PGA as the first `CO_2` fixation product was discovered in :

Options

A. Bryophyta
B. Gymnosperm
C. Angiospasm
D. Algae

Answer

To solve the question about the discovery of PGA (3-phosphoglycerate) as the first CO2 fixation product, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding PGA**:
- PGA stands for 3-phosphoglycerate, which is a three-carbon compound that plays a crucial role in the process of photosynthesis, specifically in the Calvin cycle.

2. **Historical Context**:
- The discovery of PGA as the first product of CO2 fixation is attributed to the work of Melvin Calvin, a prominent scientist in the field of photosynthesis.

3. **Melvin Calvin's Experiment**:
- Melvin Calvin conducted experiments using radioactive carbon isotopes. He introduced radioactive carbon into the photosynthetic process of plants to trace the path of carbon during photosynthesis.

4. **The Role of Algae**:
- Calvin's experiments were primarily conducted using algae, which are simple photosynthetic organisms. This choice was likely due to their simplicity and the ease of observing the photosynthetic process.

5. **Conclusion**:
- Through his experiments, Calvin was able to identify 3-phosphoglycerate (PGA) as the first stable product formed during the fixation of CO2 in photosynthesis. Thus, the correct answer to the question is that PGA was discovered in algae.

### Final Answer:
PGA as the first CO2 fixation product was discovered in **algae**.