Which of the following statements is correct

Options

A. Fusion of protoplasms between two motile on non-motile gametes is called plasmogamy
B. Organisms that depend on living plants are called saprophytes
C. Some of the organisms can fix atmospheric nitrogen in specialized cells called sheath cells
D. Fusion of two cells is called Karyogamy

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question:** The question asks to identify which of the provided statements is correct regarding biological processes and terminology.

2. **Analyzing the First Statement:**
- The first statement claims that the fusion of protoplasm between two motile and non-motile gametes is called plasmogamy.
- **Evaluation:** This statement is correct. Plasmogamy refers to the fusion of the cytoplasm of two gametes, regardless of their motility.

3. **Analyzing the Second Statement:**
- The second statement claims that organisms that depend on living plants are called saprophytes.
- **Evaluation:** This statement is incorrect. Organisms that depend on living plants are called parasites, while saprophytes feed on dead organic matter.

4. **Analyzing the Third Statement:**
- The third statement claims that some organisms can fix atmospheric nitrogen in specialized cells called sheath cells.
- **Evaluation:** This statement is also incorrect. The correct term for these specialized cells is heterocysts, which are involved in nitrogen fixation.

5. **Analyzing the Fourth Statement:**
- The fourth statement claims that the fusion of two cells is called karyogamy.
- **Evaluation:** This statement is incorrect. Karyogamy specifically refers to the fusion of two nuclei, not cells.

6. **Conclusion:**
- After evaluating all the statements, the only correct statement is the first one: "The fusion of protoplasm between two motile and non-motile gametes is called plasmogamy."

**Final Answer:** The correct statement is the first one: "The fusion of protoplasm between two motile and non-motile gametes is called plasmogamy."

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