The rate of photosysnthesis is determined by the factor available at

Options

A. very low
B. optimum
C. sub optimum
D. maximum

Answer

To solve the question regarding the rate of photosynthesis and the determining factors, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: The question asks about the conditions under which the rate of photosynthesis is determined, with options provided: very low, optimum, sub-optimum, and maximum.

2. **Recall the Law of Limiting Factors**: The rate of photosynthesis is influenced by multiple factors, including light intensity, carbon dioxide concentration, and temperature. The law of limiting factors, proposed by scientist Blackman in 1905, states that the rate of a process is determined by the factor that is in the lowest supply.

3. **Identify the Correct Factor**: According to the law of limiting factors, if one factor is at a very low level, it will limit the rate of photosynthesis, regardless of the levels of other factors. Therefore, the factor that is available at a very low amount will control the overall rate of photosynthesis.

4. **Evaluate the Options**:
- **Very Low**: This option aligns with the law of limiting factors, as the lowest factor will determine the rate.
- **Optimum**: This is not correct because optimum conditions imply that all factors are at ideal levels, not limiting.
- **Sub-optimum**: This suggests that conditions are below the ideal but not necessarily at the lowest level, which does not apply here.
- **Maximum**: This is incorrect as it suggests that all factors are at their highest levels, which does not relate to limiting factors.

5. **Conclusion**: The correct answer is "very low," as it is the factor that will determine the rate of photosynthesis when it is in the lowest amount.

### Final Answer:
The rate of photosynthesis is determined by the factor available at **very low**.