BIOLOGY [2 Mark Question Answer]

We should not use too many fertilizers and insecticides because it leads to land as well as water pollution causing damage to the living and non-living components present there. Too much use of these chemicals on crops also leads to health disorders in humans and other animals.

Air pollution leads to many respiratory diseases in humans. Heart and lung disorders are also induced by air pollution. It also leads to the acid rain which harms living organisms as well as historical monuments. The ozone layer depletion by air pollution lets the harmful UV rays enter the atmosphere. These UV rays are carcinogens (cancer cuasing).

Deforestation i.e. cutting down of trees should be checked because it leads to an ecological imbalance by causing soil erosion, loss of habitat of animals, loss of wildlife, frequent floods, decreased rainfall and global warming.

Most consumers have more than one source of food. Plant can be eaten by a cow, rabbit, goat, etc. so a plant belongs to several food chains. Similarly, animals, like frogs eat grasshoppers and caterpillars, snakes eat rabbits as well as lizards, mice and rats. Rats are also eaten by hawks. Thus, an animal may also be a part of several food chains. Such interconnected food chains form a food web.

Air pollution is caused by fumes and gases released by the exhausts of vehicles and factories. They contain gases like carbon-dioxide, sulphur-dioxide and oxides of nitrogen. These gases in the air react with water vapour to form acid. This mixture of acids and rain water fall on earth as acid rain.

Five products that we receive from plants are – paper, wood, mbber, medicines and fibres like jute, cotton.
Five products that we receive from animals are – eggs, milk, meat, silk and honey.

The female silk moth lays eggs which transform into worm like caterpillars called larva (silk worm). These caterpillars have silk glands with the help of which they weave thread like structures around its body to form cocoons. In silk farm, the thread is very carefully unwound from the cocoons and then treated chemically to make silk yam.

All food chains start with plants because all energy comes from the sun and only green plants can trap this solar energy and prepare food. Thus, solar energy is converted into chemical energy of food in plants. From plants only, the energy flows to other animals in a food chain. So, without plants, a food chain cannot start.

Scavengers and decomposers feed on dead organisms by breaking down the remains into simple substances. This releases the minerals from the decaying organisms into the environment which are reused by plants to grow. Hence, scavengers and decomposers help not only in the cleaning of the environment but also in the recycling of the minerals.

Carnivorous animals are indirectly depenedent upon plants for food as they eat herbivores which feed on plants. They also get oxygen for respiration from plants.

The distance between the sun and the earth is such that the earth receives just the right amount of solar energy. So, it is neither too hot nor too cold. This makes earth’s land and water warm enough to sustain life and hence make earth a living planet.

First level consumers or primary consumers are those organisms which eat plants (producers). They can be a herbivore or an omnivore in a food chain, e.g. deer, elephant, cow come first after the producers in a food chain and are primary consumers.

The various components of the biosphere are :
a. atmosphere (air) – layer of gases that surround the earth.
b. lithosphere (land) – the soiled portion of the earth.
c. Hydrosphere (water) – the water in form of liquid, ice or vapours on the earth. It covers 70% of earth’s surface.

About one-third of the solar energy that reaches earth is reflected back by the atmosphere directly. The rest two-third reaches the earth’s surface and heats it However, to maintain the energy balance, the earth radiates back the heat. This radiated heat is absorbed by some gases and water vapour in the atmosphere and reflected back to the earth to keep it warm. This is called the greenhouse effect and the gases that trap earth’s radiation are called greenhouse gases.

Environment is the surrounding or conditions in which an organism lives. It includes both biotic and abiotic components around us. e.g. Environment of a fish in a pond includes living things such as plants, insects and fishes and non-living things like water, gases, rocks etc.