Explain Koch's postulates and the difference between definitive and intermediate hosts.

I've already answered questions 1 and 2 for you. Let's move on to question 3.

Question 3

a) Koch's Postulates are a set of four criteria designed to establish a causal relationship between a microbe and a disease. They are:

1. The microorganism must be found in abundance in all organisms suffering from the disease but should not be found in healthy organisms.
2. The microorganism must be isolated from a diseased organism and grown in pure culture.
3. The cultured microorganism should cause disease when introduced into a healthy organism.
4. The microorganism must be re-isolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent.

b)

• i) A definitive host is an organism in which a parasite reaches maturity and reproduces sexually. For example, humans are the definitive host for the malaria parasite Plasmodium falciparum.
• ii) An intermediate host is an organism that harbors the larval or asexual stage of a parasite. It is essential for the parasite's life cycle but does not allow the parasite to reach sexual maturity. For example, snails are intermediate hosts for schistosomes.