Question

The rate of photosynthesis does not depend upon
A. Light duration
B. Light intensity
C. Light quality (Colour)
D. Temperature

Answer 1

Hint: Plants use sunlight to convert light energy into chemical energy. Oxygen is released as a by-product in this process.

Complete Answer:
- Photosynthesis consists of both light-dependent reactions and light-independent reactions. Photosynthesis rate is very critical in deciding plant yield including crop plant yields. Photosynthesis is affected by many factors, internal as well as external.
- The plant factors include number, age, size, and orientation of leaf, mesophyll cells and chloroplasts, internal $CO_2$ concentration, and chlorophyll content. The plant or internal factors are dependent upon the plant's genetic predisposition and growth.
- The external factors would include sunlight, temperature, $CO_2$ concentration and water supply. As a plant photosynthesizes, all these variables may influence its output simultaneously.
- Thus, while many factors interact and influence photosynthesis or $CO_2$ fixation, one factor is typically the main cause, or the one that restricts the output. Therefore, the rate of photosynthesis would be defined at any point by the factor present at the sub-optimal levels.

- Special pigments in plant cell chloroplasts absorb the energy from certain light wavelengths, creating a molecular chain reaction called light-dependent reactions of photosynthesis.
- The rate of the light-dependent reaction, and hence photosynthesis in general, increases proportionately as the light intensity increases. However, as light intensity increases further, photosynthesis rates are inevitably restricted by some other element.
- For example, in the presence of a green leaf and optimum light and $CO_2$ levels, if the temperature is very low the plant cannot photosynthesize.

Thus, the correct answer is light duration.

Note: Light intensity, temperature and carbon dioxide concentration are the main factors that influence the efficiency of photosynthesis. During this process, carbon dioxide from the atmosphere is taken in by leaves through stomata and used for making carbohydrates, mainly glucose and starch.