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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 counter-current flow facilitates efficient respiration in gills of fishes.

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Last updated date: 13th Jun 2024
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Answer
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Hint: Exchange of gases in animals and plants is carried by specific organs that comprise a biological system known as the respiratory system. Lungs are the primary organ for respiration in land animals, such as mammals and reptiles.

Complete answer: Statement A-The residual air in the lungs slightly decreases the efficiency of respiration in mammals: Residual air doesn't perform a vital role in respiration and is part of dead space. The air present in the lungs, which cannot be completely expelled during forced exhalation is termed as residual volume approximately about 1-1.5 litres. Because of these reasons the residual air present in the lung does not necessarily affect the efficiency of respiration. The gas exchange in mammals takes place in the respiratory bronchioles, alveolar ducts, and alveoli of the lungs.
Statement B-The presence of non-respiratory air sacs increases the efficiency of respiration in birds.: In birds, the respiratory system consists of rigid lungs which during respiration do not expand and contract. They consist of a comprehensive system of air sacs, which is distributed throughout their bodies but are not directly involved in gas exchange but increase the efficiency of respiration. The posterior sacs are filled with fresh inhaled air, whereas the anterior sacs consist of oxygen-poor air that passes through the lungs.
Statement C-In insects, circulating body fluids serve to distribute oxygen to tissues.: Insects breathe through special openings in their exoskeleton called the spiracles. The breath in the air is transmitted to every part of the body through a series of small tubes called tracheoles which are partially filled with bodily fluids. Hence, body fluids contribute to the distribution of oxygen to tissues in insects.
Statement D-The principle of counter-current flow facilities efficient respiration in gills of fishes: Fishes carry out the process of respiration through gills. The gills increase the efficiency of uptake of oxygen from the water through the utilization of the countercurrent exchange system. The countercurrent exchange system involves the flow of oxygenated water in one direction after being pumped by gills and the flow of blood in the lamellae in the opposite direction.
Hence, the correct answer is Option A.

Note: The respiratory system helps the body to absorb the oxygen from the external environment and helps in breathing. It also assists in cleansing the blood from waste gases such as carbon dioxide.