Rate of photosynthesis - Limiting Factor

Read the following text and answer the questions below.

As the chemical equation below show, carbon dioxide and water have to be present before photosynthesis can take place.

carbon dioxide + water → glucose + oxygen
CO2 + H2O  → C6H12O6 + 6O2

Although it is not a reactant, chlorophyll needs to be present. Sunlight is also needed, because it powers the reaction. If any one of these is not available, then photosynthesis slows down or stops.The factor that is missing or in short supply is called the limiting factor. In times of drought, water could be a limiting factor.If the stomata are closed to save water, then carbon dioxide cannot enter the leaf, and carbon dioxide could become the limiting factor.
At night, light is the limiting factor and there is no photosynthesis. As the sun rises, the rate of photosynthesis increases as the light intensity increases. Then, at some point, the rate of photosynthesis does not increase any further.  Something other than light is controlling the rate. When light is no longer the limiting factor, it is often the amount of carbon dioxide in the atmosphere, and the rate at which it can diffuse into the leaf, that limits the rate of photosynthesis. This is shown in this figure.

The speed (rate) of most chemical reactions increases as the temperature increases. This is true of photosynthesis too, but only up to a point.The rate of photosynthesis increases until the temperature reaches about 30°C. At this temperature, photosynthesis decreases and then stops.This is because the enzymes that help photosynthesis along are destroyed at temperatures greater than 30°C. Above 30°C the enzymes can no longer function.

Questions

  1. For the photosynthesis reaction, list the names and chemical formulas of the:·

(a) reactants

 (b)   products

  1. What else is required for photosynthesis to occur.

  2. Recall photosynthesis by writing its:

(a) word equation

(b) balanced chemical equation.

  1. Identify the limiting factor that stops photosynthesis from proceeding at night.

  2. Plants don't grow well in a drought.They may even die. Use your knowledge of photosynthesis to explain why this happens.

  3. Most caves have no plants in them. Identify the limiting factors of this environment that would make it difficult for plants to grow there.

  4. (a) State the temperature that photosynthesis stops above.

(b) Explain why photosynthesis stops above this temperature.

  1. Compare lines X andY on the graph shown below.

  1. Summarise what both lines on the graph show about photosynthesis as light intensity increases.

  2. Discuss possible reasons for the difference in the lines.

  3. Explain why the amount of oxygen produced is a good measure of the rate of photosynthesis taking place.