, a problem could arise which would affect the validity of the experiment.

Suggest the problem that may arise and how this could be solved.