- Organisms and physical surroundings interact with each other and maintain a balance in nature.
- All the interacting organisms in an area together with the non-living constituents form an ecosystem.
- Biotic components: Include all living organisms.
- Abiotic components: Include physical factors like temperature, rainfall, wind, soil and minerals.
- Natural ecosystems: Forests, ponds, lakes etc.
- Humanmade (artificial) ecosystems: Gardens, crop-fields, aquarium etc.
- Aquarium is a self-sustaining system because it includes biotic factors (fishes, aquatic plants, animals, etc.) and abiotic factors (free space, water, oxygen & food).
- Organisms can be grouped as producers, consumers and decomposers.
- Producers: They make food from inorganic compounds. E.g. Green plants and some bacteria.
Green plants make organic compounds (sugar & starch) from inorganic substances using the solar radiant energy in presence of chlorophyll. It is called photosynthesis.
- Consumers: Organisms that directly or indirectly depend on the producers for food. They consume the food from producers or by feeding on other consumers.
Types of Consumers:
o Herbivores: E.g. Grasshopper, Rabbits, Deer etc.
o Carnivores: E.g. Frog, Tiger, lion etc.
o Omnivores: E.g. Human, bears, birds, dogs etc.
o Parasites: E.g. Roundworms, tapeworms, leech etc.
- Decomposers: They break-down dead remains & waste products of organisms (complex organic substances) into simple inorganic substances. Inorganic substances go into the soil and are used up by the plants.
- If the aquarium is not cleaned, fishes and plants will be died. The microorganisms (bacteria & fungi) break-down the dead remains and waste products of organisms.
- If decomposers are absent, the garbage, dead animals and plants will not decompose. It leads to accumulation of organic materials thereby causes pollution.
- A food chain is the series of organisms feeding on one another or organisms taking part at various biotic levels.
- Each step or level of the food chain forms a trophic level.
o Autotrophs (producers): First trophic level.
o Herbivores (primary consumers): 2nd trophic level.
o Small carnivores (secondary consumers): Third trophic level.
o Larger carnivores (tertiary consumers): Fourth trophic level.
- Autotrophs capture solar energy and convert into chemical energy.
- From autotrophs, energy goes to heterotrophs and decomposers.
- The study of flow of energy reveals that
o Green plants in a terrestrial ecosystem capture about 1% of the solar energy that falls on their leaves and convert it into food energy.
o Food chains generally consist of only 3 or 4 steps since so little energy is available for the next trophic level.
o There are generally so many individuals at the lower trophic levels. Producers are in greatest number.
o Each organism is generally eaten by two or more kinds of organisms which in turn are eaten by several other organisms. This series of branching relationship of food chains is called a food web.
- Energy flow diagram shows the following features:
1. Energy flow is unidirectional. It does not revert back from autotroph to the Sun or consumer to autotroph.
2. Energy available at each trophic level gets diminished progressively due to loss of energy at each level.
- Some harmful chemicals may enter the bodies through the food chain. E.g. Pesticides and other chemicals are washed down into the soil or water. From the soil, plants absorb them. From the water bodies, aquatic plants & animals take up them. Thus they enter the food chain.
- The non-degradable chemicals get accumulated at each trophic level. This is called biological magnification. Thus cereals, vegetables, fruits & meat contain pesticide residues. Their concentration is maximum in human body because humans occupy the top level in any food chain.
- Methods to reduce intake of pesticides:
o Minimise the use of chemical pesticides.
o Wash fruits & vegetables thoroughly before use.
o Use organic fruits and vegetables.