Class 12 Biology Chapter 14 Ecosystem Notes

Class 12 Biology Chapter 14 Ecosystem Notes: Explore comprehensive notes for Class 12 Biology Chapter 14 on Ecosystem. Dive into the study of ecological concepts, components of an ecosystem, energy flow, nutrient cycling, and ecological relationships with detailed explanations and key concepts to enhance your understanding of this crucial topic.

Class 12 Biology Chapter 14 Ecosystem Notes

Ecosystem: Ecosystem is a biological community where the living and non-living components interact with each other and their physical environment. It is the functional unit of nature and varies greatly in size. Let us have a look at the structure, function and components of ecosystem.

Structure of Ecosystem:

The structure of ecosystem comprises two different components:

• Biotic
• Abiotic

Biotic Components:

Biotic Components are the living components involved in shaping the ecosystem.

It includes biotic factors such as:

Producers: All green plant in the ecosystem are termed as the producers, as they produce their own food by making use of solar energy. All living organisms are dependent on plants for both oxygen and food.

Consumers: They include both primary consumers and secondary consumers. As animals depend on plants for their food, they are called consumers. Primary consumers feed directly of Producers for their food and the secondary consumers feed on the primary consumers for their food. All herbivores animals are an example of Primary consumers. Carnivores and apex predators make up the secondary and tertiary consumers.

Decomposers: They are the saprophytes which include fungi and bacteria. Decomposers convert the dead matter into nitrogen and carbon dioxide and the process is called decomposition.

Energy Flow: Energy flow is the flow of energy along the food chain, through different trophic levels. Energy is passed from the producers to the decomposers through various trophic levels.

Abiotic Components:

Abiotic components include inorganic materials like air, water, and soil.

Ecosystem Types:

There are three main types of ecosystem:

Terrestrial Ecosystem:

These are the ecosystem found only on land. The terrestrial ecosystems include:

• Forest ecosystem
• Grassland ecosystem
• Desert ecosystem
• Mountain ecosystem
• Aquatic Ecosystem

The aquatic ecosystem is the ecosystem in the water body. It includes:

Freshwater Ecosystem:

The freshwater ecosystem can be divided into the following categories:

• Lentic: This includes slow-moving or still water such as lakes, ponds, pools, etc.
• Lotic: This includes fast-moving water bodies such as rivers and streams.
• Wetlands: These include the environment where soil is saturated with water for a certain time period.

Oceanic Ecosystem: The ocean ecosystem is the largest ecosystem. It covers about 71% of the total earth’s surface. This is also known as the marine ecosystem and is divided into deep water, shallow water and deep ocean surface. A large variety of corals, echinoderms, brown algae, cephalopods and dinoflagellates are found here.

Ecological Pyramids:

An ecological pyramid is the graphical representation of the relationship between different organisms. Each bar of the pyramid represents a different trophic level.

The different types of ecological pyramids include:

Pyramid of Numbers: This represents the number of organisms in each trophic level, irrespective of their size.

Pyramid of Biomass: This represents the total mass of organisms at each trophic level.

An energy pyramid: An energy pyramid (sometimes called a trophic pyramid or an ecological pyramid) is a graphical representation, showing the flow of energy at each trophic level in an ecosystem.

Pyramid of Productivity: It is the total amount of energy present at each trophic level and the total energy lost between each trophic level.

Ecological Succession: Ecological succession refers to the change in the structure of species of an ecological community over time. These are of two types:

Primary Succession: This is a type of succession in which plants and animals first colonize a barren piece of land.

Secondary Succession: This is the type of succession in which an ecosystem that is destroyed, revives itself.

Function of Ecosystem:

• The level of organisms regulates the flow of energy.
• The autotrophs are the producers that produce energy which is transferred through various trophic levels.
• The minerals of the biosphere are cycled through the biosphere.
• It supports life systems and provides stability.

Decomposition:

It is the process of break 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:

• Fragmentation: It is the breakdown of detritus into smaller particles by the action of detritivores.
• Leaching: It’s the phenomenon by which water-soluble nutrients sink to the soil horizon and precipitate as salts that aren’t available.
• Catabolism: It is the breakdown of detritus into simple inorganic nutrients by the action of bacterial and fungal enzymes.
• 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.
• Mineralization:  It is the process by which some microorganisms further break down humus to form simple inorganic nutrients.

Ecological Succession:

Ecological succession is the process of change in the structure of species that belongs to an ecological community over time. After a mass extinction, the time scale can be decades or even millions of years. This change occurs orderly and sequential, parallel with the changes in the physical environment. 

• Pioneer Species: The species that invade a bare area are called pioneer species. 
• Pioneer Community: The community that is capable to invade a bare area is known as the pioneer community.
• Climax Community: A community that is almost near to equilibrium with the environment is called the climax community.
• Sere: A sequence of ecological communities arising in an area from the initial pioneer community to the final climax community.
• Primary Succession: Primary succession is a type of biological and ecological succession of plant life. It occurs in an environment in which a new substrate is deposited. This new substrate is not having any kind of vegetation and other organisms. It also usually lacks soil and organic matter. It occurs in places such as land after a lava flow or area left from the retreated glacier.
• Secondary Succession: Secondary succession is a type of biological and ecological succession of plant life which takes place in a habitat that has been previously populated but has since been disturbed or damaged. For instance, regions where existing vegetation has been removed (due to tree-felling in a woodland or destructive events such as fires).

Succession of Plants:

Hydrarch: A succession that begins in a water body or aquatic environment is called Hydrosere or Hydrarch Succession.

Xerarch: Xerosere is a succession of plants that are limited in the availability of water availability. It includes the different stages in xerarch succession. Xerosere originates in extremely dry situations such as sand deserts, dunes, salt deserts, rock deserts, etc.

In secondary succession, the invasion of species depends on the availability of water, conditions of the soil, and the environment. It also depends on whether any seeds or other propagules are present. Because soil is already existent, the pace of succession is substantially faster, and the climax community is reached much sooner.

Succession always proceeds towards the mesic community.

Nutrient Cycling:

The movement of nutrients through the various components that belong to an ecosystem is called nutrient cycling. It is also called biogeochemical cycles (bio: living organism, geo: rocks, air, and water). 

Types of Nutrient Cycles: 

• Gaseous.
• Sedimentary.

Standing State: The total amount of various nutrients like nitrogen, carbon, phosphorus, calcium, etc., present in the soil at any given time, is referred to as the standing state. It differs in different kinds of ecosystems and also on the basis of season.

The atmosphere serves as a reservoir for gaseous nutrient cycles (carbon and nitrogen).

The reservoir for the sedimentary nutrient cycle (sulfur, phosphorus, etc.) exists in the earth’s crust.

The rate of release of nutrients into the atmosphere is regulated by environmental factors.

The reservoir functions to meet with the deficit occurring due to an imbalance between influx and efflux.

Ecosystem Carbon Cycle:

Carbon is contained by most of the chemicals that make up living tissue. When the organisms die the carbon contained by them is recycled to be used by future generations. The movement of carbon through the various components of the ecosystem is called the carbon cycle. 

• As a result of respiration and combustion, carbon is released into the environment as CO₂.
• Carbon dioxide is absorbed by producers during the process of photosynthesis to produce carbohydrates. 
• Animals feed on the producers. The food chain causes carbon to move along various trophic levels. During breathing, the majority of the carbon eaten is exhaled as CO₂. The animals and plants eventually die.
• Decomposers eat the dead organisms and break them down. This causes the carbon in their bodies to be returned to the atmosphere as carbon dioxide. In some extraordinary conditions, decomposition is blocked. The plant and animal material may then be turned into fossil fuel for use in the future for combustion.
• Marine animals may convert some of the carbon in their diet to calcium carbonate which is then used to make the shells for their bodies. Over time these shells of dead organisms get collected on the seabed and form or converted into limestone. Due to various activities and movements of the earth, this limestone may eventually become exposed to the air where it is subjected to weathering. This results in the back release of carbon into the atmosphere as carbon dioxide. Carbon dioxide is also released through volcanic action. 
• Human activities have significantly influenced the carbon cycle. Rapid deforestation and massive burning of fossil fuels have increased the rate of release of carbon dioxide into the atmosphere.

Phosphorus Cycle:

The phosphorus cycle is the process by which phosphorus moves through the different layers of the atmosphere that is the lithosphere, hydrosphere, and biosphere.

Steps in Phosphorus Cycle:

• Weathering: Weathering of uplifted rocks adds phosphates to the land. Eventually, some phosphates reach the ocean again.
• Fertilizers: Phosphate fertilizers from fields might run off straight into the streams. These may later become part of a soil pool or can be absorbed by the plants.
• Excretion and Decomposition: Animal excretion (on land or in the ocean) and animal and plant decomposition both produce phosphates on land and in water.
• Dissolved Phosphates: Dissolved phosphates plays important role in forming ocean sediments by precipitation. The process of conversion of these sediments into phosphate rocks is a very slow and gradual process. 
• Geological Uplift: Geologic forces can lift up the phosphate rocks very slowly from the ocean floor or the rocks thick with phosphate in them to form the huge mountains.

Ecosystem Services:

The results or outcome of ecosystem processes is called ecosystem services.

Services of Healthy Forest Ecosystems:

Purification of air and water.

Mitigation of droughts and floods.

• Cycling of nutrients.
• Generation of fertile soils.
• Providing habitats to wildlife.
• Maintenance of biodiversity.
• Pollination of crops.
• To provide storage site for carbon.
• Providing aesthetic, cultural, and spiritual values.
• The average price tag of these ecosystem services is estimated to be US $ 33 trillion annually.
• This is near twice the value of the global gross national product GNP (the US $ 18 trillion).

The Calculation, Out of the Total Cost of Various Ecosystem Services:

• Soil formation accounts for about 50% of the ecosystem services.
• Recreation for about 10% of these services.
• Nutrient cycling about 10% of them.
• The cost of climate regulation and habitat dark approximate 6% each.