What Are Plant Hormones? (NCERT Notes)

These NCERT Notes on What Are Plant Hormones? explain the meaning, characteristics, types, and functions of plant hormones in a simple and easy-to-understand manner. These notes are especially useful for Class 10 and Class 11 Biology students, as well as NEET, CUET, and other competitive exam aspirants following the NCERT syllabus. Designed in a concept-based and exam-oriented format, they help students build a strong foundation and revise the topic quickly before examinations.

Plant hormones are chemical substances (chemical messengers) produced in very small amounts inside plants that control and coordinate different activities such as growth, development, movement, flowering, fruit formation, seed germination, and response to environmental changes.

According to NCERT, plant hormones help plants respond to external stimuli and regulate body functions even though plants do not have a nervous system.

Plants produce hormones mainly in growing regions such as:

Root tips
Shoot tips
Young leaves
Developing seeds
Fruits

🌱 Definition of Plant Hormones

Plant hormones (Phytohormones) are naturally occurring chemical substances produced by plants that regulate growth, development, and responses to the environment.

Important Features of Plant Hormones

Produced in very small quantities
Act as chemical messengers
Move from one part of the plant to another
Can either promote or inhibit growth
Help plants adapt to changing conditions

🌿 Why Do Plants Need Hormones?

Plants cannot move from place to place, so hormones help them:

Grow in the correct direction
Respond to sunlight and gravity
Open and close stomata
Produce flowers and fruits
Control seed germination
Survive stress conditions

Types of Plant Hormones (NCERT)

NCERT mainly discusses five major plant hormones.

Plant Hormone	Main Function	Effect
Auxin	Cell elongation	Promotes growth
Gibberellins	Stem growth	Promotes growth
Cytokinins	Cell division	Promotes growth
Abscisic Acid (ABA)	Growth inhibition	Inhibits growth
Ethylene	Fruit ripening	Mixed effect

1. Auxins (Growth Hormone)

Auxins are mainly produced in:

Shoot tips
Young leaves

Functions of Auxin

Increases cell elongation
Helps stems bend toward light
Promotes root formation
Supports fruit development
Controls apical dominance

Example

If a plant is placed near a window, auxin accumulates on the shaded side causing bending toward light.

2. Gibberellins

Gibberellins promote rapid plant growth.

Functions

Increase stem length
Stimulate seed germination
Help flowering
Increase fruit size
Break seed dormancy

Example

Long growth in sugarcane is influenced by gibberellins.

3. Cytokinins

Cytokinins mainly stimulate cell division.

Produced In

Roots
Developing fruits
Seeds

Functions

Promote cell division
Delay aging of leaves
Support growth of lateral buds
Improve nutrient movement

Example

Fresh leaves remain green for longer due to cytokinin activity.

4. Abscisic Acid (ABA) – Growth Inhibitor

ABA is known as the stress hormone of plants.

Functions

Inhibits growth
Causes dormancy in seeds
Closes stomata during water shortage
Helps plants survive stress

Example

Plants reduce water loss during drought using ABA.

5. Ethylene

Ethylene is a gaseous plant hormone.

Functions

Ripens fruits
Helps leaf fall
Supports flowering in some plants
Influences aging process

Example

Bananas and mangoes ripen due to ethylene.

Comparison Between Growth Promoting and Growth Inhibiting Hormones

Feature	Growth Promoters	Growth Inhibitor
Hormones	Auxin, Gibberellin, Cytokinin	Abscisic Acid
Main Role	Stimulate growth	Reduce growth
Effect on Cells	Cell enlargement/division	Slow metabolism

Functions of Plant Hormones (Summary)

Plant hormones help in:

Cell growth
Cell division
Seed germination
Root development
Flower formation
Fruit ripening
Leaf fall
Stress response
Water balance
Directional growth

NCERT Quick Revision Notes

Plant hormones are chemical messengers.
They regulate growth and development.
Auxin → Cell elongation.
Gibberellin → Stem growth.
Cytokinin → Cell division.
ABA → Growth inhibition.
Ethylene → Fruit ripening.
Produced in small amounts but have large effects.

Practice Questions with Answers

1. What are plant hormones?

Answer: Plant hormones are chemical substances that regulate plant growth and development.

2. Which hormone promotes cell elongation?

Answer: Auxin.

3. Which hormone is called stress hormone?

Answer: Abscisic Acid (ABA).

4. Which hormone causes fruit ripening?

Answer: Ethylene.

5. Which hormone stimulates cell division?

Answer: Cytokinin.

Fill in the Blanks

Plant hormones are produced in very ______ amounts.
Answer: small
______ promotes stem elongation.
Answer: Gibberellin
Ethylene is a ______ hormone.
Answer: gaseous
ABA controls ______ during stress.
Answer: stomata
Cytokinin promotes ______ division.
Answer: cell

10 MCQs with Answers

1. Plant hormones are:

A. Minerals
B. Chemical messengers
C. Enzymes
D. Vitamins
Answer: B

2. Auxin mainly promotes:

A. Fruit ripening
B. Cell elongation
C. Dormancy
D. Respiration
Answer: B

3. Which hormone promotes seed germination?

A. ABA
B. Gibberellin
C. Ethylene
D. Water
Answer: B

4. Cytokinin mainly controls:

A. Cell division
B. Respiration
C. Digestion
D. Photosynthesis
Answer: A

5. ABA is:

A. Growth promoter
B. Growth inhibitor
C. Mineral
D. Protein
Answer: B

6. Ethylene helps in:

A. Fruit ripening
B. Root cutting
C. Water absorption
D. Pollination
Answer: A

7. Hormones are produced in:

A. Huge quantity
B. Small quantity
C. No quantity
D. Equal quantity
Answer: B

8. Auxin helps plants respond to:

A. Light
B. Sound
C. Heat only
D. Oxygen
Answer: A

9. Cytokinin delays:

A. Aging of leaves
B. Flowering
C. Root growth
D. Water movement
Answer: A

10. Ethylene exists as:

A. Solid
B. Liquid
C. Gas
D. Crystal
Answer: C

Frequently Asked Question (FAQ)

Are plant hormones the same as animal hormones?

No. Plant hormones regulate plant growth and responses, while animal hormones regulate body functions in animals.

Which is the fastest acting plant hormone?

Ethylene often shows rapid effects because it is gaseous.

Can one plant hormone perform multiple functions?

Yes. One hormone can control several activities depending on plant type and conditions.