One mark questions with answers
Q1. What is green house effect?

Ans1. Heating the environment due to absorption of infrared rays by CO2 is known as green house effect.

Q2. State any two harmful effects of radiations emitted by nuclear wastes.

Ans2. (i) It can cause serious diseases like cancer and leukemia.
(ii) It can damage human health.

Q3. What effect do the chlorofluoro carbons bring about in the atmosphere?

Ans3. Chlorofluoro carbons deplete the ozone layer.

Q4. How is ozone layer formed?

Ans4. Ozone layer is formed by the action of sun rays on the atmospheric oxygen.


Two mark questions with answers

Q1. What is smog? Name any two diseases caused by smog.

Ans1. The mixture of smoke and fog with water droplets discharged into air from automobiles, factories etc. is known as smog. Smoke + fog = smog.
Disease : (i) Smog reduces visibility of light at low level of traffic.
(ii) Smog is a cause of asthma, nervous tension etc.

Q2. How is ozone molecule structurally different from oxygen molecule? Where and how is the ozone formed in the atmosphere? What is the danger to us if ozone layer is depleted?

Ans2. Ozone,  molecule has three bonded atoms of oxygen while oxygen molecule has two bonded atoms of oxygen. The structure of ozone,  , Structure 

of oxygen, O=O.  Ozone is formed by the action of sunlight on atmospheric oxygen. 3O2  2O3.
If ozone layer is depleted then ultra-violet rays will reach the earth causing skin cancer.

Q3. on a very cold night, a person burnt charcoal in a stove to heat his room. He also closed the doors and windows of his room before sleeping. Next day he was found unconscious in the closed room. Explain what could be the cause of his unconsciousness?

Ans3. In his room the carbon monoxide gas is present which is formed due to incomplete combustion of charcoal. When carbon monoxide combines with haemoglobin in the blood it forms a compound carboxy-haemoglobin. Due to it the blood is unable to transport oxygen to body parts. This is the cause for his unconsciousness.

Q4. What would happen to living things if CO2 in atmosphere disappears?

Ans4. If CO2 disappears in atmosphere then photosynthesis in plants will stop because it is necessary for photosynthesis, and the environment temperature will decrease because carbon dioxide increases the environment temperature by absorbing the infra-red rays.


Three mark questions with answers

Q1. Name the radiations absorbed by ozone layer. Give any two causes of the depletion of ozone layer. Name the diseases likely to be caused due to depletion.

Ans1. Ultra-violet radiations are absorbed by the ozone layer.
Causes : (i) Free radicals causes the depletion of ozone layer.
(ii) Chlorofluoro carbons causes the depletion of ozone layer.
The diseases caused are skin cancer, skin burns etc.

Q2. State and explain three harmful effects of nuclear radiations.

Ans2. (i) Nuclear radiations cause diseases like cancer, leukemia.
(ii) Nuclear radiations destroy the cell membrane.
(iii) Nuclear radiations damage genes, chromosomes, which are called genetic defects.

Q3. Discuss what would happen if the amount of both CO2 and dust particles increase in the air.

Ans3. If the amount of CO2 increases in the air the earth temperature increases. If the dust particles increase in the air the earth's temperature decreases. If both are increased then there will be very little change in the earth's temperature.

Q4. How does nature maintain balance between CO2 and O2?

Ans4. Nature maintains balance between carbon dioxide and oxygen. The plants absorb CO2 during the process of photosynthesis from the air and produces oxygen in the air. On the other hand animals exhale carbon dioxide and inhale oxygen in respiration.

Q5. Discuss the role of plants in environment.

Ans5. The role of plants in environment is very important :
(i) Plants maintain right level of carbon dioxide and oxygen in the atmosphere.
(ii) Plants prevents soil erosion.
(iii) Plants help to maintain earth's temperature.
(iv) Plants gives shade and wood to us.
(v) Plants control the noise level.

Q6. Give the three main points to control the air pollution?

Ans6. (i) Air pollution is controlled by growing more and more trees.
(ii) Air pollution is controlled by using catalytic converter in automobiles which change harmful exhaust gases into harmless gases.
(iii) Air pollution is controlled by using unleaded petrol in automobiles which reduces the harmful pollutants into the air.
(iv) Air pollution is controlled by fixing electric plates in chimneys which can condense harmful gases.


Five mark questions with answers

Q1. What is radioactivity? Give two examples each of natural and man-made sources of radioactive pollution. What are the ill effects of the radioactive pollution on the organism?

Ans1. Some elements like uranium, thorium etc. spontaneously release invisible rays, it is known as radioactivity. These invisible rays are a-rays, b-rays, g-rays.
The natural sources of radioactive pollution are natural occurring radioactive elements for example U-235, U-238, Ra-222, Ra-224, C-14 etc. which emit harmful radioactive rays.
The man made sources of radioactive pollution are mining and refining of radioactive elements, operation of nuclear power plants, explosion of nuclear devices etc.

Causes :
(i) It causes diseases like cancer, leukemia.
(ii) It destroys the cell membrane.
(iii) It damages genes, chromosomes. These are called genetic defects.

Q2. How have urbanisation and industrialisation increased the air pollution? How can air pollution be checked?

Ans2. The urbanisation and industrialisation have increased the air pollution due to following reasons :
(i) In cities automobiles, factories etc. which emit CO2, SO2, NO2 etc. are main pollutants.
(ii) Many types of weapons increase pollution in air.
(iii) Large scale use of aircrafts, launching of satellites increase the air pollution.
(iv) Industrialisation causes deforestation. This leads to air pollution as plants and trees are main purifiers of air.
(v) Stone crushers are the main sources of particulate pollutants in atmosphere.
Air pollution is checked by growing more plants.