Which of the following statements is incorrect?

Options

A. Mitochondria, unless specifically stained are not easily visible under the microscope.
B. Physiological activity of cells determines the number of mitochondria per cell.
C. Mitochondrion, a power house of cell has DNA, RNA, ribosomes and enzymes, so it can survive outside the cell.
D. Mitochondria divide by fission.

Answer

To determine which statement about mitochondria is incorrect, we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Examine the First Statement**:
- The statement claims that "mitochondria, unless specifically stained, are not easily visible under a microscope."
- **Analysis**: This statement is correct. Mitochondria are small organelles (200 to 700 nanometers) and require special staining techniques to be visualized under a microscope.

2. **Examine the Second Statement**:
- The statement claims that "physiological activity of cells determines the number of mitochondria per cell."
- **Analysis**: This statement is also correct. Cells that have higher energy demands (like liver cells) will contain more mitochondria, while less active cells will have fewer.

3. **Examine the Third Statement**:
- The statement claims that "mitochondria have DNA, RNA, ribosomes, and enzymes, so they can survive outside the cell."
- **Analysis**: This statement is incorrect. While mitochondria do contain their own DNA and ribosomes, they cannot survive independently outside of the cell. They rely on the cell for many functions and resources.

4. **Examine the Fourth Statement**:
- The statement claims that "mitochondria divide by fission."
- **Analysis**: This statement is correct. Mitochondria replicate through a process called fission, similar to bacterial division.

### Conclusion:
The incorrect statement is the third one: "mitochondria have DNA, RNA, ribosomes, and enzymes, so they can survive outside the cell."

### Final Answer:
The incorrect statement is option number 3.

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