Light intensity (%) O2 produced
(mL/h)
30 8.8
30 26.1
50 31.3
60 31.3

The data above was collected by measuring the oxygen produced by an Elodea plant at varying levels of light intensity. Notice what happens to the oxygen produced at light intensities of 50% or higher. Everything has its limits, even chemical reactions! Think about a powerful race car. If you give it more fuel and better tires, it can go very fast. But, eventually, its speed will top out due to the limitations of the motor. Even if you kept adding fuel and tires, it couldn’t go any faster. Explain how the data in this experiment suggests there is a maximum photosynthetic rate. Be sure to discuss the reactants and products in your answer.

By the process of photosynthesis, green plants synthesize carbohydrates or food (products) from carbon dioxide and water (reactants) with the help of chlorophyll and sunlight (energy).

Oxygen is produced as a byproduct of photosynthesis.

The rate of photosynthesis depends on various factors, one of which is light intensity.

The given experiment measures the effects of light intensity on the photosynthetic rate by recording the amount of oxygen produced.

Here, the photosynthetic rate is directly proportional to the intensity of the light used. However, it also follows the saturation kinetics i.e. after a certain point further increase in the light intensity causes no change in the photosynthetic rate.

From the given data, it is clear that the maximum rate of photosynthesis was achieved at 50% light intensity as the maximum amount of oxygen was produced at that point.

In addition, a further increase in light intensity (from 50% to 60%) did not increase the rate. This also shows that the maximum rate had already been achieved.

In contrast, a further increase in light intensity could damage the photo-systems which would result in a sharp decrease in photosynthetic rate.