At a temperature above `35^(@)C`

Options

A. rate of photsynthesis will decline earlier than that of respiration
B. rate of respiration will decline earlier than that of photosynthesis
C. both decline simultaneously
D. there is no fixed pattern

Explanation

### Step-by-Step Solution:

1. **Understanding the Processes**:
- Photosynthesis is the process by which plants convert light energy into chemical energy, producing glucose and oxygen from carbon dioxide and water.
- Respiration is the process where glucose is broken down to release energy (ATP), using oxygen and producing carbon dioxide and water.

2. **Temperature Effects**:
- Both photosynthesis and respiration are affected by temperature. Each process has an optimum temperature range for maximum efficiency.
- The optimum temperature for photosynthesis is between 10°C and 40°C.

3. **Impact of High Temperature**:
- At temperatures above 35°C, the enzymes involved in photosynthesis begin to lose their shape (denature). This loss of shape affects their functionality.
- As a result, the rate of photosynthesis declines first when the temperature exceeds 35°C.

4. **Consequences of Photosynthesis Decline**:
- With the decline in photosynthesis, the production of glucose decreases. Since glucose is essential for respiration, this will eventually affect the respiration process.
- Although respiration may still occur, it will be at a reduced rate due to the lack of glucose supply.

5. **Final Observations**:
- The decline in photosynthesis occurs before the decline in respiration when temperatures exceed 35°C.
- This sequential decline indicates that photosynthesis is more sensitive to temperature increases than respiration.

### Summary:
At temperatures above 35°C, photosynthesis declines first due to enzyme denaturation, leading to a subsequent decline in respiration due to reduced glucose availability.