Class 12 Biology Organisms and Populations Major abiotic factors of the ecosystem

Major abiotic factors of the ecosystem


  • The average temperature on land varies seasonally, decreases progressively from the equator towards the poles and from plains to the mountain tops.
  • Thermal springs and deep-sea hydrothermal vents are unique habitats where average temperatures exceed 1000o
  • Temperature affects the kinetics of enzymes and through it the basal metabolism, activity and other physiological functions of the organism.
  • Organisms which can tolerate and thrive in a wide range of temperatures, they are called eurythermal organisms.Example- cat, dog etc.
  • Organisms which can tolerate a narrow range of temperatures such organisms are called stenothermal organisms. Example- fish, reptile etc.

Fig. thermal springs



  • Life on earth originated in water and is unsustainable without water.
  • For aquatic organisms the chemical composition, pH of water is important.
  • The salt concentration varies in aquatic environment.
  • The salt concentration (measured as salinity in parts per thousand), is less than 5 per cent in inland waters, 30-35 per cent the sea and > 100 per cent in some hyper saline lagoons.
  • The organisms which can tolerate a wide range of salinities, they are called euryhalineorganisms. Example- the green crab.
  • The organisms which tolerate a narrow range of temperature, they are called stenohalineorganisms. Example- goldfish.

Fig. green crab, gold fish



  • Plants are dependent on light to produce food through the process of photosynthesis.
  • Many plants are dependent on sunlight to meet their photoperiodic requirement for flowering.
  • Animals use the diurnal and seasonal variations in light intensity and duration (photoperiod) as cues for timing their foraging, reproductive and migratory activities.

Fig. photosynthesis



  • Soil composition, grain size and aggregation determine the percolation and water holding capacity of the soils, which along with parameters such as pH, mineral composition and topography determine the vegetation in any area.
  • In the aquatic environment, the sediment-characteristics often determine the type of benthic animals that can thrive there.

Fig. benthic animals  

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