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CLASS: SS2                                                                                          


(a) Types of associations

(b) Features of biological importance possessed by organism of an association


Ecology is defined as the study of living organisms and the relationships or interactions between them and their environment. The interactions between plants and animals in their environment are usually described as biotic interactions or associations. There is a close association between the biotic and abiotic components of the environment. Both affect each other and are equally important for the ecosystem.


Symbiosis is a term for all associations in which all or some of the species involved benefits or loses. It is interdependence of different species, which are sometimes called symbionts. Based upon the specific relationship between the species involved in a symbiotic association, at least one member benefits. There are three main types of symbiosis

Symbiotic relationships may be grouped as:

  1. Parasitism
  2. Mutualism
  3. commensalism

Lichens of the Splash Zone of the Intertidal Region

Lichens are actually a combination of two entirely different types of living organisms, an alga and a fungus. This association is called a symbiotic relationship. In this particular type of symbiotic relationship neither partner can live independent of the other. Lichens are very slow growing and can survive very harsh environmental conditions and are ecologically significant in that they contribute to the weathering of solid rock.

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It is a type of antagonistic association occurring between two species, in which a specie called the parasite, is gaining at the expense of the other – the host, which is losing. Parasitism is a mode of life. The benefits the parasite derives from a host may include food, oxygen, living space and support. The host is usually much bigger than the parasite. Parasitism does not usually lead to the death of the host. It can however lead to a number or harms such as reduction in growth, predisposition of the host to attack by diseases and weakening.

Life Cycle of Human Blood Flukes

Flukes of the genus Schistosoma parasitize two hosts. The young hatch from their eggs in rivers and lakes and enter a specific kind of aquatic snail, where they develop into tadpole-like larvae called cercariae. When the cercariae leave the snail, they burrow through the skin of a human host swimming or wading in infested water. Adult flukes mature in the host’s bloodstream and settle in the veins of the gut. Their eggs, deposited in the lining of the human intestine and bladder, pass back into water via the sewage system, and the cycle begins again. More than 200 million people worldwide suffer from schistosomiasis, a disease characterized by the abscesses and bleeding caused by the flukes’ infestation.

In parasitism, the parasite can be of varying types among which are the following:

  • Ectoparasite e parasite living in the outside of the host tissue e.g. tick, lice, (among animal parasites and dodder – a plant parasite.
  • Endpoparasitee. a parasite that lives in the inside of the host tissue, e.g. tapeworm, round worm, malaria parasite (plasmodium), bacteriophages which are viruses that attacks bacteria.
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Examples of plant parasites are mistletoe and dodder (cuscuta) and many other fungal and bacterial parasites

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