In plants control and coordination is done by chemical
substances called plant hormones or phytohormones.
There are five main types of plant hormones. They are :-
Auxins, Gibberillins, Cytokinins, Abscisic acid and
i) Auxins :-help in cell division, cell elongation and
ii) Gibberillins :-help in growth of stem and branches.
iii) Cytokinins:- help in cell division, formation of fruits and
iv) Abscisic acid :- inhibits growth and affects wilting of
vi) Ethylene :- helps in flowering and ripening of fruits.
6) Movements in plants :-
Movements in plants are of two main types. They are :-Tropic movements and Nastic movements.
a) Tropic movements :- are directional movements towards or
away from the stimulus and it depends on growth. They are of
different types like Phototropism, Geotropism, Chemotropism,
i) Phototropism :- is movement of plants in response to light. If it is
towards light, it is called positive phototropism. Eg:- Bending of
shoot towards light. If it is away from light, it is called negative
phototropism. Eg:- Bending of root away from light.
ii) Geotropism :-is the movement of plants in response to gravity. If it is
towards gravity it is called positive geotropism. Eg:- Downward
growth of roots. If it is away from gravity it is called negative
geotropism. Eg:- Upward growth of shoot.
iii) Chemotropism :- is movement of plant in response to chemical
stimuli. Eg:- Growth of pollen tube towards the ovule.
iv) Hydrotropism :- is the movement of plants in response to water.