Note of Chapter Three: Elementary Science For PSC Students 2017
Water for Life: The name tells us, this chapter is connected with water. This chapter is a little bit long but very easy to learn. Some parts have similarity with chapter two. This chapter is important for short answered questions and descriptive questions also. You can get many questions from this chapter. Except text questions, you will get more questions here. These will give you a unique idea about this Chapter. And it will also helpful for getting good marks in MCQ.
At a glance
- The importance of water for living things.
- Changing state of water.
- Water cycle.
- Causes, effects and prevention of water pollution.
- Water purification and four ways of getting safe water from unsafe fresh water.
This chapter will give you a detail idea about water.
Short Answered Questions (Main text)
1. What is the water cycle?
Ans: The way that water moves all around the Earth as it changes its state is called the water cycle.
2. Give three examples of how we can help prevent water pollution.
- We can prevent water pollution by reducing the use of pesticides and chemical fertilizers in agriculture.
- We should not throw chemicals and oils down the sink drain or the toilet.
- Picking up trash at the beach, river or canal helps keeping water clean.
3. Give four ways to get safe water from unsafe fresh water.
Ans: Filtration: It is the process of filtering water with filter. The filtered water needs to be boiled to make it free from germs.
Sedimentation: A water treatment process to remove suspended particles such as mud and sand from water is called sedimentation.
Boiling: It is the process of boiling water in a sealed pot to kill the germs for more than twenty minutes.
Purifying water with chemicals: It is the process of purifying water by using purifying tablets. We should remember that arsenic contaminated water cannot be purified by these treatments.
4. After rain, there is a puddle on the ground. After a short time, the puddle of water disappears. Where has the water gone? ★
Ans: After rain, there is a puddle on the ground. After a short time, the puddle of water disappears. Water from the rainfall either is absorbed into the ground or runs off into rivers. Water absorbed into the ground becomes groundwater. Some water gets evaporated due to the heat of the sun.
5. What are the three states of water? ★
Ans: The state of water is changed due to heating and cooling. When ice is heated, it changes into water. When heat is added to water, it evaporates and changes into water vapour. When water vapour is cooled, it condenses to form water. When water is cooled, it freezes and becomes ice. We can say that water can be solid, liquid or gaseous.
Figure: Three States of Water
1. Explain why the surface of the glass with ice water gets wet. ★
Ans: The surface of the glass with ice water always gets wet. Air contains some vapours all the time. Water inside the glass pot cannot come out. The glass became cold due to the cold ice. Reaching cold surface water vapours of the air turned into water drops. For this reason, the surface of the glass with ice water gets wet.
Figure: Glass With ice Water
2. Explain the process of water cycle. ★
Ans: The way that water moves all around the Earth as it changes it state is called the water cycle. State of water is always changing through this cycle. Water in oceans and rivers evaporates and becomes water vapour. As water vapour rises in the air, it cools and condenses into tiny droplets. These tiny droplets accumulate and form clouds. Large water droplets fall back to the Earth as rainfall. In arctic countries, snow also fall from into rivers. Water absorbed into the ground becomes groundwater. Water that runs off into rivers flows to sea where it evaporates back into the air.
Figuer: The Process of Water Cycle
3. Why do animals need water? ★
Ans: Water is essential for living things. Without water, living things cannot survive.
- Animals need water to survive.
- The human body is made up of about 60-70% of water. No animal can survive without water.
- When we eat food, water helps to digest it.
- Water helps to carry nutrients to all parts of the body.
- It also helps the body to absorb the nutrients.
- Water is essential to maintain the proper of our body.
4. How can we explain that water is in the air? Or, Explain air has water? ★
Ans: Water is in the air. To prove it, we have to do an experiment. For this experiment, we need some ice and a glass of water. At first, we keep the ice in the glass which is full of water. After some time, we can see some drops of water outside of the glass. Water inside the glass cannot come out. The glass became cold due to the cold ice. Reaching cold surface water vapours of the air turned into water drops. From this experiment, it is proved that water is in the air or air has water vapour.
5. How can we get safe water from pond’s water?
Ans: There are many ways to make pond water free from germs. But boiling is the best way to kill the germs properly.
- Filtration: It is the process of filtering water with filter. The filtered water needs to be boiled to make it free from germs.
- Sedimentation: If we keep river or canal water into a pitcher for a while and we will see sediments at the bottom of the pitcher. But the water in the upper part of the pitcher is clean. The process of separating clean water in this way called sedimentation. This water is not fully free from germs.
- Purifying water with chemicals: Water may be purified by mixing it with alum, bleaching powder, halogen powder etc. During the time of floods or tidal bores, this process is applicable. However, we should remember that, arsenic contaminated water cannot be purified by these treatments.
- Boiling: Boiling is the best way to make water germ free. Water should be boiled in a sealed pot to kill the germs for more than twenty minutes. Water is then cooled and filtered to make it safe for drinking.
6. Why are dew and water droplets on the surface of a glass with ice water alike? ★
Ans: Dew and water droplets on the surface of a glass with ice water are alike. The drops of water that form on cool surfaces such as grass and leaves at night are called dew. When the air comes into contact with some cold surface, water vapour in the air forms into water drops on the cold surface. Water vapour in the air is changed into water by cooling. We can find some water droplets on the surface of a glass with ice water because of same reason. So dew and water droplets on the surface of a glass with ice water are alike.
More Questions (including short and descriptive types)
1. Give some examples of natural resources and man-made resources of water.
Ans: We are surrounded by water. Natural resources of water: Rainfall, river and sea etc. Man-made resources of water: Lake, pond, well, tube-well etc.
2. Animals drink water. But plants do not drink it. How do plants use water? ★
Ans: Plants need water for their life.
- Plants contain about 90% of water in their bodies.
- Plants use water to make their food.
- Plants need water for the collection of nutrients from the soil and to transport into different parts.
- Without water, they cannot absorb the nutrients from the soil.
- Water also plays an important role of cooling the plants in extreme heat.
3. What is condensation? ★
Ans: The change of state from a gas to liquid is called condensation.
4. What is evaporation? ★
Ans: When water is heated, it changes into water vapour. The change of state from a liquid to a gas is called evaporation.
5. Why does water evaporate?
Ans: Water of earth surface mostly evaporates due to the heat of the sun and get into the air. This means that the water changes its state from liquid to water vapour.
6. What is water pollution?
Ans: Water pollution is the addition of harmful substances to water.
7. Write some causes and effects of water pollution?
Ans: Water pollution is harmful for living things.
The causes of water pollution: Water pollution is mainly caused by human activity.
- Water pollution caused by insecticide in agriculture.
- Waste water and chemicals from factories, and waste and trash from household pollute water.
- Besides, bathing cattle and washing in the river or pond also caused water pollution.
The effects of water pollution:
- Water pollution cause death of aquatic animals and disruption of water food chains.
- Humans are also affected by water pollution.
- When they drink contaminated water, they get waterborne disease such as diarrhoea or cholera.
8. How do we prevent water pollution?
Ans: We can prevent water pollution by maintaining following steps:
- We can prevent water pollution by reducing the use of pesticides and chemical fertilizers in agricultures.
- We should not throw chemicals and oils down the sink drain or the toilet.
- We should not throw trash into ponds, rivers, lakes or seas.
- We can keep water clean by picking up trash at the beach, river or canal.
9. What is water purification?
Ans: Water purification is a treatment of water to make it safe and acceptable for human use.
10. Is fresh water safe to drink? ★
Ans: Some fresh water is safe to drink for people such as water from tube well. Some fresh water is not safe for people, such as water from ponds and rivers. So, it is important to purify water before we drink and use it for cooking. So, it can be said it fresh water is not always safe to drink.