Which of the following factors are needed for the growth of corals? 1. Freshwater 2. Clear shallow salt water 3. Plenty of sunlight for photosynthesis 4. Warm water between 23 °C and 25 °C Select the correct answer using the code given below.
- A.1, 3 and 4 only
- B.2, 3 and 4 only
- C.1 and 2 only
- D.1, 2, 3 and 4
Correct answer
Explanation
The correct answer is B, 2, 3 and 4 only. Corals grow in clear, shallow, warm sea water with plenty of sunlight; fresh water kills them.
Coral reefs are built by tiny animals called polyps, which take calcium carbonate from sea water to make hard skeletons. Inside their tissues live algae called zooxanthellae, which make food by photosynthesis and give corals their colour, so corals need sunlit water, usually less than about 50 metres deep, free of mud and silt. They prefer warm tropical seas with temperatures of roughly 23 to 25 °C and normal sea salinity. When water stays too hot the corals expel their algae and turn white, which is coral bleaching.
A, C and D are wrong because they include fresh water. Fresh water lowers salinity, and river mouths also bring silt, which is why reefs are rare near the mouths of large rivers.
Exam tip: corals need warm (about 23–25 °C), clear, shallow, saline, sunlit water; the three reef types are fringing, barrier and atoll.
Practice Questions
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- A.7.0
- B.6.6
- C.5.6
- D.8.0
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- A.Ozone is found mostly at 15-55 km in the atmosphere.
- B.Ozone is produced by gaseous chemical reactions.
- C.16th November is celebrated as the International Day for the Preservation of the Ozone Layer.
- D.Ozone is a form of oxygen in which three oxygen atoms are bounded together.
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- A.Energy flow is cyclic and nutrient flow is unidirectional.
- B.Energy flow is unidirectional and nutrient flow is cyclic.
- C.Both energy and nutrient flow are unidirectional.
- D.Both energy and nutrient flow are cyclic.
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- A.Arunachal Pradesh
- B.Uttarakhand
- C.Himachal Pradesh
- D.Sikkim
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Read the full explanation →Which one of the following is related to global dimming?
- A.Fall of atmospheric pressure due to increased particulates
- B.Rise of atmospheric pressure due to increased particulates
- C.Rise of temperature due to increased particulates
- D.Fall of temperature due to increased particulates
Show answer
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