Which of the following is a good example of hterothallism?

Options

A. Spirogyra
B. Rhizopus oryzae
C. Pinus
D. Castro bean

Answer

To determine which of the options is a good example of heterothallism, we need to understand the concept of heterothallism and analyze each option provided.

### Step-by-Step Solution:

1. **Understanding Heterothallism**:
- Heterothallism is a type of sexual reproduction that occurs in certain fungi and algae. It requires the presence of two different mating types (often referred to as + and - types) for sexual reproduction to take place. This means that two compatible mating types must come into contact for fertilization and subsequent development.

2. **Analyzing the Options**:
- **Option 1: Spirogyra**:
- Spirogyra is a green algae that reproduces sexually through conjugation, but it does not require two different mating types to come into contact for reproduction. Therefore, it does not exemplify heterothallism.
- **Option 2: Rhizopus tolinifera**:
- Rhizopus tolinifera, commonly known as black bread mold, does exhibit heterothallism. It requires the presence of two different mating types for successful sexual reproduction, leading to the formation of zygospores. This makes it a good example of heterothallism.
- **Option 3: Spinus**:
- Spinus does not demonstrate heterothallism as it does not require opposite mating types for reproduction.
- **Option 4: Gastrobein**:
- Similar to Spinus, Gastrobein does not require the contact of opposite mating types for reproduction, thus it is also not an example of heterothallism.

3. **Conclusion**:
- Based on the analysis, the only option that correctly represents heterothallism is **Rhizopus tolinifera**.

### Final Answer:
The correct answer is **Rhizopus tolinifera**.