Question

Many marine animals use carbonates dissolved in sea-water to make their shells. Which of the following components is reduced in our atmosphere by this biological phenomenon?
a) Oxygen
b) Calcium carbonate
c) Carbon dioxide
d) Nitrogen

Answer 1

Hint: Molluscs have a distinct characteristic in them to form shells on the outside of their body. The shell is formed by the mantle present in their body. Mantle help in the absorption of the salts and chemicals which harden to form the shell of the organism.

Complete answer: Seashells are the covering of the molluscs used for protecting their internal organs from getting damaged. These shells are formed due to the presence of mantle which helps in their formation. The development of the molluscs takes place in the sea where the mantle present in their body absorbs the salt and chemicals present in the sea. They then secrete calcium carbonate which hardens to form the shell. As the molluscs continue to take in the salt and chemicals from the sea and the shells continue to harden and grow big in size. Once the animal dies it releases its body from the shell hence discarding it. In shells formed calcium carbonate is made with the help of the calcium ion and carbonate. The carbon dioxide reacts with the seawater and gets reduced to form the carbonate ion. The carbonate ion then combines with the calcium ion present in the sea to form the calcium carbonate layer in the molluscs.

So, the answer is ‘carbon dioxide’.

Note: When carbon dioxide is absorbed by the seawater, it leads to the occurrence of chemical reactions that reduce the ph. of the water making it more acidic in nature. It leads to a condition called ocean acidification. This is harmful to the molluscs as it degrades the shells formed if the seawater is acidic in nature.