Chapter 14 ecosystem by mohanbio

• Chapter 14:

• Ecosystem:-• A functional unit of nature where interactions of living

organisms with themselves and with physical environment takes place.

• The term ecosystem was coined by A.G.Tansley.• Types:• Artificial ecosystem: man made ecosystem. Ex: crop field,

aquarium.• Natural ecosystem: Terrestrial ecosystem and Aquatic

ecosystem.• 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

• Stratification:- Vertical distribution of different species occupying different levels in an ecosystem is called stratifiction.

1. Top trees.

2. Shrubs.

3. Herbs.

4. Grass.

• Structure and function of ecosystem.

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

• The abiotic components are non-living components. They are air, water, solar radiation, temperature etc.

• The biotic components are

• Producers- synthesis there own food. Photoautotroph and chemoautotroph.

• Consumers – pri consumer (herbivores), sec consumer (pri.Carnivores), tertiary consumer (sec.Carnivores) etc.

• Decomposers. Bacteria and fungi.

• The major function of ecosystem are,

• Productivity.

• Decomposition.

• Energy flow.

• Nutrient cycling.

• 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 (g-2) or energy (kcal m – 2).• 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.• NPP-Net Primary Productivity. • R- respiration loss.

GPP – R = NPP• GPP is not equal to NPP bcoz, considerable amount of GPP is

utilized by plants in respiration

• Secondary productivity• It is the rate of formation of new organic matter by

consumers in a given period of time.

• 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 fecas is called detritus.

• DETRITIVORES: Animals that feed on decaying organic matter (detritus). Examples: earthworms, termites, snails etc.

• Steps of Decomposition:

• 1. Fragmentation of Detritus: It is the process of breakdown of detritus into smaller particles. It is done by detritivores.

• 2. Leaching: Soluble inorganic nutrients dissolve in water and goes down to soil, get precipitated is called leaching.

• 3. Catabolism: Decomposers (bacteria, fungi) release enzymes to decompose detritus into simpler inorganic compounds.

• 4. Humification: Simplified detritus converted to humusa) Humus is a Dark, Amorphous substance.b) Highly resistant to Microbial Action. c) Undergoes Decomposition very Slowly.d) Reservoir of nutrients (due to colloidal nature).• 5. Mineralisation: Humus is degraded to releases inorganic

substances ( CO2, H2O etc) and nutrients (Ca2+, Mg2+,K + etc).

• 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.

• 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

• Eg. Grass ------- Goat -----------man.

• Detritus food chain (DFC):

• The food chain that begins with dead organic matter is called detritus food chain (DFC).

• Dead leaf -------earthworm ------ Bird.

• Saprophytes: These are decomposers (fungi, bacteria) which feed on detritus.

• Trophic level:- Each Step of the food chain is called trophiclevel.

• 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.

• Food web:

• The natural interconnection of food chains forms a web called food web.

• Energy flow: • Sun is the only source of energy for all ecosystem.• Plants capture only 2 to 10% of photosynthetically

active radiation(PAR) for photosynthesis.• Energy is transferred in ecosystem in the form of food. • "Flow of energy is unidirectional but nutrient flow is in

a cycle"• Energy flow is always from the sun to 'producers' and

to the different trophic levels. so it is unidirectional. But the nutrients are moving from the living to non-living and vice-versa.

• Major energy is used for metabolic activity. Only less amount of energy is stored as biomass.

• Lindeman’s 10% law:• Only 10 per cent of the energy is transferred to each

trophic level from lower trophic levels is called 10% law

• Ecological pyramid:- graphical representation of energy, biomass or number of different organisms in an ecosystem is in the form of pyramid is called ecological pyramid .

• characteristic 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.

• Inverted pyramid:

1. The pyramid of number in a tree ecosystem is inverted.

2. 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.

• Ecological succession:- The gradual and predictable change in the species composition of a given area.

• Primary Succession: A Succession that starts where no living organisms are there.

• Secondary succession : A Succession that starts in areas which have lost all the living organisms that existed there.

• Hydrarch succession:- That takes place in wetter areas.

• Xerarch succession:- That takes place in dry areas.

• Pioneer species:- The species that invade a bare area. Ex: lichines, phytoplankton,

• primary succession on rocks are lichens which are able to secrete acids to dissolve rock, helping in weathering and soil formation.

• Nutrient cycling/ biogeochemical cycling:-Movement of nutrient elements through the various components of an ecosystem as between biotic and non-biotic components.

• Gaseous cycle:- Cycle which have its reservoir of the nutrient in atmosphere.

• Ex: Carbon cycle, Nitrogen cycle.

• Sedimentary cycle:- Cycle which have its reservoir of the nutrient is earth crust.

• Ex: Phosphorus cycle, Sulphur cycle.

• Carbon cycle:

1. Carbon constitutes 49 % of dry weight of organism.

2. 0.003% of CO2 is present in atmosphere.

3. Carbon is fixed in the biosphere through photosynthesis.

4. Carbon returns to the atmosphere as CO2 through respiratory activities of the producers and consumers.

5. Decomposers also contribute Some amount of CO2 from dead organic matter

6. Burning of wood, forest fire , combustion of organic matter, fossil fuel, and volcanic activity are additional sources for releasing CO2 in the atmosphere.

Phosphorus cycle:

1. Phosphorus is a major constituent of organism.

2. It found in nucleic acids and cellular energy transfer systems (ATP).

3. Many animals also need large quantities of this element to make shells, bones and teeth.

4. The natural reservoir of phosphorus is rock. In which it contains in the form of phosphates.

5. When rocks are weathered, minute amounts of phosphates dissolve in soil solution and are absorbed by the roots of the plants.

6. Herbivores and other animals obtain this element from plants.

7. The waste products and the dead organisms are decomposed by phosphate-solubilising bacteria releasing phosphorus.

• ecosystem 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.