7. Hydrosphere and Biosphere
Complete solutions to the Exercise. Maharashtra State Board (Balbharati), Grade Six Geography.
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Exercise
(1) 71% of the total earth surface is covered by water.
(2) 97% of the total water in the world is stored in the oceans.
(3) Large amount of fresh water reserves are available predominantly in icebergs and glaciers (snow and ice) and groundwater.
About 70% of the fresh water is in the form of icebergs and glaciers, and 29% is groundwater.
(4) In the process of tide formation, the gravitational force of sun, moon and centrifugal force of the Earth is responsible.
(5) The highest high tide named as spring tide occurs on full moon and new moon day.
A spring tide occurs because the Sun, the Moon and the Earth are in one line on these days, so the gravitational forces of the Sun and the Moon add together. The words ‘when moon is closest to the earth’ in the question are not the reason given in the chapter.
(1) Based on the location of the habitat in the biosphere, where the amphibians live?
- a) Terrestrial
- ✓ b) Land and water
- c) Hydrosphere
- d) Plants
Answer: Land and water — in the larval stage amphibians live in water, and in the mature stage they live on land. Example: frog, salamander.
(2) What does the landform named in which part of ocean landform is emerged above the sea level?
- a) oceanic mountain
- b) oceanic plateau
- c) abyssal plains
- ✓ d) oceanic islands
Answer: oceanic islands — where the peaks of submerged oceanic mountains emerge above the ocean surface, they are called oceanic islands. Example: the Andaman and Nicobar Islands.
(1) What is meant by hydrosphere?
The hydrosphere is all the water on the Earth — in oceans, seas, rivers, lakes, groundwater, snow and ice.
(2) What are the four main forms of the hydrosphere?
The four main forms are saline sea water, snow and ice, groundwater, and fresh water available on the surface for drinking.
(3) Which is the largest ocean in the world by its area?
The Pacific Ocean is the largest ocean in the world by area.
(4) Which major landforms are included in the ocean floor?
The ocean floor includes the continental shelf, continental slope, abyssal plains, oceanic mountains, oceanic plateaus, oceanic islands, and abysses and trenches.
(5) On which lunar day neap high and low tides occur?
Neap tides occur on the eighth day after the new moon and the eighth day after the full moon (the half-moon days).
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(1) The body structures of aquatic and terrestrial animals are different.
Aquatic animals such as fish, whales and octopuses live only in water, while terrestrial animals such as elephants, dogs and cows live on land. Each group has to get oxygen, move and find food in a very different environment. Aquatic animals have gills to take in oxygen dissolved in water, fins for swimming and smooth, streamlined bodies that move easily through water. Terrestrial animals have lungs to breathe air and legs to walk and run on land. Hence their body structures are different.
(2) The rate of evaporation is higher in equatorial regions.
The Sun’s rays fall almost vertically in the equatorial regions throughout the year, so temperatures remain high. These regions also have vast stretches of ocean and dense forests. High temperature over large water surfaces turns more water into vapour. Hence the rate of evaporation is higher in the equatorial regions.
(3) Maintaining balance of environment and biosphere is important for humans.
The biosphere provides humans with food, water, the oxygen we breathe and many other resources. All living organisms — plants, animals and micro-organisms — depend on one another and on the land, water and air. If pollution or cutting of trees disturbs this balance, food and water become scarce, diseases increase and life becomes difficult. Humans are a part of the biosphere, so our own survival depends on keeping the environment and the biosphere in balance.
(1) Neap and spring tides
- Day of occurrence: Spring tides occur on the new moon and full moon days. Neap tides occur on the eighth day after the new moon and after the full moon.
- Position of Sun, Moon and Earth: During spring tides the three are in one line. During neap tides the Sun and the Moon are at right angles to each other with respect to the Earth.
- Tidal force: During spring tides the gravitational forces of the Sun and the Moon add together, giving the maximum tidal force. During neap tides the two forces act in different directions, so the tidal force is the least.
- High tide water level: During spring tides the high tide rises much higher than usual. During neap tides the high tide rises lower than the average high tide.
- Low tide water level: During spring tides the low tide falls much lower than usual. During neap tides the low tide falls less than the average low tide.
(2) Saline water and fresh water
- Proportion: About 97% of the water on the Earth is saline water. Only about 3% is fresh water.
- Location: Saline water is found in the oceans and seas. Fresh water is found in icebergs, glaciers, groundwater, rivers and lakes.
- Salt content: Saline water contains a large amount of dissolved salts. Fresh water contains very little salt.
- Use: Saline water cannot be used directly for drinking or farming; it is used for salt production, fishing and water transport. Fresh water is used for drinking, agriculture and industry.
- Availability: Saline water is plentiful. Only about 1% of the fresh water is available for use by humans.
(1) Structure of the ocean floor.
Main landforms of the ocean floor.
Like the continents, the ocean floor has mountains, plateaus, plains and deep trenches. The average depth of the oceans is about 3730 m.
- Continental shelf: The submerged margin of the continents, with a gentle slope and shallow water up to about 200 m deep. It has important fishing grounds and deposits of crude oil, natural gas and minerals.
- Continental slope: The narrow, steeply sloping ocean bed beyond the continental shelf. The depth ranges from 200 m to 3000 m.
- Abyssal plain: The gently sloping ocean bottom at the base of the continental slope, at a depth of 3000 to 5000 m.
- Oceanic mountains: Submerged mountain ranges on the ocean floor. Where their peaks emerge above the surface they form oceanic islands, such as the Andaman and Nicobar Islands.
- Oceanic plateau: An elevated part of the ocean floor with a flat, extensive top, such as the Chagos plateau in the Indian Ocean.
- Abyss and oceanic trenches: Shallow depressions are called abysses, and deep, narrow depressions are called trenches. The Mariana Trench in the Pacific Ocean is the deepest, at 11,034 m.
(2) Concept of biosphere.
The biosphere is the zone of the Earth in which life exists. It includes parts of the lithosphere, the hydrosphere and the atmosphere, because living organisms are interrelated with all three. The zone most favourable for life extends from about 8 to 10 km above the Earth’s surface, about 2 km into the lithosphere and about 10,000 m deep into the hydrosphere.
Plants, animals and many types of micro-organisms live in the biosphere, in environments ranging from the ice-covered polar regions to the equatorial regions. Based on where they live, organisms are classified as terrestrial (living on land), aquatic (living only in water) and amphibians (living both on land and in water).
The biosphere provides the food, water and air needed for life. Its living organisms depend on one another and on the non-living (abiotic) elements around them, and together they maintain the balance of the environment.
I agree that protecting the oceans is the responsibility of all of us. Oceans control the climate, absorb large amounts of carbon dioxide and produce more than half of the world’s oxygen, which is why they are called the ‘lungs of the Earth’. They give us fish, salt, crude oil, natural gas and minerals, and they are a highway for trade.
Today the oceans are being polluted by human activities. Plastic bags and bottles, sewage, industrial chemicals, fertilisers and pesticides from farms, and oil spills from ships all reach the sea. Fish swallow plastic, turtles get caught in fishing nets, corals are bleached and many marine organisms die.
No single person or government can stop this alone, because the pollution comes from all of us. Each of us can use less plastic, never throw waste into rivers or on beaches, join beach clean-up drives and spread awareness. Governments and industries must treat sewage and wastewater before releasing it and prevent oil spills. If we all act together, the oceans will remain healthy for future generations — ‘Stop the sources of pollution, save life in the ocean.’
- Fishing: The shallow water and sunlight make continental shelves the world’s important fishing grounds.
- Production of crude oil and natural gas: For example, at ‘Mumbai High’ on the continental shelf of the Arabian Sea.
- Mining of minerals: Various minerals are extracted from the continental shelf.
- Other occupations: Collecting shells, pearls and seaweed, salt production along the coast, and building ports and harbours, which support shipping and trade.
The Activity — preparing a diagram or model of the ocean floor and displaying it in class — is to be done by you. The diagram in F(1) above can guide you.