With reference to the planet Earth, consider the following statements : I. Rain forests produce more oxygen than that produced by oceans. II. Marine phytoplankton and photosynthetic bacteria produce about 50% of world's oxygen. III. Well-oxygenated surface water contains several folds higher oxygen than that in atmospheric air. Which of the statements given above is/are correct?
- A.I and II
- B.II only
- C.I and III
- D.None of the above statements is correct
Correct answer
Explanation
The correct answer is B, II only. About half of the oxygen made on Earth comes from ocean phytoplankton and cyanobacteria, more than from rain forests, and sea water holds far less oxygen than air.
Tiny drifting algae and photosynthetic bacteria such as Prochlorococcus, the smallest known photosynthesising organism, carry out roughly half of the world's photosynthesis and so release about 50% of its oxygen. Land plants, including all rain forests, make up the rest together, so rain forests alone produce less than the oceans. Oxygen dissolves poorly in water: even well-oxygenated surface water holds only a few millilitres of oxygen per litre, while air is about 21% oxygen, so air carries roughly 30 times more oxygen than the same volume of water.
A is wrong: statement I is false, because the oceans produce more oxygen than rain forests.
C is wrong: statements I and III are both false.
D is wrong: statement II is correct.
Exam tip: oceans give about 50% of Earth's oxygen; air holds about 30 times more oxygen than water.
Practice Questions
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- D.Cauvery
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- D.Basalt
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1. Itanagar
2. Imphal
3. Agartala
4. Aizawl
Which one of the following is the correct chronological order of the above places in terms of sunrise time?
- A.3-2-1-4
- B.2-1-4-3
- C.1-4-3-2
- D.4-3-2-1
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Read the full explanation →"Viticulture" is a common feature of which one of the following Australian cities ?
- A.Adelaide
- B.Darwin
- C.Hobart
- D.Brisbane
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Viticulture, the growing of grapes, is a hallmark of Adelaide, which is surrounded by Australia's best-known wine regions. Adelaide, the capital of South Australia, has a Mediterranean climate with hot, dry summers and mild, wet winters, the conditions grapevines like best.
Read the full explanation →Which of the following statements regarding Barchan is/are correct ?
1. It is a crescent shaped mound of sand, which is deposited by the wind blowing constantly from one direction in a desert.
2. The windward side has a convex steep slope with maximum height at the centre.
3. Two ends of Barchan are called horns and point opposite to the direction the wind blows.
Select the answer using the code given below :
- A.1 only
- B.1 and 2 only
- C.2 and 3 only
- D.1, 2 and 3
Show answer
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Read the full explanation →