Water

Water covers about three-fourths of the Earth's surface, but about 97.3 percent of it is in the oceans and is salty. Most fresh water is frozen in ice caps or lies underground. Water keeps moving between the oceans, air and land through the water cycle of evaporation, condensation and precipitation. Ocean water contains dissolved salts, mostly sodium chloride; on average, it has 35 grams of salts in one litre, but the Dead Sea contains 340 grams per litre, so people float in it. Ocean water is always moving through waves, tides and currents. Waves are formed when winds blow across the surface, and very large waves called tsunamis are caused by earthquakes or volcanic eruptions under the sea, as in the Indian Ocean in 2004. Tides, the rhythmic rise and fall of water twice a day, are caused by the gravitational pull of the Moon and the Sun; spring tides occur on full moon and new moon days. Ocean currents may be warm, like the Gulf Stream, or cold, like the Labrador Current.

Detailed Worksheet: Water Section A - Definitions (10 marks) 1. What is the water cycle? Name its three main processes. (2 marks) 2. What is salinity? What is the average salinity of ocean water? (2 marks) 3. Define high tide and low tide. (2 marks) 4. What is a tsunami? What causes it? (2 marks) 5. What are ocean currents? Name one warm and one cold current. (2 marks) Section B - Calculations and Applications (15 marks) 6. Ocean water has an average salinity of 35 g per litre. (i) How much salt is in 20 litres of sea water? (ii) The Dead Sea has 340 g per litre; how much salt is in 20 litres of it? (iii) How many times saltier is the Dead Sea? (to one decimal place) (3 marks) 7. Of all the water on Earth, about 97.3 percent is in oceans and 2 percent in ice caps. (i) What percentage is left for all other sources? (ii) If the total water is 1,400 million cubic km, find the volume in the oceans. (iii) Name two other sources of water. (3 marks) 8. High tide occurred at a port at 5:10 am. Tides occur about every 12 hours 25 minutes. (i) When is the next high tide? (ii) When is the low tide between them, roughly halfway? (iii) Why are tides useful for ports? (3 marks) 9. Distinguish between spring tides and neap tides on the basis of when they occur and the height of tides. (3 marks) 10. List three uses of tides and two ways in which oceans are useful to humans. (3 marks) Section C - Diagrams (10 marks) 11. Draw a labelled diagram of the water cycle showing evaporation, condensation, precipitation, run-off and infiltration. (4 marks) 12. Draw labelled diagrams showing the positions of the Sun, Moon and Earth during a spring tide and a neap tide. (3 marks) 13. On an outline world map, mark the Gulf Stream and the Labrador Current with arrows and mark the area where they meet near Newfoundland. (3 marks) Section D - Analysis and Higher-order Thinking (15 marks) 14. On 26 December 2004, a tsunami struck the coasts of many countries around the Indian Ocean. (i) What caused it? (ii) Name two Indian areas affected. (iii) Why are coastal mangroves useful against tsunamis? (iv) How can early warning systems save lives? (v) What should people living near the coast do when a warning is issued? (5 marks) 15. The areas where warm and cold ocean currents meet are among the best fishing grounds in the world. (i) Name one such area. (ii) Why are fish plentiful there? (iii) How do warm currents affect the climate of nearby coasts? (iv) Why does fog form there? (5 marks) 16. Although water is a renewable resource, many places face water shortage. (i) Why is fresh water scarce? (ii) Give two causes of water shortage. (iii) Suggest three ways to conserve water. (iv) When is World Water Day observed? (5 marks) Instructions: Time allowed 2 hours. Attempt all sections. Label diagrams clearly and use arrows to show the movement of water.