Unlike animals, some materials pass in and out of plants through diffusion. For rapid gaseous diffusion to occur, the plants possess stomata and lenticels. During the daytime the photosynthetic organs obtain carbon dioxide from outside by diffusion. The same is used for synthesis of food. Oxygen is released as a by-product. It passes out of the plant by diffusion. Simultaneously, a lot of water vapours pass out. Other materials required for building plant body are obtained from soil, e.g., nitrogen, phosphorus, other minerals, water. They are sent to chlorophyll containing organs where food is manufactured. The manufactured food is passed to all parts for utilisation and storage. If the distance between the two is small, the materials reach there by diffusion. If the distance is large, as in most plants, they have to be transported through a proper system of transportation. However, plants have a large proportion of dead cells. They do not move. Therefore, they have low energy needs.

The transport is slow: Plants possess two independent transport pathways having conducting tubes. One is xylem that moves water and minerals from soil to aerial parts. The other is phloem which carries food and hormones from the region of availability (e.g., leaves, storage organs) to the areas of utilisation (all living cells, growing points, storage organs, developing fruits).