'Pathogens' are ____________

Options

A. Substances produced against any disease.
B. Chemical substances produced by the host cells to kill the parasite animal.
C. Disease causing organisms.
D. Cells which kill the parasites

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for the definition of 'pathogens'. We need to identify what pathogens are in the context of biology.

2. **Evaluating the Options**:
- **Option 1**: "Substances produced against any disease."
- This option refers to antibodies, which are produced by the immune system to combat pathogens, but it does not define what pathogens are. Thus, this option is incorrect.

- **Option 2**: "Chemical substances produced by host cells to kill the parasite animals."
- This option mentions substances like cytokines or lymphokines, which are indeed produced by host cells but do not define pathogens. Therefore, this option is also incorrect.

- **Option 3**: "Disease Causing Organism."
- This option accurately defines pathogens. Pathogens are indeed organisms that cause disease in their hosts. This is the correct answer.

- **Option 4**: "Cells which kill the parasites."
- This option is misleading as it refers to immune cells like macrophages that can kill parasites but does not define what pathogens are. Hence, this option is incorrect.

3. **Conclusion**: After evaluating all options, the correct answer is that pathogens are "Disease Causing Organisms."

**Final Answer**: Pathogens are disease causing organisms.

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