Which of the following are the necessary conditions for the growth of coral reefs? 1. Photic conditions 2. Clean and sediment free water 3. Sea salinity of 6% 4. Tropical sea water with temperature of 20°C to 21°C Select the correct answer using the code given below:
- A.1, 2 and 4 only
- B.2 and 4 only
- C.1 and 3 only
- D.1, 2, 3 and 4
Correct answer
Explanation
The correct answer is A, 1, 2 and 4 only. Corals need sunlit, clean, warm tropical water, but a salinity of 6% is far too high for them, so statement 3 is wrong.
Reef-building corals live in partnership with tiny algae called zooxanthellae, which make food by photosynthesis. That is why corals grow only in shallow, well-lit (photic) water, usually less than about 50 to 70 metres deep. Mud and silt block light and choke the coral polyps, so the water must be clear and free of sediment; this is why reefs are absent near the mouths of large rivers. Corals also need warm tropical water, with a mean annual temperature of about 20°C to 21°C as the lower limit.
B is wrong because it leaves out the need for light. C is wrong because it includes the wrong salinity and leaves out clean water and temperature. D is wrong because corals thrive at a normal sea salinity of about 27 to 30 parts per thousand (roughly 3%), not 6%.
Exam tip: Coral needs light, clear water, about 20°C or more, and normal sea salinity; high heat causes bleaching.
Practice Questions
View allWhich one of the following statements with regard to growth of coral reefs is not correct?
- A.Coral can grow abundantly in freshwater.
- B.It requires warm water between 23 °C-25 °C.
- C.It requires shallow saltwater, not deeper than 50 metres.
- D.It requires plenty of sunlight to aid photosynthesis.
Show answer
Reef-building corals are marine animals and die in fresh water, so this statement is false. Corals are tiny polyps that build skeletons of calcium carbonate and live with algae called zooxanthellae inside their tissues.
Read the full explanation →Which one of the following biosphere reserves is spread over three States in India?
- A.Nilgiri
- B.Achanakmar-Amarkantak
- C.Seshachalam
- D.Agasthyamalai
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The Nilgiri Biosphere Reserve spreads across Tamil Nadu, Kerala and Karnataka. Set up in 1986, Nilgiri was India's first biosphere reserve, and in 2000 it became the first Indian reserve on UNESCO's World Network of Biosphere Reserves.
Read the full explanation →Which of the following is/are renewable source(s) of energy? 1. Fossil fuel 2. Biofuel 3. Uranium 4. Hydropower Select the correct answer using the code given below.
- A.2 only
- B.3 and 4
- C.1 and 3
- D.2 and 4
Show answer
Biofuel and hydropower are renewable because nature replaces them within a human lifetime, while fossil fuels and uranium are not.
Read the full explanation →Which one of the following is NOT decomposed by bacterial action ?
- A.Vegetable remains
- B.Plastic materials
- C.Animal carcasses
- D.Wastes of flowers
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Ordinary plastics are non-biodegradable, so bacteria and fungi cannot break them down in any useful length of time. Most plastics, such as polyethylene, polypropylene and PVC, are long synthetic polymers made from petroleum.
Read the full explanation →According to the Environmental Protection Agency (EPA), which one of the following is the largest source of sulphur dioxide emissions?
- A.Locomotives using fossil fuels
- B.Ships using fossil fuels
- C.Extraction of metals from ores
- D.Power plants using fossil fuels
Show answer
The EPA names the burning of fossil fuels by power plants and other industrial facilities as the largest source of sulphur dioxide.
Read the full explanation →