Plants move or bend towards light due to the growth and elongation of the cells. When plants' shoot are exposed to shady region and light is coming from one direction, auxin is synthesized at shady region. Auxin induces the cells to grow longer on the side of the parts which are away from the light and the growth of cells elongate the shoot towards light.

The presence of auxin in shady part induces cell growth causing the particular part bend towards the light. In this way, auxin is...

^{A. Gibbane ring}

^{B. Gibberellin}

Structure of gibberellin:- chemically, gibberellins belong to a large family of diterpene acid which have a comment skeleton called Gibbane ring. More than 100 gibberellins have been identified but gibbane is common in all gibberellins. They only differ in minute structure such as number and position of -OH, CH₃and -COOH groups at different C atoms of gibbane ring.

Gibberellins are acidic in nature and induce growth of the plants. Some major...

^{Kinetin zeatin}

Structure:- Cytokinins are basic in nature. They are either aminopurine or phenyl urea derivatives. They include kinetin and zeatin. They are found in coconut milk, corn endosperm and pears.

Mode of action in cytokinin

1. Control of Transcription and Translation:- It influence nucleic acid metabolism and also helps in transcription and translation.

2. Enzymes and Metabolism:- It increases the activity of respiration as an enzyme. Cytokinin induces...

Auxin and gibberellins are generally growth phytohormones. Some major effects of auxin on growth of plants are as follows:

1. Cell elongation:- Cell elongation is the most important function of auxin especially at the region of shoots and root tip behind the apical meristem. Cell enlargement is caused by the solubilisation of carbohydrates, loosening of wall of microfibril and increase permeability and respiration.

2. Root formation:- Auxin promotes root formation in cutting ends of shoots.

3....

Plant hormones are the organic substances produced in one part of plants which is translocated to another part for regulating one or more physiological reactions even in low concentration.They are also known as phytohormones.They can have promoting or inhibiting effect on a process.

They have been categorised into five types. They are

1. Auxin
2. Gibberellins
3. Cytokinin
4. Ethylene
5. Abscissic acid(ABA)