If you breathe through mouth,
(i) getting oxygen to our muscles faster
(ii) it will cause crooked teeth for children
(iii) it leads to gum disease in adults
(iv) it may cause stress to the heart and lungs.

If the clothes of a person catch fire,
(i) STOP him where he is
(ii) DROP to the floor if he stands up
(iii) ROLL him on the floor.
Through this activities, we can save the person without big loss.

The roots of a plant take up air from the spaces between the soil particles.

Our earth surrounded by a huge envelope of air is called 'Atmosphere'. Five layers of atmosphere are:
(i) Troposphere
(ii) Stratosphere
(iii) Mesosphere
(iv) Ionosphere
(v) Exosphere

If we remove plants from the aquarium
(i) All types of wastes created by aquatic animals, excess food and decaying materials level will increase in water.
(ii) The dissolved oxygen level in water will decrease.
(iii) Algae will grow due to excess nutrients and light in aquariums.
(iv) Some types of fish even breed and lay eggs on the leaves of ths plants. This will affect.

They are exposed to harsh weather conditions, dust, pollution, heat and cold. So, they can have an adverse effect on their health. Hence, they weak a mask on duty.

During monsoon, the biscuits placed in open lose its crispness. Sugar in biscuits takes up water from the atmosphere and become so soft.

A huge envelope of air surrounded the earth is called Atmosphere.
(i) This envelope is thicker near the earth's surface.
(ii) As we go higher up, the density and the availabillty of air gradually decreases.
(iii) Movement of wind, Presence of water vapours for cloud formation are the vital roles of atmosphere.
(iv) Troposphere is the responsible layer for the weather we experience on earth.
(v) Stratosphere has the Ozone layer which protects all life on earth from the harmful UV rays of the sun.

PHOTOSYNTHESIS:
Plants manufacture food by a process called photosynthesis. During photosynthesis, carbon-dioxide from the air and water from the soil react in the presence of sunlight and chlorophyll to produce food.
\(\text { Carbon-di-oxide }+\text { water } \underset{\text { Chlorophyll }}{\stackrel{\text { Sunlight }}{\longrightarrow}} \text { food }+\text { oxygen }\) 
RESPIRATIO IN ANIMAL :
When we breathe in air, the oxygen present in the air reacts chemically with digested food within the body to produce carbon-di-oxide gas, water vapour and energy.
Food + Oxygen  Carbon-di-oxide + Water + Energy
(i) carbon-di-oxide formed during respiration dissolves in the blood and is exhaled out of the body through the lungs.
(ii) Plants release oxygen during photosynthesis which is much more than the oxygen consumed by the plants, during respiration.
(iii) Thus, the balance of O₂ & CO₂ in air is maintained.

Fire extinguishers throw a stream of carbon-, di-oxide while putting - off fire. Carbon-di-oxide covers the fire and cut-off the supply of fresh air to the burning things and stop burning.