CBSE Biology Chapter 12 Ecosystem Notes Class 12 - FREE PDF Download
Summary - Class 12 Biology Ecosystem Notes (Chapter 12)
Ecosystem: The ecosystem is the functional unit of nature in which living organisms interact with each other as well as their surrounding physical environment.
Biosphere: The biosphere is a global ecosystem that includes all of the world's local ecosystems.
Types of the Ecosystem:
1. Aquatic Ecosystem: Forest, grassland, desert, etc.
2. Terrestrial Ecosystem: Pond, wetland, lake, estuary, river, etc.
These are the natural ecosystems.
An ecosystem can be artificial or man-made like the croplands, aquarium, etc.
12.1: Ecosystem- Structure and Function
Biotic Factors: This includes all the living organisms in an ecosystem.
Abiotic Factors: This includes all the nonliving factors in an ecosystem like sunlight, humidity, wind, etc.
The characteristic physical structure of an ecosystem depends on the interaction of biotic and abiotic factors.
Stratification: It is the vertical and also the horizontal distribution of different varieties that occupy different levels. For example, trees occupy the top vertical strata or layers of a forest, shrubs are the second, and herbs and grasses occupy the bottom layers.
For an Ecosystem to Function as a Unit the Following Factors are Important:
1. Productivity
2.Decomposition
3. Energy flow
4. Nutrient cycling
The Function of an Ecosystem is that the Conversion of Inorganic into Organic Material by the Subsequent Steps:
Use of the energy of the sun by the autotrophs.
Consumption of the autotrophs by various heterotrophs.
Decomposition and mineralisation of all the dead organic interest release the nutrients back into the soil for reuse by the autotrophs.
These events are repeated again and again.
As we move along the trophic levels energy moves in a unidirectional manner. Energy dissipates and is lost as heat to the environment. Example: Pond ecosystem.
Abiotic Factors:
Water with all dissolved inorganic and organic nutrients, soil rich in nutrients at the rock bottom of the pond, solar input, day-length, temperature, and other climatic factors.
Biotic Factors:
Producers or Autotrophs: Algae, phytoplankton, floating, submerged, and marginal plants in the pond.
Consumers or Heterotrophs: Zooplankton, free-living, and bottom-dwelling forms.
Decomposers: Fungi, bacteria, and flagellates are abundant in the bottom of the pond.
12.2 Productivity:
A constant input of solar power is the basic requirement for any ecosystem.
Primary Production: It is the amount of biomass produced per unit area in a given time by plants during photosynthesis. It is expressed in terms of weight (g₋2) or energy (kcal m₋2).
Productivity: It is the rate of biomass production. It is expressed as g₋2
yr₋1 or kcal m₋2 yr₋1.
Gross Primary Productivity (GPP): GPP of an ecosystem is the rate of production of organic matter during photosynthesis.
Net Primary Productivity (NPP): Gross primary productivity minus respiration losses (R), is the net primary productivity (NPP).
GPP – R = NPP
The available biomass for the consumption of heterotrophs or herbivores and decomposers is the net primary productivity.
The rate of formation of new organic matter by consumers is termed secondary productivity.
The primary productivity of an ecosystem depends on the plant species and various environmental factors and therefore, varies from place to place.
For the whole biosphere, the annual net primary productivity is approximately 170 billion tons (dry weight) of organic matter. Despite occupying nearly ${ 70 }$% of the earth’s surface, the productivity of the oceans is only around 55 billion tons.
12.3: Decomposition:
Decomposition: It is the process of breaking down complex organic matter into simpler inorganic substances such as carbon dioxide, water, and nutrients by the action of decomposers.
Detritus: Dead remains of plants and animals such as leaves, barks, flowers, faecal matter of animals, etc. constitute detritus.
Detritivores: Organisms that feed on detritus are called detritivores. Earthworms, fungi, etc. are examples of detritivores.
Steps in Decomposition:
1. Fragmentation: It is the breakdown of detritus into smaller particles by the action of detritivores.
2. Leaching: It's the phenomenon by which water-soluble nutrients sink to the soil horizon and precipitate as salts that aren't available.
3. Catabolism: It is the breakdown of detritus into simple inorganic nutrients by the action of bacterial and fungal enzymes.
4. Humification: It is the formation and continuous deposition of a dark-coloured organic amorphous substance called humus. Humus is extremely resistant to microbial action and decomposes at a very slow rate. Because it is colloidal, it acts as a nutrient reservoir.
5. Mineralisation: It is the process by which some microorganisms further break down humus to form simple inorganic nutrients.
Humification and mineralization occur in the soil.
All steps of decomposition occur simultaneously on detritus.
Decomposition is largely an oxygen-requiring process.
On both the chemical composition of detritus and climatic factors, the rate of decomposition is dependent. When detritus is rich in lignin and chitin, the pace of decomposition is slower, and when detritus is rich in nitrogen and water-soluble compounds like sugars, the rate of decomposition is faster.
The most important climatic factors that play important role in decomposition are temperature and soil moisture. They affect the activities of soil microbes.
Decomposition is favoured in warm and moist environments.
Decomposition is inhibited by low temperatures and anaerobiosis. This results in a build-up of organic materials.
12.4: Energy Flow:
The Sun is the ultimate source of energy for all ecosystems on Earth (except for the deep-sea hydrothermal ecosystem).
Photosynthetically Active Radiation (PAR): The solar radiation that can be utilized by plants for photosynthesis. Of all incident solar radiation, only ${ 50 }$% is PAR. The plants can capture only ${ 2-10 }$% of the PAR and it is this energy that sustains all life on earth.
There is a unidirectional flow of energy that is the energy from the sun flows to the producers and then the consumers. Therefore, all organisms are directly or indirectly dependent on the sun.
All ecosystems follow the First and the Second Law of thermodynamics.
First Law of Thermodynamics: The First Law of Thermodynamics explains that energy can be converted from one form to another in the presence of heat, work, and internal energy, but it can neither be created nor destroyed, under any circumstances.
The unidirectional flow of energy shows the First Law of Thermodynamics as energy from the sun is converted into chemical energy by the producers which are then utilized by the consumers. At any level, energy can neither be created nor be destroyed.
Second Law of Thermodynamics: The Second Law of Thermodynamics states that the state of entropy of the entire universe, as an isolated system, will always increase over time. The changes in the entropy in the universe can never be negative, this is explained by the second law.
To counteract the universal tendency toward increasing disorderliness ecosystems need a constant supply of energy to synthesize the molecules they require.
Energy flow in the ecosystem occurs in the form of the food chain.
Food chain: A food chain is an arrangement of species in an ecological community based on the order of predation, in which each organism feeds on the organisms below it.
Producers: All the green plants in the ecosystem utilize solar energy for photosynthesis. They are always autotrophic.
Consumers: All heterotrophs, whether directly or indirectly reliant on plants for nourishment, are referred to as consumers. Depending on their position in the food chain the organisms can be divided into primary, secondary, tertiary, or quaternary levels.
Primary Consumers/Herbivores: The organisms that are directly dependent on the producers. In the above food chain, the grasshopper is the primary consumer.
Secondary Consumers/Primary Carnivores: The organisms that are dependent on the primary consumers. The frog in the above example is a secondary consumer.
Tertiary consumers/Secondary carnivores: The organisms that are dependent on the secondary consumers.
Quaternary Consumers/Tertiary carnivores: The organisms that are dependent on the tertiary consumers. They usually hold the top position which is the carnivore in a food chain.
A food chain cannot have more than a quaternary consumer because there would not be enough energy left for the next level organism.
The detritus food chain’s (DFC) starting point is dead organic matter. It is consists of decomposers mainly fungi and bacteria which are heterotrophs too. They break down dead organic matter or detritus to meet their energy and nutrient requirements. These are also called saprotrophs in which appro means to decompose. They secrete digestive enzymes outside their body to break down dead and waste organic materials into simple, inorganic materials. These simpler substances are subsequently absorbed by them.
In an aquatic ecosystem, the major conduit for energy flow is the Grazing Food Chain (GFC). In a terrestrial ecosystem, a much larger fraction of energy flows through the detritus food chain in comparison with the GFC.
The Detritus food chain can be connected with the grazing food chain because some of the organisms of DFC are prey to the GFC animals. Also in a natural ecosystem, some animals that exist are omnivores such as cockroaches, crows, etc.
Food Web: A system of food chains in which the interlocking and interdependency are found.
Trophic Level: The specific place in the food chain occupied by an organism based on the source of their nutrition or food is called the trophic level.
First Trophic Level: Producers occupy the first trophic level.
Second Trophic Level: The primary consumers.
Third Trophic Level: The secondary consumers.
Fourth Trophic Level: The tertiary consumers.
Fifth Trophic Level: The quaternary consumers.
A food chain can have a maximum of five trophic levels as beyond that the amount of energy is insufficient to sustain another consumer.
At successive trophic levels, the amount of energy gets decreases.
When an organism dies it is converted into detritus which serves as a source of energy for the decomposers.
Standing Crop: At a particular given time the total mass at a trophic level is standing crop. It is measured as the mass of living organisms (biomass) or the number in a unit area.
Biomass can also be expressed as fresh or dry weight. However, the use of the dry weight is more accurate.
10 Percent Law: This law states that only ${ 10 }$% of the energy of a trophic level is transferred to the next level.
12.5: Ecological Pyramids:
An ecological pyramid is a graphical representation of the relationship between different organisms in an ecosystem.
Each bar of the pyramid represents a specific trophic level along with their order. The order depends on who is been eaten by whom.
This represents the flow of energy.
The base of each pyramid is the representation of the producers or the first trophic level whereas the apex is the representation of the tertiary or top-level consumers.
The three commonly studied ecological pyramids are:
(a) Pyramid of number
(b) Pyramid of biomass
(c) Pyramid of energy
All species at that trophic level should be included in any estimations of energy content, biomass, or population. At any trophic level, it is impossible to generalise based on merely a few individuals.
An organism can be a part of more than one food chain and therefore belong to different trophic levels.
The pyramids of biomass, energy, and number are upright in most ecosystems. That is, the producers are more in number than the herbivores, the herbivores are more than the carnivores, etc.
Pyramids of number and biomass can be inverted in some cases but the pyramid of energy is always upright. This is due to the fact that when energy goes from one level to another, some of it is lost as heat.
Only food chains, not food webs, can be accommodated in ecological pyramids. They are also incapable of depicting saprotrophs.
Biology Notes for Class 12 Chapter-Wise PDF FREE Download
Related Study Material Class 12 Biology
Ecosystem Class 12 Notes Biology - Basic Subjective Questions
Section−A (1 Mark Questions)
1. Give examples of natural ecosystems and man-made or artificial ecosystems.
Ans. Forests, deserts, grasslands, lakes, rivers, seas, etc. are examples of natural ecosystems. Crop fields and an aquarium may also be considered man-made ecosystems.
2. What does the base tier of the ecological pyramid represent? (Exemplar)
Ans. The base of each ecological pyramid represents the producers or the first trophic level.
3. How much time is taken by a primary succession to complete?
Ans. Primary succession is a very slow process, taking maybe thousands of years for the climax to be reached.
4. Why is the rate of assimilation of energy at the herbivore level called secondary productivity? (Exemplar)
Ans. The rate of assimilation of energy at the herbivore level is called secondary productivity because the biomass available to the organisms of the next trophic level (consumer) for further consumption is a result of the primary productivity which is formed by autotrophs (plants).
5. Define ecological succession.
Ans. The gradual and fairly predictable change in the species composition of a given area is called ecological succession.
Section−B (2 Mark Questions)
6. State the importance of phosphorus in living organisms.
Ans. Phosphorus is a major constituent of biological membranes, nucleic acids, and cellular energy transfer systems.
Many animals also need large quantities of this element to make shells, bones, and teeth.
7. Is the pyramid of biomass in the sea inverted or upright? Give a reason.
Ans. The pyramid of biomass in the sea is generally inverted. This is because the biomass of fish far exceeds that of phytoplankton. Phytoplanktons are microscopic organisms with a short lifespan but very high reproductive potential. Although their number far exceeds the number of fishes present in the sea, their biomass is much lesser than the biomass of fishes (much larger) at any given time.
8. Define pioneer species. Name the pioneer species responsible for primary succession on a rock.
Ans. The species that invade a bare area are called pioneer species. In primary succession on rocks, these are usually lichens which can secrete acids to dissolve rock, helping in weathering and soil formation.
9. Define stratification. Give an example to support your answer.
Ans. The vertical distribution of different species occupying different levels is called stratification. For example, trees occupy the top vertical strata or layer of a forest, shrubs the second, and herbs and grasses occupy the bottom layers.
10. Define GPP. How is it related to NPP?
Ans. The Gross primary productivity of an ecosystem is the rate of production of organic matter during photosynthesis. A considerable amount of GPP is utilised by plants in respiration. Gross primary productivity minus respiration losses (R), is the net primary productivity (NPP) i.e., GPP – R = NPP. Net primary productivity is the available biomass for the consumption of heterotrophs (herbivores and decomposers).
11. Why are the number of trophic levels restricted in a grazing food chain? Is there any such limitation in a detritus food chain?
Ans. In any kind of food chain, grazing or detritus, the number of trophic levels is limited to 4-5 as the transfer of energy follows the 10% law i.e., only 10% of the energy is transferred to each trophic level from the lower trophic level. Moreover, the detritus food chain starts with decomposing organic matter which is already low in energy content. Hence, the trophic levels are usually even lower than 4-5.
5 Important Topics of Biology Class 12 Chapter 12 You Shouldn’t Miss!
Some Most frequently asked Important Questions during Exams
What are the components of the Ecosystem?
What is the difference between the biotic and abiotic components of the ecosystem?
How do the decomposers get their food?
What is a food chain? How many types of food chains are there?
What do you mean by a food web? Explain with the help of a diagram.
What are the features of a nitrogen cycle in an ecosystem?
What is the impact of human activities on the carbon cycle and what are its consequences?
What are trophic levels? Name and explain the two fundamental trophic levels.
Explain in detail the ecological pyramid.
Describe the energy flow in an ecosystem.
Importance of Class 12 Biology Ecosystem Notes
Ecosystems play a vital role in maintaining the balance of life on Earth, and understanding this chapter helps students appreciate the importance of biodiversity.
Ecosystem Class 12 Notes break down complex concepts into simpler terms, making it easier to grasp topics like energy transfer and the interdependence of species.
Ecosystem Notes Class 12 PDF provides a structured approach to learning, which can be helpful for last-minute revision and preparing for board exams.
They include diagrams and explanations for ecological pyramids and nutrient cycles, which are often asked in exams.
Learning these concepts is not only crucial for exam success but also for understanding broader environmental concerns like global warming, pollution, and habitat destruction.
Studying Ecosystem Class 12 Notes enhances critical thinking about the environmental impact of human activities and the importance of sustainable practices.
Tips for Learning the Class 12 Chapter 12 Biology Ecosystem
Break down the chapter into sections, starting with understanding the basic definitions of terms like ecosystem, biosphere, and niche.
Focus on understanding the difference between biotic (living) and abiotic (non-living) components and their roles in an ecosystem.
Memorise key nutrient cycles such as carbon, nitrogen, and phosphorus cycles with the help of flowcharts for better recall during exams.
Practice questions related to energy flow and pyramids of biomass, energy, and numbers, as these are common exam topics.
Use real-life examples to connect with the concepts, such as how forests or oceans function as ecosystems, which helps make the learning process more relatable.
Regularly revise and summarise key points in your own words to ensure you fully understand and retain the concepts.
Conclusion
Vedantu’s Class 12 Biology Ecosystem Notes provide an in-depth understanding of how organisms interact within their environment and the essential processes that maintain balance in nature. By studying concepts like energy flow, nutrient cycling, and ecological pyramids, you gain insights into the functioning of natural systems. These notes make it easier to grasp these ideas and prepare effectively for exams. Understanding ecosystems is not just important for biology exams but also for appreciating the importance of sustainability and conservation in the real world.
FAQs on Ecosystem Class 12 Notes: CBSE Biology Chapter 12
1. Define Ecosystem and describe its Types.
An ecosystem can simply be defined as the functional unit of nature with which living organisms survive and interact among themselves and with the physical environment that surrounds them. Ecosystems can broadly be classified into natural and man-made. Natural ecosystems can further be bifurcated into (a) Terrestrial Ecosystems - these include grasslands, deserts, forests, etc. and (b) Aquatic Ecosystems - these ecosystems include water bodies such as wetland, lake, river, estuary, etc. On the other hand, aquariums, croplands etc, are man-made ecosystems.
2. What are the Functions of an Ecosystem?
The major or primary function of an ecosystem is the conversion of inorganic materials to organic matter. The steps involved in the conversion of inorganic materials to inorganic matter are described below:
The plants take up the radiant energy from sunlight
The heterotrophs consume various plants or autotrophs resulting in the transfer of organic matter
Dead organic matter is mineralized and decomposed which releases nutrients back into the soil for reuse by the autotrophs
Repetition of the same phenomena over and over again
3. What are the various Steps involved in Decomposition?
Decomposition is the breaking down of complex organic substrates into simpler inorganic forms by decomposers, The various steps of decomposition are:
Fragmentation - breaking down of detritus into smaller particles by the action of detrivores such as fungi, earthworm, etc.
Leaching - download movement of water-soluble nutrients into the soil horizon and their precipitation as insoluble salts.
Catabolism - break down of detritus into simpler inorganic forms by enzymes from fungi and bacteria
Humification - formation and continuous deposition of a dark amorphous substance known as the humus.
Mineralisation - the further breakdown of humus by some microorganisms to form simple inorganic nutrients.
4. Are the Class 12 Biology Chapter 12 Notes beneficial?
The CBSE Class 12 Biology Chapter 12 Ecosystem Notes by Vedantu have been carefully drafted by experts keeping in mind the needs of the students. The Class 12 Chapter 12 Biology Notes have been prepared in a concise manner so that students can have a proper understanding of the chapter and are familiar with all the important topics. The Biology Class 12 Ecosystem Notes PDF are also available for download free of cost so that students are able to access them offline as well.
5. What is an ecosystem according to Chapter 12 Ecosystem of Class 12 Biology?
Class 12 Biology Chapter 12 discusses the ecosystem which is a unit of nature. An ecosystem is a concept that describes the interdependence of living beings on one another and also about their survival strategies. Further, it goes on to talk about the interactions that living beings have with their immediate surroundings to sustain and survive in that particular surrounding or population. This is an important chapter and must be read in detail for your exam.
6. What is the aquatic ecosystem according to Chapter 12 Ecosystem of Class 12 Biology?
Ecosystem is chapter 12 from Class 12 Biology in the CBSE syllabus. The ecosystem is basically nature's functional unit that has four main components and it deals with both the terrestrial and aquatic life Aquatic Ecosystem refers to the natural ecosystems that are all related to water bodies in some way or the other. Examples of aquatic water bodies are lakes, ponds, rivers, oceans etc where we find various biotic and abiotic components. You will get questions from this chapter in your board exam and hence you must study carefully and in detail.
7. What is the Artificial ecosystem?
Vedantu, the online learning website has study materials for all classes and all subjects for the ease of students. So it also has notes for the Ecosystem chapter that describes the relationship of living organisms in an environment among themselves and with their surroundings in order to survive. Relating to this concept these days we get to see many man-made ecosystems these days that are artificially created with living and nonliving organisms and provided with all the necessary conditions is known as artificial ecosystems.
These solutions are available on Vedantu's official website(vedantu.com).
8. Which revision notes are the best for Chapter 12 Ecosystem of Class 12 Biology?
The Revision Notes for “Ecosystems”, which is Chapter 12 of the Class 12 Biology NCERT book are available to access from the site of Vedantu. These notes on ecosystems help students develop extended knowledge on the topics that they have already studied in the chapter of their book. Here, you will find topic wise notes on the ecosystem and its components for you to prepare from before you appear for your Class 12 Biology board examination.
9. How can I get the Chapter 12 Ecosystem of Class 12 Biology revision notes online?
It is very easy to find the revision notes for Class 12 Biology Chapter 12 Ecosystem online on Vedantu. Visit Vedantu’s website. After that, go to the study materials section on the website. Under this section, you will find the “Revision Notes'' section. From here, select Class 12. Then, select Biology as the subject. A list of the chapter-wise revision notes will open up. Select Chapter 12 and you’ll find the ecosystem revision notes. Download the PDF file on your device by clicking on the download PDF option.
10. What is an ecosystem?
An ecosystem is a system formed by the interaction of a community of organisms with their physical environment. It includes both biotic factors (living organisms) and abiotic factors (non-living components like air, water, and minerals).
11. What are the main components of an ecosystem?
The main components of an ecosystem are biotic (producers, consumers, decomposers) and abiotic factors (climate, soil, water, and sunlight).
12. What is the role of producers in an ecosystem?
Producers, or autotrophs, are organisms that make their food through photosynthesis (like plants) or chemosynthesis (like some bacteria). They form the base of the food chain by providing energy to other organisms.
13. What are consumers?
Consumers are organisms that obtain energy by eating other organisms. They are classified into primary consumers (herbivores), secondary consumers (carnivores that eat herbivores), and tertiary consumers (carnivores that eat other carnivores).
14. What are decomposers and their role?
Decomposers, such as bacteria and fungi, break down dead organic matter into simpler substances. They play a crucial role in recycling nutrients back into the ecosystem, which helps maintain soil fertility.
