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 about which structure in the thallus of lichen 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 Lichen**:
- Lichens are symbiotic associations between fungi and photosynthetic partners, which can be algae or cyanobacteria. The algal component is primarily responsible for photosynthesis, while cyanobacteria can fix nitrogen.

2. **Identify the Structures Mentioned**:
- The options provided are:
- A. Cephalia
- B. Soredia
- C. Cephalodia
- D. Isidia

3. **Analyze Each Option**:
- **A. Cephalia**: This term does not specifically relate to lichen structures.
- **B. Soredia**: These are small clusters of algal cells and fungal hyphae that can disperse and form new lichens but do not primarily function in moisture retention.
- **C. Cephalodia**: These are specialized structures in some lichens that contain cyanobacteria. They play a role in nitrogen fixation and can help in moisture retention.
- **D. Isidia**: These are outgrowths of the lichen thallus that can also help in reproduction but are not specifically related to moisture retention or nitrogen fixation.

4. **Determine the Correct Answer**:
- Since the question specifies a structure that helps in retaining moisture and involves an algal partner that fixes nitrogen, the correct answer is **C. Cephalodia**. This structure contains cyanobacteria, which aids in nitrogen fixation and moisture retention.

### Final Answer:
C. Cephalodia