Which do not give out `O_(2)`

Options

A. Green algae
B. Blue Green algae
C. Green plants
D. Photosynthetic bacteria

Answer

To determine which of the given options do not produce oxygen, we can analyze each option based on their photosynthetic processes:

1. **Green Algae**: Green algae are known to perform photosynthesis using sunlight, water, and carbon dioxide. During this process, they produce carbohydrates and release oxygen as a byproduct. Therefore, green algae do give out oxygen.

2. **Blue-Green Algae**: Blue-green algae, also known as cyanobacteria, also carry out photosynthesis. They use sunlight, water, and carbon dioxide to produce carbohydrates and oxygen. Thus, blue-green algae do give out oxygen.

3. **Green Plants**: Green plants are well-known for their ability to perform photosynthesis. They utilize sunlight, water, and carbon dioxide to produce glucose and oxygen. Hence, green plants also release oxygen.

4. **Photosynthetic Bacteria**: This group includes bacteria like purple bacteria and green sulfur bacteria. Unlike the other options, these bacteria do not use water as an electron donor during photosynthesis. Instead, they may use hydrogen sulfide, which leads to the production of elemental sulfur rather than oxygen. Therefore, photosynthetic bacteria do not give out oxygen.

Based on this analysis, the correct answer to the question is **photosynthetic bacteria**.

### Summary of the Steps:
1. Analyze the process of photosynthesis in green algae.
2. Analyze the process of photosynthesis in blue-green algae.
3. Analyze the process of photosynthesis in green plants.
4. Analyze the process of photosynthesis in photosynthetic bacteria.
5. Conclude that photosynthetic bacteria do not produce oxygen.