Principles of Ecology : 12th Class Biology Question Answer Lesson 25 – NIOS

Principles of Ecology : 12th Class Biology Question Answer Lesson 25 – NIOS

Principles of Ecology : 12th Class Biology Question Answer Lesson 25 - NIOS


  1. Name the various levels of organizations. – Genes → Cell → Organ → Organism → Population → Community
  2. Define the term ecology.
    Ans. Study of animals and plants in relation to their habit and habitat.
  3. What are the three physical systems that support life on earth?
    Ans. Atmosphere, lithosphere and hydrosphere
  4. Name the major components of the environment.
    Ans. (i) Abiotic (ii) Biotic
  5. Enumerate the various physical factors of the environment
    Ans. light, temperature, humidity, precipitation, pressure and soil profile
  6. Why is habitat called the address of organisms and its niche ‘the profession’?Justify.
    Ans. In nature, many species occupy the same habitat but they perform different functions. The functional characteristics of a species in its habitat is referred to as “niche”. While habitat of a species is like its ‘address’ (i.e. where it lives), niche can be thought of as its “profession” (i.e. activities and responses specific to the species). The term niche means the sum of all the activities and relationships of a species by which it uses the resources in its habitat for its survival and reproduction.
  7. What do we mean by ‘fins are an adaptation of fish to aquatic life’? Explain.
    Ans. Presence of gills and fins are examples of adaptation of fish to aquatic habitat. Adaptations can be observed in structureor behaviour or physiology of an organism. Adaptations have a genetic basis and have been evolved and perfected through the evolutionary process.


  1. A population with equal number of births and deaths will show:
    (a) Acceleration phase of growth (b) Plateau phase
    (c) Exponential growth phase (d) Initial phase of growth
  2. When population reaches carrying capacity:
    (a) Mortality rate = Birth rate (b) Mortality rate > Birth rate
    (c) Mortality rate < Birth rate
  3. Human population shows:
    (a) S-shaped growth curve (b) J-shaped growth curve
    (c) Z-shaped growth curve


  1. Define an ecosystem.
    Ans. Ecosystem is defined as functionally independent unit of nature where living organisms interact among themselves as well as with their physical environment.
  2. What are the main components of an ecosystem?
    Ans. Light, temperature, inorganic and organic compounds constitute the abiotic components of ecosystem whereas produces consumers and decomposers are its biotic components.
  3. Give reason, why are decomposers necessary in an ecosystem?
    Ans. to breakdown products of dead animals and plants tissue.
  4. What is the role of decomposers in nature?
    Ans. Helps in recycling of nutrients in the environment.
  5. Why are plants called autotroph and animals called heterotrophs?
    Ans. Plants are capable of capturing solar energy and transforming it into foodenergy. Thus they produce their own food. Animals depend upon plantsor other animals for food as they cannot produce their own food.
  6. Give one example of food chain.
    Ans. Transfer of food from the plants (producers) through a series of organisms with repeated eating and being eaten is called a food chain e.g.
    Grasses → Grasshopper → Frogs → Snakes → Hawk/Eagle

  7. Name the trophic level frog belongs to.
    Ans. Frog is secondary level consumers as it feeds on herbivorous grasshopper.
  8. Snake can be both a secondary as well as tertiary consumer Justify.
    Ans. Snake can feed on a rat and then it is a secondary consumer. It can alsofeed on a frog and then it is a tertiary consumer.


  1. What can be the maximum number of steps in a food chain?
    Ans. Upto five (5)
  2. Why is energy flow linear in ecosystem?
    Ans. Energy from solar radiation is fixed in the form of food by the producer. This energy is passed on to the consumers of different trophic level. At each trophic level energy is used by the member for metabolism and only left over energy is passed on each trophic level (10%).
  3. Define : (a) biomass (b) pyramid of number.
    Ans. Biomass – The energy enters into the ecosystem in the form of solar radiation and is convertedinto food (plant biomass) by the producers. Food stored by the plants and their biomass (matter) is the chemical form of energy.
    Pyramid of number – The graphical representation of standing crop expressed as number biomass orenergy is called pyramid of number
  4. What is meant by community stratification?
    Ans. Vertical and horizontal distribution of plants in the ecosystem


  1. Fill in the blanks
    (a) The relationship between two organisms where one receives benefits at the cost of other is known as Commensalism
    (b) A group of several species living together with mutual tolerance or
    adjustment and beneficial interactions in a natural area is known as
    (c) A force that acts against maximum population growth is ……………..
    (d) Association between insect polinated flowers and pollinating insect is an association termed as symbiosis


  1. Define alpine tundra ecosystems.
    Ans. Its an ecosystem that occurs high mountain peak above the tree line.
    Environmental conditions are very severe and show day and night temperature variation.

  2. Give two examples of plants of tundra.
    Ans. Cotton grass, sedges, dwarf leath, willows, birches and lichens (any two).
  3. Give two common characteristics of tundra and desert biome.
    Ans.  (b) both of them have very harsh climatic conditions. (b)Scarce vegetation.
  4. Names of three main types of forests.
    Ans. Tropical rain forest temperature, Deciduous boreal or north, Coniferous rain forest.
  5. Where are savannas found?
    Ans. Eastern Africa, South America, Australia and India (any two).
  6. What are deciduous trees?
    Ans. Trees which shed their leaves in autumn and grow new foliage during


  1. What are plankton?
    Ans. Free floating microscopic organisms
  2. Name two phytoplanktons and two bottom dwellers in fresh water ecosystem.
    Ans. diatoms, algae, prawn, crabs, snail (any two)
  3. What is the maximum pressure in ocean.
    Ans. 1000 atmosphere
  4. Give an example of (a) wet land (b) lotic type of ecosystem.
    Ans. (a) swamps, marshes and mangroves (any one)
    (b) streams, rivers, springs (any one)


  1. What does the following sequence represent:
    Blue green algae ⎯→ Crustose lichens

    shrubs ←⎯ mosses ←⎯ Foliose lichens

    Dicotyledonous trees
    (a) Ecological succession
    (b) Genetic drift
    (c) Phylogenetic trend
    (d) A food pyramid
  2. A community which starts succession in a habitat is:
    (a) Pioneer community
    (b) Social community
    (c) Biotic community
    (d) Ecosere
    Ans. a
  3. In ecological succession, beginning from pioneer and ending in climax community, the biomass shall
    (a) decrease
    (b) increase and then decrease
    (c) decrease and then increase
    (d) Increase continuously


  1. Define nutrient cycle.
    Ans. Movement of nutrient elements through the various components of an
    ecosystem is called nutrient cycle.

  2. Where are the bulk of nutrient stored in an ecosystem?
    Ans. In the Reservoirs pool
  3. Name the nutrient cycle where atmosphere acts as the main reservoir.
    Ans. Gaseous cycle
  4. List any two human activities that have led to increase in atmospheric CO2.
    Ans. Industrialization, urbanization, increased used of automobiles (any two)
  5. Name the reservoirs for water cycle.
    Ans. Polar ice caps and water present deep in the oceans.
  6. How do humans affect the phosphorus cycle?
    Ans. A study of phosphate cycle reveals that the return of phosphate to the cycle is inadequate to compensate the loss. It is human beings who have hastened the rate of loss of phosphorus.
  7. How do the sea birds contribute to the phosphorus cycle?
    Ans. Sea birds play an important role in bringing back phosphorus to the cycle through their guano deposits.


  1. What are the three physical life support systems on the planet earth?
  2. Name the various biotic and abiotic components of the environment
  3. Give differences between natural and human modified ecosystem
  4. Why is the number of trophic levels restricted to four or five in a food chain?
  5. Give only two differences between fresh water and marine biome.
  6. What will happen if all the floating animals are removed from a lake ecosytem?
  7. What are the benefits of natural ecosystems?
  8. Give two differences between energy flow and biogeochemical cycle in an ecosystem.

NIOS 12th class biology Q Ans

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