which of the following structure is present in the the thallus of lichen which helps in retaining moisture and its algal partner fixes nitrogen?

Options

A. Cyphellae
B. soredia
C. cephalodia
D. Isidia

Answer

To solve the question regarding the structure present in the thallus of lichen that helps in retaining moisture and has an algal partner that fixes nitrogen, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Components of Lichens**: Lichens are symbiotic associations between fungi and photosynthetic partners, which can be green algae or cyanobacteria. The fungal partner provides structure and protection, while the algal partner performs photosynthesis.

2. **Identify the Structures**: The question presents four options:
- Cyphilia
- Soridia
- Cephalodia
- Isidia

3. **Analyze the Functions of Each Structure**:
- **Cyphilia**: Not a recognized structure in lichens.
- **Soridia**: These are small, vegetative propagules that can help in reproduction but are not specifically known for moisture retention or nitrogen fixation.
- **Cephalodia**: These structures are specialized parts of some lichens that contain cyanobacteria, which can fix nitrogen and help in moisture retention.
- **Isidia**: These are outgrowths of the lichen thallus that can also help in reproduction but do not specifically assist in nitrogen fixation or moisture retention.

4. **Determine the Correct Answer**: Given that cephalodia contain cyanobacteria, which are known for their ability to fix nitrogen and help retain moisture, the correct answer to the question is **Cephalodia**.

### Final Answer:
The structure present in the thallus of lichen that helps in retaining moisture and has an algal partner that fixes nitrogen is **Cephalodia**.

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