CBSE Class 12 Biology Chapter 14 Notes

Class 12 Biology Chapter 14 Notes

Class 12 Biology Chapter 14 explains the Ecosystem. The major goal of the Class 12 Biology chapter Ecosystem revision notes is to clarify further the concepts covered in the chapter on Ecosystems. The coordinated interactions of the surrounding living things are referred to as an Ecosystem. To survive, each of these depends on the other. This comprises an ecosystem comprised of different plants and animals found on land and in water.

The collection of Chapter 14 Biology Class 12 Notes meets the current CBSE specified requirements and rules because it covers all the topics and gives students a thorough explanation. Students can utilise the Class 12 Biology Chapter 14 Notes to study, revise, and lighten their exam load. These notes were written by the academic specialists at Extramarks using data from the NCERT textbook and other relevant sources.

Students may register on Extramarks to access the Class 12 Biology Notes Chapter 14 and CBSE Class 12 Syllabus. Along with the Syllabus, students may also refer to CBSE Revision Notes, CBSE Sample Papers, CBSE Important Questions, CBSE Extra Questions, and CBSE past years’ question papers.

Key Topics Covered In Class 12 Biology Chapter 14 Notes

Following are the topics included in Biology Chapter 14 Class 12 Notes:

• Ecosystem- Structure and Function
• Productivity
• Decomposition
• Energy Flow
• Ecological Pyramids
• Ecological Succession
• Nutrient Cycling
• Ecosystem Services

Introduction:

An ecosystem is defined as the structural and functional unit of the biosphere, which comprises the living organisms and their nonliving environment where there exists interaction by means of food chains and  chemical cycles that result in energy flow, biotic diversity, and material cycling to form a stable, self-supporting system. There is a mutual relationship between the biotic community and the non-living environment. The environment affects the community, and the community also modifies the environment.

An ecosystem is not isolated or a closed unit instead, it is an open system. The materials move from one ecosystem to the other ecosystem.For example, leaves are blown from a forest into the lake, frogs move from ponds onto the land, and birds migrate during the summer and winter seasons.

CLASSIFICATION OF ECOSYSTEM:

• Based on nature:

1. Natural
2. Artificial 

• Based on duration

1. Natural
2. Permanent

• Based on size

1. Microecosystem
2. Macro ecosystem 

The study of the ecosystem is important because it also includes:

• Nutritive relationship between the organisms
• Interaction between the organisms and the environment
• Cycling of matter
• Flow of energy
• The structural and functional aspects of the ecosystem is equally important.

ECOSYSTEM: STRUCTURE AND FUNCTION

Components of the ecosystem:

There are two basic components of the ecosystem. They are

• Abiotic or non-living
• Biotic and living organisms.

Biotic components:

The biotic components are:

• Producers
• Consumers
• Decomposers

Stratification or layering:

Stratification or layering is the vertical dispersion of species in an ecosystem. This shows the relationship between their physical and physiological requirements.

Class 12 Biology Chapter 14 Notes explains the examples of the stratification 

• Forest which includes four layers of the forest community, trees, shrubs, herbs and the ground layer of mosses, and lichens.
• Lakes or large ponds have three zones:

Littoral zone, which contains the rooted vegetation.

The limnetic zone contains open water containing floating plankton.

Profundal zone which is deep and has only heterotrophs.

• Polar or frigid zones:

These are the cold zones, and the sun’s rays are not received during the long winter.

PRODUCTIVITY:

Productivity is defined as the amount of organic matter or biomass produced at  any level, for example, individual organism, population, community or ecosystem, during a given period of time. The size of biomass production by living organisms is known as productivity ecology.

The variations in productivity are

• Highest in the coral reef.
• Lowest in the desert
• The algal population is low in the winter, and in the summer, it is high.
• More vegetation occurs in the summer than in the winter.

There are two types of productivity. They are primary and secondary.

1. Primary productivity:

This is of two types:

Gross primary productivity: This is defined as the rate at which organic compounds are formed in green plants per unit of time and area. This is measured as an increase in biomass or an increase in stored energy.

Net primary productivity is equal to gross primary productivity minus respiration loss.This is basically the building of biomass or the storage of energy by green plants or producers in a given unit of time and area.

The energy is used by plants to maintain a steady state and for storage. Plants require energy to transport materials into and out of cells via biosynthesis and cell division.Through the process of respiration, they get the energy to perform these activities through the breakdown of organic compounds.

Plants use the remaining organic compounds to produce new organs, for example, roots, shoots, leaves, flowers, fruits, and seeds. This results in the addition of new biomass or energy, as well as its storage.The new biomass is available for heterotrophs.

The net production of biomass and the storage of energy by a community per unit of time and area is called community productivity.

2. Secondary productivity:

The energy is partly used for maintenance or respiration and partly stored. If, due to the storage of energy, the total biomass of the given consumer population is greater at the end of a given time than at the beginning, the net secondary productivity is the rate of increase. This may be related to the rate at which heterotrophs build up biomass per unit of time and area.

The total plant matter that is eaten up by the herbivore minus the material that is passed out in faeces is known as the gross secondary productivity, so it can be said that it is the amount of food absorbed from the alimentary canal, of which a part is used in respiration. The remainder is calculated as net secondary productivity.

The gross secondary productivity shows variations among different animals. For example, when a caterpillar eats leaf material, half of it is absorbed, and the rest is left as faeces.

Out of the total food absorbed, two third is used in respiration, and one-third becomes the net secondary productivity. 

The secondary productivity of any trophic level is about 10 % of the previous trophic level. The average is lower for herbivores and higher for carnivores. A given amount of meat contains more nutrients than the animals need compared to the same weight of plant food.

DECOMPOSITION:

This is the process of breaking down the substance into its constituent parts; it is also called decay or putrefaction. The process is performed by the bacteria and fungi, and these organisms break down the dead and decaying organic matter into small organic molecules which can be utilised by them and the inorganic compounds which are released into the environment.

There is variation in the rate of decomposition. There is rapid decomposition of carbohydrates and fats, while the rate is very slow for cellulose, chitin, lignin, etc, which are organic compounds.

The site of decomposition is the upper layer of soil in the terrestrial ecosystem, while in the aquatic ecosystems, the bottom portion of the Benthic zone is the site where the decomposition occurs.

The decomposition mechanism can be explained as:

The dead remains of plants and animals are known as detritus. It is of two types, i.e. the above-ground detritus and the below-ground detritus. The mechanism of degradation is a very complex enzymatic process.The three steps of degradation are

• Fragmentation of detritus: Detritivores are the detritus-feeding microscopic invertebrates that act on the detritus and lead to its breakdown into smaller fragments. As detritus passes through the digestive tract, it is pulverised. Fragmentation is responsible for increasing the surface area of detritus particles for microbial action.
• Leaching includes the soluble substances such as sugar and the nutrients from the fragmented detritus particles, which get dissolved in the water percolating through the soil and are removed due to the leaching action.
• Catabolism is the process carried out by the decomposers, for example, bacteria and fungi, which releases extracellular enzymes for the enzymatic conversion of the detritus particles to simpler compounds and inorganic substances.
• Humidification is the process by which the simple detritus is converted to the dark-colored humus, which is the amorphous substance in the soil. It is highly resistant to microbial action, and the rate of decomposition is extremely slow. Humus is the reservoir of nutrients.
• Mineralisation is the process that leads to the release of inorganic substances such as carbon dioxide, water, and nutrients in the soil. The nutrients are the ammonium, calcium, magnesium, and potassium.

Significance of decomposition:

The complex and enzymatic process of decomposition is a highly significant process because it is related to the release of nutrients from dead and decaying organic matter. If this process does not occur, then there will be no release of the nutrients, which will remain locked and will be marked as unavailable for the indefinite recreation of the living matter.Factors affecting decomposition:

Extramarks Class 12 Biology Chapter 14 Notes explains there are numerous factors which affect the decomposition. They are:

• Climatic factors like temperature and moisture content of the soil.
• The chemical quality of the detritus. This is basically related to  sugar, polyphenols, lignin and nitrogen which are the water soluble substances. Lignin and chitin slows down the detritus rate of decomposition. The nitrogen rich detritus which has a low amount of lignin has a rapid rate of decomposition.
• High temperatures and moist conditions result in rapid decomposition.
• When the moisture is lower and the temperature is lower than 10 degrees Celsius, the rate of decomposition declines sharply.

Energy flow:

• Only 1 to 4 percent of the solar energy is utilised by the plants for photosynthesis, and the rest is reflected back and absorbed by the ground, water, and atmosphere.
• Sugarcane is the most efficient solar energy user, accounting for 10 to 12 percent of global production.
• Energy flow is unidirectional, which means it is from producers to secondary consumers and not back.
• Each trophic level consumes more and more energy.

 Energy of the producers > primary consumers > secondary consumers > tertiary consumers.

• Lindemann gave the law of 10% for energy flow, which is also called  the 10% energy transfer law.  According to this law, only 10% of the total energy received by one trophic level is transferred to the next trophic level.
• The second law of thermodynamics states that when there is a transformation of energy from one form to another, the amount of total useful energy is reduced, and some energy is also degraded into heat and dissipated.
• Decomposition of dead animals also releases chemical energy.

The characteristics of energy flow are:

• There is a constant, unidirectional flow of energy or the transfer of energy from sunlight through plants and plant-eating animals to flesh-eating animals in the form of food.
• A decrease in useful energy at each successive level of nutrition due to the loss of some energy as heat at each transformation of energy.
• The return of the entire solar energy that enters living systems back to the non-living world as heat but not as light.
• The transfer of energy is the basis of life.
• Food chain and food web are the systems of energy transfer.
• The main basis of life is the transfer of energy.
• The means of transfer of both matter and chemical energy in the living world is food.

Reasons for a few trophic levels:

• The food which is available at one trophic level is not eaten by animals at the next trophic level, so it can be said that some energy is lost in this way.
• All the food which is eaten by animals is not useful.
• A herbivore gets enough amino acid only when it takes a lot of plant materials  and then this is utilised for its growth and development.
• There is a loss of a lot of energy in respiration to drive the organism’s metabolism.
• There is not enough energy to drive the higher trophic levels on land.

Producers:

Producers are autotrophs. They are the chlorophyll bearing organisms, and they produce their own food through the  fixation of light energy in the presence of simple inorganic biotic substances. Examples are green plants, yellow green algae, brown red algae.

Consumers:

Consumers or phagotrophs, are heterotrophic organisms, which means that the food is produced by another organism. These organisms ingest their food. There are three types of consumers based on the nature of their feeding habits. They are primary consumers, secondary consumers, and tertiary consumers.They are primary consumers, secondary consumers and tertiary consumers.

• Primary consumers are called herbivores and they feed directly on the producer like green plants. For example, rabbits, deer and sheep.
• Secondary consumers are also called primary carnivores. These feed on the herbivores like fox, snake, owl, peacock.
• Tertiary or secondary carnivores are those animals that feed on the secondary consumers like for example lions and tigers.

Decomposers are also called saprotrophs. They consist of the bacteria and the fungi that feed on the dead and  decaying matter. They secrete  extracellular digestive enzymes to decompose the organic remains.

FOOD WEB:

Food web is defined as the network of food chains which  become interconnected at various trophic levels so as to form a number of feeding connections amongst the  different organisms of a  biotic community.

image source: MTG Rapid biology

Some of the characteristics of the food web are

• They are never straight.
• They are formed by interlinking of the food chain
• It provides alternative pathways of food availability.
• The food web has a characteristic that the greater the number of alternative pathways, the more stable  the ecosystem.
• It checks overpopulation.
• Aid in the development of the ecosystem.

There are three types of  food webs. They are

• Predator chains that begin with plants and then proceed from small organisms to large organisms.
• Parasitic chain proceeds from large organisms to small organisms.
• Saprophytic chain proceeds from dead animals to the micro-organism.

The food web has an important significance in the ecosystem. It aids in providing stability to the ecosystem.

ECOLOGICAL PYRAMIDS:

An ecological pyramid is defined as the graphical representation of the numbers or the biomass or the status of accumulated energy at different trophic levels in a food chain in an ecosystem.

The idea of ecological pyramids was first developed by an English Biologist called Charles Elton in 1927. They are also known as Eltonian pyramids.

The three types of ecological pyramids are explained by Extramarks Class 12 Biology Chapter 14 Notes

1. Pyramid of numbers:

• It is a graphical representation of the number of individuals from different trophic levels in an ecosystem’s food chain.
• It is found in animal communities all over the world.
• The shape is upright or inverted.
• The shape is determined by whether the producers are more numerous, such as phytoplanktons in aquatic ecosystems, or less numerous, such as oak trees in a parasitic food chain.
• The example of an inverted pyramid of numbers can be explained as parasitic food chains.
• A single oak tree is the producer and it supports a large number of fruit-eating birds which support a large number of ice and bugs ( these are the parasites).
• Bacteria, fungi and actinomyces are the hyperparasites which are the greatest in number and occupy the top of the inverted pyramid of numbers.

1. Pyramid of biomass

• It is the graphical representation of  biomass which is present per unit area in the different trophic levels.
• Biomass is the total amount of living or organic matter in an ecosystem at any time.
• This depicts the quantitative relationships of the standing crops.
• It may be straight or inverted.
• The example of an upright or straight pyramid could be grasslands and forest ecosystems; there is a gradual decrease in the biomass of organisms at successive trophic levels from the producers onward to the top carnivores.
• An example of an inverted pyramid is seen in the pond ecosystem. The smallest organisms are the producers, and the largest organisms are the carnivores. There is a gradual increase in the biomass of organisms at the successive trophic levels from producers onward to top carnivores, and this forms the pyramid with an inverted shape.
• The maximum amount of biomass occurs in producers.
• Biomass is  the amount of living matter that is measured in terms of dry weight.

1. Pyramid of energy

• This presents energy per unit area in different trophic levels of a food chain.
• This gives a presentation of the overall nature of the ecosystem.
• There is a gradual decrease in energy at the successive trophic levels, and this is in accordance with the second law of thermodynamics.
• Pyramids of energy are always upright.
• At the producer level, the energy is the highest.
• Production energy is always greater than primary consumer energy.

ECOLOGICAL SUCCESSION:

• It is also known as biotic succession.
• It is the natural development of biotic community series, one after the other in the same area, till the establishment of a permanent climax community.
• When the existing plants and animals are replaced with new communities in an orderly change due to alterations in the physical conditions is known as ecological or biotic succession.
• Pioneer community is the first one to inhabit the area.
• The succeeding communities are the transitional communities.
• The last community to inhabit is the climax community. This is stable, and due to the lack of disturbance, it persists for a long time. It shows considerable diversity.
• Sere refers to the entire community’s series.
• If the ecological succession begins on bare rock, sand, or any other terrestrial habitat, the seral stages from the pioneer to the climax community are called xeroseres; if it begins in open water, it is called hydroseres.
• There are two types of xeroseres. They are lithospheres and psammoseres. Lithoseres start on the bare rock, and the psammoseres begin on the sand.
• The ecological succession that takes place in water is known as the “hydrarch.”

The characteristics of the ecological succession are:

• It begins with the small and short lived plants.
• It progresses toward the large and long-lived plants.
• It lead from low to high diversity of life.
• There is progress towards the state of stability.
• There is complete adjustment to the environment.
• Biomass increases gradually.
• Niche specialisation is considerable.
• The soil and the humus content develops in a considerable manner.
• There is a change from simple food chains to complex food webs.
• The stages are regular and directional.
• Plant and animal communities evolve in tandem.

There are two types of ecological succession:

• Primary succession occurs in the barren, uninhabited regions, etc. It takes a long time and is challenging for the communities.
• Secondary succession occurs in the previously uninhabited regions but disturbed areas. It is easy and is quickly completed.

NUTRIENT CYCLING:

• The nutrients are used up again and again by the living organisms, which shows that they are recycled.
• Nutrient cycling refers to the regular exchange of inorganic materials between living organisms and their non-living environment, like soil and water.
• The cycle is highly significant.
• The cycle results in the long-term preservation of the environment’s raw materials.
• Reducers play an important role in nutrient cycling.
• It leads to the indefinite recreation of  living matter.
• The cycle of life continues.

BIOGEOCHEMICAL CYCLES:

• The nutrients required in large amounts by living organisms are carbon, hydrogen, oxygen, nitrogen, sulphur, phosphorus, potassium, and calcium.
• The nutrients are obtained from the components of the biosphere, which include the lithosphere, hydrosphere, and atmosphere.
• There is continual recycling of the elements.
• Biogeochemicals or biogenetic nutrients are nutrients that are used by organisms for growth and metabolism.
• The movement of the nutrient elements through any particular ecosystem is known as the biogeochemical cycle or the cycle of matter.
• The nutrient elements pass between the atmosphere, earth, water, and organisms.
• The reservoir pool is the portion of the biogeochemical system that is not in use.
• The part of the cycle that is used up again and again is the pool.

TYPES OF BIOGEOCHEMICAL CYCLES:

They are of two types:

• Gaseous cycles.
• Sedimentary cycles.

ASPECTS OF NUTRIENT CYCLING:

There are three aspects of nutrient cycling. They are as explained by Class 12 Biology Chapter 14 Notes:

• Input of nutrients.
• Output of nutrients 
• Internal nutrient cycling

The main sources of the input of nutrients are  wet deposition (dissolved state from the rainfall in the ecosystem), dry deposition ( the nutrients in the particulate state), symbiotic biological fixation of nitrogen, and weathering of rocks to release the nutrients from the free state.

The output of nutrients is related to their movement out of the ecosystem. This includes some nutrients like calcium and magnesium, which are lost due to  runoff water and  soil erosion, the loss of nitrogen via denitrification ( involving conversion of nitrites and nitrates to ammonia and then free nitrogen into the air), loss of nutrients in the process of harvesting  agricultural crops or the transportation of logs, etc.

There is a balance between the input of nutrients and the output of nutrients. If there is any severe disbalance, like the falling of trees, fire, soil erosion, etc., then it creates instability in the ecosystem..

The internal nutrient cycling is related to the fact that soil is the reservoir of the nutrients, and these nutrients are continuously regenerated and stored in the forms that are available to the plants. The nutrient regeneration is done by the bacteria, fungi, and actinomycetes through detritus decomposition. Then these nutrients are stored in the soil for reutilisation. Plants also absorb large amounts of nutrients, and there is a dynamic relationship maintained between the regeneration of soil and its absorption.

CARBON CYCLE:

• Carbon is the main basis of life.
• Carbon is a crucial factor in maintenance of plants and animals.
• Carbon that has been locked up within organisms should be available for reuse by returning to the environment.
• Air, water, rock and fossil fuel are the main sources of carbon.
• Carbon dioxide is drawn from the atmosphere by green plants for photosynthesis and by corals for making the calcareous skeleton.
• Carbon is added to the biosphere through respiration in organisms, decaying of dead and organic waste, burning of fuel ,weathering of rocks and volcanic activity.

NITROGEN CYCLE:

• Nitrogen is a component of proteins and nucleic acids which are the essential components of the living system. It is also a component of ATP which is the source of energy in all the living organisms.
• The main source of nitrogen for green plants is the nitrate ions of the soil and water.
• There are six processes involved in the nitrogen cycle:

Nitrate assimilation means the nitrate ions are absorbed by the plants, and the plants form vegetative proteins from them. Even ammonium ions can be used by plants to form proteins. When the herbivorous animals eat the plant, the plant protein is converted to animal protein. When the herbivores are eaten up by the carnivores, then these proteins are used by them to make their own proteins.Ammonification means the animals excrete waste materials such as urea, uric acid, and ammonia. There are putrefying bacteria like Bacillus ranosus and Bacillus vulgaris that are found in the soil and the mud at the bottom of the water bodies and that convert urea and uric acid to ammonia and carbon dioxide. These can also decompose the proteins of dead plants and animals and convert it into ammonium phosphate, carbon dioxide, and water. This process is known as ammonification.

 The ammonium compounds formed are oxidised by the nitrite bacteria to soluble nitrites, which are further oxidised to soluble nitrates. This is known as nitrification.

Denitrifying bacterias are present in the anaerobic fertile mud of ponds, lakes and estuaries. These convert nitrites and nitrates to molecular nitrogen which escapes into the atmosphere or may be added to the water,this process is known as denitrification.

Prokaryotes, cyanobacteria, and symbiotic bacteria found in the roots of legumes such as beans and peas fix atmospheric nitrogen.The bacteria take up the nitrogen in the atmosphere, and it is converted to soluble nitrates like potassium nitrate. Some of it passes into the soil and is then absorbed by the plants, while the rest is used by the bacteria to synthesise their own proteins. This is known as nitrogen fixation, and the bacteria causing it are known as nitrogen fixing organisms.

OXYGEN CYCLE:

• Oxygen is the essential component of biomolecules and is required for respiration.
• It is available in the air in molecular form.
• A dynamic state of equilibrium is maintained by the oxygen in the atmosphere. It is taken up by plants by air or water, and it comes back to the environment either in combination with carbon as carbon dioxide or with hydrogen as water.
• The carbon dioxide and water are used in the process of photosynthesis by the plants, and this process liberates free oxygen in the air, which is used in respiration, and in this way the cycle is completed.

PHOSPHORUS CYCLE:

• This is one of the most important for all living organisms, as it is a component of cell membranes, membranes of the cell organelles, nucleic acids, and ATP.
• In animals, phosphorus is also a component of the bones and teeth.
• This actively participates in respiration, photosynthesis, and metabolic reactions.
• The main reservoirs are the phosphate rocks and fossil bone deposits.
• It is deposited in the soil by the erosion of rocks and by various human activities.
• As rock is eroded, a small amount of phosphorus is dissolved in the form of phosphates and is seeded deeply into the soil.
• Through rain and floods, phosphorus is washed away into the sea.
• Phosphorus is taken up by seaweeds, which are passed onto fish and seabirds.
• The phosphorus rich faeces of sea birds deposit on land.
• Plants take phosphorus from the soil.
• Animals get phosphorus from plants or through small animals.
• Animals excrete phosphorus as phosphates, which are immediately used by plants. This is returned to the soil and water through the decay of the excreta and the dead bodies of the organisms.

IMPORTANCE OF BIOGEOCHEMICAL CYCLES:

• The cycle shows the intrinsic relationship that exists between the different organisms.
• Plants and animals depend on the nitrogen fixing bacteria to convert the atmospheric nitrogen into the form of soluble nitrates.
• The bacteria are dependent on the denitrifying bacteria to return nitrogen to the environment.
• This is a characteristic of the ecosystem.

ABIOTIC COMPONENTS:

These include non-living physiochemical factors of the environment. They affect not only the distribution and structure of the organisms but also their behaviour and their interrelationships. These are:

• Inorganic substances include carbon, nitrogen, oxygen, water, carbon dioxide, calcium and phosphorus.
• Organic compounds like carbohydrates, proteins, lipids, nucleic acids, etc.
• Climatic factors like light, temperature, humidity, wind, rainfall, water, atmospheric gases.
• Edaphic factors like soil and substrate, topography, minerals, pH, etc.

FUNCTIONAL PERSPECTIVE OF ECOSYSTEM:

AUTOTROPHIC COMPONENT:

This primarily includes green plants, photosynthetic bacteria and cyanobacteria. They are capable of making organic food from simple inorganic substances like carbon dioxide and water. The radiant energy of the sun is trapped in photosynthesis andconverted into chemical energy. These are termed producers and include herbs, shrubs, large  trees, free floating microorganisms called phytoplanktons.  Plants use organic food like glucose to synthesise complex organic compounds like starch and carbohydrates, proteins, lipids, and so on.

HETEROTROPHIC COMPONENT:

These can be micro consumers and macro  consumers.

Macroconsumers are those animals which eat the producers directly or indirectly. They have four categories:

• Primary consumers or consumers of first order: These are called herbivores.

Herbivores of the terrestrial ecosystem include rabbit, rat, mice, deer, goat, grasshopper, grazing cattles, etc.

Herbivores of the aquatic ecosystem are crustaceans, molluscs, etc.

• Secondary consumers or consumers of the second order: They include primary carnivores like centipedes, fishes, frogs, snakes, predatory birds, wild cats, foxes, etc. and they feed on the herbivore animals.
• Tertiary consumers or consumers of the third order: They include secondary carnivores e.g. wolves which eat upon the secondary consumers or primary carnivores like for example, wolves eat foxes.
• Quaternary consumers or consumers of the fourth order are the group that includes tertiary carnivores for example lions, tiger, etc., which eat  the tertiary consumers, or secondary carnivores. These are not eaten by the animals.

Microconsumers:

They are also referred to as saprophytes, decomposers, and reducers.They are involved in breaking down the complex organic substances of dead plants and animals to release most of the inorganic substance back to the environment so that they can be used by the producers. The decomposers secrete  digestive enzymes to digest the organic compounds externally. Bacteria and fungi are examples of decomposers.

FOOD CHAIN:

Extramarks Class 12 Biology The food chain is defined in Chapter 14 Notes as the sequential inter-linking of organisms involving the transfer of food energy from producers through a series of organisms with repeated eating and being eaten.The food chain is always straight, and it proceeds in a  line.

The characteristics of food chain are:

• There is nutritive interaction between the living organisms or the biotic components of the ecosystem. There occurs repeated eating.
• It is always straight.
• There is a unidirectional flow of energy from the sun to the producers.
• There are 4 to 5 trophic levels in the food chain.
• As per the second law of thermodynamics, 80 to 90 % of energy is lost as heat at each transfer.

There are two types of food chain:

• Grazing food chain
• Detritus food chain

BIOMES:

• These are the major ecosystems.
• Different parts of the world inhabit a variety of species of plants and animals.
• The major terrestrial biotic communities of the world comprising the characteristic array of plants and animal life are called the biomes.
• They contain many ecosystems.
• They are defined by the climate like the temperature and precipitation.
• The factors affecting biomes are total annual rainfall, seasonal distribution of rain,temperature range, nature of soil, geographical barriers like mountain, river, seas, topography, latitude, and longitude, and water mass.
• The examples of the terrestrial biomes are:

Tundra

Northern coniferous forests

Temperate deciduous forests

Tropical rain or evergreen forests

Tropical deciduous forests

Chaparral

Tropical grassland

Temperate grassland

Desert

• The examples of the aquatic biomes are:

Marine biomes are sea shores, open seas and estuaries.

Freshwater biomes are streams and rivers, lakes and ponds and marshes.

 Class 12 Biology Chapter 14 Notes: Exercises & Solutions

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