Talk about the following two questions with your partner.

1. Is photosynthesis affected by many factors?

2. How does photosynthesis depend on light intensity, temperature, wind velocity, carbon dioxide level?

Then scan the text to compare your ideas with the author`s.

■ Read the given text and make your essential assignments:

The rate of photosynthesis can be measured as the volume of carbon dioxide taken in by a part per init time, or as the amount of carbohydrate produced per unit time. In laboratory investigations, the rate is commonly estimated as the volume of oxygen released per unit time, which is more easily measured. However, this method does not give an accurate measure of photosynthesis. Some of the oxygen generated by photosynthesis is used by the plant for respiration. Respiration goes on all the time, even when photosynthesis is at its height. So using oxygen liberation as a measure of photosynthesis gives an underestimate of the true rate. We are actually measuring the rate of photosynthesis above a point called the compensation point,defined as: the point at which the rate of photosynthesis in a plant is in exact balance with the rate of respiration, so there is no net exchange of carbon dioxide or oxygen. The compensation point is usually related to a particular light intensity or carbon dioxide level.