Ch 14 - Ecosystem || Class 12 ||

ECOSYSTEM || Biology || Class 12 || NCERT ||

1. Chapter 14 ECOSYSTEM

2. Ecosystem A functional unit of nature where interactions of living organisms with themselves and with physical environment takes place . An ecosystem is a community of living organisms ( plants, animals and microbes) in conjunction with the nonliving components of their environment (things like air, water and mineral soil), interacting as a system. The term ecosystem was coined by A.G.Tansley . Father of ecosystem ecology – E.P. Odum Types: Artificial ecosystem: man made ecosystem. Ex: crop field, aquarium. Natural ecosystem: Terrestrial ecosystem and Aquatic ecosystem.

3. • Terrestrial ecosystem is classified into forest, grassland, desert etc . • Aquatic ecosystem is classified into freshwater and salt water ecosystem. • Freshwater ecosystem are lentic - ponds, lakes and lotic - river, streams . • Salt water ecosystem are wetlands, estuaries, marine

4. Stratification Vertical distribution of different species occupying different levels in an ecosystem is called stratification. 1. Top trees. 2. Shrubs. 3. Herbs. 4. Grass.

5. Structure of ecosystem • The structure of ecosystem consists of biotic and abiotic components .

6. Producers - synthesis there own food. All the autotrophs of ecosystem are called Producers. Green plants are main Producers (Photosynthesis- main process) Energy Enters into Ecosystem through the producers . Solar energy is the ultimate source of energy In aquatic ecosystem Phytoplankton are major Autotrophs. 2 types - Photoautotroph and chemoautotroph.

7. 2. Consumers All the heterotrophs of ecosystem are known as consumers They digest their food inside the body. (First ingestion than digestion) They are also known as Macro consumers/ Phagotrophs / holozoic. These are of 3 types – Primary consumer (herbivores ) : Cow, Rabbit etc S econdary consumer (primary Carnivores ) : Dog, Cat, Snake etc. T ertiary consumer/ Top Consumers (sec. Carnivores ) : Lion, Man etc .

8. 3. Decomposers Those living organism which decomposes the dead body of producers and consumers are known as decomposers / Reducers / Transformers / Osmotrophs They are also known as Micro Consumers. They convert complex organic material into simpler organic substance. Eg . Bacteria and fungi.

9. The major function of ecosystem Productivity Decomposition Energy flow Nutrient cycling

10. Productivity The rate of biomass production per unit area during a given period of time is called productivity. It is measured in terms of weight or energy. It is used to compare productivity of different ecosystems . Primary productivity : It is the amount of biomass produced per unit area in a given time period by Plants during Photosynthesis. GPP-Gross Primary Productivity : It is the rate of production of organic matter during photosynthesis.

11. GPP – R = NPP NPP-Net Primary Productivity. R- respiration loss. GPP is not equal to NPP because, considerable amount of GPP is utilized by plants in respiration. 2. Secondary productivity It is the rate of formation of new organic matter by consumers in a given period of time.

12. Decomposition : It is the process of breaking down of dead organic matter into smaller organic and inorganic molecules by Decomposers (bacteria, fungi ). DETRITUS Raw materials of decomposition as dead plants , animals and animal feces is called detritus . DETRITIVORES Animals that feed on decaying organic matter (detritus). Examples: earthworms, termites, snails etc.

13. Steps of Decomposition : Fragmentation of Detritus : It is the process of breakdown of detritus into smaller particles. It is done by detritivores . Leaching : Soluble inorganic nutrients dissolve in water and goes down to soil, get precipitated is called leaching. Catabolism : Decomposers (bacteria, fungi) release enzymes to decompose detritus into simpler inorganic compounds. Humification : Simplified detritus converted to humus. Humus is a Dark, Amorphous substance. Highly resistant to Microbial Action. Undergoes Decomposition very Slowly. Reservoir of nutrients (due to colloidal nature). 5 . Mineralization: Humus is degraded to releases inorganic substances ( CO2 , H2O etc ) and nutrients (Ca2+, Mg2+,K + etc ).

14. Factors affecting rate of Decomposition : Chemical composition - decomposition rate will be slow when detritus is rich in lignin and chitin. The rate increases when detritus is rich in nitrogen and water soluble substances like sugars . Climatic conditions – warm and moist environment favour decomposition. Low temperature and anaerobiosis inhibit decomposition.

15. Food chain Transfer of energy / food from the producer through a series of organisms is known as food chain. Food chains represent energy flow through ecosystems. Different steps in a food chain are called trophic levels. Grazing food chain (GFC ): • The food chain that begins with producers continued with herbivores is called grazing food chain.

16. 2. Detritus food chain (DFC ) • The food chain that begins with dead organic matter is called detritus food chain (DFC ). • Saprophytes: These are decomposers ( fungi, bacteria ) which feed on detritus . 3. Parasitic Food chain (PFC)

17. Trophic level Each Step of the food chain is called trophic level. 4 trophic level are present in ecosystem because level of energy decreases during the flow of energy from one trophic level to another trophic level. Standing crop: Each trophic level has a certain mass of living material at a particular time is called standing crop. The standing crop is measured as the mass of living organisms (biomass) or the number in a unit area . First trophic level T1 Producers 100% Second trophic level T2 Primary Consumers 10% Third trophic level T3 Secondary consumers 1% Fourth trophic level T4 Top consumers 0.1%

18. Food web: The natural interconnection of food chains forms a web called food web.

19. Energy flow The storage, expenditure, transformation of energy is based on 2 basic laws of thermodynamics.

20. Ecological pyramid Graphical representation of ecological parameters at different trophic level in ecosystem is called Pyramids. These are energy , biomass or number of different organisms. C haracteristic features of ecological pyramids. The base of the pyramid is broad and it is narrow at the apex. The relationship can be expressed in terms of number, energy or biomass. The base of the pyramid represented by producer and apex is the top consumer , other trophic levels are in between. In most ecosystems, all the pyramids of number, energy and biomass are upright .

21. Inverted pyramid : The pyramid of number in a tree ecosystem is inverted. The pyramid of biomass in sea also inverted because the biomass of fishes is more than phytoplankton. Pyramid of energy is always upright , can never be inverted. Because when energy flows from a particular trophic level to the next, some energy is always lost as heat at each step .

22. Limitations of Ecological Pyramids It does not take into account the same species belonging to two or more trophic levels. It does not accommodate a food web. Saprophytes do not have any place.

23. Ecological succession Development of plant community on a barren area is called Ecological succession or Biotic succession. There is a gradual and predictable change in the species composition of a given area. Biotic communities are never stable. Pioneer species - The first species that invade a bare area. Climax species – The last and stable community in an area. Seral stages – In succession stages which comes between pioneer community and climax community is called transitional or seral community.

24. Characteristics – Gradual replacement Continuous change towards stability Increase in species diversity Decrease in net productivity Parallel evolution Change in number and type of animals and decomposers .

25. Cause of succession Biotic factors – favorable for next community Physiological factors – unfavorable conditions Types of Succession Primary Succession - A Succession that starts where no living organisms are there. E.g. Volcanic lava, land slides etc. Secondary succession - A Succession where vegetation was present previously but destroyed due to natural or artificial causes. E.g. Fire, Flood etc.

26. Hydrarch Succession Stages of hydrosere or hydrarch succession in the newly formed lake or pond. Phytoplankton stages – pioneer community, first coming minute autotrophic organism, These produce organic matter. E.g. Cyanobacteria Rooted submerged stages – E.g. Vallisneria Free floating stages – E.g. Nymphea Reed swamp stages (Amphibious stages) – E.g. Azolla Sedge meadow stage (marsh meadow stage) – E.g. muddy plant Scrub stage – E.g. Woody shrubs Forest stage – E.g. Tree

27. Xerarch Succession Stages of Lithoosere or Xerarch succession on the rocks. Crustose lichen stages – pioneer community, Produce organic acid which cause weathering of rocks. Foliose lichen stages – large lichen with leafy thalli Moss stages Herb stages Shrub stage Forest stage

28. Nutrient cycling/ biogeochemical cycling A nutrient cycle (or ecological recycling ) is the movement and exchange of organic and inorganic matter back into the product ion of living matter. The process is regulated by food web pathways that decompose matter into mineral nutrients . Nutrient cycles occur within ecosystems. Ecosystems are inter connected systems where matter and energy flows and is exchanged as organisms feed , digest , and migrate. Minerals and nutrients accumulate in varied densities and uneven configurations.

29. There are two types of cycles – Gaseous cycle – Cycle which have its reservoir of the nutrient in atmosphere. Ex: Carbon cycle, Nitrogen cycle. 2. Sedimentary cycle – Cycle which have its reservoir of the nutrient is earth crust. Ex :, Sulphur cycle

30. Carbon constitutes 49 % of dry weight of organism. 0.003 % of CO2 is present in atmosphere. Carbon is fixed in the biosphere through photosynthesis. Carbon returns to the atmosphere as CO2 through respiratory activities of the producers and consumers. Decomposers also contribute Some amount of CO2 from dead organic matter Burning of wood, forest fire , combustion of organic matter, fossil fuel, and volcanic activity are additional sources for releasing CO2 in the atmosphere . Carbon cycle

31. Phosphorus cycle Phosphorus is a major constituent of organism. It found in nucleic acids and cellular energy transfer systems (ATP ). Many animals also need large quantities of this element to make shells, bones and teeth. The natural reservoir of phosphorus is rock. In which it contains in the form of phosphates. When rocks are weathered, minute amounts of phosphates dissolve in soil solution and are absorbed by the roots of the plants. Herbivores and other animals obtain this element from plants. The waste products and the dead organisms are decomposed by phosphate- solubilising bacteria releasing phosphorus.

32. E cosystem services • The products of ecosystem processes are called as ecosystem services. Ex : Forest ecosystems purify air and water, • It avoids droughts and flood. • It cycle nutrients and generate fertile soils. • It provide wildlife habitat, maintain biodiversity. • It provide storage site for carbon. • It also provide aesthetic, cultural and spiritual values .

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