At least a half of the total `CO_(2)` fixation on earth is carried out thorugh photosysnthesis by

Options

A. angiosperms
B. gymnosperms
C. algae
D. bryophytes.

Explanation

To solve the question regarding which organisms carry out at least half of the total CO₂ fixation on Earth through photosynthesis, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Process of Photosynthesis**:
- Photosynthesis is the process by which green plants, algae, and some bacteria convert carbon dioxide (CO₂) and sunlight into glucose and oxygen. This process is crucial for the fixation of CO₂ in the atmosphere.

2. **Identify the Main Contributors to CO₂ Fixation**:
- While many organisms participate in photosynthesis, the question asks specifically about those that contribute significantly to CO₂ fixation.

3. **Consider Different Groups of Organisms**:
- The main groups that perform photosynthesis include:
- **Angiosperms** (flowering plants)
- **Gymnosperms** (non-flowering seed plants)
- **Algae** (simple non-flowering plants found in water)
- **Cyanobacteria** (photosynthetic bacteria)

4. **Evaluate the Contribution of Each Group**:
- Angiosperms and Gymnosperms do contribute to CO₂ fixation, but they are primarily terrestrial.
- Algae, particularly phytoplankton in aquatic environments, are known to fix a significant amount of CO₂. In fact, it is estimated that algae contribute to more than 50% of the total CO₂ fixation on Earth.

5. **Select the Correct Answer**:
- Based on the information gathered, the correct answer to the question is **Algae**. They play a crucial role in the aquatic ecosystem and are responsible for a significant portion of CO₂ fixation.

### Final Answer:
The correct option is **Alga** (Option 3).

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