Question

Which one of the following statements is incorrect?
(a) The residual air in the lungs slightly decreases the efficiency of respiration in mammals
(b) The presence of non-respiratory air sacs, increases the efficiency of respiration in birds
(c) In insects, circulating body fluids serve to distribute oxygen to tissues
(d) The principle of countercurrent flow facilitates efficient respiration in the gills of fishes

Answer 1

Hint: Increase in respiratory capacity and cooling is achieved due to the presence of air sacs in birds (aves). Gills have a broad surface area that increases the diffusion rate and thus the exchange of gas. The countercurrent exchange mechanism makes it incredibly effective to exchange gas.

Complete answer:
- The amount of air remaining in the lungs of mammals is referred to as the respiratory reserve or residual volume after all the expiratory reserve volume has been exhaled.
- Large variations in the level of breathing gases, such as oxygen and carbon dioxide, are avoided by the air left in the lungs or the residual volume. This residual volume does not reduce respiration efficiency in mammals.
- With the help of gills, respiration in fish takes place. The majority of fish have gills on either side of their heads.
- Gills are tissues made up of feathery structures called gill filaments that provide a large gas exchange surface area. The filaments in fish gills are arranged in the gill arch in rows. Lamellae, which are discs supplied with capillaries, contain each filament. Via these tiny blood vessels, blood flows in and out of the gills.
- Via tiny holes in the body walls called spiracles, and then through tiny blind- ended, air- filled tubes called tracheae, oxygen travels to insect tissues. The distance oxygen can travel through the tracheae depends on its concentration in the air.
- The avian respiratory system differs from other vertebrates, with birds having relatively small lungs plus air sacs that play an important role in respiration (but are not specifically involved in gaseous exchange).
- The air sacs cause air to flow through the lungs unidirectionally.
So, the correct answer is '(a) The residual air in the lungs slightly decreases the efficiency of respiration in mammals'.

Note:
- Using a highly efficient process called countercurrent exchange, fish transfer oxygen from the seawater to their blood. Countercurrent exchange means that the flow of water over the gills into the capillaries in the lamellae is in the opposite direction to the flow of blood.