gas exchange takes place at gill lamellae in the gills.
where does gas exchange take place in the gills?
gill lamellae
some multicellular organisms such as flatworms (platyhelminthes) are relatively large but very thin, allowing their outer body surface to act as a gas exchange surface without the need for a specialised gas exchange organ. flatworms therefore lack gills or lungs, and also lack a circulatory system. other multicellular organisms such as sponges (porifera) have an inherently high surface area, because they are very porous and/or branched. sponges do not require a circulatory system or specialised gas exchange organs, because their feeding strategy involves one-way pumping of water through their porous bodies using flagellated collar cells. each cell of the sponge's body is therefore exposed to a constant flow of fresh oxygenated water. they can therefore rely on diffusion across their cell membranes to carry out the gas exchange needed for respiration.
gas exchange
amphibians have three main organs involved in gas exchange: the lungs, the skin, and the gills, which can be used singly or in a variety of different combinations. the relative importance of these structures differs according to the age, the environment and species of the amphibian. the skin of amphibians and their larvae is highly vascularised, leading to relatively efficient gas exchange when the skin is moist. the larvae of amphibians, such as the pre-metamorphosis tadpole stage of frogs, also have external gills. the gills are absorbed into the body during metamorphosis, after which the lungs will then take over. the lungs are usually simpler than in the other land vertebrates, with few internal septa and larger alveoli; however, toads, which spend more time on land, have a larger alveolar surface with more developed lungs. to increase the rate of gas exchange by diffusion, amphibians maintain the concentration gradient across the respiratory surface using a process called buccal pumping. the lower floor of the mouth is moved in a "pumping" manner, which can be observed by the naked eye.
gas exchange