Ecology: Ecosystem, Food Chains, Biodiversity, Pollution and Conservation
Ecology is the branch of biology that studies the relationship between living organisms and their surroundings. It examines how organisms depend on one another, how energy and nutrients move through nature, and how human activities disturb this balance. In the present time, when climate change, deforestation, pollution and the loss of species are serious concerns, ecology has become one of the most relevant subjects in the general-science paper. For candidates preparing for APSC, ADRE, DHS, SSC, Railway and police examinations in Assam, questions are frequently asked on ecosystems, food chains, trophic levels, biodiversity, pollution and conservation.
This article offers a complete deep-study revision of ecology. It first explains the basic vocabulary, then takes up the structure and function of the ecosystem, food chains and food webs, the flow of energy, biogeochemical cycles, ecological pyramids, biodiversity and conservation, and environmental pollution. Finally, the examination trends, common mistakes and a practical preparation plan are discussed. Every definition is connected to a real example so that the concepts remain clear and useful.
Basic Terms
- Ecology: the study of the relationship between organisms and their environment.
- Environment: everything that surrounds an organism, both living and non-living.
- Habitat: the place where an organism lives.
- Population: all the individuals of the same species living in an area.
- Community: all the populations living together in an area.
- Ecosystem: a community of living organisms interacting with the non-living environment.
- Biome: a large natural region with a characteristic climate and vegetation.
- Biosphere: the part of the earth where life exists.
- Producer: an organism that makes its own food, usually a green plant.
- Consumer: an organism that depends on others for food.
- Decomposer: an organism that breaks down dead matter, such as bacteria and fungi.
- Food chain: the sequence in which energy passes from one organism to another.
- Biodiversity: the variety of life found in a particular area.
- Pollution: the addition of harmful substances to the environment.
Core Concepts and Formulas
- An ecosystem has two components: biotic (living) and abiotic (non-living).
- Energy flows in one direction, from the sun to producers and then to consumers.
- According to the ten per cent law, only about 10 per cent of the energy passes from one trophic level to the next.
- The number of trophic levels in a food chain is generally limited to four or five because of energy loss.
- Ecological pyramids are of three types: pyramid of number, pyramid of biomass and pyramid of energy.
- The major biogeochemical cycles are the carbon, nitrogen, oxygen and water cycles.
- The main greenhouse gases are carbon dioxide, methane, nitrous oxide and water vapour.
- Hotspots of biodiversity in India include the Western Ghats, the Eastern Himalayas, Indo-Burma and Sundaland.
The Ecosystem
An ecosystem is a self-regulating unit in which living organisms interact with one another and with their physical surroundings. It has two parts. The abiotic component includes sunlight, air, water, soil, temperature and minerals. The biotic component includes producers, consumers and decomposers. Producers are green plants and some bacteria that make food by photosynthesis. Consumers are herbivores, which eat plants, carnivores, which eat other animals, and omnivores, which eat both. Decomposers, such as bacteria and fungi, break down dead plants and animals and return the nutrients to the soil. Ecosystems may be natural, such as forests, ponds and oceans, or artificial, such as croplands and aquariums. A balanced ecosystem keeps a steady flow of energy and a continuous recycling of nutrients.
Food Chains and Food Webs
A food chain shows how energy passes from one organism to another. It begins with producers and ends with top carnivores. A simple example is grass, which is eaten by a grasshopper, which is eaten by a frog, which is eaten by a snake, which is eaten by a hawk. Each step in a food chain is called a trophic level. The first trophic level has the producers, the second has the herbivores or primary consumers, the third has the small carnivores or secondary consumers, and the fourth has the larger carnivores or tertiary consumers. In nature, food chains rarely exist alone; they are linked together into a food web. A food web makes the ecosystem more stable, because if one species becomes scarce, a predator can turn to another source of food.
Flow of Energy and Ecological Pyramids
The ultimate source of energy for every ecosystem is the sun. Green plants capture a small part of the solar energy and convert it into food during photosynthesis. When a herbivore eats a plant, only about ten per cent of the energy of the plant is transferred to the herbivore; the rest is lost as heat, used in respiration, or left in the undigested matter. This is called the ten per cent law, and because of this loss, food chains cannot be long and the number of trophic levels is limited. The transfer of energy between trophic levels can be shown graphically by ecological pyramids. The pyramid of number counts individuals, the pyramid of biomass measures the total mass, and the pyramid of energy shows the energy content at each level. The pyramid of energy is always upright, because energy decreases at every step.
Biogeochemical Cycles
Nutrients are not lost from the ecosystem; they move in cycles between living organisms and the environment. These cycles are called biogeochemical cycles. In the carbon cycle, carbon dioxide is fixed by plants during photosynthesis and returned to the atmosphere by respiration, the burning of fuels and the decomposition of dead matter. In the nitrogen cycle, nitrogen gas is fixed into usable compounds by nitrogen-fixing bacteria and lightning, is taken up by plants, passes to animals, and is finally returned to the soil and air by decomposers and denitrifying bacteria. The oxygen cycle, the water cycle and the phosphorus cycle are the other important cycles. These cycles keep the nutrients in balance and make life on earth possible.
Biodiversity and Conservation
Biodiversity is the variety of living organisms found on earth, and it is studied at three levels, genetic diversity, species diversity and ecosystem diversity. India is called a mega-diverse country because of its rich variety of plants and animals, and the Western Ghats, the Eastern Himalayas, Indo-Burma and Sundaland are its biodiversity hotspots. Biodiversity is important because it maintains the balance of ecosystems, provides food, medicine and raw materials, and keeps the climate stable. It is threatened by habitat destruction, deforestation, pollution, over-hunting, the spread of invasive species and climate change. Conservation may be in situ, that is, the protection of species in their natural habitat through national parks, sanctuaries and biosphere reserves, or ex situ, that is, the protection of species outside their habitat in zoos, botanical gardens and gene banks.
Environmental Pollution
Pollution is the addition of harmful substances to the environment. Air pollution is caused by the smoke of factories and vehicles, the burning of fossil fuels and fireworks, and it leads to diseases of the lungs and to acid rain. Water pollution is caused by domestic sewage, industrial waste, agricultural fertilisers and pesticides, and it spreads diseases and harms aquatic life. Soil pollution is caused by the careless use of chemicals and by non-biodegradable waste such as plastic. Noise pollution is caused by traffic, loudspeakers and machines and harms hearing and mental health. The accumulation of greenhouse gases causes global warming, which in turn leads to the melting of glaciers and a rise in the sea level. The hole in the ozone layer, caused mainly by chlorofluorocarbons, allows harmful ultraviolet rays to reach the earth.
Examination Trends
In competitive examinations, ecology questions usually test terms such as ecosystem, habitat and niche, the components of an ecosystem, the difference between a food chain and a food web, trophic levels and the ten per cent law, the types of ecological pyramids, the example and importance of each biogeochemical cycle, the levels and hotspots of biodiversity, and the causes and effects of different kinds of pollution. Objective questions frequently ask the ultimate source of energy, the first trophic level, the decomposers, the greenhouse gases, the gases responsible for the ozone hole, and the examples of in situ and ex situ conservation. A regular set of questions tests the national parks and biosphere reserves of India and Assam.
Common Mistakes to Avoid
- Do not confuse a food chain with a food web; a web is many interconnected chains.
- Remember that energy flows in one direction only and is never recycled, while nutrients are recycled.
- Do not say that the amount of energy increases at higher trophic levels; it always decreases.
- Do not interchange in situ and ex situ conservation.
- Distinguish between biodegradable and non-biodegradable pollutants before answering.
How to Prepare This Topic
Start with the definitions and fix one clear example for each term. Draw a simple food web and mark the trophic levels, and write the ten per cent law beside it. Prepare a chart of the carbon and nitrogen cycles, because these are asked again and again. Make a table of the types of pollution with their causes, effects and control measures. Learn the main greenhouse gases and the gases responsible for the ozone hole separately. Finally, memorise the important national parks, wildlife sanctuaries and biosphere reserves of India and Assam, and practise previous years' questions to become familiar with the exact style of the examination.
Frequently Asked Questions
What is an ecosystem and what are its components?
An ecosystem is a self-regulating unit in which living organisms interact with one another and with their non-living surroundings. It has two components: the abiotic component, such as sunlight, water, air, soil and temperature, and the biotic component, which includes producers, consumers and decomposers.
What is the ten per cent law in ecology?
The ten per cent law states that only about ten per cent of the energy available at one trophic level is transferred to the next trophic level. The remaining energy is lost mainly as heat, which is why food chains are short and the number of trophic levels is limited.
What is the difference between a food chain and a food web?
A food chain is a single straight sequence in which energy passes from producers to consumers. A food web is a network of several interconnected food chains. A food web makes the ecosystem more stable because a predator can switch to another prey if one becomes scarce.
What is biodiversity and why is it important?
Biodiversity is the variety of living organisms on earth, studied at the genetic, species and ecosystem levels. It is important because it maintains the balance of ecosystems, supplies food, medicine and raw materials, and helps keep the climate stable.
What is the difference between in situ and ex situ conservation?
In situ conservation protects species in their natural habitat, as in national parks, wildlife sanctuaries and biosphere reserves. Ex situ conservation protects species outside their natural habitat, as in zoos, botanical gardens and gene banks.