Samacheer Kalvi Class 4 Science Solutions Term 3 Chapter 3 Air We Breath

I. Choose the correct answer :

Question 1. Air is a
(b) Compound
(c) Complex
Answer: (a) Mixture
In simple words: Air is a combination of different gases mixed together. It is not a single element or a fixed compound.

🎯 Exam Tip: Remember that air is primarily a mixture of gases like nitrogen and oxygen, rather than a pure substance or a compound.

Question 2. Percentage of oxygen in air is about
(a) 21
(b) 78
(c) 1
Answer: (a) 21
In simple words: About 21 percent of the air we breathe is oxygen. Nitrogen makes up most of the rest of the air.

🎯 Exam Tip: It's important to know the approximate percentages of the main gases in the atmosphere, especially oxygen and nitrogen.

Question 3. Root nodules of some plants contain .
(a) Oxygen
(b) Nitrogen
(c) Neon
Answer: (b) Nitrogen
In simple words: Nitrogen gas is found in the small bumps, called nodules, on the roots of certain plants. These plants use it to grow.

🎯 Exam Tip: Understand the role of nitrogen-fixing bacteria in root nodules for plant growth and soil fertility.

Question 4. The major reason for air pollution is
(a) Waste
(b) Smoke
(c) Water vapour
Answer: (b) Smoke
In simple words: Smoke is the main cause of air pollution. It comes from factories, vehicles, and burning things, making the air dirty and unhealthy.

🎯 Exam Tip: Identify common sources of air pollution and their impact on the environment and human health.

II. Who Am I?

Question 1. I am a mixture of gases.
Answer: Air
In simple words: I am made up of many different gases mixed together, which we breathe every day.

🎯 Exam Tip: Be able to describe the basic composition and characteristics of air.

Question 2. I give you oxygen.
Answer: Plants
In simple words: I take in carbon dioxide and give out oxygen, which all living beings need to breathe.

🎯 Exam Tip: Recall the process of photosynthesis and the vital role plants play in producing oxygen.

Question 3. I am not the supporter of burning.
Answer: Nitrogen
In simple words: I am a gas that makes up most of the air, but I do not help things burn. In fact, I can sometimes slow down burning.

🎯 Exam Tip: Distinguish between gases that support combustion (like oxygen) and those that do not (like nitrogen).

Question 4. You help me to decrease pollution by riding on me.
Answer: Bicycle
In simple words: I am a two-wheeled vehicle that does not use fuel, so riding me helps keep the air clean.

🎯 Exam Tip: Think about eco-friendly modes of transport and their benefits for reducing pollution.

III. Write 'True' or 'False' :

Question 1. Plants need nitrogen for their growth.
Answer: True
In simple words: Yes, plants truly need nitrogen to grow healthy and strong. It is a key nutrient for them.

🎯 Exam Tip: Remember that nitrogen is a vital nutrient for plant development, especially for forming proteins.

Question 2. Air is made up of oxygen only.
Answer: False
In simple words: This statement is wrong. Air is actually a mix of many gases, not just oxygen. Oxygen is only one part of it.

🎯 Exam Tip: Always remember that air is a mixture of various gases, with nitrogen being the most abundant.

Question 3. The gas used for burning things is argon.
Answer: False
In simple words: This is incorrect. The gas that helps things burn is oxygen, not argon. Argon is an inert gas.

🎯 Exam Tip: Clearly differentiate between gases that support combustion (oxygen) and inert gases (argon, nitrogen).

Question 4. Carbonated drinks are bad to health.
Answer: True
In simple words: Yes, carbonated drinks are indeed unhealthy because they often contain a lot of sugar and can harm your teeth and body.

🎯 Exam Tip: Be aware of common health concerns related to sugary and carbonated beverages.

IV. Match the Following :

Question 1.
Answer:
1. Layer of air - Atmosphere
2. Electrical energy - Wind mill
3. Nitrogen - 78%
4. Oxygen - 21%
5. Palm leaves - Hand fan
In simple words: Layer of air is called the atmosphere. Wind mills produce electrical energy. Nitrogen makes up 78% of the air. Oxygen makes up 21% of the air. Palm leaves are used to make hand fans.

🎯 Exam Tip: Pay attention to key facts like gas percentages in the air and the functions of various technologies and natural elements.

V. Fill in the Blanks :

Question 1. Air is a mixture of many ______
Answer: Gases
In simple words: Air is made up of a combination of many different gases. These gases include oxygen and nitrogen.

🎯 Exam Tip: Remember that air is a mixture, and its primary components are various gases.

Question 2. Amount of carbon dioxide in the air is ____ %
Answer: 0.03
In simple words: The amount of carbon dioxide in the air is very small, about 0.03 percent. Even though it's a small amount, it's important for plants.

🎯 Exam Tip: Note the relatively small but crucial percentage of carbon dioxide in the atmosphere.

Question 3. We inhale ____ gas.
Answer: Oxygen
In simple words: When we breathe in, we take in oxygen gas from the air. Oxygen is vital for our bodies.

🎯 Exam Tip: Understand that oxygen is the gas essential for human respiration.

Question 4. ____ is used in fire extinguishers.
Answer: Carbon dioxide
In simple words: Carbon dioxide gas is used in fire extinguishers because it can help put out fires by cutting off their oxygen supply.

🎯 Exam Tip: Know practical applications of different gases, such as carbon dioxide in fire suppression.

VI. Answer the Following Questions in Brief :

Question 1. What are the importance of air in our daily life?
Answer: Air is very important for our daily lives.

• We can speak and hear sounds because air carries them.
• Air also helps spread seeds so new plants can grow.
• Wind, which is moving air, causes monsoons and rain.
• Lastly, air helps keep the Earth's temperature steady.

🎯 Exam Tip: List several diverse roles of air, from sound transmission to climate regulation, to show a complete understanding.

Question 2. What are the components of air?
Answer: Air is made up of different gases. The main parts of air include:

• Nitrogen
• Oxygen
• Argon
• Carbon dioxide
• Other gases

🎯 Exam Tip: Be ready to name the main gases that make up air, especially nitrogen, oxygen, and carbon dioxide.

Question 3. What are the adverse effects of air pollution?
Answer: Air pollution has many bad effects.

• It causes the Earth to get hotter, which is called global warming.
• It also creates smog, which is a mix of smoke and fog.
• Acid rain, which harms plants and buildings, can also form.
• Pollution can lead to aerosol formation and the thinning of the ozone layer, which protects us from harmful sun rays.

🎯 Exam Tip: Focus on the major environmental problems caused by air pollution, like global warming and acid rain.

Question 4. List uses of oxygen.
Answer: Oxygen is very important for many things.

• All living beings need oxygen to breathe and stay alive.
• In hospitals, oxygen tanks are used to help patients who have trouble breathing normally.
• Also, oxygen is used in gas welding, a process where metals are joined together.

🎯 Exam Tip: Provide both biological and industrial uses of oxygen to demonstrate its wide importance.

VII. Give Short Answers :

Question 1. How can we reduce air pollution?
Answer: We can reduce air pollution in several ways:

1. We should use cleaner energy sources, like solar power, instead of burning fossil fuels.
2. Air filters can stop bad gases from getting into the air.
3. Cars and vehicles should have regular checks to make sure they don't release too much smoke.
4. Planting more trees is also important because they help absorb carbon dioxide.

🎯 Exam Tip: When suggesting solutions for pollution, include a mix of technological, policy, and environmental approaches.

Question 2. What are the diseases caused due to air pollution?
Answer: Air pollution can cause many health problems. It can make our eyes, nose, and throat itchy. People might also wheeze, cough, and have trouble breathing.
Some serious effects of air pollution on human beings include:

• Respiratory diseases, for example, flu and tuberculosis.
• Cardiovascular damage, affecting the heart and blood vessels.
• Fatigue, headaches, and anxiety.
• Nervous system damage.

🎯 Exam Tip: Mention a range of health impacts, from immediate irritations to long-term chronic diseases affecting different body systems.

Question 3. List out the uses of carbon dioxide.
Answer: Carbon dioxide has many uses.

• Plants use it to make their own food through a process called photosynthesis.
• It is also used to put out fires in fire extinguishers.
• In refrigerators, it can be used as dry ice to keep things very cold.
• Additionally, carbon dioxide is used to create plastics and other materials like polymers.

🎯 Exam Tip: Highlight both the natural biological role of carbon dioxide and its industrial applications.

Activity (Text Book Page No. 88)

Question 1. Take a squeezable bottle. Make a hole on the lid and close the bottle tightly. Bring the bottle near your face and press the bottle. What do you feel?
Answer: When you press the bottle near your face, you will feel a burst of air coming out through the small hole. This shows that the bottle contained air, which was forced out.
In simple words: When you press the bottle, you will feel air rushing out, proving there was air inside.

🎯 Exam Tip: For activity-based questions, describe the observable outcome and what it demonstrates about scientific principles.

Let Us Do (Text Book Page No. 89)

Question. From the given objects, find out the objects which has air in it.
Answer: The objects that have air in them are the balloon, the hot air balloon, and the gas cylinder. These items are designed to contain gases. The other objects shown, such as the spinning top, marbles, and metal rods, do not primarily contain air as their main content.
In simple words: The balloon, hot air balloon, and gas cylinder contain air.

🎯 Exam Tip: Think about which objects are designed to contain gases or have internal spaces filled with air to perform their function.

Let Us Do (Text Book Page No.90)

Question. Tick (✔) the objects which gives out water vapour.
Answer: The objects that give out water vapor are the clothes drying on the line, the tree (through transpiration), and the candle flame (from combustion). The umbrella, the beach scene, and the dolls do not directly release water vapor.
In simple words: Drying clothes, a tree, and a burning candle give out water vapor.

🎯 Exam Tip: Consider processes like evaporation, transpiration from plants, and combustion as sources of water vapor in the environment.

Activity (Text Book Page No.91)

Question 1. Write the percentage of the gases present in air.
Answer: In the air we breathe, the approximate percentages of the main gases are:

• Nitrogen: 78%
• Oxygen: 21%
• Carbon dioxide: 0.03%
• Other gases: 0.07%
• Water vapour: About 4% (this amount can change)

🎯 Exam Tip: Memorize the approximate percentages of the main gases in the atmosphere for quick recall.

Activity (Text Book Page No.91)

Question 1. You might have seen some huge colourful balloons flying high in malls. Those balloons are filled with nitrogen gas. Write the reason for filling nitrogen gas in balloons.
Answer: Big colorful balloons in malls are filled with nitrogen gas for two main reasons.
First, nitrogen makes up about 78% of the air, and it's lighter than the surrounding air. This lightness allows the balloons to float upwards. Second, nitrogen is a gas that does not catch fire easily (it's non-flammable), which makes it a safe choice for balloons, especially indoors. It provides a stable and safe lift for the balloons.
In simple words: Nitrogen is used because it is lighter than air, helping balloons float, and it is also safe because it does not burn.

🎯 Exam Tip: Understand the concepts of density (for floating) and flammability when discussing gas applications for safety and function.

Activity (Text Book Page No.93)

Question. Classify the following (Dog, cat, Coconut tree, monkey, brinjal plant, papaya plant)
Answer:

🎯 Exam Tip: Remember that plants perform photosynthesis to release oxygen, and animals perform respiration to release carbon dioxide.

Activity (Text Book Page No.95)

Question. Tick (✔) the causes of global warming
Answer: Based on the pictures, activities that cause global warming include: factory smoke (releasing greenhouse gases), deforestation (cutting down trees that absorb carbon dioxide), and large forest fires (releasing trapped carbon). Wind turbines are a clean energy source, planting trees helps combat global warming, and spray cans are a smaller contributor compared to the others mentioned.
In simple words: Factory smoke, cutting down forests, and forest fires cause global warming.

🎯 Exam Tip: Focus on activities that release greenhouse gases or remove carbon-absorbing agents as main causes of global warming.

Activity (Text Book Page No.96)

Question 1. Write slogans on harmful effects of air pollution in a chart and stick it on the display board
Answer: Here are some slogans about the dangers of air pollution:

1. Be kind to Earth, keep our air clean.
2. Share solutions, not pollution.
3. Care for trees, breathe fresh air with ease.
4. Shout 'No' to air pollution.

🎯 Exam Tip: Slogans should be short, catchy, and clearly convey the message about air quality and its harmful effects.

I. Choose the Correct Answers :

Question 1. ____ is important for all living creatures.
(a) Dust
(b) Pure air
(c) Unclean air
Answer: (b) Pure air
In simple words: Pure air is very important for all living beings because it allows them to breathe and stay healthy.

🎯 Exam Tip: Emphasize the necessity of clean and unpolluted air for life.

Question 2. Air has no ____ & ____
(a) smell
(b) colour
(c) smell & colour
Answer: (c) smell & colour
In simple words: Air naturally has no smell and no colour. We cannot see or smell clean air.

🎯 Exam Tip: Remember the basic physical properties of clean air: it is colorless, odorless, and tasteless.

Question 3. ____ gas is filled in tyres of vehicles.
(a) Oxygen
(b) Nitrogen
(c) Carbon dioxide
Answer: (b) Nitrogen
In simple words: Nitrogen gas is often filled in vehicle tires because it helps keep the tire pressure more stable and lasts longer.

🎯 Exam Tip: Know the practical uses of nitrogen gas, such as in tire inflation due to its inert properties.

Question 4. ____ is used in gas welding, medicine manufacturing, constructions and transportation.
(a) Oxygen
(b) Nitrogen
(c) Carbon dioxide
Answer: (a) Oxygen
In simple words: Oxygen is a gas that is used in many industries like gas welding, making medicines, in building work, and for transportation (like in aircraft). Oxygen helps in burning fuels efficiently.

🎯 Exam Tip: Be able to list the diverse industrial and medical applications of oxygen.

II. Fill In The Blanks:

Question 1. ______ present in the air is needed for respiration.(Oxygen / Helium)
Answer: Oxygen is the gas found in the air that all living things need to breathe. Without oxygen, we cannot live. It is essential for life.
In simple words: Oxygen is the gas in the air we breathe to stay alive.

🎯 Exam Tip: Remember that respiration is the process of breathing, and oxygen is the key gas involved in it for most living organisms.

Question 2. Monsoon and rain occurs due to the _______ . (wind action / sun action)
Answer: Monsoon seasons and rainfall happen because of wind action. Winds carry moisture from oceans to land, which then falls as rain. The movement of air is vital for weather patterns.
In simple words: Wind movement helps bring monsoons and rain.

🎯 Exam Tip: Understanding the role of wind in weather helps explain how different climates form across the globe.

Question 3. Composition of the component of air _______ from place to place. (vary / Constant)
Answer: The amounts of different gases in the air can vary from one place to another. For example, air near cities might have more pollution than air in the countryside. The composition is not always fixed everywhere.
In simple words: The air's make-up changes depending on where you are.

🎯 Exam Tip: While major gases like nitrogen and oxygen have fairly consistent percentages, other components like water vapor, pollutants, and noble gases can show local variations.

Question 4. _______ is the main component of air. (Carbon dioxide / Nitrogen)
Answer: Nitrogen is the most common gas in our air. It makes up about 78% of the atmosphere, much more than oxygen or carbon dioxide. This gas plays a big role in many natural cycles.
In simple words: Nitrogen is the biggest part of the air we breathe.

🎯 Exam Tip: Knowing the percentages of key gases in the atmosphere is important for understanding climate and environmental science.

Question 5. _______ covered carbon dioxide is present in air. (Joseph priestly / Joseph black)
Answer: Joseph Black was the scientist who discovered carbon dioxide. He showed that this gas is different from regular air. His work was very important for understanding atmospheric gases.
In simple words: Joseph Black found carbon dioxide.

🎯 Exam Tip: Remembering the names of key scientists and their discoveries helps trace the history of scientific understanding.

III. True Or False:

Question 1. All living things use oxygen for breathing.
Answer: True. Almost all living creatures, from humans to tiny insects, need oxygen to breathe and live. Oxygen is crucial for cellular respiration, which produces energy.
In simple words: It's true, every living thing needs oxygen to breathe.

🎯 Exam Tip: While most living things use oxygen, remember there are some tiny organisms (anaerobic) that can live without it.

Question 2. The main component of air is oxygen
Answer: False. The main gas in the air is nitrogen, not oxygen. Nitrogen makes up about 78% of the atmosphere, while oxygen is around 21%. Nitrogen helps dilute oxygen and prevents rapid burning.
In simple words: This is false; nitrogen is the main gas in air, not oxygen.

🎯 Exam Tip: Be careful not to confuse the most important gas for life (oxygen) with the most abundant gas in the atmosphere (nitrogen).

Question 3. Plants need nitrogen for growth.
Answer: True. Plants use nitrogen to grow strong and healthy. They need it to make proteins and chlorophyll, which helps them make their food. This is why nitrogen-rich fertilizers are important.
In simple words: Yes, plants really do need nitrogen to grow well.

🎯 Exam Tip: Nitrogen is one of the essential nutrients for plants, often referred to as a macronutrient along with phosphorus and potassium.

Question 4. Nitrogen is essential for burning
Answer: False. Nitrogen does not help things burn; in fact, it slows down burning. Oxygen is the gas needed for things to burn. Nitrogen acts as a diluent, controlling the intensity of combustion.
In simple words: This is false, nitrogen stops burning, it does not help it.

🎯 Exam Tip: Oxygen supports combustion, while nitrogen is generally non-reactive in burning processes and helps moderate them.

Question 5. Air is important for ships and boats to sail.
Answer: True. Air, especially as wind, is very important for ships and boats to move across the water. Wind pushes the sails, making the boats travel. This method of travel has been used for thousands of years.
In simple words: It's true, wind from the air helps ships and boats move.

🎯 Exam Tip: Remember that wind is essentially moving air, and its energy can be harnessed for various purposes, including transportation.

IV. Match The Following:

Question 1. Match the following.
1. Layer of air - a. Hand fan
2. Electrical energy - b. 21%
3. Nitrogen - c. Wind mill
4. Oxygen - d. Atmosphere
5. Palm leaves - e. 78%
Answer:
1. Layer of air - d. Atmosphere
2. Electrical energy - c. Wind mill
3. Nitrogen - e. 78%
4. Oxygen - b. 21%
5. Palm leaves - a. Hand fan
In simple words: Match the terms on the left to their correct descriptions or related items on the right. For example, "Layer of air" matches with "Atmosphere," and "Oxygen" matches with "21%" (its percentage in air).

🎯 Exam Tip: For matching questions, connect items based on their definitions, functions, or known facts like percentages of gases in the air.

V. Answer The Following:

Question 1. What is the mixture of air?
Answer: Air is a mix of many gases, along with tiny bits of dust and smoke. The main gases are oxygen, nitrogen, and carbon dioxide. Water vapor is also present, which changes the air's humidity. Air is a fundamental part of our environment.
In simple words: Air is a mix of gases like oxygen, carbon dioxide, nitrogen, plus water vapor, dust, and smoke.

🎯 Exam Tip: When describing air, always mention it as a mixture and list its major components to show a complete understanding.

Question 2. What is moving air called?
Answer: Moving air is simply called wind. Wind happens when air moves from one place to another due to differences in air pressure. It is an important part of Earth's weather system.
In simple words: Moving air is called wind.

🎯 Exam Tip: Keep definitions simple and direct for basic science questions. Wind is a key term in meteorology.

Question 3. Do sailors need the help of wind to sail?
Answer: Yes, sailors do need wind to help their ships and boats sail. The wind pushes against the sails, which then moves the vessel across the sea. This has been a primary method of navigation for centuries.
In simple words: Yes, ships and boats use wind to move on the sea.

🎯 Exam Tip: Relate concepts to real-world examples, like how wind powers sailing vessels, to illustrate understanding.

Question 4. Name two examples for wind instruments.
Answer: Two good examples of wind instruments are the nathaswaram and the flute. These instruments make sounds when air is blown into them. They are played by pushing air through them to create music.
In simple words: The nathaswaram and flute are two wind instruments.

🎯 Exam Tip: Be sure to provide distinct examples when asked for two or more items.

Question 5. Which gas is essential for burning?
Answer: Oxygen is the gas that is very important for things to burn. Without oxygen, a fire cannot start or keep burning. Oxygen acts as an oxidizer, reacting with fuel to produce heat and light.
In simple words: Oxygen gas is needed for anything to burn.

🎯 Exam Tip: Remember the "fire triangle" – fuel, heat, and oxygen – where oxygen is the critical gaseous component.

Question 6. What was the old name of nitrogen?
Answer: The old name for nitrogen was "Noxious air." This name was given because it was understood that nitrogen does not support life or combustion, unlike oxygen. Scientists later named it nitrogen.
In simple words: Nitrogen used to be called "Noxious air."

🎯 Exam Tip: Knowing historical names for elements shows an appreciation for the evolution of scientific knowledge.

Question 7. What is the presence of harmful substance in the air called?
Answer: When harmful substances are present in the air, it is called pollution. Air pollution can come from many sources like factories and cars, and it makes the air unhealthy to breathe. It affects human health and the environment.
In simple words: Harmful things in the air are called pollution.

🎯 Exam Tip: Understand that pollution refers to any undesirable change in the physical, chemical, or biological characteristics of air, water, or soil.

Question 8. How do we get cool water from a clay water pot on hot sunny days?
Answer: Clay pots keep water cool on hot days because they have many tiny holes, or pores. Water seeps out through these pores and evaporates from the surface. This evaporation takes heat away from the water inside the pot, making it cool. This natural cooling process is very efficient.
In simple words: Clay pots have tiny holes that let water evaporate, which makes the water inside cool.

🎯 Exam Tip: This phenomenon is an excellent example of cooling by evaporation, a principle used in many natural and artificial cooling systems.

VI. Answer In Detail:

Question 1. Write a note on nitrogen.
Answer: Nitrogen is the most common gas in our atmosphere, making up about 78% of the air. It is very important for life on Earth. Here are some key points about nitrogen:

• Nitrogen gas fills up food packages to keep food fresh for longer.
• Liquid nitrogen is used to store living cells and samples at very low temperatures.
• Plants need nitrogen to grow and produce proteins; it is a vital nutrient for them.
• Some plants have root nodules that contain bacteria, which help them get nitrogen from the air.
• Nitrogen gas is also used to fill vehicle tires, improving their performance and safety.
• Some compounds made from nitrogen are used in explosives.

🎯 Exam Tip: When writing a detailed note, always include its abundance, key properties, and diverse applications in different fields.

Question 2. Explain carbon dioxide and its uses.
Answer: Carbon dioxide is a gas found in the air, but only in small amounts, about 0.03%. Even though it's a small part, it's very important and has many uses. You can test for carbon dioxide because it turns clear limewater milky. This gas is a critical part of Earth's carbon cycle.
Uses of carbon dioxide:

• Carbon dioxide helps plants make their food through a process called photosynthesis.
• It is used in fire extinguishers to put out fires because it removes oxygen.
• Carbon dioxide is used as dry ice in refrigerators to keep things cool.
• It is also used to make plastics and polymers.

🎯 Exam Tip: When explaining a gas like carbon dioxide, include its percentage in air, how to test for it, and list its key applications to provide a comprehensive answer.