Organisms and Populations

Notes

Organisms and Populations

1. Ecology

Ecology is a branch of science which studies the interactions among organisms and between organisms and their physical (abiotic) environment.

It consists of two branches:

• Autecology: Study of ecology at the level of species.
• Synecology: Study of ecology at the level of communities.

2. Levels of Biological Organisation

Ecology deals with different levels of biological organisation:

• Organism: A living entity which can function on its own.
• Population: A group of living organisms of the same species living in a particular geographical area.
• Community: A group of populations of different species living together in one place.
• Biome: A large geographical area characterised by particular types of plants and animals.

3. Environment

An environment is the sum total of all external factors which influence organisms in terms of survival and reproduction.

Ecological studies deal with how different organisms are adapted to their environments in terms of their survival and reproduction.

Different organisms are adapted differently to environmental conditions. Rotation of the Earth around the Sun and the tilt of its axis cause annual variations in temperature and seasons.

Variations in temperature, annual precipitation and other environmental conditions lead to the formation of different biomes such as deserts, rainforests and tundra.

Regional and local variations in environmental conditions also result in a wide variety of habitats.

Both abiotic and biotic components characterise an environment.

4. Major Abiotic Factors

The major abiotic factors of an ecosystem are:

1. Temperature
2. Water
3. Light
4. Soil

4.1 Temperature

The average temperature on land varies seasonally and decreases progressively from the equator towards the poles and from plains to mountain tops.

Thermal springs and deep-sea hydrothermal vents are habitats where average temperatures may exceed 100°C.

Temperature affects the kinetics of enzymes and, therefore, influences basal metabolism, activity and other physiological functions of organisms.

• Eurythermal organisms: Organisms that can tolerate and thrive in a wide range of temperatures. Examples include cat and dog.
• Stenothermal organisms: Organisms that can tolerate only a narrow range of temperatures. Examples include polar bear, fish and reptiles mentioned in the PDF.