1. Explain photosynthesis in terms of energy transfer.
Answer
Photosynthesis is an endothermic reaction in which energy is transferred from the environment to the chloroplasts by light.
2. Name the green pigment found in chloroplasts that absorbs light energy.
Answer
The green pigment found in chloroplasts is chlorophyll.
3. Give the chemical symbols for carbon dioxide, glucose, oxygen and water.
Answer
CO2 , C6H12O6 , O2 , H2O
4. List the four main limiting factors for photosynthesis.
Answer
Temperature, light intensity, carbon dioxide concentration and the amount of chlorophyll.
5. The figure below shows some apparatus used to investigate photosynthesis. Describe how you would use the apparatus to investigate the effect of light intensity on the rate of photosynthesis.
Answer
Set up the equipment as shown in the diagram with the boiling tube a set distance away from the lamp, for example, 20 cm. Put the tank of water between the lamp and the boiling tube to control the temperature. Leave the pond weed for two minutes to adjust to each light intensity before taking any measurements. Count the number of bubbles released from the pondweed in one minute. Repeat this measurements two more times at the same distance so a mean can be calculated. Repeat the measurements at another four distances from the lamp. Use the same piece of pondweed each time. Plot the mean number of bubbles (y-axis) against the distance from the boiling tube (x-axis).
6. A student investigated the effect of light intensity on the rate of photosynthesis by counting the number of bubbles produced by pondweed. Explain why more bubbles are released when the distance between the pondweed and the lamp is 10 cm rather than 20 cm.
Answer
The light intensity is higher at 10 cm, so more energy is available for photosynthesis.
7. The rate of photosynthesis can be affected by carbon dioxide concentration and temperature. Describe and explain how these two factors affect the rate of photosynthesis.
Answer
Carbon dioxide is one of the raw materials used in photosynthesis so the rate of photosynthesis increases when more is available. The rate levels off when another factor, such as light intensity, becomes the limiting factor.
The rise in temperature increases the rate of reaction as the molecules have more kinetic energy. The
rate of photosynthesis decreases because enzymes denature at high temperatures.