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Exercises, The teacher can help the students complete exercises I, II, III and IV orally. The students, can be asked to write the answers on their own., Enrichment Activities, A wide variety of activities have been given keeping in mind the fact that the students in a, classroom have multiple intelligences. You could use them to assess the understanding of, the students either at the end of the chapter, or at the end of each section., • Presentation/Website: Search for relevant information and pictures for the topic and, complete the activity., • Chart work: Ask the students to complete the activity and display their work in class., • Report writing: The students can find out the countries that were affected by the, 2004 tsunami and mark them on a map., • Role play: The students can write the dialogues and enact the play in class., • Peer and self-assessment: Use the Fill in the blanks, True and false and MCQs for peer, and self-assessment., HOTS, The HOTS question can be discussed in class., Life skills, Ask the the students to first think of ways to conserve water. Then, they can write catchy, slogans, create jingles or use any other advertising campaign to conserve water., Values that enrich, Ask the students to discuss the answers for the question., Follow-up, , • Find out interesting facts about the oceans., , Answer key for the exercises in the lesson, Exercises, I., , Fill in the blanks., 1. The water table is high in wet regions., 2. Ocean water contains 3.5 % salt., 3. The distance between two troughs of a wave, is its wavelength., 4. Tides keep river mouths free of sediments., 5. The Gulf Stream is a warm current., II. True or false?, 1. Strong winds carry water molecules across, the seas, leading to waves. (T), 2. ‘Neap tide’ is another name for ‘low tide’. (F), , NGASS 7 TM fin.indd 145, , 3. Tides can be used to generate electricity. (T), 4. An aquifer is a water-bearing layer of rock, under the ground. (T), III. Give reasons., 1. Though water covers 71% of the Earth, very, little can be used by humans., • 97% of the Earth’s water is found in the, oceans and it is salty., • Only 3% of the water on Earth is fresh, water., • 2% of the water is found in the form of, glaciers and ice sheets., , 15-Sep-17 3:04:58 PM

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•, , •, , Only 1% of the fresh water is found in, liquid form on the surface of the Earth, and as streams and lakes., This makes fresh water a critical resource., In many places the water is also polluted, making it really scarce for humans., , 2. The oceans are becoming saltier., Rivers and underground streams empty the, dissolved salts that they carry into the oceans., The salts that come from volcanic eruptions, in the mid-ocean ridges also contribute to, the saltiness. With global warming, the rate, of evaporation has become higher. This has, caused the oceans to become saltier., 3. Winds are the most common factor for, formation of waves., • Strong winds blow across the open, oceans transferring the energy to the, water molecules on the surface of the, ocean., • The water molecules in turn transmit, this energy through the water in the, form of waves., • The molecules of water do not move, forward but up and down in the same, place causing waves., • This wave motion is transmitted across, the ocean surface., 4. Convergence zones of hot and cold, currents are busy though they are, dangerous areas., • Though the convergence zones of hot, and cold currents are dangerous areas,, they are busy because:, • They make excellent fishing grounds due, to the presence of rich plankton, • help ships move swiftly, using currents,, as they help save fuel and travel time., IV. Answer the following questions., 1. Explain how evaporation, condensation and, precipitation are essential for the water, cycle., • The continuous interchange of the forms, of water on Earth is called the water, cycle or the hydrological cycle., , NGASS 7 TM fin.indd 146, , •, , •, , •, , •, , It involves the three different processes, of evaporation, condensation and, precipitation., Water from the surface of the Earth, evaporates on heating and changes into, water vapour (from a liquid to gas)., The water vapour that rises up in the, air gets cooled by the low temperature, there and condenses (changes back to, the liquid state) to form clouds, droplets, of water and ice crystals., When the cloud particles get too heavy, to remain suspended, they fall back to, the Earth as precipitation. Precipitation, occurs in the form of hail, rain, snow,, sleet, fog, mist and dew., , 2. Explain the following terms: a. swash b., backwash, • As the wave approaches land, its lower, part slows down as a result of friction., The upper part continues at the same, speed, causing the wave to curve, forward and break onto the beach. This, breaking wave is called the swash., • The receding wave is called backwash., 3. With the help of diagrams, show how the, gravitational pull of the Sun and the Moon, affect the tides., • When the Sun, the Moon and the, Earth are in a straight line, the Sun’s, gravitational pull gets added to that of, the Moon. The tides then have a higher, tidal range., • During these times, the high tides are, especially high and the low tides are, especially low. Such tides are called, spring tides. They occur on full moon, days and new moon days., • If the Sun and the Moon are at right, angles to one another, the gravitational, pull of the Sun on the Earth partially, cancels that of the Moon., • During these periods the high tides are, not very high and the low tides are not, very low. These tides are called neap, tides. They occur during the quarter, phases of the Moon., • (Refer to the diagram in the textbook.), , 15-Sep-17 3:04:58 PM

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4. How do ocean currents influence coastal, areas?, • Ocean, currents, influence, the, temperature of the region they travel, through., • Warm currents increase the temperature, of the coasts along which they move. Sea, breezes that blow over warm currents, get warmed in turn and absorb moisture., Then they carry the warmth and moisture, to neighbouring coastal areas., • For example, the North Atlantic Drift,, carrying warm equatorial waters, northwards, increases temperatures, along the coast of north-western Europe, and helps to keep ports along these, coasts open (i.e., not frozen) throughout, the year.On the other hand, winds that, blow over cold currents become cold, and dry., • Along the western coasts of most land, masses, these dry, cold winds have led, to the development of deserts like the, Atacama (South America) and the Namib, (Africa) deserts., 5. What causes water pollution? Why is it a, problem?, • Contamination of both the underground, and surface water is called water, pollution. Contamination makes water, unfit for use., , •, , •, , •, , •, , •, , Domestic wastes and untreated, industrial effluents emptied into water, bodies cause water pollution., Polluted water may contain bacteria,, parasites, viruses, sewage, animal, wastes, toxic chemicals etc. Toxic, wastes include pesticides, fungicides,, insecticides and many other nonbiodegradable carcinogenic solid wastes., Water pollution is a serious problem, because it leads to a lot of waterborne diseases like jaundice, diarrhoea,, malaria, amoebic dysentery, etc., Water, as we know is already a scarce, resource. Water pollution makes it, difficult for us to get even clean drinking, water., It therefore becomes our duty to, conserve water and prevent further, pollution., , Multiple Choice Questions, 1. a, 6. b, , 2. c, 7. c, , 3. b, 8. c, , 4. a, , 5. a, , Values that enrich, •, •, •, , Being grateful—the three men were grateful, to the captain of the ship, Being compassionate, Being brave (The captain took a risk), , Question bank, I., , Distinguish between the following., 1. Warm currents and cold currents, 2. Crests and troughs, II. Answers in brief., 1. List out a few factors that cause ocean, currents., 2. Define water table., 3. What are planktons?, , 4. What are aquifers?, 5. What are tides? What are the two types of, tides?, III. Answer in detail., 1. Write a brief note on waves with a suitable, diagram., 2. What are tides? Explain in detail about its, classification., , 147, , NGASS 7 TM fin.indd 147, , 15-Sep-17 3:04:58 PM