Climatic factors

Light and heat are abiotic factors which affect on such basic physiological processes of plants as photosynthesis, transpiration, seed germination, flowering etc, and thus is of much concern in environment. Where they play important role in the species compositions and development of vegetation being influenced by some such factors as atmospheric gases, suspended particles, water layers, vegetation and such topographic factors as direction and slope of the land surfaces which cause marked variations in intensity and daily duration of insulation. Radiation from the sun produces a direct heating effect and photo chemical transformation in the individual producing heat energy, with few exceptions, light is essential for all plants and animals. It also maintains temperature in soil, water and atmosphere. Directly or indirectly, light affects plant life in the following processes

1. Chlorophyll Production :  Except few plants like ferns, mosses and algae, most of the plants need light for chlorophyll formation. Without light plants cannot produce chlorophyll. If there is no chlorophyll it means plant cannot produce food. It means there is no food chain. So the plants and all animals totally depend on light for food.

2. Heating Actions : Exposure of parts of the plants to light increase to their temperature, affect their related life process.

3. Effect on Transpiration Rate: Sun light affects transpiration rate through increase in temperature. Transpiration rates correspondingly affect water absorption also. Thus high light intensities are always related with dry habitats and high transpiration rates.

4. Stomatal  Movement : Opening and closing of stomata is regulated by sun light which is related to transpiration and absorption of plants.

5. Distribution of Plants: Light intensity affect the distribution of plants. Light conditions of poles are different from other parts of earth. Thus, total amount of radiation received by the earth's surface differs with distance from the equator. This may be one of the reasons for the difference in the vegetation at poles and at other parts of the earth.

6. Overall Vegetative Development of Plant Parts: Sometimes plants are classified as Helophytes and Sciopthytes. Helophytes are that types of plants which grow best in full sunlight and Sciophytes are that types of plants which grow best at lower light intensities.

7. Photoperiodism :  Total length of the daily light period to which plants are exposed is known as photoperiodism. It affects on the vegetative growth as well as flowering og the plants. On the basis of their photo period, the plants may be short-day plants, that develop normally only when the photo period is less than a critical maximum; and long-day plants, those demanding a photo period in excess of certain critical minimum. Light has far-reaching effects on animals also. It affects their several types of physiological activities like pigmentation, reproduction, development, growth, locomotion, migration, etc which are mentioned below:

A) Metabolism : Light affects metabolic process of animals through its heating effects on tissues and protoplasm. This all results into an increase in the enzymatic activities, general metabolic rate and degree of solubility of salts and minerals. Animal receiving poor light in caves thus shows low rate of metabolism. Light also affects photo-oxidation and respiration rates.

B) Reproduction : In animals, light initiates the breeding activities. In some birds gonads become active with increased light intensity during summer. Thus, animals are long-day, short-day and indifferent to day length.

C) Development : Some animals undergo development only under sufficient-light intensity, in the absence of light they cannot develop. But mystiques larvae in their earlier stages grow larger in darkness than in light.

D) Eyes :  The degree of eye development sometimes depends upon the available light intensities. The eyes of the animals, which liven in caves and deep sea levels, are absent or rudimentary.

E) Vision :  Higher animals including man are able to see various objects only in the presence of one or other from of light.

F) Pigmentation : Most of the chemical changes that result into the formation of pigments are initiated by light energy. The process of pigmentation in animals is thus influenced by light in a number of ways as in the development of skin color or in protective coloration.

G) Locomotion :   The speed of locomotion on some lower animals is regulated by light. This phenomenon is known as photo kinesis .

H) Photo periodism : Animals are known to respond to the length of the day through the effect of total light period on such processes as gonad activities, reproduction, metamorphosis, migration, etc.