Class 10 Science Chapter 13 Important Questions

(i) Biotic components: Plants and animals.
(ii) Abiotic components: Air, water, soil, etc.

Biodegradable: 1. They can be broken into simplest form by biological processes.
2. They do not produce more pollution.
3. They remain for less time in environment.
Non-biodegradable: 1. They cannot be broken by biological processes.
2. They produce more pollution.
3. They remain for a long time in the environment.
Effect of biodegradable substance: (i) They release harmful gases like Methane.
(ii) They release foul smell.
Effect of non-biodegradable substances: (i) They are very harmful for the various members of the ecosystem.
(ii) They cause more pollution of air, water and soil.

Spoilt food, vegetable peels, plastic, PUC used tea leaves, milk packets, empty cartons, used clothes, empty medicine bottles, bubble packs, broken footwear, etc.

The various links in the food chain called are called trophic levels. They are the food habits of organism.

The plant trap 1% of solar energy and only 10% energy of the available energy is transferred from one trophic level to the next trophic level. This is called 10% law of energy transferred.

An aquarium comprises green aquatic plants, fish and other aquatic animals. These biotic factors for the community. Water, sand, temperature, light, etc., are the abiotic factors. There is a constant ecosystem exchange of material between living and non-living components. Aquatic green plant is the producer of the aquarium. Animals are the consumers. The green plant gives out oxygen which taken up by the animals. Gives out carbon dioxide which plants utilise in photosynthesis. Animal excrete decomposed by the decomposer and the simple compounds produced are taken up by the plants. Thus an aquarium is self-perpetuating functional unit. Therefore, it is known as eco-system. An aquarium is a manmade ecosystem, so it is known as artificial eco-system.

(a) All the interacting organism in an area together with the non-living components of the environment form an ecosystem.
Main component is (i) Biotic components (ii) Abiotic components.
(b) An aquarium does not have adequate variety of decomposers, like ponds and lakes, for wastes, to decompose completely. So it has to be cleaned once a while. Moreover, due to increase in nutrients there is enormous growth of algae which makes aquarium water turbid and deficient of oxygen.

A producer is always a green plant. It synthesis its own its own food by trapping light energy. A consumer is an animal or a non-green plant which cannot synthesise its own food. A consumer directly or indirectly obtains its food from producer.

The organic dead remains and waste would pile up and the nutrition would not be recycled that’s why complex compound would not break to form simplest compound that can be taken up from the soil by the plant for their use. Natural replacement of the soil would not take place. All the nutrition cycles have decomposers as their components. In their absence these nutrient cycles would not be completed. There will be no recycling of matter between biotic and abiotic components of an ecosystem, because all the matter will remain locked up in the dead bodies. Thus existence of life on this earth will become impossible.

A natural eco-system is a balanced system because it consists of producer, herbivores, carnivores and decomposers. Organisms of an eco-system are well adjusted with the biotic component. In natural eco-system there is provision of constant flow of energy through food chains and recycling of the nutrient through decomposers. Thus a natural eco-system is self-sufficient system.
The removal of phytoplankton from a pond eco-system will stop constant flow of energy disturbing the whole food web in the pond. First larvae and small fishes will die in want of food and ultimately fishes which feed on them will die.

It is not possible that the food chain has more than six tropic levels. This is because of loss of 90% energy at each tropic level and only 10% energy is available at each successive level. In a food chain having more than six steps energy available to the top carnivore will not be sufficient for his survival.

It is not possible that the food chain has more than six tropic levels. This is because of loss of 90% energy at each tropic level and only 10% energy is available at each successive level. In a food chain having more than six steps energy available to the top carnivore will not be sufficient for his survival.

When any harmful chemical like DDT, BHC enters in a food chain the concentration of chemical increases as the trophic level is increased. This phenomenon is called biological magnification.
These Chemicals get accumulated occupy the top trophic level so there is maximum at top trophic level. The tertiary consumers occupy the top trophic level so there is maximum concentration of the harmful chemicals and they are affected badly.

There is layer of ozone gas in the stratosphere. Ozone at higher level of the atmosphere in a product of UV radiation acting on oxygen molecules. The higher energy UV radiation split apart some molecular O2 into free oxygen O atoms. These atoms then combine with O2 to form O3. Ozone layer protects us from sun’ s harmful UV radiation by cutting them off.

Due to the depletion of stratospheric ozone a seasonal hole in the ozone layer at polar regions is formed due to the vortex in the atmosphere. This is known as the ozone hole. Areas of human habitation under this hole are more vulnerable to the effect at UV rays from the sun.
Depletion of the ozone layer could cause:
(i) Temperature changes and rainfall failures on earth.
(ii) Cancer in human beings, especially skin cancer, eye cancer, or cataracts.
(iii) Destruction of aquatic life and vegetation.
(iv) Loss of immunity humans.
(v) Destruction of microbes, even useful bacteria which are very useful for us.

CFCs
(ii) Free chlorine
(iii) Aerosols
(iv) Nitrogen Monoxide

Chlorofluorocarbon compounds.

CFCs are very harmful to ozone layer and cause depletion of ozone layer. Which allow harmful UV rays to enter in the earth atmosphere.

Ozone depletion allows more UV radiations from the sun to reach us. This may directly harm our health:
(i) Cancer in human being especially skin cancer, eye cancer.
(ii) Weakening of our immune system, due to which we can fall prey to many diseases.

(i) Paper of paper bags can be recycled. During recycling it does not produce poisonous gases like plastic bags.
(ii) Paper bags are biodegradable and do not pollute the environment like non-biodegradable plastic bags.

(i) They are biodegradable and do not produce harmful gases on recycling.
(ii) They do not pollute environment on disposal.

Harmful effects: (i) Polythene bags when buried, soil render that area barren and leads to soil pollution.
(ii) Plastic bags often book drains leading to overflow of drains causing foul smell and source of spread of diseases.
(iii) On burning they release toxic gases that cause pollution.
Alternative to plastic bags: You can use cloth, jute and paper bags to carry your purchased items.

(i) Non-biodegradable are inert and simply persist in the environment for a long time.
(ii) They may harm the various members of the ecosystem.
(iii) The vital elements trapped in them are not released back to environment in the natural ways for recycling.
Safe disposal:
(i) Some of the non-biodegradable substance can be used for land refill.
(ii) Some of the non-biodegradable substance can be recycled for example broken glass bottle, cans, others metal items.

Excessive use of fossil fuel, even when we have to go nearby we use car, motor cycle, etc. instead going on foot or by cycle. Fossil fuels, on burning produce oxides of carbon, nitrogen and sulphur which cause air pollution.

Paper is bio-degradable while plastic is not. Further, plastic may have certain materials which can mingle with hot tea/coffee and cause harm to the body.

(i) We can as a first step use only those materials which come packed in biodegradable packs such as paper, coir, jute, etc.
(ii) We can separate the waste general into recyclable and non-recycled parts.
(iii) We may reduce our use of certain products which are not so essential for our life.
(iv) We may recycle plastic, paper, glass and metal item.
(v) We can reuse certain things like paper, plastic and glass bottle.

Cause of depletion of ozone layer:
(i) use of chlorofluorocarbon compounds.
(ii) use of aerosol refrigerants.
Harmful effects of depletion of ozone layer:
(i) UV rays reach the earth which cause skin cancer and sun burn.
(ii) It causes various global disorders including killing of even useful microbes.

The demand of energy as increased it has led to utilization of non-renewable resources of energy at a faster rate. Due to which an imbalance is created in our environment. It also led to pollution at a large scale.

They decomposes dead remains of plants and animals and their waste organic products into simple inorganic substance which are released into the atmosphere for reuse by the plants. Thus they help in recycling of materials.

Some substances are biodegradable because there are specific enzymes that can digest them while non-biodegradable substance cannot be broken down by any enzymes. They are acted upon by physical processes like heat and pressure.

Two ways in which biodegradable substance would affect the environment are:
(a) Increased quantities of these substance would increase the growth/number of decomposers.
(b) It would result in release of trapped organic molecule/nutrients into the environment, thus enriching the soil.

Two ways in which non-biodegradable substance would affect would affect the environment are:
(a) Would result in accumulation of garbage around in our environment.
(b) Would result in biological magnification that’s why accumulation of more chemicals in organism as we go higher up in the food chain.

If we kill all the organisms in our tropic level the number of individual in the next tropic levels. The next tropic level will decrease due to non-availability of food. Also the number of individual in the previous tropic level will increase because there is no one to feed on them. This will cause imbalance in the environment.

Yes, the impact of removing all the organism of a trophic level will be different for different trophic levels. The effect will be time related. If we remove all the producer, primary consumers will be affected instantly. Secondary consumers will be affected after a gap and tertiary consumers after a long gap. Organisms of any trophic level cannot be removed without causing any damage to the ecosystem.

The phenomenon of progressive increase in concentration of certain harmful non-biodegradable chemicals such as DDT at different levels of food chain is called biological magnification. The concentration of harmful chemicals will be different at different trophic levels. It will be lowest in the first trophic level and highest in the last trophic level of the food chain. This is because as we move higher up in the food chain, the non-biodegradable chemicals, which may have entered the food chain at any level will go on accumulating.

(i) Non-biodegradable pesticides and fertilisers run off with rain water to water bodies cause water pollution and affect the soil by making it either acidic or alkaline.
(ii) Some of the non-biodegradable pesticides like DDT enter the food chain and cause bio magnification in humans and other animals.

It will have only short term impact on environment. The action of decomposers will slow down and some air/water pollution will be caused. However, in longer term there will be no impact of biodegradable waste on the environment.

Ozone layer stops ultraviolet radiations from the sun from reaching the earth. Ultraviolet rays cause cancer, cataract and damage to the immune system of human beings. In 1987, United Nation Environment Programme succeeded in foreign an agreement between nations to freeze chlorofluorocarbon production to 1986 levels, CFCs are the main cause of ozone layer depletion.

Vegetarian food habits involve two step food chains. The two chains are:
(i) Producer plants
(ii) Herbivorous animals
Energy flows according to ten per cent law from one trophic level to the next trophic level. So vegetarians get much more energy than non-vegetarians. More energy in the produce plants can feed large number of people. Thus vegetarian food habits can sustain a larger number of people.

Food chain is the sequence of different organism through which energy in the form of food is transmitted in different trophic levels.
The study of food chains helps us to understand
(i) the energy transfers through organism.
(ii) ecological balance in a habitat.
(iii) harmful human activities and disruption in ecological balance.
An example of food chain in a lake:
Phytoplankton → Zooplankton → Small fish → Large fish