Chapter 15: Air Around Us

    I. Multiple Choice Questions (MCQs).
    Q.1. The earth is surrounded by an envelope of air, is known as
    a) environment
    b) surroundings
    c) atmosphere
    d) ionosphere
    Answer: c) atmosphere
    Q.2. Who discovered active and inactive parts of the air?
    a) Lavoisier
    b) Cavendish
    c) Priestle
    d) None of these
    Answer: a) Lavoisier
    Q.3. Helium, neon, argon, krypton and xenon are collectively called
    a) noble gases
    b) halogens
    c) chalcogens
    d) none of these
    Ans: (a) noble gases
    Q.4. Plants contribute a major portion of water vapour to the atmosphere through the process of
    a) transpiration
    b) evaporation
    c) vaporisation
    d) all of these
    Answer a) transpiration
    5. The part of the air that is supports in burning, is called
    a) hydrogen
    b) nitrogen
    c) oxygen
    d) none of these
    Answer: c) oxygen
    II. Fill in the blanks by selecting appropriate words from the given list: List : Nitrogen, oxygen, Winnowing, evaporates, photosynthesis

    Q.1. _______________ is more effective in moving air.
    Q.2. Water _______________ and forms water vapour.
    Q.3. _______________ does not support burning.
    Q.4. Plants also need air to make their own food by the process of ______________ .
    Q.5. Aquatic animals and plants used dissolved ________________ in the water.

    Answer:
    1-Winnowing,
    2- evaporates,
    3- Nitrogen,
    4- photosynthesis,
    5- oxygen

    III. Match the items of Column A with those of Column B.

     

    Answer: 1- c, 2-d, 3-b, 4-e, 5-a
    IV. Write ‘T’ for the true and ‘F’ for the false statements.
    Q.1. Carbon dioxide is a colourless and odourless gas.
    Q.2. The plants use oxygen while making their food.
    Q.3. Animals and plants both use oxygen for respiration.
    Q.4. The plants and animals are interdependent.
    Q.5. The animals living in the soil do not need oxygen to respire.

    Ans 1-T, 2-F, 3-T, 4-T, 5-F

    V. Very Short Answer Questions.
    Q.1. Define atmosphere.

    Answer: The earth is surrounded by an envelope of air, which extends upto 200 km into space. It is known as atmosphere.

    Q.2. Write the percentage of carbon dioxide in air.
    Answer: 0.03%

    Q.3. How do dust and smoke particles come to air?
    Ans: Dust and smoke particles come to air from the smokes of automobiles and the tall chimneys of factories and industries.

    Q.4. Define respiration.
    Answer: Respiration is the process through which we get energy from the food.
    VI. Short Answer Questions.

    Q.1. How can you say that air supports life?
    Answer: All plants and animals take in oxygen. Plants also need air to make their own food by the process of photosynthesis. They use carbon dioxide while making their food. Thus we can say that air support life.

    Q.2. Why should we not cover our faces while sleeping?
    Answer: We should not cover our face while sleeping because we may feel suffocated.

    Q.3. How do the animals and plants living in the water get oxygen?

    Answer: Animals and plants living in the water uses dissolved oxygen in water. Oxygen is absorbed by diffusion through gills in animals and body surface in plants.

    Q.4. What is air made up of? Explain with an experiment that how to ‘investigate the presence of air in the atmosphere.

    Answer: Air not only contains oxygen and nitrogen but a variety of other gases also, for example– carbon dioxide, water vapour, ozone and noble gases (helium, neon, argon, krypton and xenon are collectively called noble gases.) Other constituents of air are dust particles, carbon particles, carbon monoxide, nitrogen dioxide, sulphur dioxide and chlorofluorocarbons [CFCs].
    To investigate the presence of air in the atmosphere you need an empty glass, a tub with water.
    Procedure : Take an empty glass. Now immerse the glass in water with the open end inside the water. Now, you tilt the glass, air bubbles rush out from the opening and water rushes in to fill the empty space inside the glass. Now you can conclude that air occupies space, and no place is without air.

    Q.5. How can you say that air contains water vapour? Verify with an experiment that air contains oxygen.

    Answer: Take out a bottle of soft drink from the refrigerator and place it on the table. Observe for few minutes. You will see small drops of water appearing on the outer surface of the bottle. This is because water vapour present in the air condenses and forms small drops of water. This activity proves that air contains water vapour.

    If a lighted candle is allowed to burn in certain amount of air, a part of the air is used up for burning. The part of the air that is used up while burning, is called oxygen. When all the oxygen in the glass has been utilised for burning, the candle is put out, because rest part of the air in the glass does not support burning, which is made up of nitrogen.

    Q.6. Verify with an experiment that air contains carbon dioxide.
    Answer: Experiment to show that air contains carbon dioxide. For this you require – Limewater, a long test tube with a cork with two openings and straw.

    Procedure: Take a test tube and fill two-third of it with limewater. Breathe out air by your mouth through a straw into the limewater. Observe the effect of gas on it. The lime water turns milky. Since, carbon dioxide is a colourless and odourless gas, it is detected by its action on limewater, which turns milky.

    Q.7. Discuss that air contains dust and smoke particles.

    Answer: Air contains dust and smoke particles Have you noticed the sun rays entering through slit in a dark room? You may notice tiny particles moving in sun rays. These are dust particles. Air contains dust and smoke particles. These particles come from the smokes of automobiles and the tall chimneys of factories and industries.

    VII. Long Answer Questions.

    Q.1. How does oxygen become available to animals and plants living in water? Explain with an experiment.
    Answer: Animals and plants uses dissolved oxygen (air) in the water.

    Lets us do an activity to understand that the water dissolves air (oxygen).

    For this you will require, glass vessel or beaker, tripod stand, bunsen burner.

    Procedure : Take some water in a glass-vessel or beaker. Heat it slowly on a tripod stand with a bunsen burner. Now, observe the inner surface of the vessel before boiling the water. You can see tiny bubbles at the bottom. When water is heated, the air dissolved in it escapes. If you keep on heating, the water turns into vapour and begins to boil.

    Q.2. How does oxygen become available to animals and plants living in soil? Explain with an experiment.
    Answer: The animals living in the soil, also need oxygen to respire and they get oxygen (air) present between the soil particles.

    To observe the presence of air in the soil you need a lump of dry soil and a beaker containing water.

    Procedure – Take a lump of dry soil and drop it gently into the beaker containing water. Now, you can see air bubbles coming out from the soil. The water displaces the air present in the soil, which is seen in the form of bubbles. This shows that the air is present between the soil particles.

    Q.3. (a) How is the oxygen in the atmosphere replaced?
    (b) Describe uses of air in our daily lives.
    Answer. a) : plants are refilling oxygen in the atmosphere through the process of photosynthesis. During photosynthesis, the plants consume water and carbon dioxide in the presence of chlorophyll and sunlight, and convert it into food and oxygen. This oxygen is consumed by animals for the respiration (break down of food), and release carbon dioxide.

    b) Uses of air
    (a) Air is essential for respiration.
    (b) It helps in the dispersal of seeds and pollens of plants.
    (c) Fast moving wind helps in the movement of sailing boats and gliders.
    (d) Air helps in the transmission of sound.
    (e) Wind is used for running windmills. The windmills are used for drawing underground water, flour mills and for generating electricity.

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