In a polluted lake

Options

A. BOD and DO are high
B. BOD is high and DO is low
C. Both are low
D. BOD is low and DO is high

Answer

### Step-by-Step Solution:

1. **Understanding Polluted Lake**: A polluted lake is characterized by the presence of dead organic material, such as dead fish, animals, and plant parts. This organic matter can also include human-made materials like clothes and wooden blocks.

**Hint**: Identify what constitutes a polluted lake and the types of organic matter involved.

2. **Role of Microorganisms**: In a polluted lake, microorganisms act as decomposers. They possess enzymes that help break down the dead organic matter. This process of decomposition requires oxygen.

**Hint**: Consider the role of microorganisms in the ecosystem and their function in decomposition.

3. **Biochemical Oxygen Demand (BOD)**: The demand for oxygen by decomposers to break down organic matter is known as Biochemical Oxygen Demand (BOD). A higher amount of dead organic matter leads to a higher BOD.

**Hint**: Relate BOD to the amount of organic matter present in the water.

4. **Dissolved Oxygen (DO)**: The oxygen that is dissolved in water is referred to as Dissolved Oxygen (DO). In a polluted lake, as the BOD increases due to higher decomposition activity, the amount of dissolved oxygen decreases.

**Hint**: Understand the relationship between BOD and DO in the context of pollution.

5. **Relationship Between BOD and DO**: In a polluted lake, the relationship is such that an increase in BOD (due to more organic matter) results in a decrease in DO. Therefore, in a polluted lake, BOD is high and DO is low.

**Hint**: Remember the inverse relationship between BOD and DO when pollution increases.

6. **Conclusion**: Based on the relationships established, in a polluted lake, we conclude that:
- BOD is high (due to high organic matter).
- DO is low (due to high demand for oxygen by decomposers).

**Hint**: Summarize the findings to answer the question clearly.

### Final Answer:
In a polluted lake, the Biochemical Oxygen Demand (BOD) is high, and the Dissolved Oxygen (DO) is low.