Transport

Abstract

Unicellular organisms and individual cells of multicellular organisms possess a large surface-area-to-volume ratio. Efficient exchange of materials between these cells and their environment takes place by diffusion, active transport and endoand exocytosis. The distances that materials travel within the cell are small enough for diffusion and cytoplasmic streaming to be fast and efficient. However, in the bodies of large multicellular organisms different cells are far apart from each other and/or their external environment and diffusion is inadequate. Thus long-distance mass-flow transport systems have been developed.