TRANSPORT

in plant physiology, the movement of water and nutrients across a cell membrane. The fundamental type of distribution of water and nutrients is found in the unicellular algae; the exchange of substances with the water in which they live occurs through their cell membranes. In nonvascular plants, fluid containing nutrients is passed from the apoplast (space where water can flow freely, between and within cell walls) into the cell by enzyme activity, and from cell to cell through cytoplasmic joints called plasmodesmata. In most vascular land plants, water is transported from the soil from the roots up to the leaves via a system called the xylem (in trees, the xylem is the wood). The products of photosynthesis are carried to other parts of the plant via the phloem (in trees, the inner bark is the phloem).