ORGANISMS AND ENVIRONMENT

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 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:

·         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:

·         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.

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 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.

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.

 Migrate:

  • 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.

Suspend:

  • 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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