·         Rotation of sun and the tilt of its axis cause annual variations in the intensity and duration of temperature, resulting distinct seasons.

·         These variations along with annual variations in precipitation, forms major biomes, such as desertrain forest, and tundra.

·         Temperature, water, light and soil are the key elements that lead to so much variation in the physical and chemical conditions of habitats.

·         Both abiotic (physic-chemical) and biotic components (pathogen, parasites, predators, competitions) characterize the habitat of an organism.

Major abiotic factors:


·         Temperature decreases progressively from equator towards the pole and high altitudes to > 50o C in tropical deserts in summer.

·         Thermal springs and deep-sea hydrothermal vents are unique with >100o C.

·         Temperature affects the kinetics of enzymes, BMR and other physiological actions.

·         Eurythermals: organism which can tolerate wide range of temperatures.

·         Stenothermal: organism which can tolerate narrow range of temperatures.



·         Water is also important factor that influence the life of organism.

·         The productivity and distribution of plants is also depends on water.

·         The salinity varies in aquatic environment:

o    5% in inland waters (fresh water)

o    30-35 in sea water

o    More than 100percent in hyper saline lagoons.


·         Euryhaline: organism which can tolerate wide range of salinity

·         Stenohaline: organism which can tolerate narrow range of salinity.



·         Plant produce food by photosynthesis, which only possible in presence of light. Hence it very important for autotrophs.

·         Plant species (herbs and shrubs) adapted for photosynthesize under canopy

·         Sunlight is required for photoperiodic response like flowering.

·         Animals use diurnal and seasonal variations in light intensity and photoperiod as cues for timing their foraging, reproductive and migration.


·         Properties of soil vary according to the climate, the weathering process.

·         Soil composition, grain size and aggregation determine the percolation and water holding capacity of the soil.

·         These characteristic along with pH, mineral composition and topography determine to a large extent the vegetation in any area.

·         The sediment-characteristic often determine the type of benthic animal in aquatic environment.

Response to Abiotic Factors:

·         Homeostasis; the process by which the organism maintain a constant internal environment in respect to changing external environment.

How does organism cope with the changing environment?


·         Some organisms are able to maintain homeostasis physiological (sometimes behavioral also) means which ensures constant body temperature, constant osmotic concentration.

·         All birds and mammals and few lower invertebrates are capable of such regulation i.e. thermoregulation and osmoregulation.

·         Success of mammals is due to thermoregulation.

·         We maintain a constant body temperature of 37oC.

·         When outside temperature is high we sweat profusely and evaporative cooling take place to bring body temperature down.

·         In winter due to low temperature outside our body temperature falls below 37oC, we start to shiver, to generate heat to raise body temperature.


·         Majority (99%) of animals and plants cannot maintain a constant internal environment; their body temperature varies according to ambient temperature.

·         In aquatic animals the osmotic concentration of body fluid varies with ambient water osmotic concentration.

·         All the above animals and plants are simply called as conformer.

Why the conformer not evolved to became regulators?

·         Thermoregulation is energetically expensive for many animals.

·         Small animal like shrews and humming birds cannot afford so much energy for thermoregulation.

·         Heat loss or heat gain is a function of surface area.

·         Small animals have larger surface area relative to their volume, they tend to lose body heat very fast when it is cold outside; then has to expend much energy to generate body heat through metabolism.

·         This is why very small animals are rarely found in Polar Regions.

Alternative response for stressful conditions is localized or remains for short duration.


  • The organism moved away temporarily from the stressful habitat to a more hospitable area and return when stressful condition is over.
  • Bird migrate form the colder region to warmer region.


  • Thick walled spores are formed in microbes to overcome unfavourable stressful external environment. Spores germinate in favourable condition.
  • In higher plants seeds and other vegetative reproductive structures are means to tide over the stress. They reduce their metabolic activity and going into a state of ‘dormancy’.
  • Hibernation: during winter animals like bears escape in time
  • Aestivation: animals like snail and fish avoid summer related problem like heat and desiccation.
  • Diapauses: many zooplanktons undergo a stage of suspended development in unfavourable conditions.

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Population is a group of individual living in a well defined geographical area, share or compete for similar resources or potentially interbreed. size of population changes according to some factors. Adaptation is any attribute of an organism that enable the organisms to survive and reproduce in its habitat.


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