1. What is an "endothermic reaction" ?
Answer
An endothermic reaction takes in (or absorbs) energy from the surroundings.
2. Write the word equation for photosynthesis.
Answer
3. What is a "limiting factor" ?
Answer
A limiting factor is a factor that directly affects the rate of a reaction, for example, light intensity and carbon dioxide concentration are both limiting factors for photosynthesis. Increasing light intensity will increase the rate of photosynthesis until carbon dioxide becomes the limiting factor and then the rate will level off.
4. Describe some ways that plants use glucose produced by photosynthesis.
Answer
Plants use the glucose produced by photosynthesis in several ways. It is used in respiration to provide energy. Some of it is converted into insoluble starch for storage. Glucose is also used to produce fats or oils, which serve as energy reserves. Additionally, it is used to synthesize cellulose, which strengthens the cell walls.
5. A student investigated the effect of light intensity on the rate of photosynthesis in pondweed. He took measurements at three distances between the pondweed and the lamp. Suggest some ways the student could improve their results.
Answer
Repeat multiple times at each distance or use more distances.
6. A student investigated the effect of light intensity on the rate of photosynthesis by counting the number of bubbles produced by pondweed. When the distance between the lamp and the pondweed is 40 cm, 4 bubbles are released in 1 minute. Predict the number of bubbles released in 1 minute when the distance between the lamp and the pondweed is 80 cm.
Answer
As the distance from the lamp doubles, the light intensity falls to a quarter. This means the rate of photosynthesis, measured by bubble production, also decreases to a quarter - so only one bubble would be released compared to four at the shorter distance.
7. The graph in the figure below shows the effect of carbon dioxide concentration on the rate of photosynthesis in a plant at two different temperatures. A student concludes that carbon dioxide concentration is not the limiting factor for photosynthesis when the temperature is 10°C and the carbon dioxide concentration is 0.16%. Explain why the student is correct, and state some factors that could be limiting the rate of photosynthesis in this case.
Answer
He is correct because increasing the carbon dioxide concentration does not increase the rate of photosynthesis (the curve has levelled off). The factors that could be limiting the rate of photosynthesis are temperature, light intensity, and the amount of chlorophyll.