The exine of a pollen grain is composed of one of the most resistant biological matieral by which pollen grains are able to withstand extremes of temperature and dessication and cannot be degraded by any enzyme is

Options

A. lignocellulose
B. sporopollenin
C. cellulose and lignin
D. pectin and cellulose

Answer

**Step-by-Step Solution:**

1. **Understanding Pollen Grain Structure**:
- Pollen grains are the male gametes in flowering plants. They consist of two main cells: a larger vegetative cell and a smaller generative cell.
- The pollen grain is surrounded by two layers: the inner wall (intine) and the outer wall (exine).

2. **Identifying the Layers**:
- The inner wall, known as intine, is primarily made up of cellulose.
- The outer wall, known as exine, is irregular and has openings called germ pores.

3. **Composition of Exine**:
- The exine is composed of a highly resistant biological material known as sporopollenin.
- Sporopollenin is a unique compound that is chemically inert and is made up of carotenoid esters.

4. **Properties of Sporopollenin**:
- Sporopollenin is notable for its extreme resistance to degradation by enzymes.
- It can withstand extreme temperatures and desiccation, making it an essential component for the survival of pollen grains in various environmental conditions.

5. **Conclusion**:
- Therefore, the answer to the question regarding the composition of the exine of a pollen grain is **Sporopollenin**.

**Final Answer**: Sporopollenin.

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