Molecules of `RuBP` required to produce 20 molecules of serine in photorepiration are

Options

A. 60
B. 40
C. 20
D. 80

Answer

To determine the number of molecules of RuBP required to produce 20 molecules of serine during photorespiration, we can break down the process step by step.

### Step-by-Step Solution:

1. **Understanding the Reaction**:
- In photorespiration, 2 molecules of RuBP (ribulose bisphosphate) react with oxygen. This reaction produces 2 molecules of 2-phosphoglycolic acid and 2 molecules of 3-phosphoglycerate (3-PGA).

2. **Conversion of 2-Phosphoglycolic Acid**:
- The 2-phosphoglycolic acid is then converted into glycolic acid. For every 2 molecules of 2-phosphoglycolic acid, we get 2 molecules of glycolic acid.

3. **Oxidation of Glycolic Acid**:
- The glycolic acid is oxidized to form glyoxylic acid. This means that from 2 molecules of glycolic acid, we produce 2 molecules of glyoxylic acid.

4. **Formation of Glycine**:
- The glyoxylic acid undergoes transamination to form glycine. Each molecule of glyoxylic acid produces 2 molecules of glycine. Therefore, from 2 molecules of glyoxylic acid, we get 4 molecules of glycine.

5. **Conversion of Glycine to Serine**:
- Finally, 2 molecules of glycine are converted into 1 molecule of serine in the peroxisome. This means that from 4 molecules of glycine, we can produce 2 molecules of serine.

6. **Calculating RuBP for 20 Molecules of Serine**:
- Since 2 molecules of serine are produced from 2 molecules of RuBP, we can establish that 1 molecule of serine requires 2 molecules of RuBP.
- Therefore, to produce 20 molecules of serine, we will need:
\[ 20 \text{ molecules of serine} \times 2 \text{ molecules of RuBP per molecule of serine} = 40 \text{ molecules of RuBP} \]

### Final Answer:
The number of molecules of RuBP required to produce 20 molecules of serine in photorespiration is **40**.

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