Describe the effects of untreated sewage and excess fertiliser on aquatic ecosystems

Explain the importance of the following in controlling the spread of disease: (a) a clean water supply (b) hygienic food preparation (c) good personal hygiene (d) waste disposal (e) sewage treatment (details of the stages of sewage treatment are not required)

Identify and state the factors affecting the rate of population growth for a population of an organism, limited to food supply, competition, predation and disease