Plants respond to things like light, gravity, touch, water etc. These are environmental stimuli for a plant. Plants coordinate their behavior by using their hormones and respond to the environmental changes. This they do by affecting the growth of a plant.
3. PHYTO-HORMONES
The hormones present in plants are called phyto-hormones.
1. Auxin:-
It is present on tip of plants.
It helps in growth of plant (cell multiplication, cell enlargement and cell
maturation), breaks seed dormancy. (auxin breaks dormance seed which
plants germinate more seed).
2. Gibberellins:-
It is also growth hormone.
It also promotes growth of plants as it increases the height of plant.
3. Ethylene:-
It helps in ripening of fruits and vegetables.
4. Cytokinin:-
It helps in closing of stomata, breaks seed dormancy.
4. PHYTO-HORMONES
5. Abscisic acid(ABA):-
It is a negative hormone.
It retards growth of plant, it promotes senescence (it promotes toward
death), it cause premature falling of fruits and vegetables.
6. Tropic movements:-
The movements caused in plant in response to stimulus.
The stimulus can be; light, chemical, gravity and water etc.
Phototropism:-
The movements caused in plant or plant pats in response to light. [Response
of the plant to the direction of plant] i.e., Plants moves toward the light.
8. WHY PLANT DROOP WHEN IT IS KEPT INSIDE
THE ROOM?
The plant droop when it is kept inside the room as it doesn’t get complete
sunlight, so auxin get accumulated only at one side.
Therefore the growth occurs in only that region where auxin accumulates
hence the plant droops. (whereas the auxin does not get equally distributed
so therefore the plant droops)
9. Geotropism:-
The movement caused in plant in response to gravity.
Chemotropism:-
The movement caused in plant in response to chemical.
Nastic movements:-
This is the movements that occurs in the direction of stimulus.
For examples: it is seen in touch me not plant (mimosa pudica).
The stimulus for it is touch when touch leaf closes.
13. PHOTO-PERIODISM
It is the period of light to which the plant is exposed to sunlight.
Actually there is a blue-green pigment called phyto-chrome in plants that
responds to light.
Some plants need more light, some need less light or some need neither
more nor less sunlight, i.e., moderate.
Accordingly plants are classified as:
1. Long day plants
2. Short day plants
3. Day neutral plants