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Nitrogen compounds mainly as nitrates or ammonium ions (NH₄⁺) are taken up from soils by plants which are then used in the formation of plant proteins and as animals eat these plants, animal proteins are synthesised.

• Nearly 97% of all the water on the earth is in the oceans, and so only about 3% is freshwater. 
• About 2% of this fresh water is permanently frozen in glaciers and at the polar ice caps. 
• Thus only about 1% is available fresh water. 
• Again about 1/4 of this 1% is present as underground water.
• Only about 0.009% of water on earth is in the rivers and lakes. 
• Rest is present in the bodies of living organisms, as soil moisture, as humidity of atmosphere, etc. 
• Water is the most essential, abundant substance in living things. 
• The human body, for example, is composed of about 70% of water.

Hydrological cycle.

• The whole process in which water evaporates and falls back on the surface of the earth as rain and other forms of precipitation including its flow from land into the sea/oceans via several routes likerivers, ground water channels, etc., is known as the water – cycle.
• All of the water that falls on the land does not immediately flow back into the sea. 
• Some of it seeps into the soil and becomes part of the underground reservoir of fresh water. 
• Some of this underground water finds its way to the surface through springs. We bring it to the surface for our use through wells or tube wells. 
• Water is continuously exchanged between sea, land and atmosphere.

• The earth’s water supply stays the same but humans can alter the cycle. As population increases, and living standards rise this can increase the demand for water. 
• Human impact the water cycle by polluting the water in rivers, streams, reservoirs etc. 
• We are polluting it with harmful chemicals and disgusting substances. Technically we cannot alter the water cycle, however we can mess it up by dumping waste in to the ocean.

Correct option is B) Nitrogen

D) All the above

Correct option is B) 3

Ozone is a poisonous gas and is present in a thin layer in the stratosphere. If all the oxygen is converted to ozone (O₃) the environment becomes poisonous and kills all living things.

The living or biotic components (plants and animals) and the non – living or physial components (air, water, soil, light and temperature) interact and affect each other resulting in the establishment of a complex and complete balance in the environment. There is a continuous cycle of nutrients among the biotic and abiotic components.

• Oxygen has two atoms and it is colorless and odour less. 
• Ozone is a molecule containing three oxygen atoms. It is blue in colour and has a strong odour.

A) Biogeochemical cycles

D) Burning of fossil fuels, deforestation, industrialization

• Addition of hot water to the fish tank may leads to their death. 
• Addition of poisonous mercury compounds in water may leads to their death. 
• Blockage of gills of fishes with any pollutant may be .a cause for their mass death.

The water vapour present in air when condenses due to very low temperature is called fog. The smoke released in the air due to burning of fuels mixes with the fog and forms smog. 

Smoke + Fog = Smog 

a) Smog reduces visibility 

b) Smog creates respiratory diseases like asthma etc.

• Biodegradable pollutants could have serious environmental consequences if large quantities are released in a small area. 
• For example, dumping of biodegradable waste in to a small pond will deplete the •pond’s oxygen supply. 
• Microorganisms in the ponds uses oxygen for degrading biological wastes. 
• More amount of oxygen will be utilised by microorganisms for degradation. 
• Left with no oxygen the aquatic organisms like fish die.
• Thus biodegradable substances become pollutants.

• Denitrification is the conversion, principally by bacteria, of compounds of nitrogen in solid and aquatic systems to the gases, nitrogen (N₂) and nitrous oxide (N₂O) and eventual release of these into the atmosphere. 
• Denitrification occurs primarily in wet soils where water makes it difficult for microorganisms to get oxygen. 
• Under these conditions, certain organisms – known as denitrifying bacteria – will process nitrate to gain oxygen, leaving free nitrogen gas as by-product.

• Oxygen helps in burning things. 
• Oxygen is required for survival of living organisms. 
• Respiration utilizes oxygen releasing carbon dioxide to atmospheric pool maintaining a balance in nature. 
• Dissolved oxygen supports aquatic life. 
• Oxygen is needed for the decomposition of organic waste.

Methane (CH₄ ), 

Carbon dioxide (CO₂ ), and 

Carbon monoxide(CO).

a) The phenomenon of naturally warming up by CO and water vapour is called “Green house effect”. 

b) USA 

c) Fully or partly halogenated paraffin hydro carbons that contain only carbon (C), hydrogen (H) chlorine (Cl) and fluorine (F) which are volatile are called chloro fluorine. 

Ex : Freon – 12, R – 410A, R -134 

d) 

i) Stop deforestation 

ii) Restrict the usage of fossil fuels 

iii) Introducing eco friendly fuels like CNG. 

iv) Introducing alternative energy resources like solar energy, wind power etc.

D) All of the above

Correct option is D) C₆ H₆

• Some gases present in the atmosphere such as carbon dioxide, carbon monoxide, methane, and water vapour trap heat from radiating back to the space. 
• The natural green house gases act like a big blanket around the earth, keeping it warm and making life possible without which temperatures would have fallen to sub zero values. 
• This phenomenon of naturally warming up is called ‘Green house effect’.

• If all the vegetation in the pond dies, the animals which are herbivores also die due to the lack of food materials. 
• So, the herbivores depend on vegetation for their food, dies immediately.

1. Deforestation 

2. Burning of excess of fossil fuels in industries and automobiles. 

3. Power genaration and utilization 

4. Refrigerators, coolers, cell towers 

5. Automobiles and cement roads etc. 

6. Forest fires and burning of firewood.

C) Chlorofluoro carbons

• Due to human activities, an excessive amounts of carbon dioxide and other green house gases has been emitted to the environment. 
• As a result, more heat gets trapped. 
• This causes the temperature of the earth to rise, which results in global warming. 
• Global warming is the recorded increase in the average temperatures of the earth’s atmosphere and oceans. 
• Global warming affects the weather patterns on earth and cause climate change. 
• Climate change results in higher sea levels, more rainfall, and severe droughts and floods.

1) Global warming affects the weather patterns on Earth and causes climatic change. 

2) Climatic changes results in higher sea levels, more rainfall, severe droughts and floods.

Aim :

To prove the green house effect on temperature.

Appratus : 

Two glass bottles, two corks, two thermometers, vinegar, baking soda, high voltage lamp 

Procedure: 

1. Take 100ml of vinegar and a table spoon of baking soda in one bottle and close its mouth with cork. 

2. Insert the thermometer into the bottle through cork such that the bulb of the thermometer should not touch the material in the bottle. 

3. Insert another thermometer into the empty bottle through the cork.

4. Keep these two bottles opposite to a high voltage bulb such that both bottles receives the same amount of temperature. 

5. Note down the initial temperatures and record the temperatures for an hour.

Observation: 

1. We can observe that the vinegar and baking soda in the first bottle react with each other to produce CO₂ . 

2. This CO₂ absorbs and retains the more heat from the bulb than the normal air in the second bottle. Inference : This proves the green house effect (green house gases such as CO₂ ) increases the temperature of the earth.

• Planting trees in open fields and wastelands. 
• Minimising the usage of motorcycles and start using cycles which are eco-friendly. 
• Stop burning of firewood, which release the green house gases start using LPG cylinders for cooking.

D) Land, sea and atmosphere

A constant interaction between biotic and abiotic components of the biosphere makes a system and this flow of components form a cycle is called bio-geochemical cycle.

Increase growth of algae in lakes and ponds is called Eutrophication.

C) Antarctica region

Correct option is B) 70%

Correct option is B) Oxygen

CO₂ (Carbon dioxide)

C) Hydrogen, oxygen

Nitrogen – 78% 

Oxygen-21%

Conversion of free nitrogen present in the atmosphere into compounds of nitrogen is called nitrification.

D) All the above

D) Rhizobium

• Nitrates can also be converted to ammonia by the denitrifying bacteria in the soil. 
• The nitrifying bacteria may then use this ammonia to synthesize compounds for their own cell and eventually convert to proteins, nucleic acids, nitrites, and nitrates. 
• Nitrites are produced mainly by nitrosomonas, while nitrates by nitrobacters that are also capable of utilizing nitrites and converting them to nitrates.
• Death of these organisms add the nitrogenous compounds to the soil.

C) 1 – c, 2 – b, 3 – a

A) Nitrosomonas

Water (H₂O).

D) 1 – c,2 – b,3 – a

B) Photosynthesis