Simple organisms

Simple organisms - Simple organisms Single-celled organisms...

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Unformatted text preview: Simple organisms Single-celled organisms, such as bacteria and protozoa, are in constant contact with their external environment. Gas exchange occurs by diffusion across their membranes. Even in simple multicellular organisms, such as green algae, their cells may be close to the environment, and gas exchange can occur easily. In larger organisms, adaptations bring the environment closer to the cells. Liverworts, for instance, have numerous air chambers in the internal environment. The sponge and hydra have water-filled central cavities, and planaria have branches of their gastrovascular cavity that connect with all parts of the body. Plants Although plants are complex organisms, they exchange their gases with the environment in a rather straightforward way. In aquatic plants, water passes among the tissues and provides the medium for gas exchange. In terrestrial plants, air enters the tissues, and the gases diffuse into the moisture gas exchange....
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