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Importance of air for survival of plants and animals
Respiration in plants
Plants require energy for their growth and hence respiration also occurs in plants. During respiration, plants take in oxygen and release carbonâ€“diâ€“oxide, just as animals do. Gaseous exchange with air in atmosphere takes place in plants with the help of tiny holes called stomata present on their leaves.
Plants manufacture food by a process called photosynthesis. During photosynthesis, Carbon-di-oxide from the air and water from the soil react in the presence of sunlight to produce food. Most plants possess a green pigment called chlorophyll and it is also used-up in the process of photosynthesis. The word equation given below explains the process of photosynthesis.
Carbon-di-oxide +water --- Sunlight Chlorophyllâ†’ Food + Oxygen Chlorophyll
Plants release oxygen during photosynthesis which is much more than the oxygen consumed by the plants, during respiration.
Respiration in Animals
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.
This energy is required to carry out many processes in the body such as movement, growth and repair. This process by which oxygen reacts with digested food to form carbon-di-oxide, water vapour and energy is called respiration. The process can be represented by a word equation as given below :-
Food + Oxygen â†’ Carbon-di-oxide + water + Energy
Carbon-di-oxide formed during respiration dissolves in the blood and is exhaled out of the body through the lungs. The inhaled and exhaled air thus contain the same substances but in different proportion, except nitrogen which is present in the same amount. Inhaled air contains more oxygen while the exhaled air contains more carbon-di-oxide.
Let us have a look at the following table to compare the composition of air in inhaled and exhaled air.
Respiration of plants and animals in water
The water of ponds, lakes, rivers and seas have some amount of dissolved air containing oxygen in it. The plants and animals that live in water use the oxygen dissolved in water for breathing. For example, frogs respire through their skin, fish respire using their gills.
When carbon-di-oxide is cooled to -570 C, it directly becomes a solid, without changing to its liquid state. It is called dry ice and is a good refrigerating agent. Dry ice is used in trucks or freight cars for refrigerating perishable items such as meat and fish while transporting them.
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