Question

The respiratory organs of Molluscs are:
a. Gills or ctenidia
b. Mantle cavity
c. Pulmonary sac
d. All of the above

Answer 1

Mollusc is the species present in the freshwater as well as on land. They consist of a soft body made up of a calcareous shell. The molluscs possess sensory tentacles, which present in the anterior head region of molluscs.

Complete answer:
Molluscs are defined as animals having a soft body. The body is covered with the hard calcareous shell, which is also known as an exoskeleton. The molluscs are mostly aquatic.
The hard shell is secreted by a thin sheet of tissue, which is known as the mantle. It encloses the internal organs.
The gill hangs within the mantle cavity that is used to exchange oxygen and carbon dioxide during respiration.
Gills are also used for filter-feeding apart from respiration in some bivalves.
Moreover, the pulmonary sac or pulmonary cavity is an organ used for aerial respiration. This is present in the land molluscs.

Hence, the correct answer is option (D).

Additional information:
Respiration is described as a process through which the food we eat becomes oxidized and releases energy in the form of ATP.
External respiration is described as the process that occurs in the lungs. It involves the diffusion of oxygen into the blood and also the diffusion of carbon dioxide into the alveolar air. On the contrary, internal respiration is described as the process that occurs in the metabolizing tissues. The oxygen diffuses out of the blood, and also, the carbon dioxide diffuses out of the cells.

Note: The molluscs possess a muscular foot for locomotion. It varies in shape and function that depends on the type of molluscs. The foot is of the same size in the shelled molluscs. The foot is also provided anchorage and also known as an extendable organ.