Plus Two Botany Notes Chapter 7 Ecosystem is part of Plus Two Botany Notes. Here we have given Plus Two Botany Notes Chapter 7 Ecosystem.
|Text Book||NCERT Based|
|Category||Plus Two Kerala|
Kerala Plus Two Botany Notes Chapter 7 Ecosystem
Simplified Detailed Notes
It is a functional unit of nature, an association of organisms and their physical environment, interconnected by a continuous flow of energy and a cycling of nutrients. Ecosystem can be divided into two:
1. Terrestrial ecosystem: Forest, grassland and desert are some examples of terrestrial ecosystems.
2. Aquatic ecosystem: Pond, lake, wetland, river and estuary are some examples of aquatic ecosystems.
- Crop fields and an aquarium may also be considered as man-made ecosystems.
Structure and Functions of Ecosystem
1. Structure Interaction: Structure Interaction of biotic and abiotic components results in a physical structure that is characteristics for each type of ecosystem.
- Biotic component: It consists of producers, consumers, decomposers and detritivores.
- Abiotic components: It consists the physical environment.
2. Species Composition: It is determined by the plant and animal species occupying an ecosystem.
3. Stratification: It is the vertical distribution of different species occupying different levels in an ecosystem.
eg., trees occupy top vertical strata or layer of a forest, shrubs the second, herbs and grasses occupy the bottom layers.
Components of Ecosystem
It is the rate of biomass production per unit area over a time period. It is expressed as g-2 j yr1 or (kcal nr2) yr’1. It can be two types:
i. Primary Productivity: It is the amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis. It has two aspects:
- Gross Primary Productivity (GPP): The rate of total capture of light energy, or the rate of total production of biomass.
- Net primary productivity (NFP): The balance energy or biomass remaining after meeting the cost of respiration of producers. Net primary productivity is the available biomass for the consumption to heterotrophs (herbiviores and decomposers).
Net productivity = Gross productivity -respiration loss
Factors affect Primary productivity are:
- the plant species inhabiting a particular area.
- It also depends on a variety of environmental factors availability of nutrients and photosynthetic capacity of plants.
ii. Secondary Productivity: It is defined as the rate of formation of new organic matter by consumers.
It is the process of breaking down of complex organic matter into inorganic substances like water, carbon dioxide, nutrients etc.
Dead plant remains such as leaves, bark, flowers and dead remains of animals, including fecal matter, constitute detritus, which is the raw material for decomposition. Different steps in decomposition are:
- Fragmentation: Detritivores (eg.earthworm) break down detritus into smaller particles. This process is called fragmentation.
- Leaching: By the process of leaching, water-soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts.
- Catabolism: Bacterial and fungal enzymes degrade detritus into simpler inorganic substances. This process is called as catabolism.
- Humification: It’is the process by which simplified detritus is changed into dark coloured amorphous substance called humus.
- Mineralisation: It involves the release of inorganic substances (water, C02) and other nutrients.
Decomposition is largely an oxygen-requiring process. The rate of decomposition is controlled by chemical composition of detritus and climatic factors. In a particular climatic condition, decomposition rate is slower. Temperature and soil moisture are the most important climatic factors that regulate decomposition.
3. Energy Flow
- Sun is the only source, of energy for all ecosystems. Out of the incident solar radiation, less than 50% of it is Photosynthetically Active Radiation (PAR).
- Plants and autotrophs use sun radiation to produce food. So these are producers in ecosystem. Primary producers in an aquatic ecosystem are various species like phytoplankton, algae and higher plants.
- All animals depend on plants (directly or indirectly) for their food needs. They are hence called consumers and also heterotrophs. They are two types:
- Primary consumers: If the animals feed on the producers, the plants, they are called primary consumers. Primary consumers will be herbivores.
- Secondary consumers: If the animals eat other animals which in turn eat the plants (or their produce) they are called secondary consumers.
The consumers that feed on these herbivores are carnivores, or more correctly primary carnivores (though secondary consumers). Those animals that depend on the primary carnivores for food are labelled secondary carnivores.
A straight line sequence of ‘who eats whom’ in an ecosystem is called food Chain. There are two types of food chains.
a. Grazing Food Chain (GFC): In which energy flows from plants to herbovores and then through carnivores.
eg., Grass -> Goat -> Man
b. Detrital Food Chain (DFC): In which energy flows from photosynthetic organisms through detrivores and decomposers.
eg., Dead leaves -> Wood louse ->Black bird
Organisms occupy a place in the natural surroundings or in a community according to their feeding relationship with other organisms. Based on the source of their nutrition or food, organisms occupy a specific place in the food chain that is known as their trophic level. Producers belong to the first trophic level, herbivores (primary consumer) to the second and carnivores (secondary consumer) to the third.
According to which the number of trophic levels in the grazing food chain is restricted, as the transfer of energy follows 10% law. That is 10% energy is transferred to each trophic level from the lower trophic level.
Standing crop: Each trophic level has a certain mass of living material at a particular time called as the standing crop. The standing crop is measured as the mass of living organisms (biomass) or the number in a unit area. The biomass of a species is expressed in terms of fresh or dry weight.
Ecological pyramids are the diagrammatic ilustration of connection between different trophic levels in terms of energy, biomass and number of an organism.
The base of each pyramid represents the producers or the first trophic level, while the apex represents tertiary or top level consumer.
The three types of ecological pyramids are:
1. Pyramid of number: It shows relationship between producers and consumers in an ecosystem in terms of numbers.
2. Pyramid of biomass: It shows relationship between producers and consumers in an ecosystem terms of biomass. It can be:
- Upright-eg.in case of grassland ecosystem.
- Inverted-eg.in case of pond ecosystem.
3. Pyramid of energy: It shows relationship between producers and consumers in an ecosystem in terms of flow of energy. It is always upright because energy is always lost as heat at each step.
Climax Community: The changes lead finally to a community that is near equilibrium with the environment is called climax community.
The gradual and fairly predictable change in the species composition of a given area is called ecological succession. During succession some species colonise an area and their populations become more numerous, whereas populations of other species decline and even disappear.
Ecological succession can be of two types:
- Primary succession: It begins in an area where no living organisms were existed before the establishment of new biotic community. It is a slow process.
- Secondary succession: It begins in an area where natural biotic communities have been already destroyed,
eg., burned or cut forests, lands that have been flooded etc.It is a faster process when compared to the primary one. Due to this, the climax community also reached more quickly.
Succession of Plants
Based on nature of habitat, plant succession is of two types:
- Hydrarch succession: It takes place in wetter areas and is the successional series progress from hydric to the mesic conditions (neither too dry nor too wet).
- Xerarch succession: It takes place in dry areas and is the series progress from xeric to mesic conditions.
Primary Succession on rocks:
- Pioneer species are the first ones to in vade a bare area, i.e., on rocks.
- These are usually lichens which secrete acids to dissolve rock, helping in weathering and soil formation.
- This paves way for some very small plants like bryophytes, which are able to grow in the small amount of soil.
- Over the time, they are succeeded by bigger plants and after several more stages, ultimately a stable climax forest community is formed.
- The climax community remains stable if the environment remains unchanged.
- With time, the xerophytic habitat gets converted into a mesophytic one.
Primary Succession on Water:
- The pioneers are the small phytoplanktons.
- They are replaced with time by free-floating angiosperms, then by rooted hydrophytes, sedges grasses and finally the trees.
- The climax again would be a forest.
- Lastly the water body is converted into land.
4. Nutrient Cycling
The movement of nutrient elements through the various components of an ecosystem is called nutrient cycling or biogeochemical cycles.
The amount of nutrients, such as carbon, nitrogen, phosphorus, calcium, etc., present in the soil at any given time, is referred to as the standing state.
Nutrient cycles are two types:
- gaseous – exist in the atmosphere
(eg; nitrogen, carbon cycles).
- sedimentary– exist in the Earth’s crust
(eg;sulphur, phosphorus cycles).
Carbon Cycle: It occurs through atmosphere, ocean and through living and dead organisms. A large amount of carbon returns to the atmosphere as C02 through:
- Respiratory activities of the producers and consumers.
- Breakdown activities of decomposers.
- Forest fire and combustion of organic matter.
- Volcanic activity.
- Rapid deforestation.
- Burning of wood and fossil fuel.
Phosphorus Cycle: Phosphorus is a major constituent of biological membranes, nucleic acids, cellular energy transfer systems (ATP) and also of shells, bones and teeth.
- The natural reservoir of phosphorus is rock, which contains phosphorus in the form of phosphates.
- When rocks are weathered, minute amount of these 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.
The products of ecosystem processes are termed as ecosystem services.
Forests are the major sources of ecological services. These are useful in following ways:
- Purification of air and water.
- Preventing droughts and floods.
- Cycling nutrients.
- Generating fertile soils.
- Providing wildlife habitat.
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