CIE IGCSE Biology

Topic Questions

IGCSEBiologyCIETopic Questions6. Plant Nutrition6.1 Photosynthesis & Leaf Structure

6.1 Photosynthesis & Leaf Structure

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1a
Sme Calculator7 marks

Fig. 1 is a photomicrograph of a cross-section of part of a leaf.

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Fig. 1

i)

Draw a large diagram to show the layers present in the leaf section shown in Fig.1.

Do not draw any cells.

[3]

ii)

Measure the thickness of the leaf along the line AB on Fig.1.

Calculate the actual thickness of the leaf using your measurement and the formula.

Include the units.

magnification space equals space fraction numerator length space of space line space AB space on space Fig.1 over denominator actual space thickness space of space leaf end fraction

[3]

iii)

Fig. 2 shows a photomicrograph of cells from one type of tissue found in leaves.

cie-2019-p6-q2a-microscope-image

Fig. 2

Label the layer on your drawing, with the letter X, to show where this type of tissue is found.

[1]

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1b
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Scientists carried out an investigation into the effect of light on the growth of leaves.

Plants of the same species (A) were grown in three different light intensities.

The plants were grown in the same soil and kept in glasshouses with automatic watering.

A sample of 100 leaves was selected at random and collected from plants in each of the three different light intensities. A total of 300 leaves were collected.

The scientists studied the variations in the size and structure of the leaves in each sample.

i)

Suggest why the scientists used large samples of leaves.

[1]

ii)

Suggest why the leaves in each light intensity were selected at random.

[1]

iii)

A grid, divided into millimetre squares, was used to measure the surface area of the leaves.

Outline how the grid could have been used.

[2]

iv)

State the variable that was changed (independent variable) in this investigation.

[1]

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1c
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The scientists collected data from one other plant species (B).

Table 1 shows the results.

Table 1

Light intensity / arbitrary units Average leaf area / mm2
Species A Species B
100 3600 2800
50 3900 3400
10 6500 2900

i)

Calculate the percentage difference in the average leaf area for species A from a light intensity of 50 arbitrary units to 10 arbitrary units.

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

[2]

ii)

Plot a bar chart on the grid to show the average leaf area for species A and B, at each light intensity.cie-2019-p6-q2b-graph

[4]

iii)

Describe the trends shown in your graph for species A and species B.

[2]

iv)

The scientists want to determine more precisely the light intensity that results in the largest leaf area for species B.

Suggest how the method used in the investigation could be modified to achieve this.

[1]

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2a
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A student investigated the effect of light intensity on the rate of photosynthesis.

  1. They placed a 10 cm piece of Elodea pondweed in a beaker of water placed 10 cm away from a lamp.
  2. A glass tank with water was placed between the lamp and the beaker containing the pondweed.
  3. The pondweed was left for 5 minutes before the number of bubbles were counted and recorded over a period of 2 minutes.
  4. A thermometer was used to monitor the temperature throughout the experiment.
  5. Step 3 was repeated when the lamp was placed at different distances from the pondweed.
  6. The experiment was repeated once more.

Fig. 1 shows the experimental setup.


experimental-setup

Fig. 1

Fig. 2 shows the results for the two repeats that the student wrote in their notebook.

picture4

Fig. 2

(i)

Prepare a suitable results table to present the data.

Your table should include:

  • Distance from the lamp
  • The rate of photosynthesis in bubbles min-1 

[4]

(ii)

State a conclusion for the results.

[1]

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2b
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Calculate the difference in the mean rate of photosynthesis when the lamp was moved from a distance of 10 cm to 50 cm away from the pondweed.

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2c
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.

(i)

State the independent variable for this investigation.

[1]

(ii)

State two variables that should be kept constant in this investigation.

[2]

(iii)

Suggest an improvement for determining the rate of photosynthesis in this investigation.

[1]

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2d
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Describe how this experiment could be adapted to investigate the effect of carbon dioxide on the rate of photosynthesis.

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