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Transpiration:  The rate of transpiration increases with rise in temperature. Extremely high temperature, if prolonged, may cause water stress to plants.

Vernalization: many species plants require low temperature treatment for seed germination and flowering, a phenomenon known as vernalization.


Latitudinal zones: As many as six temperature-based terrestrial latitudinal zones are differentiated north of equator, each being characterized by specific vegetation type e.g. Snow, tundra, coniferous forests, deciduous forests, grasslands or deserts and tropical rainforests.

Altitudinal zones: As many as four temperature based terrestrial altitudinal zones are differentiated in Himalayas, each having specific vegetation type. Alpine (having Rhodendron, Juniperus),temperate (mainly conifers, oaks and Magnolia),tropical and subtropical zones (having mixed forests, bamboos, sal, etc.



In animals, the maturation of gonads and activity of spermatogenic tissue are also temperature dependent, which varies from species to species. In blow fly, Calliphora sericate, the number of eggs laid per Female, increases with increase in temperature upto 32.5(after which the number decreases. similarly, in chrotogonustrachypterus(an acridid insect),egg Laying increases from 25 to 300C.Thus,temperature also affects the fecundity(reproductive capacity)of animals. Similarly, an increase in temperature from 22 to 320C increases the egg laying about 20-30 times in Melanopussanguinipes.

Growth and Development: In Ostrea virginea, the length of body increases from 1.5 to 10.3 mm with an increase in temperature from 10 to 200C.

Thermoregulation and homeostasis: The birds and mammals have constant Body temperature and are called homeothermal or endothermic or warm blooded animals to deal with temperature extremes. This is achieved through evaporation of water from their bodies during summer and through Insulating action of fur, feathers, fats, etc.


Temperature is the degree of hotness or coldness of a substance. It is the most important ecological factor affecting almost all the metabolic activities of the Organism. Every physiological function has an optimum temperature at which it show the maximum metabolic rate.

The vertical temperature gradient over Earth’s surface is called lapse rate. This value comes equal to 6.50C per 1000mElevation.Change in temperature is affected by factors like latitude, altitude, Topography, vegetation and slope. Temperature shows a great amount of variation altitudinally and latitudinally.

The bacteria and cyanobacteria are known to survive even in thermal spring (60-900C) or permafrost (–30 to –500C) But most of the organisms are killed By higher temperatures due to denaturation of enzymes while others are killed By very low temperature due to freezing of body fluids except dry seeds, spores And cysts which have no water.

Tolerance power to the extremes of temperature varies from species to species.


Synthesis of pigments: The plants grown in the absence of light become etiolated.

Photosynthesis: The light intensity at which rate of photosynthesis is just sufficient to meet the requirements of respiration is called compensation point.

Photoperiodism: angiosperms are divided into three categories. Long-day plants(e.g. Radish, Spinach, Scale cereale, etc.) short-day plant(e.g. xanthium, Chrysanthemum, Cosmos, Datura, salvia, Cannabis)and day-neutral Plants(e.g. Cotton Gossypium, Tomato—Lycopersicum, Potato solanum)


Plant growth

Stomatal opening


Phytoplanktons are found on illuminated surface of water. On the other hand, benthic organisms are found at the sediments of a lake. Three zones in a lake can be identified which are determined by gradients of light, oxygen and temperature from the water surface to bottom.

Littoral zone: It is shallow water zone present at the edge of lake. It bears rooted plants.

Limnetic zone: It is present behind littoral zone and contains often water. Here phytoplankton’s are found in plenty. Light can penetrate from 20-40m.depthdepending on clarity of water.

Profundal zone (dark zone): In this zone light fails to reach. Bottom of lake constitutes benthic region where micro-organisms, snails and sluge etc. are found.

most important role of atmosphere

Role of atmosphere

Air functions as a medium for Locomotion of insets, birds etc. Ozone layer of atmosphere protects the living organisms from harmful radiations of sun.

Air is the source of oxygen, carbon dioxide and nitrogen required for various metabolic activities of living beings. It helps in dispersal of spores, pollen, seeds etc. Air transmits sound for communication. Burning of fire takes place in presence of oxygen.


The gases present in the atmosphere are chiefly oxygen, carbon dioxide and nitrogen which greatly influence the living organisms. Atmosphere is the thick gaseous envelope around the earth. The composition of Atmospheric air is: Oxygen—20.84%, Nitrogen—-78.64%, Carbon dioxide—0.03%, Water vapors—0.1%


Light is a very important of the climatic factors which is directly responsible for the growth, development and differentiation of plants. Similarly, light as a complex physical factor, also affects the colour vision, eye-size, skin pigmentation, Migration, reproduction and biological periodicity of the animals. Thus, light is a Factor of physical and physiological importance.


Size of eye: Marine animals of 500-3,000 meters depth have larger eyes than those found in surface water.

Photo-periodism: It refers to the response of organisms to the duration of sunlight in a day (photoperiod).In many animals’ migration, hibernation and Reproductive behaviors are controlled by relative lengths of day and time. Metabolism: Light increases the enzymatic activities and general metabolic Rate. It also increases photo oxidation and respiration rates. Animals found in Caves have low rate of metabolism.