Substrate of photorespiration is
(a) OAA
(b) Glycolic acid
(c) 3-PGA
(d) PEP

Options

A. OAA
B. Glycolic acid
C. 3-PGA
D. PEP

Answer

To determine the substrate of photorespiration, we need to understand the process and the compounds involved. Here’s a step-by-step solution:

### Step 1: Understand Photorespiration
Photorespiration is a process that occurs in plants when the concentration of oxygen is high and the concentration of carbon dioxide is low. It is considered a wasteful process because it consumes energy and does not produce useful products.

**Hint:** Photorespiration occurs under specific environmental conditions related to oxygen and carbon dioxide levels.

### Step 2: Identify the Role of Rubisco
The enzyme Rubisco (Ribulose-1,5-bisphosphate carboxylase/oxygenase) plays a crucial role in photorespiration. It can bind to both carbon dioxide and oxygen. When oxygen levels are high, Rubisco tends to bind with oxygen instead of carbon dioxide.

**Hint:** Rubisco is the key enzyme that initiates the photorespiration process by binding with oxygen.

### Step 3: Determine the Initial Substrate
In photorespiration, the initial substrate that is formed when Rubisco binds with oxygen is glycolic acid, which is a two-carbon compound. This compound is crucial for the photorespiration cycle, also known as the C2 cycle.

**Hint:** The initial product formed from the reaction of Rubisco with oxygen is a two-carbon compound.

### Step 4: Analyze the Options
Now, let's analyze the given options:
- (a) OAA (Oxaloacetic acid) - Not the substrate for photorespiration.
- (b) Glycolic acid - This is the correct substrate for photorespiration.
- (c) 3-PGA (3-Phosphoglycerate) - This is a product of the Calvin cycle, not the substrate for photorespiration.
- (d) PEP (Phosphoenolpyruvate) - Not the substrate for photorespiration.

**Hint:** Compare each option with the knowledge of the photorespiration process to find the correct substrate.

### Conclusion
Based on the analysis, the substrate of photorespiration is **(b) Glycolic acid**.

**Final Answer:** (b) Glycolic acid