What Are Air and Water Their Composition and Importance in Living Organisms
Earth is the one and only planet till now that is known to sustain life. The most important natural resources present on Earth, without which life could not be possible are air, water and soil. In this chapter, we will study the importance of air and water and how it is getting affected in modern times.
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Air
Air is present around us everywhere. It forms the atmosphere of the Earth. It is made up of a mixture of gasses. 78% of the air is made up of nitrogen, 21% is made by oxygen and the rest 1% contains carbon dioxide, water vapour and other gases.
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Properties of Air
We cannot see, touch or taste air; but it can be felt when it blows.
Air has no colour or smell.
Air fills space.
Air has an indefinite shape and volume.
Air is a matter; and therefore, has mass and weight.
Importance of Air
We breathe in oxygen, which is an important component of air and breathe out carbon dioxide. We will die in a minute without it.
Oxygen is also needed for burning.
Air is important for the sound to travel.
Air is important to regulate the temperature of the earth. It causes different weather patterns.
Air can hold water and its movement causes rain in monsoon season.
Water
Water is another important natural resource, which is important for the existence of life on earth. Nearly, 70% of the earth’s surface is covered by water. It is made up of two molecules of hydrogen and one molecule of oxygen. Its chemical formula is H2O.
Forms of Water
Water is known to exist in three different forms - Solid, Liquid and Gas.
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These forms of water are interconvertible.
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Properties of Water
The word ‘water’ refers to its state as ‘liquid’. It means it flows.
Water has no taste, colour or smell.
Water has no definite shape of its own. It takes on the shape of the container it is kept in.
Water is a universal solvent. It means many substances like salt, sugar dissolve in it.
Sources of Water
The main and primary source of water is considered as the ‘rain water’. The rain water fills up the river, ponds, seas and oceans. When some of the water seeps into the ground, it comes to be known as ‘underground water’. This subsurface water is obtained by using wells, tube wells and handpumps. Dams are the reservoir that is a large lake where water is stored to be used by a particular area, city, etc.
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Importance of Water
Water is needed for drinking, cooking, bathing, and cleaning purposes.
Water is needed for irrigating the agricultural fields.
Water is also required to generate electricity, which is known as ‘hydroelectricity’.
Water also acts as habitat for many animals like fishes, turtles, sharks and whales that live in rivers, ponds and oceans.
It is also used for recreational purposes like surfing, swimming and boating.
Pollution of Air and Water
Pollution is defined as anything that makes the earth unhealthy and dirty. Air pollution and water pollution are the two main types of pollution, which we will be studying here.
Air Pollution - It happens when the air gets dirty, and we are not able to breathe properly. Air can be polluted by cars smoke, industrial chemicals, wildfires, burning fossil fuels (oil, coal). It is responsible for causing cough, asthma, burning eyes, bronchitis, and cancer.
Water Pollution - It happens when the water bodies get contaminated due to discharge of dirty substances or chemicals directly or indirectly into water. Dumping of wastes, agricultural runoff, oil leakage from ships are some other reasons for water pollution. Drinking polluted water can cause dysentery, amoebiasis, typhoid, jaundice and cholera.
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How to Control Pollution?
Many environmental groups, ordinary people and the government are working to control pollution. Some of the individual steps to control pollution are:
We should walk or ride a bicycle, whenever possible.
We should support organic farming and consume organically grown food, because it does not use harmful chemicals for growing the crops.
We should not buy things that become waste after a point of time. Instead, we should always try to recycle them.
We should not use open fire to dispose of waste such as plastic, as it releases toxic gasses on burning.
We should plant more trees, as they help to filter the air.
Solved Questions
What will happen if air has no oxygen?
Ans: In the absence of oxygen in the air, all life forms will come to an end. Human beings and other organisms breathe in oxygen and give out carbon dioxide. Plants take in carbon dioxide and give off oxygen. Every organism is dependent on each other. If one vanishes, others will vanish too.
Mention the name of the process by which gases convert into liquids.
Ans: The process by which gases convert into liquids is known as condensation.
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Which is the purest form of water?
Ans: Rain water is considered to be the purest form of water. It is because when the water present in rivers, oceans, and seas gets evaporated by the heat of the sun, it forms clouds. In this process, all the impurities present in water on earth are lost and the water that comes in the form of rain becomes pure.
Fun Facts
The thick blanket of air which surrounds the earth is known as ‘atmosphere’.
Air can hold tiny water droplets, which makes the air humid.
75% of the human brain is made up of water.
Our Earth surface contains 70% water. Out of this, 97% water is present in oceans, which is too salty to drink. The rest 3% exists as freshwater, but approximately 98% of it exists as ice and glaciers. So, only a small fraction of freshwater is present in rivers and lakes that are fit for consumption.
Summary
In this section, we have learned about air and water as a natural resource, their properties and importance. We have also studied how these resources are being polluted and what steps should be taken in order to control the pollution.
Learning By Doing
1. Look at the photos given below and write the corresponding forms of water as S (solid), L (liquid) and G (gas)
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2. Look at the images and description below and fill in the blanks-
FAQs on Air and Water in Biology and Life Processes
1. What is air and what is it made of?
Air is a mixture of gases that forms the Earth's atmosphere and is essential for life. The main components of air are:
- Nitrogen (78%) – supports plant growth indirectly through the nitrogen cycle.
- Oxygen (21%) – required for respiration in most living organisms.
- Carbon dioxide (0.04%) – used by plants for photosynthesis.
- Small amounts of water vapor, argon, and other gases.
Air supports respiration, combustion, weather formation, and various biological processes.
2. Why is air important for living organisms?
Air is important because it provides oxygen for respiration and carbon dioxide for photosynthesis. In biology, air supports life in the following ways:
- Oxygen is used by animals and plants to release energy from food.
- Carbon dioxide is used by green plants to make glucose.
- Air helps in pollination and seed dispersal.
- The atmosphere protects organisms from harmful ultraviolet radiation.
Without air, most forms of life on Earth would not survive.
3. What is water and why is it essential for life?
Water is a chemical compound made of hydrogen and oxygen (H₂O) and is essential for all known forms of life. In living organisms, water:
- Acts as a solvent for biochemical reactions.
- Helps in transport of nutrients and waste.
- Regulates body temperature through sweating and transpiration.
- Maintains cell shape and structure.
Most cells are made up of 70–90% water, highlighting its biological importance.
4. What are the main properties of air?
Air has physical properties that make it vital for environmental and biological processes. The main properties of air include:
- It occupies space and has mass.
- It exerts atmospheric pressure.
- It is compressible.
- It supports combustion and respiration due to oxygen.
These properties influence weather patterns, breathing, and flight in birds and insects.
5. What are the main properties of water?
Water has unique physical and chemical properties that support life on Earth. The key properties of water are:
- High specific heat capacity, which stabilizes temperature.
- Excellent solvent property due to its polarity.
- Cohesion and adhesion, enabling capillary action in plants.
- Lower density in solid form (ice floats).
These properties are crucial for processes like transpiration, circulation, and climate regulation.
6. How does air support the process of respiration?
Air supports respiration by supplying oxygen, which cells use to release energy from food. The process works as follows:
- Oxygen from air enters the lungs during inhalation.
- It diffuses into the blood through the alveoli.
- Cells use oxygen in cellular respiration to produce ATP.
- Carbon dioxide is expelled during exhalation.
This exchange of gases is essential for survival in humans and most animals.
7. How does water help in photosynthesis?
Water is a raw material in photosynthesis and provides electrons and hydrogen for glucose formation. During the process:
- Roots absorb water from the soil.
- Water reaches leaves through the xylem.
- In the presence of sunlight and chlorophyll, water splits in a process called photolysis.
- Oxygen is released as a by-product.
Without water, plants cannot produce food or release oxygen.
8. What is the water cycle in biology?
The water cycle is the continuous movement of water between the Earth's surface and the atmosphere. The main stages include:
- Evaporation – water turns into vapor due to heat.
- Condensation – vapor cools and forms clouds.
- Precipitation – water falls as rain, snow, or hail.
- Transpiration – plants release water vapor.
This cycle maintains freshwater availability and supports ecosystems.
9. What is the difference between air and water?
Air is a mixture of gases, while water is a chemical compound (H₂O) in liquid form under normal conditions. The main differences are:
- Composition: Air contains nitrogen and oxygen; water contains hydrogen and oxygen.
- State: Air is gaseous; water is liquid at room temperature.
- Function in biology: Air provides oxygen; water acts as a solvent and transport medium.
Both are essential for survival but serve different biological roles.
10. How do plants and animals depend on air and water?
Plants and animals depend on air and water for respiration, nutrition, and survival. Their dependence includes:
- Animals use oxygen from air for respiration and drink water for hydration.
- Plants use carbon dioxide from air and water for photosynthesis.
- Water transports minerals and nutrients in plants and animals.
- Air and water together regulate ecosystem balance.
Without air and water, life processes in both plants and animals would stop.
