Our Environment Class 10 Notes

An ecosystem is a community of all the organisms living in a particular area, interacting with one another and with the non-living components of their surroundings. The word covers the living organisms, the physical surroundings and, importantly, the processes that link them, namely the flow of energy and the cycling of nutrients.The two components are named separately and are asked as a two-mark question. The biotic component consists of the living organisms and is divided into producers, consumers and decomposers, while the abiotic component consists of the non-living factors such as sunlight, water, soil, air, wind, temperature, humidity and the mineral salts in the soil.

• Ecosystem: a community of organisms interacting with one another and with the non-living components of their environment in a particular area.
• Biotic component: the living parts, namely producers, consumers and decomposers.
• Producers: autotrophic green plants and blue-green algae that make their own food by photosynthesis using sunlight.
• Consumers: animals that cannot make their own food, divided into primary, secondary and tertiary consumers.
• Abiotic component: sunlight, water, soil, air, wind, temperature, humidity and mineral salts.
• Examples of ecosystems: a pond, a forest, a grassland, a lake and a garden, and the two that are named most often are the pond and a forest ecosystem.

A food chain is a series of organisms feeding on one another in a definite order, in which the flow of energy is unidirectional and cannot return to the starting point. The first trophic level is occupied by the producers, the second by the herbivores or primary consumers, the third by the small carnivores or secondary consumers, and the fourth by the larger carnivores or tertiary consumers.In an ecosystem no organism eats only one kind of food, so several food chains are linked together into a food web. The position of an organism in a food chain is called its trophic level, and the number of trophic levels in a food chain is limited by the amount of energy still available at the top.

• Food chain: a sequence of organisms in which the food of one becomes the food of the next, with energy flowing in one direction only.
• Trophic level: the position of an organism in a food chain, such as the first level for producers and the second for herbivores.
• Grass, grasshopper, frog, snake and eagle form a five-level food chain that is used in almost every paper.
• A food web is formed when several food chains of the same ecosystem are interconnected, which happens because most organisms eat more than one thing.
• Decomposers such as bacteria and fungi break down the remains of organisms at every level and return the nutrients to the soil.
• Flow of energy in a food chain is unidirectional, since the energy lost as heat at one level is not available to the next level or returned to the previous one.

Energy enters an ecosystem as sunlight and passes from the producers to the consumers and then to the decomposers. At every single step a large part of the energy is used up by the organisms themselves in respiration, movement, digestion and maintenance, and is lost to the surroundings as heat.The 10% law states that only about ten per cent of the energy available at one trophic level is actually passed on to the next trophic level, the remaining ninety per cent being lost largely as heat during respiration. This is why the energy available keeps falling, why a food chain normally has no more than four or five levels, and why the number of individuals also falls at higher levels.

• About ten per cent of the energy at one trophic level is passed to the next, which is called the 10% law of energy flow.
• The remaining energy is used in respiration, movement, digestion and maintenance, and most of it is lost as heat.
• If one thousand joule reach the producers, about one hundred joule reach the primary consumers and about ten joule the secondary consumers.
• The energy flow in a food chain is unidirectional, since the lost energy is not returned to the earlier level.
• Because of this steady loss, food chains rarely have more than four or five trophic levels.
• The pyramid of energy is always upright, since the energy available at each level is less than at the level below it.

Human activity has altered the natural balance of the environment in a number of ways, and the chapter names these as a list of problems rather than deriving any of them. The greenhouse effect, air pollution, water pollution, soil erosion, depletion of the ozone layer and the loss of biodiversity are the ones asked.The greenhouse effect itself is natural, since gases such as carbon dioxide, methane and water vapour trap heat and keep the earth warm enough to support life. The problem is the enhancement of it by human activity, in which the burning of fossil fuels and the release of chlorofluorocarbons add so much of these gases that the earth's temperature rises, the ice melts, the sea level rises and the rainfall pattern changes.

• Greenhouse effect: heat-trapping gases such as carbon dioxide, methane and water vapour warm the earth's surface.
• Global warming: the enhanced greenhouse effect, caused mainly by the burning of fossil fuels, leading to a rise in temperature and a rise in sea level.
• Air pollution: smoke, dust and harmful gases from vehicles and factories cause respiratory diseases and damage plants and buildings.
• Water pollution: domestic sewage, industrial effluents and fertilisers run off into rivers and ponds, making the water unfit for use and reducing the oxygen available to aquatic life.
• Soil erosion: the removal of topsoil by wind, water or deforestation, which reduces the fertility of the land and leads to desertification.
• Biodiversity loss: the disappearance of species because of habitat destruction, over-hunting, pollution and the introduction of alien species.

The ozone layer is a blanket of ozone gas high in the atmosphere, in the stratosphere, and its function is to absorb the harmful ultraviolet radiation coming from the Sun. Without it the intensity of ultraviolet light reaching the earth's surface would be far greater than it is.The layer is being destroyed by chlorofluorocarbons, commonly called CFCs, which are used in refrigerators, fire extinguishers, foam and sprays. Ultraviolet radiation high in the atmosphere breaks down the CFC molecules and releases chlorine, and the chlorine then combines with and destroys ozone. The thinning over Antarctica is called the ozone hole, and the world has responded by banning CFCs, which were first suspended and then completely phased out.

• The ozone layer is in the stratosphere and absorbs the harmful ultraviolet radiation from the Sun.
• Chlorofluorocarbons, or CFCs, are the main cause of its depletion and were used in refrigerators, fire extinguishers, foams and sprays.
• Ultraviolet light breaks down the CFC molecules high in the atmosphere and releases chlorine.
• The chlorine freed in this way combines with ozone and destroys it, and the process continues for as long as the chlorine is present.
• The thinning of the ozone layer over Antarctica is called the ozone hole, which is the thickest over the poles.
• The effects are skin cancer and cataracts in human beings, damage to the crop plants, and the death of plankton and of fish that feed on them.

Domestic and industrial activity produces a great deal of solid waste every day, and the municipal solid waste of a city includes paper, plastic, glass, metal, vegetable matter, glassware and inert items such as broken glass and clay. If this is not managed it simply accumulates and pollutes the surroundings, so the problem is solved by preventing the waste, by reducing what is produced, and by treating what is left over.The three words to remember are reduce, reuse and recycle. Reducing means cutting the quantity of waste at source, reusing means using an article again instead of throwing it away, and recycling means processing a material to make a new product, which is the only way in which non-biodegradable substances can be dealt with. Composting vegetable and other biodegradable waste makes manure, while inert waste is disposed of in sanitary landfills.

• Reduce: cut the amount of waste produced, for example by avoiding unnecessary packaging and by using refillable containers.
• Reuse: use an article again, such as a cloth bag for shopping or a container for storing food.
• Recycle: process the material to make a new product, and this is the only way to deal with non-biodegradable waste.
• Composting: biodegradable waste such as vegetable peelings is turned into manure by decomposers in a compost pit.
• Landfilling: inert waste such as broken glass and clay is buried in sanitary landfills where it does not harm the surroundings.
• Segregation at source: separating biodegradable from non-biodegradable waste at home makes every later step easier and cheaper.

A substance is biodegradable if it can be broken down by the action of microorganisms such as bacteria and fungi into simpler harmless substances, and such a substance does not stay in the environment for long. Examples are vegetable peelings, fruit, paper, wood, cotton, jute, wool, leather and cow dung.A substance is non-biodegradable if there is no natural decomposer in the environment that can break it down, so it stays there for a very long time and accumulates. Examples are plastic, glass, metals such as aluminium and steel, cans, and DDT. Recycling is the only practical way of dealing with these, and the difficulty is that separating them from the mixed waste is expensive.

• Biodegradable: broken down by microorganisms into simpler harmless substances within a short time.
• Examples of biodegradable substances: vegetable peelings, fruit, paper, wood, cotton, jute, wool, leather and cow dung.
• Non-biodegradable: no decomposer in the environment can break them down, so they accumulate.
• Examples of non-biodegradable substances: plastic, glass, aluminium, steel, cans and DDT.
• Plastic is the most troublesome, since it persists for a very long time and bags block drains and suffocate animals.
• DDT sprayed against insects is non-biodegradable, so it passes up the food chain and is not broken down.