Gases let out to atmosphere causes climatic change. Emission of dust and aerosols from industries, automobiles, forest fire, SO₂ and DMS (dimethyl sulphur) play an important role in disturbing the temperature level of any region. Aerosols with small particles is reflecting the solar radiation entering the atmosphere. This is known as Albedo effect.

Nitrogen -78% , Oxygen -21 %, Carbon-di-oxide -0.03%, Argon and other gases - 0.93%.

Euryhaline: Organisms which can live in water with wide range of salinity. Examples: Marine algae and marina angiosperms.
Stenohaline: Organisms which can withstand only small range of salinity. Example: Plants of estuaries.

Timber line is an imaginary line in a mountain or higher areas of land that marks the level above which trees do not grow. The altitudinal limit of normal tree growth is about 3000 to 4000 m.

Raunkiaer classified the world's vegetation into the following four types. They are megatherms, mesotherms, microtherms and hekistotherms.

Heliophytes - Light loving plants. Example: Angiosperms.
Sciophytes - Shade loving plants. Example: Bryophytes and Pteridophytes

(a) Photosynthesis
(b) Transpiration
(c) Seed germination
(d) Flowering

Light, Temperature, Water, Wind and Fire.

The environment (surrounding) includes physical, chemical and biological components. When a component surrounding an organism affects the life of an organism, it becomes a factor. All such factors together are called environmental factors or ecological factors.

An ecological niche refers to an organism's place in the biotic environment and its functional role in an ecosystem.

(a) Autecology is the ecology of an individual species and is also called species ecology.
(b) Synecology is the ecology of a population or community with one or more species and also called as community ecology.

The interaction of organisms with their environment results in the establishment of grouping of organisms which is called ecological hierarchy.

Earnest Haeckel defined "Ecology is the study of the reciprocal relationship between living organisms and their environment."