Which of the following statements incorrect?

Options

A. The human liver fluke depends on two intermediate hosts (a snail and a fish) to complete its life cycle.
B. The malarial parasite needs a vector (mosquito) to spread to other host organisms
C. All the parasites cause disease in their hosts organisme
D. The life cycles of endoparasites are more complex because of their extreme specialisation.

Answer

To determine which statement is incorrect, let's analyze each statement one by one:

1. **Statement 1**: "The human liver fluke depends on two intermediate hosts: one is a snail and another is a fish to complete its life cycle."
- **Analysis**: This statement is correct. The human liver fluke (Fasciola hepatica) indeed relies on a snail as its first intermediate host and a fish as its second intermediate host to complete its life cycle.

2. **Statement 2**: "The malarial parasite needs a vector, the mosquito, to spread to other host organisms."
- **Analysis**: This statement is also correct. The malarial parasite (Plasmodium spp.) requires the Anopheles mosquito as a vector to transmit the parasite to humans.

3. **Statement 3**: "All parasites cause disease in their host organisms."
- **Analysis**: This statement is incorrect. While many parasites do cause diseases, not all parasites lead to disease in their hosts. Some parasites can exist in a host without causing harm, and there are exceptions where certain parasites may even have a neutral or beneficial relationship with their host.

4. **Statement 4**: "The life cycle of endoparasites is more complex because of their extreme specialization."
- **Analysis**: This statement is correct. Endoparasites often have complex life cycles due to their specialization in adapting to their host environments.

Based on the analysis, the incorrect statement is:

**Answer**: "All parasites cause disease in their host organisms."