Question

Spot the incorrect statement.

• A. Fishes have counter-current exchange of gases
• B. Molluscs use gills whereas earthworms use moist skin for respiration
• C. Frogs respire through skin and lungs
• D. Cockroaches have blood that helps primarily in gaseous transport

Answer 1

The correct option is D Cockroaches have blood that helps primarily in gaseous transport

The cockroach respiratory system has no lungs. Instead, they draw in air through external openings known as spiracles. Then, they transport this air directly to the cells with the help of tubes called trachea. This air diffuses into various tissues and cells of the body. Here, oxygen is used up to liberate energy. Likewise, carbon-dioxide rich air passes into the trachea and moves to the outward surfaces through the spiracles. Carbon dioxide is given out as a result of the respiratory process. The cockroaches have colourless blood or haemolymph. Since there is no respiratory pigment in their blood, it does not help in gaseous transport. As, it is the respiratory pigments such as haemoglobin in humans that help in transportation of oxygen to longer distances in the body
In fishes, the oxygen transfer from water to blood takes place via counter-current exchange. Counter-current exchange means the flow of water over the gills is in the opposite direction to that of the flow of blood through the capillaries in the gill lamellae, which are plate-like foldings for an increased surface area.
Mollusc gills are termed as ctenidia. They are composed of a series of thin filaments of tissues. These resemble the teeth of a comb. Ctenidia helps in gaseous exchange in molluscs.
Earthworms breathe through their moist skin. Their skin needs to stay moist for the passage of dissolved oxygen into the bloodstream.
Frogs respire through moist skin, buccopharyngeal cavity and lungs. While completely submerged in water, all of the frog's respiration happens via their thin membranous skin. Frogs have a respiratory surface in their mouth (buccopharyngeal cavity) for gaseous exchange. At rest, this is their predominant form of breathing, while it fills the lungs occasionally. Frogs also breathe much like a human, by taking air in through their nostrils and down into their lungs. Frogs tend to force air into the lungs by increasing the pressure higher than the atmospheric pressure.