Plant Hormone

Question 1 What are phytohormones?

Question 2 Name the three phases of plant growth?

Question 3 What is the function of growth regulators. Give example?

Question 4 What are growth inhibitors? Give example?

Question 5 What are auxins?

Question 6 What are Gibberellins?

Question 7 What is the function of cytokinins?

Question 8 Name the  stress hormone in plants that function during night?

Question 9 Name plant hormone which are growth promoters?

Question 10  Which plant hormone help in ripening of fruits?

Question 11 How does control and coordination take place in plants?

 

Plant Hormone (Phytohormones)

Phytohormones are naturally occurring organic chemical substances present in plant which bring about control and coordination of various activities in them.

These phytohormones are synthesised in minute quantities in one part of plant body and simply diffuse to other parts where they influence specific physiological process.

Growth Regulators

Growth in plants mainly occur by the activity of meristematic cells. The new cells are continually Produced by cell division in a meristem.

Meristematic cells are present at the apex of every root and shoot.

Three phases of cell growth are:
(1) Cell division
(2) Cell enlargement
(3) Cell maturation

They are controlled by phytohormones.

5 Major type of phytohormones which are involved in control and coordination are:

• Auxins
• Gibberellins
• Cytokinins
• Abscisic acid
• Ethene

 

Growth Promoters

These stimulate the plant growth .
For Example : Auxins, Gibberellins, Cytokinins, Ethene

Growth Inhibitors

These retard the plant growth.

Auxins

When a plant detect light, auxin hormone is synthesised at the shoot tip, help the cells to grow longer.
When light is coming from one side of plant, auxin diffuse towards shady side of shoot. This concentration of auxin stimulate the cells to grow longer on the side of shoot which is away from light. Thus plant appear to bend towards light.

It promotes stem, fruit, growth, regulates tropism.

Gibberellins

They help in growth in stem and fruits, cell enlargement, cell differentiation.

Cytokinins

They promote cell division, help in breaking dormancy of seeds, delay the ageing of leaves, promote opening of stomata, promote fruit growth.

Ethene

It promote growth and ripening of fruit, help in breaking the dormancy in bud.

Abscisic Acid

It promotes dormancy in seeds and buds and thus inhibits growth, promote closing of stomata, falling of leaves.