Class 12th Important notes of chapter -14 Ecosystem for NEET/Board .

                       Ecosystem

• A.G.Tansley – The term "ecosystem" first of all coined by A.G. Tansley.            
• According to Tansley – Ecosystem is symbol of function and structure of environment.
•   E.P. Odum – Father of ecosystem ecology.                                                              
•   Ecosystem is the basic unit of ecology.

Definition – All organism of an area interect with their physical environment and forming a working system called ecosystem.

Note :

•  The boundaries of ecosystem are indistinct and have a overlapping character over each other.
• Ecosystem is the smallest structural and functional unit of nature or environment. It is a self regulatory and self sustaining unit.
• Ecosystem may be large or small. 
•  Ecosystem may be temporary or permanent.

              TYPE OF ECOSYSTEM

 (1) Natural Ecosystem –

(a) Terrestrial Ecosystem – e.g. forest, grassland, tree, desert ecosystem

(b) Aquatic ecosystem – Aquatic ecosystem is again of two type :

(i) Lentic ecosystem —> Stagnant water e.g. lake, pond, swamp.

 (ii) Lotic – Running fresh water ecosystem e.g. - river.

(2) Artificial ecosystem – Man made e.g. cropland, Gardens etc.

Based on size, types of ecosystem

(i) Mega ecosystem – Ocean/Sea

(ii) Macroecosystem – Forest

(iii) Microecosystem – Pond

(iv) Nanoecosystem – Drop of water

 

        

           COMPONENTS OF ECOSYSTEM

 ecosystem have two ecosystem -

(A) Biotic component (B) Abiotic component

              (A) Biotic components

1. Producers –

All the autotrophs of ecosystem are called producers. They prepare their own food.                            The green plants are the main producers. In photosynthesis light energy from sun is converted to chemical energy or carbohydrates by producers.                                                   Energy enters into the ecosystem through the producers. The sun is the ultimate source of light energy . 

• In aquatic ecosystem : Floating plants called phytoplankton are the major autotrophs.

2. Consumers -  all animals which depend on producrs for food.  They directly orr indirectly depend on producers. 

Types of consumer

(i) Macroconsumers (ii) Microconsumers

(i) Macro consumers (Phagotrophs or holozoic) –                                                                                  They digest their food inside the body i.e. first ingestion then digestion.

Macro consumers are of following types:

(a) Primary consumer – the living organisms which gain their food directly from producers or plants are known as primary consumers.                                                            e.g. herbivores of ecosystem, cow, grazing cattle, Rabbit etc. 

• These are also known as secondary producers .

(b) Secondary consumers or primary cornivores – Animals which depend upon  primary consumers for obtaining food. Those carnivores which kill and eat the herbivores.

e.g. Dog, cat, snake etc.

(c) Top Consumers – The animals which eat another animal which in turn eat producer's or plants are called top consumers .

e.g. Lion, man, hawk, peacock etc.

(ii) Micro Consumers/Decomposers or Saprotrophs/osmotrophs –

Those living organisms which decompose the dead body of producers and consumers are known as decomposers or reducers or transformers or osmotrophs.

Note –

• The main decomposers in ecosystem are bacteria and fungi.
• Decomposers play a significant role in mineral cycle. Decomposers are responsible

For detritus food chain. 

• In Bacteria and fungi, process of decomposition completely takes place outside the body.

Functional aspects of ecosystem :-

(i) Energy flow

(ii) Nutrient cycling

(iii) Productivity

(iv) Decomposition

                     Food Chain 

   TYPE OF FOOD CHAINS :  3 types -

1. Grazing food chains or Predatory food chain – Most common type of food chain present in nature . This food chain start  with plants (producers) and in successive order it goes to tertiary consumers.

2. Parasitic food chain – This food chain also starts from plants or producers but in next  order it goes from big organism to the smaller organism.   e.g.

Tree ecosystem –

Tree  –>  Birds  —> Parasites 

  |               |                   |

T1               T2                T3

Note : Both above food chains are directly dependent on Sun energy or  radiation (as a primary source of energy) and have rapid energy flow.

3. Detritus food chain or Saprophytic food chain – This food chain begins with dead organic matter. It is made up of decomposers. In this food chain primary consumers are bacteria and fungi.

Dead organic matter —> bacteria, fungi

Note :

• In detritus food chain energy flow is rather very slow yet magnitude of energy is great.
• In mangrove vegetation this food chain goes up to big organism.

Dead mangroves leaves  —> Bacteria & fungi —> Amphipds, molluscs, crabs, nematodes  —> small fishes  —> Tiger.

• In an aquatic ecosystem, GFC (Grazing Food Chain) is the major conduit (source) of energy flow. As against this, in a terrestrial ecosystem, a much larger energy flow through the (DFC) Detritus food chain than through the grazing food chain.
• In Sunderbans, Tigers feed on the fishes and crab in the absence of their natural prey.
  
  

                       Special points 

• Nutrient Immobilisation- In the process of decomposition, some nutrients get tied up with the biomass of some  microbes become temporarily unavailable to other organisms. Such incorporation of nutrient in living microbes (bacteria & fungi) is called nutrient immobilisation.
• In aquatic system whale is secondary consumer. This  is an example of filter feeder because it feeds on Phyto plankton.
•  Plant parasites are known as primary consumers while animals parasites (E.coli bacteria, Entamoeba, hook worm , liver fluke, tapeworm) are known as secondary consumers.
• Man, peacock, cockroach and crow are omnivores.
• Organisms which use milk or curd as food, are known as secondary consumer.

Note : Inorganic materials (CO2, H2O, Light), autotrophs (Producers) and decomposers  all are essential in ecosystem but, macro consumers are non essential.

                         FOOD WEB

In big ecosystem many food chains are interrelated and interdependent and form a food web.

              GOLDEN KEY POINTS

1. The boundaries of ecosystem are indistinct and have a overlapping character over each other.

2. Natural ecosystem show high stability as compare to artificial ecosystem due to high species diversity.

3. During photosynthesis primary producers absorb solar energy and convert it into chemical energy so producers

are also called transducer or converters.

4. Decomposers play a significant role in mineral cycle so that presence of decomposers is essential for stability

or existence of ecosysystem.

5. There are two basic function of ecosystem (i) Energy flow (ii) Nutrient cycling

6. Ecosystem are not exempt from the second law of thermodynamics.

7. Tertiary consumer is present in between the secondary consumer and top consumer.

8. Generally the decomposers (Bacteria/Fungi) are not included in the food chain but when included then included

as the last trophic level.

9. Pyramid of number shows biotic potential of a ecosystem. Pyramid of biomass show the standing crop of ecosystem. Pyramid of energy represent the productivity of ecosystem.

10. Net primary productivity (NPP) is the available biomass for the consumption to heterotrophs.

BIO-GEO CHEMICAL CYCLE OR NUTRIENT CYCLE

   Bio – Living organism

   Geo – Rock, Soil, Air, Water

   Chemical – Material or Nutrients

1. Carbon Cycle – PathMain reservoir of carbon are atmosphere, Ocean, Carbonate, Rocks, Coal and Petrolium.                  The carbon released from them is present in the atmosphere in the form of Co2 again . Carbon is present in every organic component of organism. The green autotrophs utilize CO2 from the atmosphere directly to synthesise organic food material,  which is obtained by other organisms as food. Carnivores  gain  their carbonic food from the herbivores ( primary consumers). 

•   These carbonic matter (food)  produce CO2 through the oxidation and respiration which dissolve in air or water and again utilized by the plants.

•  If we look at the total quantity of global carbon, we find that 71 per cent carbon is found dissolved in oceans. 
•  Carbon cycling occurs through atmosphere, ocean and through living and dead organisms.
• According to one estimate 4 × 1013 kg of carbon is fixed in the biosphere through photosynthesis annually.   

          2. PHOSPHORUS CYCLE

• Main source of phosphorus is rocks. It obtained from the weathering of rocks containing phosphorus  in the soil.
• Plants absorb this inorganic phosphrous from the soil and transfer this phosphate to animals and after the death of consumers it is released again into the lithosphere (upper layer of soil) by the action of decomposers. Phosphorus is the main constituent of protoplasm, plasma membrane, bones and teeth.

 Note :- 

Plants absorb phosphate from the soil in the form of orthophosphate (Po4

3–)

Note : Biosphere (space ship or earth) is a closed system for minerals and biosphere is an open system in regards with the energy.

               GOLDEN KEY POINTS

1. The reservoir function is to fulfill the deficit in biogeochemical cycle created by imbalance between Influx

and Efflux.

2. The formation of biome is mainly decided by two abiotic factor temperature and precipitation.

3. Upper soil of temperate deciduous forest is more fertile than tropical rain forest.

 

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