Plant Biology

Plants are multicellular organisms that produce their own food via photosynthesis. The main organs of a flowering plant are: roots (anchor, absorb water and minerals), stem (support, transport), leaves (photosynthesis, gas exchange), and flowers (reproduction). Water and dissolved minerals travel from roots to leaves via the xylem (one-way). Sugars produced in leaves travel throughout the plant via the phloem (both directions). Transpiration is the evaporation of water from leaves — mainly through stomata. Stomata open (guard cells swell) in daylight for gas exchange and close at night. The transpiration stream creates a negative pressure that pulls water up the plant. Plant growth is regulated by hormones: auxins (elongation, phototropism — plant bends toward light because auxin accumulates on the shaded side), gibberellins (stem elongation, germination), and cytokinins (cell division).