Question

The pigment haemocyanin is found in
A. Chordata
B. Annelida
C. Mollusca
D. Echinodermata

Answer 1

Hint: Hemocyanin are colourless in the reduced or deoxygenated state and blue when exposed to air or to oxygen dissolved in the blood.

Complete Answer:
A breathing pigment binds to oxygen and transmits it throughout the body, keeping the organs and tissues oxygenated. When a pigment molecule binds to an oxygen molecule, it absorbs a certain colour of light, and the light that has not been absorbed is visible to us. As a result, the pigment molecules have various shades, and so does the blood that carries them. Haemoglobin, haemocyanin, hemerythrin and chlorocruorin are the four most important respiratory invertebrate pigments.

The red pigment haemoglobin containing iron is found in all vertebrates and in some invertebrates. Haemoglobin is present exclusively in red cells (erythrocytes) in almost all vertebrates. The red cells of the lower vertebrates (e.g. birds) have a nucleus, while the human red cells do not have a nucleus. The size of the red cells varies widely between the mammals.

The concentration of haemoglobin within the red cell varies significantly between species. Haemocyanin is a respiratory pigment containing copper, present in many molluscs and arthropods. They are colourless when deoxygenated, but turn blue when oxygenated. Some annelids have an iron-containing green pigment chlorocruorin, while others have an iron-containing red pigment hemerythrin.

Thus, the correct answer is option C, Mollusca.

Note: The most commonly distributed respiratory pigments are red haemoglobins, which have been identified in all groups of vertebrates, most invertebrates, and even some plants.