(a)Succession can be defined as a progressive natural development of vegetation towards a climax during which one community is gradually replaced by others. The abandoned farm land is a secondary succession as a result of the fact that it follows a partial destruction of the original vegetation.
The process is as follows:
(i) Decay of plants and animals of the old farm enhances nutrient of the soil.
(ii) The pioneer or initial colonizers are insects' eggs, larvae, worms and seeds of plants carried by animals or by wind. There are also underground stems like rhizomes and stem tubers.
(iii) Next stage includes the hatching of eggs of insects, larvae development, germination and growth of herbaceous plants like grasses and lilies.
(iv) Growth of vegetation attracts rodents to feed on grasses.
(v) Lizards are also attracted to feed on the insects.
(vi) Herbs are displaced by shrubs.
(vii) Shrubs are in turn displaced by trees.
(viii) Trees attract birds, monkeys and tree reptiles.
(ix) Presence of herbivores, carnivores and omnivores (animal community) makes the community to develop or reach a climax. This results in a complex food web.
(b) Ways by which micro-organism can be controlled to maintain good health are:
(i) People should be vaccinated against killer diseases.
(ii) There should be personal hygiene, e.g. regular cleanliness of our body, environment, teeth and clothes.
(iii) Avoid overcrowding to prevent infectious diseases, e.g. tuberculosis.
(iv) Destroy breeding ground for mosquitoes.
(v) Isolate people with highly infectious diseases, e.g. leprosy
(vi) Promote health education
(vii) Cover food to prevent contamination by rats, flies, cockroaches, etc.
(viii) Encourage ventilation of houses.
(ix) Cut bushes around the house and drain stagnant water properly.