Question

When day light hours are increased, the rate of photosynthesis

• A. Increases
• B. Decreases
• C. Remains unchanged
• D. None of the above

Answer 1

The correct option is C Remains unchanged

The external factors which affect the rate of photosynthesis include the availability of sunlight, temperature, CO${}_2$ concentration and water. When several factors affect any biochemical process, then Law of Limiting factors given by Blackman's comes into effect. This states that- If a chemical process is affected by more than one factor, then its rate will be determined by the factor which is nearest to its minimal value. It is the factor which directly affects the process if its quantity is changed.

Light is an essential factor for photosynthesis. It affects the rate of photosynthesis as light intensity, light quality and duration of light.

There is a linear relationship between the light intensity and CO${}_2$ fixation rate at low intensities. At higher light intensities as such when day light hours are increased gradually the rate does not show further increase that is remains unchanged as other factors become limiting.

So, the correct answer is 'Remains unchanged'.