STD 9 Geography: Chapter 05 Ocean and Man - Questions and Answers
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Class 9 Geography Questions and Answers
Chapter 5: Ocean and Man
1. What is the difference between bay and strait?
Bay-A sea surrounded by three sides of the land
Strait-The narrow stretch of sea between two landmasses.
3. Difference between Islands and peninsula.
- Islands are land surrounded by sea on all sides.
- The landmasses surrounded by sea on three sides are called a peninsula.
4. Which ocean is known as ‘the Southern ocean’?
- Antarctic Ocean
5. Which is the smallest ocean?
- Arctic Ocean
6. Name the deepest part of the Atlantic Ocean?
- Puerto Rico trench
7. Which is the deepest part of the Pacific Ocean?
- The Challenger Deep
8. Identify the important features of seawater.
Temperature, salinity, and density are the important characteristics of seawater. These are not uniform in all oceans.
9. The following table contains the names of some major islands and peninsulas in the world. With the help of an atlas find out the names of the oceans to which they below. (Page No: 68)
1. Indian Ocean
2. Indian Ocean
3. Pacific Ocean
4. Atlantic Ocean
5. Atlantic Ocean10. How does ocean temperature vary in different latitudes? What are the reasons?
- The highest temperature is recorded between 10° latitudes on either side of the equator. The average temperature here is about 27°C. As we move away from the Equator, the temperature decreases considerably. The temperature falls to about 10°C in the mid-latitudes and up to -2°C in the polar regions.
- Variation in the amount of insolation received on the earth, the ocean currents and winds are the reasons behind the variation in ocean temperature.
11. Define Salinity?
The salinity of oceans is the amount of salt present in seawater. Salinity is usually expressed as the number of grams of dissolved salts in 1000 grams of seawater. The average salinity of seawater is 35 parts per 1000 grams. This is expressed as 35‰. It means that 35 grams of salt are dissolved in 1000 grams of water. It is 3.5%.
12. What is The main reason for the salinity of oceans?
The main reason for the salinity of oceans is the dissolved sodium chloride
(common salt).
13. Name the major contents of seawater.
• Sodium chloride
• Magnesium Chloride
• Magnesium Sulphate
• Calcium Sulphate
• Potassium Sulphate
• Calcium Carbonate
• Magnesium Bromide
14. What are the factors responsible for the variation in salinity of seawater?
• Salinity will be more in land-locked seas.
• Salinity increases in areas of high evaporation.
• Salinity decreases in areas where snow meltwater reaches in large quantity.
• Salinity decreases at river mouths.
• Heavy rainfall leads to a reduction in salinity.
15. Prepare a note on the relationship between salinity and density of seawater.
The density of seawater is not the same everywhere in the oceans.
This is due to the difference in the salinity and temperature of the seawater.
As the temperature increases, the density decreases.
Density increases with increasing salinity.
16. The equatorial regions; record a high amount of salinity as compared to the polar regions why? (TextBook Page No: 70)
- The temperature is high in equatorial regions compared to polar regions. Density decreases as temperature increases, and it increases as salinity increases. High density is associated with high salinity. There is the possibility of high evaporation in equatorial regions. That is why equatorial regions record a high amount of salinity.
17. Why does salinity increase in landlocked seas? (TextBook Page No: 70)
- In the landlocked seas, the evaporation takes away the water as vapour leaving the salts in the seawater. This increases the salt content of seawater.
18. Why is salinity less at river mouths? (TextBook Page No: 70)
- Water levels increase in the seas where many rivers flow (river mouth). This is why salinity is reduced in these areas.
19. What causes movements in seawater.
- The density of seawater is not uniform everywhere. This is due to the variations in salinity and temperature of seawater. As the temperature increases, the density decreases. Density increases with increasing salinity. The temperature, salinity and density of seawater are not uniform everywhere. These variations lead to movements in seawater.
20. Which are the movements of seawater.
- Waves, tides, and ocean currents are the movements of seawater.
21. What are sea waves? What are the reasons?
- The up and down motion of the water along the surface of the sea is called sea waves. The friction exerted by winds on the ocean surface is the reason for waves.
22. Identify what is marked as A, B, C and D in the picture of wave below.
(a) Distance between 2 adjacent crests - Wavelength
(b) Vertical distance between the crest and the trough - Wave height
(c) The summit of the wave - Wave crest
(d) Bottom part of the wave - Wave trough
23. Sea Surges cause severe damage along the shores. What are the measures taken to prevent damages?
• Depositing boulders along the seashore.
• Construction of interlocking concrete structures (Pulimuttu)
• Planting of mangroves.
24. Name the sea waves generated by earthquakes and volcanos
- Seismic sea waves or tsunami waves.
25. Prepare a note on the mud bank
- Mudbank is a phenomenon that develops in the Arabian Sea during the onset or the end of the monsoon season. Planktons grow luxuriantly in the turbulent muddy water along the seashore during the monsoon rains. Schools of fish such as shrimp, sardine, and mackerel arrive to feed on the planktons and the mud, giving fishermen a good catch. This phenomenon is known as a mud bank.
26. What do you mean by tides?
Tides are the periodic rise and fall of the water level in the ocean.
27. Difference between high tide and low tide.
The rise in the level of ocean water is the high tide and the lowering of the water level is known as the low tide.
28. What are the causes of Tides?
Tides are formed as a result of the gravitational pull exerted by the moon and the sun along with the centrifugal force due to the earth's rotation.
29. Illustrate with the help of a figure the occurrence of high tide and low tide.
- The water level on the part of the earth facing the moon rises. The rise in water level due to the gravitational pull exerted by the moon leads to high tide. At the same time, the water level on the opposite side also has risen. The centrifugal force due to the earth's rotation is the reason for the rise in water level here. It can be seen that the water level goes down at places located 90° away from the places of tidal influence. This is due to the draining of water towards the tidal regions. The phenomenon of fall of water level is known as low tide.
30. Observe figures A and B and explain the types of tides represented by them.
A - Spring tides
- The sun, moon and earth come in a straight line on the new moon and full moon every month. The tidal force will be intense due to the combined influence of the Sun and Moon. As a result, stronger tides formed these days.B - Neap tides
- The sun, the moon, and the earth reach 90-degree angles after the new moon and full moon, 7 days later. These days, the sun, the moon, and the earth attract the Earth from 90-degree angular distances, causing very weak tides. These are known as Neap tides.
31. How do tides affect human life?
High tides and low tides have many effects.
• The debris dumped along the seashores and ports are washed off to the deep sea.
• The formation of deltas is disrupted due to strong tides.
• Brackish water can be collected in salt pans during high tides.
• The fishermen make use of the tides for going and returning from the sea in catamarans.
• Tidal energy can be used for power generation.
• Ships can be brought to shallow harbours during high tides.
32. Prepare a note on ocean currents.
- Ocean currents are the continuous flow of seawater from one direction to another. These are ocean currents. They can be classified as warm currents and cold currents. Warm currents are the currents that flow from the tropical or subtropical regions towards the polar or subpolar regions. Similarly, cold currents are the currents that flow in from the polar or the subpolar regions towards the tropical or subtropical regions.
33. Complete the table using fig. 5.7 in textbook
34. List the warm and cold currents of the Atlantic Ocean. Identify the continents near which they flow (Page No: 76)
35. Complete the following table based on the currents of the Indian ocean. (Page No: 77)
• Influence the climate of coastal regions.
• Fog develops in the regions where warm and cold currents meet.
• The regions where the warm and cold currents meet provide favourable conditions for the growth of fish.
37. Categorize the following currents into warm currents and cold currents
Gulf Stream currents
Kuroshio currents
The Brazilian currents
Peru currents
Oyashio currents
Benguela currents
38. Name the oil field situated in the Arabian Sea about 162 km to the west of Mumbai shore?
- Mumbai High
39. Where do you find the highest Ocean temperature?
- Between 10° latitudes on either side of the equator
40. Which of the following is a warm current through the Atlantic?
A. Peruvian current B. Brazilian current C. Oyashio current D. Kuroshio current
Answer: B. Brazilian current
41. Oceans are useful to man in different ways. Explain.
Oceans play a significant role in the life of human beings.
Climate
Oceans have a decisive role in controlling the climate along the coastal regions. The sea breeze during the day and the land breeze at night regulate the temperature over the coasts. Oceans play a part in the formation of weather phenomena like rain, wind, and cyclones. Generally, the coastal regions have a moderate climate, whereas severe summer and winter prevail in regions away from the sea.
Mineral deposits
Almost all the minerals found on land are also found in the sea.
Apart from the deposits of common salt, bromine, magnesium chloride etc, the oceans contain iron ore, coal, petroleum and natural gas.
Power generation
Energy can be produced from sea waves and tides. The waves that strike the turbines on the shores produce electricity by turning them. Sometimes reservoirs are constructed for storing seawater. Seawater that enters the reservoir at high tides is released during low tide. The turbine moves at both instances and electricity is generated.
Oceans as a source of food
Fish is one of the important food of man. Japan, Peru, China, Norway, and the United States of America are the leading fishing nations. Marine organisms are the source of many medicines. They are used for the production of antibiotics, steroids, and vitamins.
Drinking water from the sea
We can purify seawater for drinking purposes. Seawater is purified into drinking water by seawater distillation, evaporation, and condensation, as well as by electrodialysis and reverse osmosis.
The following are the other uses of oceans to man.
• Provide several job opportunities in various sectors like fishing, it's processing and marketing.
• Possibilities for tourism.
• Ocean transport is ideal for the transportation of heavy goods at cheaper rates from one continent to another.
42. We can purify seawater for drinking purposes. Which are the methods to purify seawater? Prepare a flow chart.
Freshwater is separated from brackish water by seawater distillation, evaporation, and condensation.
b. Separating salt from brackish water
Seawater can be purified by extracting salts from seawater by electrodialysis and reverse osmosis.
43. Explain how marine flora and fauna benefit to man.
- Fish is one of the important food of man. Japan, Peru, China, Norway, and the United States of America are the leading fishing nations. Besides, oceanic flora and fauna are sources of several medicines. Antibiotics, steroids, vitamins and tonics are commercially manufactured in large quantities from them.
44. Which among the following statements is not related to the Indian Ocean?
a. The southern part of this ocean extends up to the Antarctic Ocean.
b. The average depth is more than that of the Atlantic Ocean.
c. The Puerto Rico trench is situated in this ocean.
d. It ranks third in the area.
Answer: c. The Puerto Rico trench is situated in this ocean.
45. Which among the following places record the least salinity? Why?
* Landlocked sea.
* Areas of heavy rainfall.
* Areas of high evaporation.
Answer: Areas of heavy rainfall.
Heavy rainfall leads to a reduction in salinity.
46. Is there any relation between the intensity of waves and the wavelength? substantiate
- yes
- As the intensity of waves increases the wavelength also increases.
47. High tide occurs twice a day. Explain this statement.
- Tide is a phenomenon caused by the gravitational pull of the moon and sun on the earth and the centrifugal force caused by the rotation of the earth. Twice a day, the tide rises. The interval between two tides is 12 hours and 25 minutes. Therefore, two tides occur in 24 hours.
48. Select the appropriate from column B to match column A
49. Ocean currents are classified into two types. What are they? Make a difference between them.
1. warm currents
2. Cold currents
warm currents
warm currents are the currents that flow from the tropical or subtropical regions towards the polar or sub-polar regions. They are warmer than the water in the flowing areas.
Cold currents
Cold currents are the currents that flow in from the polar or sub-polar regions towards the tropical or subtropical regions.
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