O Level Biology Ecology
Topics: Ecology, Food chain, Trophic level, Photosynthesis, Ecosystem, Metabolism / Pages: 7 (1560 words) / Published: Mar 4th, 2013

Biology Notes
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● Ecology is the study of interactions among organisms, and between organisms and the physical and chemical factors making up their external environment
● Ecologists study both the non-living (abiotic) or physical environment, and the living (biotic) environment.

Physical environment
● Amount of light
○ Light intensity affects the distribution and growth of both plants and animals ● Amount of water
○ Xerophytes are plants which can live in conditions of prolonged drought in their habitat
○ Plants which live in water or very wet places are called hydrophytes
○ Pneumatophores arise from the root system and project above the surface ● Temperature
○ Within a certain range, a fall in temperature usually results in a decrease in the metabolic activities of the organisms

● Salinity and pH of the soil or water
○ The salt concentration of the cytoplasmic contents of freshwater organisms is usually higher than that of the surrounding water so that water tends to enter these organisms by osmosis
○ Aquatic organisms are sensitive to the effects of the pH of the water and may be killed if the pH changes appreciably

Biotic environment
● Habitat: the place where an organism lives
● An organism in any habitat is never an independent unit.
○ Its daily existence depends on and is influenced by other organisms around it ● Ecological niche: the function of an organism or the role it plays in the habitat is known as the
● Population: a group of individuals of the same species occupying a given area – expressed in terms of density (number of individuals per unit area)
○ Population increases when the number of new individuals added to it exceeds the number lost through death or migration and vice versa

● Ecological unit: when different populations of plants and animals live together and interact within the same environment
● Ecosystem: an ecological system formed by the interaction

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