Ncert Solutions for Class 12 Biology Chapter 12 Ecosystem

Ecosystem ncert solutions: Class 12th biology chapter 12 ncert solutions

Textbook	NCERT
Class	Class 12
Subject	Biology
Chapter	Chapter 12
Chapter Name	Ecosystem class 12 ncert solutions
Category	Ncert Solutions
Medium	English

Are you looking for Ncert Solutions for Class 12 Biology Chapter 12 Ecosystem? Now you can download Ncert class 12 biology chapter 12 questions and answers pdf from here.

Question 1: Fill in the blanks.
(a) Plants are called as_________because they fix carbon dioxide.
(b) In an ecosystem dominated by trees, the pyramid (of numbers) is_________type.
(c) In aquatic ecosystems, the limiting factor for the productivity is_________.
(d) Common detritivores in our ecosystem are_________.
(e) The major reservoir of carbon on earth is_________.

Solution 1:

(a) Autotrophs
(b) inverted
(c)Light
(d)Earthworm
(e)Ocean

Question 2: Which one of the following has the largest population in a food chain?
(a) Producers
(b) Primary consumers
(c) Secondary consumers
(d) Decomposers

Solution 2: (d) Decomposers

Decomposers form the largest population in food chain. They include microbes such as bacteria and fungi, that derive their nutrition by disintegrating the remains of animals and dead plants.

Question 3: The second trophic level in a lake is
(a) Phytoplankton
(b) Zooplankton
(c) Benthos
(d) Fishes

Solution 3: (b) Zooplankton

In a typical aquatic food chain, phytoplankton are the primary producers (first trophic level), and zooplankton are the primary consumers (second trophic level), as they feed on phytoplankton. Benthos and fish occupy higher trophic levels in the food chain.

Question 4: Secondary producers are
(a) Herbivores
(b) Producers
(c) Carnivores
(d) None of the above

Solution 4: (d) None of the above

The term “secondary producers” is not typically used in ecology because producers are organisms that create their own food (usually through photosynthesis) and are always primary producers. Herbivores are primary consumers, and carnivores are secondary or tertiary consumers. Therefore, none of the options correctly define “secondary producers.”

Question 5: What is the percentage of photosynthetically active radiation (PAR) in the incident solar radiation?
(a) 100%
(b) 50 %
(c) 1-5%
(d) 2-10%

Solution 5: (b) 50%

Photosynthetically Active Radiation (PAR) refers to the portion of sunlight (wavelengths between 400 and 700 nanometers) that plants use for photosynthesis. About 50% of the total incident solar radiation falls within this range and is available for photosynthesis.

Question 6: 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

Solution 6: The differences are as follows:

Grazing Food Chain	Detritus Food Chain
Involves primary producers (plants) being consumed by herbivores, followed by predators.	Starts with dead organic matter, which is broken down by decomposers like fungi and bacteria.
Sunlight is the primary source of energy.	Dead organic matter and detritus serve as the energy source.
Flow of energy occurs from producers to herbivores to carnivores.	Energy flows from dead organic matter to decomposers and then to detritivores.
Grass → Grasshopper → Frog → Snake	Fallen leaves → Earthworms → Microbes

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Production	Decomposition
Process of converting solar energy into chemical energy by producers (e.g., photosynthesis).	Breakdown of organic matter into simpler substances, releasing nutrients back into the environment.
Organisms Involved: Mainly plants, algae, and photosynthetic bacteria.	Organisms Involved: Decomposers like bacteria, fungi, and detritivores.
Results in the formation of biomass.	Results in the release of nutrients (e.g., carbon, nitrogen).
Essential for creating new organic matter and energy flow.	Important for nutrient recycling in ecosystems.

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Upright Pyramid	Inverted Pyramid
Pyramid shape where the number, biomass, or energy decreases from the base to the top.	Pyramid shape where the number, biomass, or energy increases from the base to the top.
Common in energy and biomass pyramids (e.g., forest ecosystems).	Common in certain aquatic ecosystems where producers have a high turnover rate.
Grassland ecosystem (large number of producers, few top predators).	Aquatic ecosystem (phytoplankton as producers have less biomass but reproduce quickly).

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Food Chain	Food Web
A linear sequence of organisms where each is eaten by the next.	A complex network of interconnected food chains in an ecosystem.
Simple and straightforward, involving only one path of energy flow.	Complex, showing multiple paths and interactions between different organisms.
Less stable as disruption in one link can affect the entire chain.	More stable as organisms have multiple feeding options.
Grass → Grasshopper → Frog → Snake	A forest ecosystem where deer, rabbits, and insects feed on plants, and are preyed upon by multiple predators.

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Litter	Detritus
Fresh, undecomposed organic material like fallen leaves and branches.	Partially decomposed organic matter, including fragments of leaves, dead animals, and feces.
Role in Ecosystem: Litter forms the initial input for decomposition.	Role in Ecosystem: Detritus is broken down further by decomposers, releasing nutrients back into the soil.
Fallen leaves, twigs, plant matter.	Humus, decomposing animal remains.

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Primary Productivity	Secondary Productivity
The rate at which producers (e.g., plants) convert sunlight into chemical energy (biomass).	The rate at which consumers convert the energy they obtain from producers into their own biomass.
Involves producers like plants, algae, and photosynthetic bacteria.	Involves herbivores, carnivores, and decomposers.
Measured in terms of energy or biomass per unit area over time (e.g., kcal/m²/year).	Also measured similarly but refers to energy accumulation in consumer biomass.
Represents the energy available to higher trophic levels.	Indicates the energy transfer efficiency from producers to consumers.

Question 7: Describe the components of an ecosystem.

Solution 7: An ecosystem consists of various components that interact with each other, forming a complex and dynamic system. Here are the primary components of an ecosystem:

1. Biotic Components

These are the living components of an ecosystem, including:

• Producers (Autotrophs): Organisms that can produce their own food through photosynthesis (plants, algae) or chemosynthesis (certain bacteria).
• Consumers (Heterotrophs): Organisms that cannot produce their own food and rely on consuming other organisms.
• Types of consumers include:
  • Primary Consumers: Herbivores that eat producers (e.g., rabbits, deer).
  • Secondary Consumers: Carnivores that eat primary consumers (e.g., foxes, birds of prey).
  • Tertiary Consumers: Carnivores that eat secondary consumers (e.g., hawks, lions).
• Decomposers: Organisms such as bacteria and fungi that break down dead organic matter, recycling nutrients back into the ecosystem. They play a critical role in decomposition and nutrient cycling.

2. Abiotic Components

These are the non-living physical and chemical factors that influence the ecosystem, including:

• Climate: Temperature, humidity, precipitation, and wind patterns that affect the types of organisms that can live in an area.
• Soil: The composition and quality of soil, including its minerals, organic matter, pH, and moisture content, which influence plant growth and, consequently, the entire food web.
• Water: Availability and quality of freshwater and saltwater resources, which are essential for all living organisms.
• Light: Sunlight is crucial for photosynthesis, influencing plant growth and, thus, the entire ecosystem’s energy dynamics.
• Nutrients: Essential elements such as nitrogen, phosphorus, and potassium that support plant growth and are vital for the functioning of ecosystems.

3. Trophic Levels

These represent the hierarchical levels in an ecosystem based on the flow of energy:

• Producers: First trophic level (plants).
• Primary Consumers: Second trophic level (herbivores).
• Secondary Consumers: Third trophic level (carnivores).
• Tertiary Consumers: Fourth trophic level (top predators).
• Decomposers: Break down organic matter at all levels, recycling nutrients.

Question 8: Define ecological pyramids and describe with examples, pyramids of number and biomass.

Solution 8: An ecological pyramid is a graphical representation of various ecological parameters such as the number of individuals present at each trophic level, the amount of energy, or the biomass present at each trophic level. Ecological pyramids represent producers at the base, while the apex represents the top level consumers present in the ecosystem. There are three types of pyramids:

(a) Pyramid of numbers
(b) Pyramid of energy
(c) Pyramid of biomass

Pyramid of numbers: It is a graphical representation of the number of individuals present at each trophic level in a food chain of an ecosystem. The pyramid of numbers can be upright or inverted depending on the number of producers. For example, in a grassland ecosystem, the pyramid of numbers is upright. In this type of a food chain, the number of producers (plants) is followed by the number of herbivores (mice), which in turn is followed by the number of secondary consumers (snakes) and tertiary carnivores (eagles). Hence, the number of individuals at the producer level will be the maximum, while the number of individuals present at top carnivores will be on the other hand, in a parasitic food chain, the pyramid of numbers is inverted. In this type of a food chain, a single tree (producer) provides food to several fruit eating birds, which in turn support several insect species.

Pyramid of energy: An energy pyramid is a graphical model of energy flow in a community. The different levels represent different groups of organisms that might compose a food chain. From the bottom-up, they are as follows: Producers bring energy from nonliving sources into the community.

Pyramid of biomass: A pyramid of biomass is a graphical representation of the total amount of living matter present at each trophic level of an ecosystem. It can be upright or inverted. It is upright in grasslands and forest ecosystems as the amount of biomass present at the producer level is higher than at the top carnivore level. The pyramid of biomass is inverted in a pond ecosystem as the biomass of fishes far exceeds the biomass of zooplankton (upon which they feed).east.

Question 9: What is primary productivity? Give brief description of factors that affect primary productivity.

Solution 9: Primary productivity of an ecosystem is the amount of energy fixed or biomass synthesized by primary producers or green plants per unit area per unit time during photosynthesis.

Primary productivity of an ecosystem depends on the variety of environmental factors such as light, temperature, water, Carbon Dioxide Concentration, precipitation, etc. It also depends on the availability of nutrients and the availability of plants to carry out photosynthesis. 

Question 10: Define decomposition and describe the processes and products of decomposition.

Solution 10: Decomposition is the biological process through which organic matter, such as dead plants, animals, and waste products, is broken down into simpler organic and inorganic substances. This process is primarily carried out by decomposers, including bacteria, fungi, and detritivores (organisms that feed on dead organic matter).

Processes of Decomposition Decomposition occurs in several stages, each involving different processes and organisms:

Leaching:

• Description: The initial stage where water-soluble substances are dissolved and carried away from the decomposing material.
• Process: Rainwater or moisture penetrates organic matter, causing nutrients like sugars, salts, and minerals to dissolve and leach into the surrounding soil.

Fragmentation:

• Description: Physical breakdown of larger organic matter into smaller pieces.
• Process: Larger detritivores, such as earthworms and insects, feed on the organic matter, breaking it down into smaller particles, which increases the surface area for microbial action.

Biological Decomposition:

• Description: The microbial breakdown of organic materials by bacteria and fungi.
• Process: Decomposers secrete enzymes that break down complex organic compounds into simpler substances (e.g., carbohydrates, proteins). This results in the conversion of organic matter into microbial biomass and nutrient-rich substances.

Humification:

• Description: The transformation of decomposed material into humus, a stable organic matter component.
• Process: As organic matter continues to decompose, some of it becomes resistant to further decomposition and forms humus, which enhances soil fertility and structure.

Mineralization:

• Description: The conversion of organic nutrients into inorganic forms that can be absorbed by plants.
• Process: Microbial activity leads to the breakdown of organic compounds into inorganic substances (like nitrates, phosphates, and carbon dioxide), which can be utilized by plants and other autotrophs. 

Question 11: Give an account of energy flow in an ecosystem.

Solution 11: Energy flow in an ecosystem refers to the transfer of energy from one trophic level to another, starting from the primary producers and moving through various levels of consumers. The process begins with primary producers (autotrophs), such as plants and phytoplankton, which capture solar energy through photosynthesis and convert it into chemical energy stored in organic compounds. This energy then flows to primary consumers (herbivores) when they consume the producers. As energy moves up the food chain to secondary consumers (carnivores) and tertiary consumers (top predators), a significant amount of energy is lost at each trophic level, primarily as heat due to metabolic processes, respiration, and other life activities. Typically, only about 10% of the energy from one trophic level is passed on to the next; this is known as the 10% Rule. Additionally, decomposers (bacteria, fungi) play a crucial role in the energy flow by breaking down dead organic matter, recycling nutrients back into the ecosystem and allowing primary producers to utilize them again. This continuous flow of energy sustains ecosystem productivity and maintains ecological balance, highlighting the interdependence of organisms within their environments.

Energy Flow Pathway

1. Solar Energy → Producers:
   • Solar energy is captured by producers through photosynthesis, converting it into chemical energy (carbohydrates).
2. Producers → Primary Consumers:
   • Herbivores consume the energy-rich biomass of plants, extracting energy for their growth and reproduction.
3. Primary Consumers → Secondary Consumers:
   • Carnivores eat herbivores, transferring energy up the food chain.
4. Secondary Consumers → Tertiary Consumers:
   • Higher-level carnivores consume secondary consumers, further transferring energy.
5. Decomposers:
   • Upon death, organisms are broken down by decomposers, releasing stored energy back into the soil and atmosphere and facilitating nutrient cycling.