Plant growth depends on both internal and external factors. Hormones are internal chemical signals that affect growth, flowering, and fruit development. The main plant hormones are auxin, gibberellins, cytokinins, abscisic acid, and ethylene. Auxin promotes cell elongation and is involved in tropic responses like phototropism. Gibberellins stimulate stem growth and seed germination. Cytokinins promote cell division and delay aging. Abscisic acid mediates stress response and promotes dormancy. Ethylene causes fruit ripening. External factors like light, gravity, temperature and moisture also influence plant growth and development.

1. Plant Responses

18. More Auxin Less Auxin Animation

20. Phototropism

39. Photoperiodism of Short-Day Plant