NCERT Solutions for Class 12 Biology Chapter 14 - Ecosystem

Aakash NCERT Solutions for Chapter 14 of Class 12 Biology NCERT book consists of detailed solutions for the answers given in the exercise at the back of the chapter. An ecosystem is the most prominent topic which is explained as a functional unit of nature, where living organisms interact among themselves and also with the surrounding physical environment. With the help of Aakash NCERT Solutions students can learn about the structure of the ecosystem, transfer of energy (food chain) and other important topics.

Q1. Differentiate between Diapause and Hibernation?
Answer:

Q2. Fill in the blanks.
(a) Plants are called as_________because they fix carbon dioxide. 
Answer: Plants are called as autotrophs because they fix carbon dioxide.

(b) In an ecosystem dominated by trees, the pyramid (of numbers) is _________type. 
Answer: In an ecosystem dominated by trees, the pyramid (of numbers) is an inverted type. 

(c) In aquatic ecosystems, the limiting factor for productivity is _______.
Answer: In aquatic ecosystems, the limiting factor for productivity is light.  

(d) Common detritivores in our ecosystem are_________. 
Answer: Common detritivores in our ecosystem are earthworms 

(e) The major reservoir of carbon on earth is_________. 
Answer: The major reservoir of carbon on earth is the ocean.  

Q3. Which one of the following has the largest population in a food chain? 
(a)Producers
(b)Primary consumers 
(c)Secondary consumers 
(d)Decomposers 
Answer: 
(d) Decomposers 
Decomposers are microorganisms including fungi and bacteria. These break down the remains of dead plants and animals. Decomposers form the largest community of organisms in a food chain. 

Q4. The second trophic level in a lake is 
(a)Phytoplankton 
(b)Zooplankton 
(c)Benthons
(d)Fishes 
Answer: (b) Zooplankton 
In a lake, the first trophic level is formed by phytoplankton while the second trophic level is formed by zooplankton. 


Q5. Secondary producers are: 
(a) Herbivores 
(b) Producers
(c) Carnivores 
(d) None of the above 
Answer: (d) None of the above 
In a food chain, plants are the only producers, there are no other producers. Herbivores and carnivores are primary and secondary consumers respectively. 


Q6. What is the percentage of photosynthetically active radiation (PAR) in the incident solar radiation?
(a)100% 
(b)50 % 
(c)1-5% 
(d)2-10%
Answer: (b) 50%.
Out of total incident solar radiation, 50 % is formed by photosynthetically active radiation 


Q7. Distinguish between 
(a)Grazing food chain and detritus food chain 
(b)Production and decomposition 
(c) Upright and inverted pyramid
(d)Food chain and Food web 
(e)Litter and detritus 
(f)Primary and secondary productivity

Answer: (a)Grazing food chain and detritus food chain 

Answer: (b)Production and decomposition 

Answer: (c) Upright and inverted pyramid

Answer: (d) Food chain and Food web 

Answer: (e) Litter and detritus 

Answer: (f) Primary and secondary productivity 

Q7. Describe the components of an ecosystem. 
Answer: An ecosystem refers to be the functional unit of nature in which living organisms interact among themselves and also with their surrounding physical environment in order to perform nutrient cycling, energy flow, decomposition and productivity. There are many types of ecosystems such as pond ecosystem, forest ecosystem etc. 
Components of ecosystem-
The components of the ecosystem can be divided into abiotic components and biotic components .

1. Abiotic components- These include the non-living components of nature such as light, temperature, water, soil, air, inorganic nutrients etc. 
2. Biotic components- The biotic components of an ecosystem refer to the living organisms present in that ecosystem. The biotic components are divided as producers, consumers and decomposers. Producers are plants, consumers include animals which can be herbivores or carnivores and decomposers include microorganisms like fungi and  bacteria. 



Q8. Define ecological pyramids and describe with examples, pyramids of number and biomass. 
Answer: Ecological pyramid- The graphical representation of an ecological parameter such as number, biomass or energy, sequence wise in various trophic levels of a food chain in which producers are at the base, herbivores in the middle and carnivores at the top level.  Ecological pyramids can be upright, inverted, or spindle-shaped. The three common types of ecological pyramids include the pyramid of number, pyramid of biomass and pyramid of energy. 
1. Pyramids of number- It is the number of individuals per unit area at various trophic levels. It is generally upright, however, the pyramid of number in case of a big tree is generally inverted because number of insects that feed on tree generally exceeds in number. 
2. Pyramids of biomass- It represents the biomass in various trophic levels. A pyramid of biomass is upright except in an aquatic food chain. A pyramid of biomass in the sea is generally inverted because the biomass of fishes is generally more than that of phytoplankton. 
3. Pyramids of energy- It is the graphic representation of the amount of energy trapped at different trophic levels per unit area. Pyramid of energy is always upright. 



Q9. What is primary productivity? Give brief description of factors that affect primary  productivity. 
Answer: Primary productivity refers to the amount of organic matter or biomass produced by producers per unit area over a period of time. The primary productivity of an ecosystem depends upon a number of factors such as light, temperature, water, precipitation, availability of nutrients etc. 



Q10. Define decomposition and describe the processes and products of decomposition. 
Answer: Decomposition is the process of breaking down complex organic matter of detritus into inorganic substances such as carbon dioxide, water and nutrients. Dead remains of plants and animals constitute detritus. The process of decomposition involves steps like fragmentation, leaching, catabolism, humification and mineralization. 
1.Fragmentation of Detritus- In this step, the detritus is broken down into small fragments by earthworms 
2.Leaching- In leaching the water-soluble nutrients, seep down into the soil and become unavailable salts. 
3.Catabolism- The small fragments of decomposed by decomposers like fungi and bacteria with the help of action of enzymes. 
4.Humification- In this step, humus is formed. Humus is a dark colored, amorphous solid substance that acts as a nutrient reserve. 
5.Mineralization- In this step by the action of microbes, the inorganic nutrients are released from the humus. 



Q11. Give an account of energy flow in an ecosystem 
Answer: Energy Flow in an ecosystem: 
All living organisms are dependent for their food on producers, directly or indirectly. There is a unidirectional flow of energy from the sun to producers and then to consumers.  Photosynthetically active radiation (PAR) is responsible for the synthesis of food by plants. Animals obtain their food from plants, so they are called consumers. The process of eating and being eaten is called a food chain in which energy flows from producers to consumers. For example, In Grazing food chain, the grass is eaten by goats and Goats are further eaten by man. Similarly, in the detritus food chain, the sequence begins with dead organic matter. It is made up of decomposers which are heterotrophic organisms (fungi and bacteria). These are also known as saprotrophs. Decomposers secrete digestive enzymes that breakdown dead and waste materials into simple, inorganic materials, which are subsequently absorbed by them. Natural interconnection of food chain forms the food web. Thus, in an ecosystem, energy flow occurs through food chains and food webs. 

Q12. Write important features of a sedimentary cycle in an ecosystem. 
Answer: The important features of the sedimentary cycle are as follows: 
1. These nutrient cycles have their reservoirs in the Earth's crust. 
2. Sulphur, calcium, phosphorous etc. have sedimentary cycles. 
3. Sedimentary cycles are slow; they take more time to complete their circulation and are considered fewer perfect cycles 

Q13. Outline salient features of carbon cycling in an ecosystem.
Answer: Salient features of carbon cycling are as follows 
1. Carbon cycling occurs through atmosphere, ocean and through the living and dead organisms. 
2. Most of the carbon is fixed by plants during the process of photosynthesis and returns to the atmosphere in the form of CO2 during respiration. 
3. Burning of wood, forest fire and combustion of organic matter, fossil fuel, and volcanic activity are some other sources of releasing CO2 in the atmosphere. 

An outline of C-cycle is depicted in the figure given below: 
 

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