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NCERT Class 9 Social Science Important Chapter 10 Oceans and Life
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Oceans and Life
Chapter – 10
| Part – II: Understanding Society India and Beyond |
| Important Question Answer |
Answer the Following Question:
1. What is ocean or submarine relief?
Ans: Ocean or submarine relief refers to the physical landforms and topography found beneath the ocean surface, including underwater mountains, valleys, plateaus, abyssal plains, and deep ocean trenches.
2. What is the continental shelf, and why is it ecologically and economically important?
Ans: The continental shelf is the shallow, gently sloping submerged edge of a continent extending under the sea. It is important because its sunlit waters support rich marine life and coastal fish, while holding key non-living resources like oil, natural gas, and sand.
3. What is the main difference between a seamount and a guyot?
Ans: A seamount is an underwater mountain rising from the ocean floor that does not reach the sea surface. A guyot is a flat-topped underwater mountain that was formerly a seamount whose summit was eroded by wave action and later submerged.
4. What causes ocean waves, and what landforms do they create?
Ans: Ocean waves are generated primarily by winds blowing across the water surface. Wave erosion creates landforms like sea caves, arches, stacks, and stumps, while wave deposition creates beaches.
5. Define wavelength.
Ans: Wavelength is defined as the horizontal distance between two consecutive wave crests or two consecutive wave troughs.
6. How do tides differ from waves?
Ans: While waves are surface oscillations driven mainly by wind energy, tides are the rhythmic rise and fall of ocean water levels occurring twice a day due to the gravitational pull of the Sun and Moon.
7. What alignment causes spring tides?
Ans: Spring tides occur on full moon and new moon days when the Sun, Earth, and Moon align in a straight line, producing high tides of unusual heights and unusually low low-tides due to their combined gravitational pull.
8. Why do neap tides have a smaller difference between high and low water?
Ans: Neap tides occur when the Moon is in its first- and third-quarter phases, causing the gravitational forces of the Sun and Moon to act in perpendicular/different directions, which reduces the tidal difference.
9. What is the Coriolis force?
Ans: The Coriolis force is an apparent force caused by Earth’s rotation that deflects free-moving objects to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
10. How does the Gulf Stream current influence Norway’s climate?
Ans: The Gulf Stream is a warm current that flows toward Norway, keeping its coastal waters relatively warm and preventing sea ice from forming easily despite its high latitude.
11. What is GEMINI, and how does it help coastal fishermen?
Ans:GEMINI is a handheld satellite receiver device that receives GAGAN satellite data and transmits real-time weather, wave, cyclone, and potential fishing zone alerts to fishermen’s mobile phones via Bluetooth in regional languages.
12. How does the World Bank define the “Blue Economy”?
Ans: The World Bank defines the Blue Economy as the sustainable use of ocean resources to promote economic growth, improved livelihoods, and jobs, while preserving the health of marine ecosystems.
13. What is the legal extent of a country’s Territorial Sea?
Ans: The Territorial Sea is the maritime belt extending up to 12 nautical miles (NM) from a country’s baseline, over which the coastal state exercises near-complete control and sovereignty.
14. What is the principle of “Innocent Passage”?
Ans: Innocent Passage is an international maritime law principle that permits foreign vessels to navigate through a coastal state’s territorial waters continuously and expeditiously without stopping, provided they do not threaten the peace, good order, or security of the coastal nation.
15. What are COLREGs and MARPOL?
Ans: COLREGs are international “rules of the road” for safe ship navigation to avoid collisions, whereas MARPOL is an international agreement aimed at preventing and reducing marine pollution from ships.
Answer the Following Question:
1. Describe the major landforms of ocean relief and analyze their significance for marine life and human activities.
Ans: Major Features of Ocean Relief: Ocean relief comprises physical landforms on the ocean floor, including the continental shelf, continental slope, abyssal plain, mid-ocean ridges, seamounts, guyots, and deep ocean trenches. The continental shelf is the shallow, gently sloped margin extending from land under water, which leads into the steep continental slope marking the true continental edge. Beyond the slope lies the vast, flat abyssal plain, punctuated by underwater volcanic mountain systems like the Mid-Ocean Ridge and deep ocean trenches such as the Mariana Trench.
Significance for Marine Life: Shallow continental shelves receive ample sunlight, supporting dense populations of coastal fish, submerged vegetation, and coral reef ecosystems. Submarine features like seamounts and guyots create isolated marine habitats and nutrient upwellings for deep-ocean aquatic life.
Significance for Human Activities: Continental shelves serve as major hubs for commercial fishing, offshore petroleum and natural gas extraction, and sand or mineral mining. Mapping these features through bathymetry is essential for marine navigation, laying underwater communication cables across abyssal plains, and safe deep-sea exploration.
2. Explain the three primary movements of ocean water and their impact on climate, navigation, and coastal ecosystems.
Ans: Waves: Ocean waves are surface oscillations driven primarily by wind blowing across the water. Waves act as “coastal architects” by eroding headlands into cracks, sea caves, arches, stacks, and stumps, while depositing sand along shores to form beaches. Undersea earthquakes can generate giant, highly destructive waves known as tsunamis.
Tides: Tides are the twice-daily rhythmic rise and fall of ocean water levels caused by the gravitational forces of the Sun and Moon. High tides raise coastal water levels, enabling large vessels to enter shallow harbors and sea channels safely without running aground. High tides also bring fish closer to shore for local fishing communities, and tidal changes generate strong tidal currents that can be harnessed for renewable blue energy in sites like the Gulf of Khambhat, Gulf of Kutch, and Sundarbans.
Ocean Currents: Ocean currents are continuous streams of water flowing across the sea in definite directions, driven by winds, Earth’s rotation, temperature/salinity variations, and continental boundaries. Warm currents transport warmth to high-latitude regions such as Norway to keep coastal waters ice-free, whereas cold currents carry freezing water and icebergs. Where warm and cold ocean currents converge, nutrient-rich waters form major global fishing grounds.
3. Detail the structure of maritime zones under international law (UNCLOS) and compare the rights of coastal states in each zone.
Ans: Territorial Sea: Extending up to 12 nautical miles from the baseline, a coastal state holds near-complete sovereignty over water, seabed, and airspace, enabling it to enforce national legal frameworks regarding customs, immigration, fiscal matters, and pollution control. Foreign ships enjoy the right of “innocent passage” as long as transit is continuous and peaceful.
Contiguous Zone: Spanning from 12 to 24 nautical miles from the baseline, the coastal state exercises limited control to prevent and punish infringements of its customs, fiscal, immigration, or sanitary laws.
Exclusive Economic Zone (EEZ, up to 200 NM): Defined under the United Nations Convention on the Law of the Sea (UNCLOS), the EEZ extends up to 200 nautical miles from the baseline. The coastal nation possesses sole economic rights to explore, harvest, manage, and conserve natural living resources (fisheries) and non-living resources (oil, gas, minerals, ocean energy). However, the nation does not fully own the water, and foreign ships retain rights of peaceful navigation and overflight.
The High Seas (Beyond 200 NM): Covering roughly 64% of global oceans, international waters belong to no single country and form part of the global commons. All nations enjoy equal freedoms of navigation, overflight, fishing, scientific research, and laying undersea cables under flag-state jurisdiction.
4. How do Early Warning Systems protect coastal populations from natural hazards like tsunamis and cyclones? Highlight key systems used in India.
Ans: Tsunami Early Warning Operations: Tsunamis are giant waves caused by underwater earthquakes. Seismic networks detect undersea earthquakes in real time. Ocean Bottom Pressure Recorders on the seafloor confirm the passage of tsunami waves, while coastal tide gauges and real-time detection buoys track wave movement. The Indian Tsunami Early Warning Centre disseminates rapid alerts via satellite networks, SMS, and emails to emergency response authorities and coastal communities to execute timely evacuations.
Cyclone and Storm Surge Tracking: Cyclones form due to atmospheric disturbances over warm ocean waters. Satellites detect atmospheric disturbances to model storm paths. In India, INCOIS and IMD operate the Storm Surge Early Warning System to forecast cyclone-induced coastal inundation, while the National Cyclone Risk Mitigation Project builds cyclone shelters and equips disaster management authorities with a Decision Support System.
Direct Warnings for Fishermen: India developed the GEMINI device to transmit satellite alerts directly to fishermen’s mobile phones via Bluetooth in nine regional languages, providing advisories on wave heights, wind speeds, potential fishing zones, and hazard warnings. Combining satellite technology with public awareness and traditional disaster knowledge helps coastal populations respond effectively before disasters strike.
5. Explain the importance of marine resources and outline strategies for their sustainable utilization under the Blue Economy framework and SDG 14.
Ans: Significance of Marine Resources: Oceans store vital living resources (coastal and oceanic fish, marine bio-organisms, submerged aquatic vegetation) and non-living resources (petroleum, natural gas, deep-sea minerals, sand, gravel, and gas hydrates). Marine resources ensure food security, supply essential protein, carry 90% of global trade by volume, support multi-billion dollar coastal tourism, generate renewable ocean energy, and hold sacred cultural value.
The Blue Economy Concept: The World Bank defines the Blue Economy as the sustainable use of ocean resources to promote economic growth, improved livelihoods, and jobs while preserving marine ecosystem health.
Sustainable Strategies under SDG 14: Sustainable ocean management requires:
(i) Reducing marine pollution and regulating plastic/chemical waste.
(ii) Addressing ocean acidification and protecting fragile marine habitats like coral reefs.
(iii) Setting sustainable fishing quotas, eliminating harmful fishing subsidies, and expanding Marine Protected Areas (MPAs).
(iv) Adhering strictly to international agreements like MARPOL to eliminate ship-sourced pollution.
(v) Harnessing non-conventional renewable “blue energy” to power coastal economies cleanly without destroying aquatic habitats.
Fill in the Blanks:
1. The ____________ Trench in the Pacific Ocean is the deepest place on Earth.
Ans: Mariana.
2. Ocean waves are primarily caused by ____________ blowing across the surface of the water.
Ans: winds.
3. Spring tides occur on full moon and new moon days when the Sun, Earth, and Moon are aligned in a ___________ line.
Ans: straight.
4. The apparent deflection of ocean currents to the right in the Northern Hemisphere and to the left in the Southern Hemisphere is caused by the _____________ force.
Ans: Coriolis.
5. An Exclusive Economic Zone extends from a coastal baseline up to ______________nautical miles under UNCLOS.
Ans: 200.
True and False
1. A guyot is a flat-topped underwater mountain that was formerly a seamount whose summit was eroded by wave action.
Ans: True
2. Neap tides produce a larger difference between high tide and low tide than spring tides.
Ans: False.
3. Warm currents, such as the Gulf Stream, help keep northern coastal waters relatively warm and prevent sea ice from forming easily.
Ans: True.
4. The GEMINI device currently transmits real-time satellite information to fishermen up to 1,000 nautical miles into the ocean.
Ans: False.
5. The principle of “Innocent Passage” allows foreign vessels to conduct fishing activities and military operations in a coastal country’s territorial sea.
Ans: False.
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