The green alga used by T.W Engelmann in his prism experiment is

Options

A. Chlorella
B. Spirogyra
C. Cladophora
D. Ulothrix

Answer

To solve the question regarding the green alga used by T.W. Engelmann in his prism experiment, we will follow these steps:

### Step-by-Step Solution:

1. **Understand the Experiment**: T.W. Engelmann conducted an experiment to determine the action spectrum of photosynthesis. This involves identifying which wavelengths of light are most effective for photosynthesis.

2. **Identify the Organism Used**: Engelmann used a green alga in his experiment. The question provides four options: Chlorella, Spirogyra, Cladophora, and Ulothrix.

3. **Recall the Details of the Experiment**: Engelmann used a prism to split light into its component colors and directed this light onto the green alga. He observed the accumulation of aerobic bacteria in regions of the light spectrum where photosynthesis was most effective.

4. **Determine the Correct Alga**: From historical context and scientific literature, it is known that Engelmann specifically used **Cladophora** for his experiments. This alga was chosen because it allowed for the observation of bacteria accumulation in response to light.

5. **Evaluate the Options**:
- Chlorella: Incorrect
- Spirogyra: Incorrect
- Cladophora: Correct
- Ulothrix: Incorrect

6. **Conclude the Answer**: The green alga used by T.W. Engelmann in his prism experiment is **Cladophora**.

### Final Answer:
The green alga used by T.W. Engelmann in his prism experiment is **Cladophora** (Option C).

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