Class 12 Biology Chapter 12 Ecosystem Solutions. Explore Class 12 Biology Chapter 12 Ecosystem Solutions with easy-to-understand answers, important questions, and exam-focused explanations to master key ecological concepts, revise effectively, and prepare confidently for exams.
Class 12 Biology Chapter 12 Ecosystem Solutions
A. Very Short Answer Questions (1 mark each)
- What is an ecosystem?
Ans: An ecosystem is an environment in which biotic and abiotic factors interact with one another in such a way that they collectively support the survival of all living organisms.
- What are the two main types of ecosystems?
Ans: Terrestrial and aquatic ecosystems.
- Define gross primary productivity.
Ans: The total amount of production obtained through photosynthesis is called gross primary productivity.
- What are autotrophs or producers?
Ans: Green plants can directly capture solar energy and use it to prepare food for their nourishment. Therefore, such plants are called autotrophs or producers.
- What are the autotrophic components of a pond ecosystem?
Ans: Algae and all other green plants.
- What is net primary productivity?
Ans: The amount of organic matter remaining after deducting the portion of total production used by plants for their own respiration is called net primary productivity.
- Give some examples of heterotrophs or consumers.
Ans: Animals, fungi, non-green protists, and organisms belonging to the Monera kingdom.
- Explain the process of leaching during decomposition.
Ans: In the first stage of decomposition, detritus is broken into smaller pieces by earthworms and other animals present in the soil. Afterwards, water-soluble inorganic substances move down into the soil through leaching.
- Which type of food chain is more prevalent in the ocean?
Ans: The grazing food chain is prevalent in the ocean. It begins with tiny algae and ends with large fish. Although the total biomass of algae is lower than that of fish, algae reproduce rapidly, allowing the food chain to continue. Therefore, the biomass pyramid in this ecosystem is inverted.
- What are green plants known as?
Ans: Producers.
- What is the role of fungi in an ecosystem?
Ans: Fungi act as decomposers and break down organic matter in an ecosystem.
- Into which levels can consumers be divided?
Ans: Consumers can be divided into the following levels:
(i) Primary or first-order consumers.
(ii) Secondary or second-order consumers.
(iii) Tertiary or third-order consumers.
- What is ecological succession? HS ’24
Ans: Plants of one kind cannot occupy a place permanently under all conditions. Gradually, one type of plant community is replaced by another type. The new community may, in turn, be replaced by another community. This process is called ecological succession. It may proceed from a hydric to a xeric condition or from a xeric to a hydric condition.
- What is a climax community?
Ans: The final, relatively stable community of organisms established as a result of ecological succession is called a climax community.
Fill in the blanks (Class 12 Biology Chapter 12 Ecosystem Solutions)
- The pyramid of biomass in the ocean is generally __________.
Ans: Inverted.
- When many individual organisms of the same species live in a particular area, they form a __________.
Ans: Population.
- Less than 50% of the solar radiation reaching the Earth is called __________.
Ans: Photosynthetically active radiation (PAR).
- The process by which bacteria and fungi break down organic matter with the help of enzymes is called __________.
Ans: Decomposition.
- The total quantity of living organisms present at a particular trophic level at a given time is called __________.
Ans: Standing crop.
- In primary succession, grass is a __________ species.
Ans: Pioneer.
- The flow of energy in an ecosystem is __________.
Ans: Unidirectional.
- The detritus food chain begins with __________ organic matter.
Ans: Dead.
- Productivity in the ocean is limited by the availability of __________.
Ans: Nitrogen.
- The components of the atmosphere remain uniform up to an altitude of __________ km.
Ans: 40 km.
- __________ productivity is the rate at which consumers form new organic matter.
Ans: Secondary.
- The major reservoir of carbon on Earth is the __________.
Ans: Ocean.
- Plants are called __________ because they absorb carbon dioxide and prepare their own food.
Ans: Autotrophs.
B. Short-Answer Questions (Class 12 Biology Chapter 12 Ecosystem Solutions)
- Why are earthworms called friends of farmers?
Ans: Earthworms break down organic matter into smaller pieces and help in its decomposition. This increases the fertility of the soil. They also make tunnels in the soil, improving aeration. As a result, crops grow better and yield more. Therefore, earthworms are called friends of farmers.
- What are the raw materials for decomposition?
Ans: Organic matter, particularly plant-derived material, is the raw material for decomposition.
- What are the functional components of an ecosystem?
Ans: The functional components of an ecosystem are of two types: abiotic and biotic.
The abiotic components include air, water, soil, and solar energy.
The biotic components include green plants (producers), animals (consumers), and microorganisms (decomposers).
- On which factors does ecosystem productivity depend?
Ans: Ecosystem productivity depends on the following factors:
(i) Light.
(ii) Nutrients.
(iii) Moisture.
(iv) The stage of the plant life cycle.
(v) Photosynthetic capacity.
(vi) The length of the food chain.
(vii) The energy captured by the ecosystem.
- What is humus? What is its importance?
Ans: Humus is a substance formed during the decomposition of organic matter.
Its importance is that it stores nutrients required by plants. It also provides a suitable habitat for many microorganisms that help improve soil fertility.
- Differentiate between a grazing food chain and a detritus food chain.
Ans:
A grazing food chain begins with green plants or producers.
Example: Grass → Goat → Human.
A detritus food chain begins with dead organic matter.
Example: Dead plant parts → Earthworm → Microorganisms.
- What is a food web?
Ans: Food chains do not always operate independently. An organism may feed on different kinds of organisms rather than following only one food chain. For example, a snake does not always eat frogs, and an eagle does not always eat snakes. Different food chains are interconnected and form a complex network. This interconnected network of food chains is called a food web.
- Differentiate between primary succession and secondary succession.
Ans: The differences between primary and secondary succession are as follows:
(a) Primary succession: It occurs in places where plants have never grown before, such as newly formed volcanic surfaces or bare rocks. The process is generally slow. Lichens, which can grow on bare surfaces without developed soil, are often among the first organisms to establish themselves. As organic matter accumulates and soil develops, other plants gradually appear.
(b) Secondary succession: It occurs in an area where an existing community has been destroyed by natural or other causes, but the soil remains. Since soil is already present, succession generally proceeds more rapidly than primary succession. However, the resulting community may not be exactly the same as the original one.
- Define ecosystem services.
Ans: The various benefits obtained from the environment are called ecosystem services. These include purifying air and water, improving soil fertility, reducing damage caused by droughts and floods, and assisting in pollination.
- What are the different levels of consumers? What is the position of a goat in a grazing food chain?
Ans: The different levels of consumers are:
(i) Primary consumers.
(ii) Secondary consumers.
(iii) Tertiary consumers.
In a grazing food chain, a goat is a primary consumer.
- What is a sedimentary cycle?
Ans: In an ecosystem, substances undergo cyclic transformations between organic and inorganic forms. These cycles are broadly classified into gaseous cycles and sedimentary cycles. In gaseous cycles, substances circulate mainly through the atmosphere and water. In sedimentary cycles, substances such as sulphur and phosphorus circulate through rocks, soil, and living organisms. These substances are released through the weathering of sedimentary rocks.
C. Descriptive Questions (Class 12 Biology Chapter 12 Ecosystem Solutions)
- Briefly describe the factors controlling primary productivity in an ecosystem.
Ans: Green plants are the primary producers in an ecosystem. Primary productivity depends on several factors, including:
(i) Solar energy.
(ii) Temperature.
(iii) Animals.
(iv) Soil.
(v) Other organisms present in the ecosystem.
(vi) The cycling and transformation of materials.
Solar energy is the main source of energy captured and stored by plants. Without sunlight, plants cannot survive for long. Among the physical factors, soil fertility, water, and oxygen are important. Other organisms, particularly microorganisms, also influence plant survival and growth. Microorganisms help in the cycling of materials and release inorganic nutrients that plants can use.
- What is energy flow? Discuss the different stages of energy flow.
Ans: The transfer of energy obtained from the Sun among different organisms in an ecosystem is called energy flow.
Energy flow can be discussed under three stages:
(i) Energy capture: Plants capture solar energy through photosynthesis and convert it into chemical energy stored in organic matter. According to the source text, only about 0.1% of the solar energy is captured in this way. This stored energy supports the living organisms of the Earth.
(ii) Utilisation of energy: Organisms at each trophic level obtain energy from the trophic level below them. A large proportion of the energy they acquire is used for biological activities, while only a smaller proportion is stored as biomass in their bodies. The source text gives these proportions as approximately 90% used for biological activities and 10% stored as biomass.
(iii) Transfer of energy: Green plants convert solar energy into chemical energy. This energy passes through the different trophic levels as organisms feed on one another. Producers supply energy to primary consumers, which in turn supply energy to higher-level consumers. Thus, energy is transferred from one trophic level to another.
- What is a food chain? Describe the two main types of food chains.
Ans: The Sun is the primary source of energy in most ecosystems. Green plants capture solar energy and convert it into chemical energy through photosynthesis. This energy passes from plants to primary consumers, then to secondary and tertiary consumers, and eventually to decomposers. Since organisms depend on one another for food and energy, a feeding sequence is formed. This is called a food chain.
The two main types of food chains are:
(i) Grazing food chain: This food chain begins with green plants and passes through herbivores to carnivores. Energy is transferred from producers to primary consumers and then to higher-level consumers. Energy is lost at each trophic level, so the number and biomass of organisms generally decrease towards the higher levels, forming an upright pyramid in many terrestrial ecosystems.
Examples:
Grass → Grasshopper → Frog → Snake → Eagle.
Grass → Deer → Tiger.
(ii) Detritus food chain: This food chain begins with dead organic matter and proceeds through detritus-feeding organisms and decomposers. Small organisms first break down the dead material into smaller pieces. Leaching and microbial decomposition then take place. Finally, organic matter is converted into simpler inorganic substances and mineral nutrients.
- Describe an ecosystem with the help of an example.
Ans: A pond is an example of an ecosystem. Like other ecosystems, it contains producers, primary consumers, secondary consumers, higher-level consumers, and decomposers.
The components of a pond ecosystem are described below.
Biotic components
(i) Producers: Algae, water hyacinth, Azolla, lotus, aquatic grasses, Vallisneria, Hydrilla, and other aquatic plants produce food using solar energy.
(ii) Primary consumers: Various insects and their larvae, small fish, Paramecium, and snails obtain food directly from plants or plant material.
(iii) Secondary consumers: Fish, frogs, leeches, crabs, and prawns feed on primary consumers.
(iv) Higher-level consumers: Humans, birds, otters, and snakes obtain energy by feeding on organisms at lower trophic levels. Humans, birds, and otters may eat fish, while birds may also feed on leeches, snakes, and frogs.
(v) Decomposers: Microorganisms present in the soil and water break down the remains of dead producers and consumers. Through decomposition, organic matter is converted into inorganic substances and nutrients are released back into the environment.
Abiotic components
The pond ecosystem also involves the cycling of carbon, oxygen, nitrogen, phosphorus, and other materials. Nutrients such as nitrogen, phosphorus, and sulphur may enter the pond through water flowing from the surrounding land and through soil.
- Describe primary succession in an aquatic habitat.
Ans: Primary succession in an aquatic habitat begins in a newly formed water body where an established community of plants and other organisms is initially absent.
Phytoplankton and small insects may establish themselves first. Gradually, the amount of organic matter in the water increases. Floating and submerged plants then begin to grow, followed by grasses and other larger plants near the margins.
As organic matter accumulates, sediments build up and the bottom of the water body becomes shallower. Aquatic grasses and plants such as water hyacinth may establish themselves. Eventually, the water body may gradually develop into a terrestrial habitat supporting larger plants and trees.
Thus, succession may proceed from a hydric condition towards a mesic condition.
- What is an ecosystem? Describe its different components.
Ans: An ecosystem is a defined environment in which biotic and abiotic factors interact with one another and collectively support the survival of living organisms. It functions as an integrated system.
The components of an ecosystem are broadly divided into two categories: biotic and abiotic.
(i) Biotic components: According to their functions, biotic components are classified into three groups: producers, consumers, and decomposers.
(ii) Abiotic components: The main abiotic components are water, air, soil, temperature, light, and rainfall.
Water and air: Water is an essential component of living cells and biological processes. It also serves as a medium through which dissolved inorganic salts enter primary producers. Oxygen, carbon dioxide, and nitrogen in the atmosphere are important for living organisms.
Soil: The nature of an ecosystem depends partly on the characteristics of its soil. Soil is a reservoir of inorganic nutrients required by living organisms. Green plants absorb essential elements such as nitrogen, calcium, potassium, sulphur, phosphorus, and iron from the soil.
Temperature: Temperature influences the physical and biological processes of an ecosystem. Changes in temperature can affect the biological activities of organisms.
Light: Sunlight is the primary source of energy for most living organisms. Green plants capture this energy and make it available to other organisms through food chains.
Rainfall: Differences in rainfall across regions influence the distribution and diversity of plants. These differences also affect the diversity of animals found in different ecosystems.
- Why is a pond considered an excellent example of an ecosystem? Discuss a pond as an ecosystem.
Ans: A pond is considered an excellent example of an ecosystem because it contains different biotic and abiotic components that interact with one another. Its water level changes with the seasons, often increasing during the rainy season and decreasing at other times. Ponds are particularly important in rural areas and provide habitats for algae, aquatic plants, insects, fish, and birds. Human activities such as bathing, washing clothes, swimming, and providing water for cattle and buffaloes may also affect pond water quality.
The biotic components of a pond ecosystem are as follows:
(i) Producers: Algae, water hyacinth, Azolla, lotus, Hydrilla, and other aquatic plants prepare food using solar energy.
(ii) Primary consumers: Various insects and their larvae, small fish, snails, earthworms, and other organisms obtain food from plants or plant material.
(iii) Secondary consumers: Fish, frogs, leeches, crabs, prawns, and similar organisms feed on primary consumers.
(iv) Higher-level consumers: Humans, birds, otters, and snakes obtain energy by feeding on organisms at lower trophic levels. Humans, birds, and otters may eat fish, while birds may also feed on snakes, leeches, and frogs.
(v) Decomposers: Microorganisms in the soil and water decompose the remains of dead producers and consumers. They convert organic matter into simpler inorganic substances and release nutrients back into the environment.
The abiotic components include water, air, soil, sunlight, temperature, and nutrients. These components support the organisms living in the pond and take part in nutrient cycles.
- What is decomposition? Explain the process of decomposition.
Ans: Decomposition is the process by which complex organic molecules present in dead plants and animals are broken down into simpler substances through the activities of decomposers.
The main processes involved in decomposition are:
(i) Fragmentation: This is the first stage of decomposition. Detritivores break detritus into smaller pieces.
(ii) Leaching: Water dissolves soluble nutrients and carries them down into deeper layers of the soil, where they may accumulate as mineral substances.
(iii) Catabolism: Bacteria and fungi break down complex organic matter into simpler substances with the help of enzymes.
(iv) Humification: This process produces a dark-coloured, colloidal substance called humus. Humus stores nutrients and makes them available to plants over time.
(v) Mineralisation: Microorganisms further break down humus and release inorganic nutrients into the soil. This release of inorganic substances from humus is called mineralisation.
D. Additional Questions and Answers (Class 12 Biology Chapter 12 Ecosystem Solutions)
- Name a ringed animal that acts as a detritivore.
Ans: Earthworm.
- Why do water-soluble inorganic substances move away during decomposition?
Ans: Due to leaching, water-soluble inorganic substances move down into the soil. Therefore, they may no longer remain in the upper layer during decomposition.
- What is primary productivity?
Ans: Primary productivity is the rate at which producers capture solar energy through photosynthesis and convert it into organic matter.
- What happens after producers capture solar energy?
Ans: After capturing solar energy, producers convert it into chemical energy and make it available to consumers through feeding relationships. When organisms die, their remains may enter the detritus food chain.
- What are ecological pyramids?
Ans: Ecological pyramids are graphical representations of the trophic structure of an ecosystem. Each level represents a group of organisms at a particular trophic level. Producers form the base, while consumers occupy the higher levels. In many cases, the pyramid becomes narrower towards the top.
- What is a microhabitat?
Ans: A microhabitat is a small, specific part of a larger habitat that has its own environmental characteristics and supports particular organisms. Examples include mud at the bottom of a pond, the water surface, the pond margins, rocks beneath or above the water, tree bark, and the forest floor.
- How do decomposers help in the recycling of mineral nutrients?
Ans: Decomposers are organisms, particularly microorganisms, that obtain nutrients from dead organisms. They break down organic matter and release inorganic elements back into the environment. This process is essential for the recycling of nutrients and for the functioning of biogeochemical cycles. 0 0 0
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