VBQs Ecosystem Class 12 Biology

VBQs for Class 12

VBQs Ecosystem Class 12 Biology with solutions has been provided below for standard students. We have provided chapter wise VBQ for Class 12 Biology with solutions. The following Ecosystem Class 12 Biology value based questions with answers will come in your exams. Students should understand the concepts and learn the solved cased based VBQs provided below. This will help you to get better marks in class 12 examinations.

Ecosystem VBQs Class 12 Biology

Very Short Answer Type Questions

Question. How is ‘stratification’ represented in a forest ecosystem ? 
Answer :
 Stratification is the formation of different layers (strata where vegetation is dense such as tropical rain forest). It represents vertical distribution of species at different levels.
There may be many strata such as long trees, medium trees, short tress, shrubs, herbs and ground flora etc. Trees occupy vertical strata, shrubs the second layer and herbs / grasses occupy the bottom layers.

Question. Write a difference between net primary productivity and gross productivity.
Answer : 
Gross productivity – Rate of production of organic matter during photosynthesis.
Net primary productivity – Available biomass for the consumption of heterotrophs.
GPP – R = NPP. 
Detailed Answer:
The rate of production of organic matter during photosynthesis represents the gross primary productivity (GPP) while the net primary productivity is the available biomass for the consumption by the heterotrophs.
(Gross primary productivity–Respiration = Net primary productivity)

Question. Why are green algae not likely to be found in the deepest strata of the ocean ?
Why are green plants not found beyond certain depth in ocean? 
Answer : 
Green algae are not found beyond a certain depth in ocean because only about 1 percent of sunlight penetrates at this depth which is not sufficient for the plants to photosynthesize and thus grow and survive. 

Question. Why is an earthworm called detrivore ?
Answer :
 Earth worms are called detrivores because they break down the detritus i.e. the dead plant and animal remains including faecal matter into smaller particles. 

Short Answer Type Questions

Question. Write about ‘humification’ and the ‘mineralisation’ occurring during the process of decomposition.
Answer :
 Humification leads to break down of complex organic matter and accumulation of humus in the form of a dark amorphous substance in soil.
Mineralisation is a process in which humus is degraded by microbes to release inorganic nutrients. 

Question. How does the dead organic matter get decomposed in nature ? Explain.
Answer :
 In nature, the dead organic matter gets decomposed by the micro-organisms like bacteria and fungi. These microorganisms called decomposers break down the complex organic matter into simpler inorganic substances like CO2, water and nutrients. 

Question. What does secondary productivity in an ecosystem indicate ? List any two factors by which productivity is limited in an aquatic ecosystem.
Answer :
 Secondary productivity indicates the organic matter synthesized by the consumers specially
by the primary consumers or herbivores. The two factors by which the productivity is limited in an aquatic ecosystem are light and nutrient supply. 

Question. Why is earthworm considered a farmer’s friend?
Explain humification and mineralisation occurring in decomposition cycle.
Answer :
Earthworms are called farmer’s friends because they bring about the fragmentation of detritus and loosening of soil.
Humification is the process of formation of humus from detritus. Mineralization is the process of release of inorganic substances as both non-mineral and minerals from organic matter. 

Question. (i) What is primary productivity ? Why does it vary in different types of ecosystems ?
(ii) State the relation between gross and net primary productivity. 
Answer :
(i) Primary productivity : Production of biomass / produced energy per unit area in a certain time period (per year) by plants during photosynthesis.
It depends upon – plant species inhabiting a particular area, environmental factors, availability of nutrients, photosynthetic capacity of plants.
(ii) GPP – R = NPP
NPP = Net Primary Productivity
GPP = Gross Primary Productivity
R = Respiration Losses

Long Answer Type Questions 

Question. (i) Explain primary productivity and the factors that influence it.
(ii) Describe how oxygen and chemical composition of detritus control decomposition.
Answer :
(i) Primary productivity : Amount of biomass / organic matter produced per unit area over a time period by the plant during photosynthesis.
Factors : availability of nutrients / quality of light available / availability of water / temperature of the given place / type of plant species of the area / photosynthetic capacity of the plants.
(ii) Oxygen increases rate of decomposition.
Decomposition is an oxygen consuming process. It takes place under aerobic conditions i.e. in presence of oxygen.
Chemical decomposition is slow when chitin and lignin are present and fast when cellulose and water soluble substances are present.

Question. Taking a small pond as an example of an ecosystem, list the four components of this ecosystem. How do these components function as a unit in a small pond ? 
Answer :
Four components of small pond ecosystem are:
Abiotic components – air, water, soil, light, temperature, other climatic conditions.
Biotic components – producers-phytoplanktons, some algae, floating and submerged plants.
Consumers of various order – Zooplanktons
Decomposers – Fungi, bacteria and other flagellates.
Components work as a unit for the following functions :
Productivity : Conversion of inorganic into organic material through photosynthesis with the help of solar energy and consumption of autotrophs by heterotrophs i.e. secondary productivity.
Decomposition : Decomposition and mineralisation of the dead matter.
Nutrient Cycling : To release the nutrients / elements back for use by autotrophs.
Energy Flow : Unidirectional flow of energy and its subsequent dissipation as one moves towards higher trophic levels.

Question. (i) Taking an example of a small pond, explain how the four components of an ecosystem function as a unit.
(ii) Name the type of food chain that exists in a pond.
Answer :
(i) Productivity : Conversion of inorganic substances into organic material with the help of radiant energy / sunlight by the autotrophs / producers (phytoplankton, algae, floating, submerged plants). 
Decomposition : Decomposers (fungi, bacteria, flagellates) breakdown dead decayed organic matter into simpler compounds. 
Energy flow : Unidirectional movement of energy towards higher trophic levels (producer to consumer) and its dissipation and loss as heat to the environment. 
Nutrient cycle : Mineralisation of dead matter to release them back for reuse of autotrophs. 
(ii) Grazing food chain / detritus food chain. 
Detailed Answer :
(i) The various aspects taken into consideration to study the functioning of ecosystem are :
Productivity, decomposition, energy flow and nutrient cycling. The four components of ecosystem (viz : abiotic, biotic, consumers and decomposers) function as a unit as follows :
(a) Productivity : If we take the example of pond ecosystem, the phytoplanktons are the organisms that capture the solar energy to perform photosynthesis. Thus, they contribute to primary productivity.
(b) Energy flow : They are then consumed by the zooplanktons. Zooplanktons are eaten by small fishes, which are in turn eaten by big fishes.
Hence, there is constant unidirectional flow of energy between different trophic levels from producer to consumers.
(c) Decomposition and Nutrient cycling : When any organisms dies at any trophic level, the various microbes present in the pond water decompose the dead remains. The nutrients that are released in the process of decomposition are again available to the producers for the primary productivity.
(ii) Grazing detritus type of food chain is present in a pond ecosystem.