(a)[4]
Describe the physical digestion that takes place in humans and explain why it matters.
(b(i))[1]
State the chemical in the stomach that kills many ingested bacteria.
(b(ii))[2]
Bacteria that are not destroyed in the stomach may cause disease. State the term used for organisms that cause disease, and the type of immunity gained after infection by disease-causing organisms.
(c)[3]
Disease can be caused by viruses. Yellow fever is an example of a disease caused by a virus. Outline how a weakened form of the virus that causes yellow fever can be used to give a person long-term immunity against the disease.