In Engelmann's experiment, bacteria were used to

Options

A. split light into its spectral components.
B. detect the sites of `O_2` evolution.
C. absorb the spectra of chlorophyll is a and b using Cladophora.
D. detect the sites of `CO_2` evolution and monitor the algal photosynthesis.

Answer

**Step-by-Step Solution:**

1. **Understanding Engelmann's Experiment**: Engelmann's experiment was designed to investigate the process of photosynthesis and to identify which wavelengths of light were most effective in promoting oxygen production.

2. **Use of a Prism**: Engelmann used a prism to split sunlight into its spectral components (the different colors of light). This allowed him to observe how different wavelengths affected photosynthesis.

3. **Cladophora and Aerobic Bacteria**: In the experiment, Engelmann placed the green algae Cladophora in a suspension of aerobic bacteria. Cladophora is a type of green algae that performs photosynthesis.

4. **Detection of Oxygen Evolution**: The aerobic bacteria were utilized to detect the sites of oxygen evolution. As the algae photosynthesize, they release oxygen, which the bacteria can use. The accumulation of bacteria in certain areas indicates where the most oxygen is being produced.

5. **Observations**: Engelmann observed that the bacteria accumulated mainly in the blue and red light regions of the spectrum. This suggests that these wavelengths are most effective for photosynthesis, as they correspond to the absorption spectra of chlorophyll A and B.

6. **Conclusion**: Based on Engelmann's findings, the correct answer to the question is that in Engelmann's experiment, bacteria were used to detect the sites of oxygen evolution.

**Final Answer**: Detect the sites of oxygen evolution.

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