(a) Describe the process of succession in an abandoned farm land. (b) List seven ways by which micro-organisms can -be controlled to maintain good health.

(a) Process of succession on an abandoned farm land

Succession is the gradual and orderly replacement of one community of organisms by another over a period of time until a stable community is reached. On an abandoned farm land it proceeds as follows:

1. Colonisation by pioneer plants: the bare, exposed soil is first invaded by fast-growing weeds and grasses whose light seeds are easily dispersed. These are the pioneer species.
2. Improvement of the soil: as these plants grow, die and decay, they add humus to the soil, improving its fertility, water-holding capacity and structure.
3. Replacement by larger plants: the enriched soil now supports taller herbs and shrubs, which grow up and shade out and replace the grasses (they compete for light, water and nutrients).
4. Development of woody plants: shrubs are in turn replaced by small trees and then larger trees as conditions continue to improve.
5. Climax community: eventually a stable, self-maintaining community of tall trees (a forest, in a rainforest zone) develops. This final stage, which remains in balance with the environment, is the climax community. Each stage is called a sere.

Alongside the plants, the animal community also changes, so that the animals present at each stage match the vegetation.

(b) Seven ways by which micro-organisms can be controlled to maintain good health

1. Sterilization of instruments and materials by heat (e.g. autoclaving, boiling).
2. Use of antiseptics on the skin and wounds (e.g. iodine, Dettol).
3. Use of disinfectants on floors, surfaces and toilets (e.g. bleach, phenol).
4. Pasteurization of milk and other drinks to kill harmful microbes.
5. Proper cooking and refrigeration of food to kill or slow the growth of microbes.
6. Personal and environmental hygiene such as regular washing of hands, bathing and proper disposal of refuse and sewage.
7. Immunization (vaccination) and the use of drugs such as antibiotics to fight micro-organisms in the body.