ORGANISMS AND POPULATIONS

 

ORGANISM AND ITS ENVIRONMENT:

• 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 desert, rain 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:

• Temperature decreases progressively from equator towards the pole and high altitudes to > 50^o C in tropical deserts in summer.
• Thermal springs and deep-sea hydrothermal vents are unique with >100^o 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:

• 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:
  • 5% in inland waters (fresh water)
  • 30-35 in sea water
  • 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.

Light:

• 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.

Soil:

• 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?

Regulate:

• 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 37^oC.
• 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 37^oC, we start to shiver, to generate heat to raise body temperature.

Conform:

• 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.

 

CBSE Biology (Chapter Wise) Class XII ( By Mr. Hare Krushna Giri )
Email Id : [email protected]