Major Abiotic Factors - Practice Questions & MCQ

Temperature:

• The average temperature on land varies seasonally, decreases progressively from the equator towards the poles and from plains to the mountain tops. 
• It ranges from sub zero levels in polar areas and high altitudes to >50oC in tropical deserts in summer. 
• There are unique habitats such as thermal spring and deep-sea hydrothermal vents where average temperatures exceed 100oC. 
• The significance of temperature to living organisms is that it affects the kinetics of enzymes and through it the basal metabolism, activity and other physiological functions of the organism.
• A few organisms can tolerate and thrive in a wide range of temperatures they are called eurythermal.
• A vast majority of animals are restricted to a narrow range of temperatures. Such organisms are called stenothermal. Examples: Penguin, Python, Crocodile 
• The levels of thermal tolerance of different species determine to a large extent their geographical distribution. Examples: cat, dog, man, goat, tiger, etc
• Eurythermal plants also can tolerate a wide range of temperatures for growth, and can be transplanted from the home country to the tropics or to the temperate and colder regions,e.g. roses, daisies, oak trees, some fruits and vegetables.
• Stenothermal plants are those that are quite restricted to either low or high temperatures for growth, e.g. plants that grow only at the Poles, or conversely those plants that grow only at the Equator of the planet. 
• Polar plants include algae, reindeer moss, lichens. 
• Equatorial plants include the Banyan and Peepal trees, Yams, chillies, Strangler Fig Tree, Croton, Bougainvillea, vines and orchids, etc,.

Water:

• Next to temperature, water is the most important factor influencing the life of organisms. 
• Its availability is so limited in deserts that only special adaptations make it possible to live there. 
• The productivity and distribution of plants is also heavily dependent on water. 
• The organisms living in oceans, lakes and rivers also face water-related problems. 
• For aquatic organisms the quality (chemical composition, pH) of water becomes important. 
• 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 hypersaline lagoons. 
• Some organisms are tolerant of a wide range of salinities (euryhaline) but others are restricted to a narrow range (stenohaline). 
• Many freshwater animals cannot live for long in sea water and vice versa because of the osmotic problems they would face.
• Examples of euryhaline organisms are: Atlantic stingray, the bull shark, and the green chromide.
• Examples of stenohaline organisms are: goldfish, haddock fish.
   

Light:

• Since plants produce food through photosynthesis, a process which is only possible when sunlight is available as a source of energy, so the importance of light for living organisms, particularly autotrophs is superior.
• Many species of small plants (herbs and shrubs) growing in forests are adapted to photosynthesise optimally under very low light conditions because they are constantly overshadowed by tall, canopied trees.
• Many plants are also dependent on sunlight to meet their photoperiodic requirement for flowering.
• For many animals too, light is important in that they use the diurnal and seasonal variations in light intensity and duration (photoperiod) as cues for timing their foraging, reproductive and migratory activities. 
• The availability of light on land is closely linked with that of temperature since the sun is the source for both. 
• But, deep (>500m) in the oceans, the environment is perpetually dark and its inhabitants are not aware of the existence of a celestial source of energy called the Sun. 
• The deep ocean environment where sunlight cannot reach, energy sources are available from:
  • After the death of fishes and other aquatic organisms the dead bodies sediment at the bottom to provide huge amounts of organic matter to the deep sea levels.
  • There are several hydro thermal vents present at the bottom of the sea that emit chemicals. Some chemosynthetic bacteria are present that can use those chemicals as a source of energy.
• Among the red, green and brown algae that inhabit the sea, red algae is found in the deep waters because of the pigment it contains - ‘phycoerythrin’.
• This phycobilin/phycoerythrin can absorb the blue light (it can penetrate upto 500ft depth) and use it for photosynthesis, thus using the little solar energy that reached the deepest part of the ocean for manufacturing food. 
• Hence, the red algae is able to survive the deepest quarters of the oceans while the others can’t.

Soil:

• The nature and properties of soil in different places vary; it is dependent on the climate, the weathering process, whether soil is transported or sedimentary and how soil development occurred. 
• Various characteristics of the soil such as soil composition, grain size and aggregation determine the percolation and water holding capacity of the soils. 
• These characteristics along with parameters such as pH, mineral composition and topography determine to a large extent the vegetation in any area. 
• This in turn dictates the type of animals that can be supported. 
• Similarly, in the aquatic environment, the sediment-characteristics often determine the type of benthic animals that can thrive there.