Science [2 Mark Questions]

Most of the solid waste in urban areas is dumped in low line areas of ground and covered with earth to level the uneven ground. This method is called landfill.

The micro-organisms which break down the complex organic compounds present in dead organisms like dead plants and animals and their products like faeces, urine, etc., into simpler substances are called decomposers.
Example: Bacteria and Fungi.

If the ozone layer in the atmosphere disappears completely, then all the extremely harmful ultraviolet radiations coming from the sun would reach the earth. These ultraviolet radiations would cause skin cancer and other ailments in men and animals, and also damage the plants.

An eco system is a self contained unit of living things(plants, animals and decomposers), and their non living environment (soil, air and water). Example – a grassland and a forest.

The advantages of using disposable paper cups over disposable plastic cups are:

1. Paper cups are biodegradable. So, even if paper cups are thrown away after use, they will decompose (break down) automatically by the action of micro-organisms in due course of time. On the other hand, plastic cups are non-biodegradable. They will remain as such and pollute the environment.
2. Paper cups can be disposed off by burning without causing much air pollution. On the other hand, burning of plastic cups produces toxic gases (poisonous gases) which causes too much air pollution.

UNEP – United Nation Environment Program. In 1987, in an attempt to protect ozone layer, the United Nations Environment Program (UNEP) forged an agreement among its member countries to freeze CFC production at 1986 levels.

Food chain generally consists of three or four steps because after that the energy available for the next organism will be so small that it will be insufficient to sustain the life of that organism.

If we kill all the organisms in one trophic level, then the transfer of food (and energy) to the next trophic level will stop due to which the organisms of next trophic level will starve and die or migrate to other areas. The killing of all the organisms in one trophic level will also lead to the overpopulation of organisms in the previous trophic level. These effects will cause an imbalance in the ecosystem. For example, if we kill all the herbivorous animals like deer, rabbits, etc., in a forest, then the carnivorous animals like lions, tiger, etc., will not get food. Due to this, the lions and tigers etc., will starve and die or migrate from forest and go towards human settlements and attack people. Moreover, in the absence of herbivores like deer, rabbits, etc., the population of the previous trophic level ‘plants’ (or vegetation) will increase too much (because there are no deer or rabbits to eat them). All these effects will create an imbalance in the ecosystem.

No. The impact of removing all the organisms of a trophic level will be different for different trophic levels.

The organisms belonging to the first trophic level are producers which make their own food with the help of sun’s energy. For example – Green plants. The organisms of third trophic level are carnivores that feed upon herbivores. For example – Lion and Tiger.

The waste materials which can be broken down to non- poisonous substances in nature in due course of time by the action of micro-organisms like certain bacteria are called biodegradable waste materials. Example? Paper and wool.

The solid wastes like papers, plastics and metals are recycled. For example – waste paper is send to paper mills where it is reprocessed to form new paper once again.

In the absence of decomposers, the dead bodies of plants and animals would keep lying as such and the elements of plant and animal bodies would never be returned to their original pool like soil, air and water. The cycling process of life and death would be disrupted. The nutrient pool will not be replenished and would exhaust soon.

The flow of energy in the ecosystem is said to be unidirectional because the energy lost as heat from the living organisms of a food chain cannot be reused by plants in photosynthesis.

	Food chain	Food web
1.	Food chain is a straight sequence of organism.	Food web is a complex network formed of many food chain.
2.	Food chain do not have any cross linkages.	Food web has many cross linkages.

The law given by Lindeman is 10% law. According to 10% law, only 10% of the energy entering a particular trophic level of organisms is available for transfer to next higher trophic level.

The dirty drain water containing urine and faeces which is carried from our homes by the underground pipes (called sewers) is called sewage. Sewage is disposed off by treating it at the sewage treatment plant (or sewage works). The treatment of sewage produces clean water which is discharged into the river. The organic matter present in sewage is ‘digested’ in the digesters of sewage treatment plant to produce ‘sewage gas’ (which is kind of biogas) and manure.

Incineration means reducing to ashes. It is used to destroy the household waste, chemical waste and biological waste.

Biotic component: The biotic components of the ecosystem is a community of organisms which is made up of many different inter-dependent populations. It includes – producers, consumers and decomposers.
Abiotic components: The abiotic components of the ecosystem (non living components) include the physical environment like soil, water and air alongwith the in organic substances like carbon dioxide, nitrogen, water and phosphorous.

If all the lions are removed, then there will be no predator control over the population of deer due to which its populations will greatly increase and deer will eat all grass. Over grazing will eliminate the grass and other green plants completely and turn the lush green forest into a desert area having no vegetation at all.

Producers are the organisms which can be prepare their own food from simple inorganic substances like carbon dioxide and water by using sunlight energy in the presence of chlorophyll.
Example: Green plants and certain blue-green algae.
Those organisms which consume food (eat food) prepared by producers are called consumers.
Example: Lion and Tiger.

Pesticides are non – biodegradable chemicals, so they get accumulated at each trophic level. Since humans occupy the top level in any food chain, so the maximum amount of harmful chemical pesticides gets accumulated in our bodies. This damages our health gradually.

The various modes of waste disposal are:

1. Recycling.
2. Preparation of compost.
3. Incineration.
4. Landfill.
5. Sewage treatment.

1. If the number of foxes increases, it will lead to foxes consuming more rabbits as food, which will lead to a decrease in the number of rabbits. Hence, grass plants will grow denser as there will be fewer rabbits to consume them.
2. If the number of foxes decreases, then there will be fewer foxes to consume rabbits as food, so the number of rabbits will increase, which will in turn lead to rabbits consuming more grass plants as food. Hence, grass plants will become sparser.

Preparation of compost is a method in which the disposal of household wastes such as leftover food, fruit and vegetable peels and leaves of potted plants can be converted into compost by burying in a pit dug into the ground and is used as manure.

1. If the number of rabbits increases, it will lead to rabbits consuming more grass plants, and hence grass plants will become sparser. As foxes consume rabbits, any increase in the number of rabbits will lead to an increase in the number of foxes.
2. If the number of rabbits decreases, then there will be less food for foxes. Hence, they will not be able to survive, because of the shortage of food, and their number will decrease. A decrease in the number of rabbits will lead to an increase in the density of grass plants, as there will be fewer rabbits to consume them.

The depletion of ozone layer is due to the use of chemicals called chlorofluorocarbons. Skin cancer is caused if the ozone layer will become thinner.

Harmful effects of ozone depletion are:

1. It can cause skin cancer.
2. It damages the eyes by causing the eye disease called cataract.
3. It damages the immune system by lowering the body’s resistance to diseases.

We take a piece of paper and a plastic bag (Polythene Bag). Now dig the ground to about 15 centimeters depth and place the piece of paper and plastic bag in the dug up ground separately. After a month, we dig up the buried material and observe them. We will find that the piece of paper has been partially eaten up but the plastic bag has been remained unaffected. This means that the paper have been decomposed by the micro-organisms present in the soil. So paper is biodegradable. On the other hand, the plastic bag has not been decomposed by the micro? organisms present in the soil, therefore It is non-biodegradable.

Ozone layer absorbs most of the harmful ultra violet radiations coming from the sun and prevents them from reaching the earth.

The accumulation of harmful chemicals such as pesticides in the living organisms like plants, animals and humans (men) through the food chain is called bio-concentration of pesticides. DDT has accumulated in human body through food chains.

Pond is a complete eco system having decomposer organisms which are the cleansing agents themselves. Aquarium is an incomplete ecosystem and does not have decomposer organisms for cleansing purposes.

Ozone layer protect us from harmful effects as it absorbs most of the ultraviolet radiations coming from the sun and prevents them from reaching the earth.