Chapter 1 – (b) Response and Chemical Coordination in Plants – Hormones | Life Science Solution Class 10

1. Charles Darwin
2. Francis Darwin
3. Darwin and Francis Darwin
4. Kogl

1. Somatotrophic hormone
2. Auxin
3. ISH
4. Gibberellins.

Question

1. ____ hormones have been referred to as “growth regulators” or “growth substances. 
2. ____ are chemical messengers as they function at a site far away from their place of origin. 
3. ____ is the group name of plant hormones. 
4. Three natural plant hormones are ____, ____ and cytokinin. 
5. Growth, bud formation, seed germination and stopping of premature leaf and fruit fall, etc., are the physiological functions of the ____ hormones. 
6. Auxin is produced at the tip of the apical ____.
7. Auxin (Indole Acetic Acid) is synthesized from the amino acid. 
8. Auxin plays most important role for the ____ of the plants. 
9. ____ occur naturally in maturing seeds, germinating seedlings and in the growing tissues of expanding cotyledon or leaf. 
10. The chemical nature of gibberellins are ____ plant hormones. 
11. ____ influences leaves, flowers and fruits to increase in size. 
12. Chemical nature of kinin is a ____ compound plant hormones. 
13. Cytokinins stimulate mitotic cell division in the ____ tissues. 
14. Auxin hormone promotes ____ dominance in plants. 
15. ____ help for seed germination by removing dormancy of seeds. 
16. Tropic movement is controlled by ____.
17. ____ hormone helps in control of weeds. 
18. Indole acetic acid is the chemical name of ____.
19. The endosperms and in growing embryo of matured seeds produce ____.
20. Plant hormone ____ plays active role in cell division.
21. ____ retards senescence in plants. 
22. The word hormone was derived from the ____ word. (Greek / Latin / Bengali) 
23. The name of the first hormone discovered is ____. (Auxin / Secretin / Thyroxine) 
24. Development of roots is helped by ____. (Auxin / Kinin / Gibberellin) 
25. ____ is very effective in the blooming of flowers. (Auxin / Kinin / Gibberellin)

Answer

1. Plant
2. Hormones
3. Phytohormones
4. Auxin, Gibberellin, and Cytokinin
5. Plant
6. meristem
7. Tryptophan
8. Growth
9. Gibberellins
10. Diterpenoid
11. Gibberellins
12. Nitrogen-containing
13. Meristematic
14. Apical
15. Gibberellins
16. Auxin
17. Allelopathic
18. Auxin
19. Abscisic acid
20. Cytokinin
21. Abscisic acid
22. Greek
23. Auxin
24. Auxin
25. Gibberellin

Very Short Answer (VSA) type questions

Question 1

From which word hormone is derived? 

Answer

The word hormone is derived from the Greek word “hormon” meaning “to set in motion”.

Question 2

Answer

The term hormone was first coined by English physiologist Ernest Starling in 1905.

Question 3

Which hormones are called growth regulators?

Answer

Plant hormones are often referred to as “growth regulators” or “growth substances.”

Question 4

Name one chemical substance which is known as the chemical co-ordinators. 

Answer

Hormones are often referred to as chemical co-ordinators.

Question 5

Mention the source (place of secretion) of Auxin. 

Answer

Question 6

Name a hormone which is found in plant. 

Answer

Auxin.

Question 7

What is auxin? 

Answer

Auxin is a type of plant hormone that plays a crucial role in the growth and development of plants, including stem elongation, root growth, and the development of fruits and flowers.

Question 8

Which hormone is found in the coleoptile of the plant?

Answer

Auxin hormone is found in the coleoptile of the plant.

Question 9

Name a growth promoting hormone in plant. 

Answer

Gibberellin is a growth promoting hormone in plants.

Question 10

What is the chemical name of Auxin ? 

Answer

The chemical name of Auxin is Indole Acetic Acid (IAA).

Question 11

What is the full name of lAA? 

Answer

The full name of lAA is Indole-3-acetic acid.

Question 12

Mention one function of Auxin. 

Answer

The full name of lAA is Indole-3-acetic acid.

Question 13

Which hormone does help to produce seedless fruit?

Answer

Gibberellins hormone can help to produce seedless fruit.

Question 14

How many types of Auxin are found in the plant body? 

Answer

There are several types of auxins found in the plant body, including indole-3-acetic acid (IAA), indole-3-butyric acid (IBA), and naphthalene acetic acid (NAA), among others.

Question  15

Which hormone helps for tropic movement in plants? 

Answer

Auxin hormone helps for tropic movement in plants.

Question 16

Which hormone does help check fall of leaves and fruit?

Answer

Auxin hormones help in checking the fall of leaf and fruit.

Question 17

Mention the source of gibberellins. 

Answer

Gibberellins are produced in the apical meristems of the plants, young leaves, and embryos.

Question 18

Name two main functions of Gibberellin. 

Answer

Two main functions of Gibberellin are stem elongation and promoting seed germination.

Question 19

Which hormone is found in green coconut water? 

Answer

Cytokinin is found in green coconut water.

Question 20

Name one function of cytokinin. 

Answer

One function of cytokinin is to stimulate cell division and promote the growth of lateral buds.

Question 21

Which hormone in the plant body does retard the ageing of plants? 

Answer

The hormone that retards the ageing of plants is cytokinin.

Question 22

Which hormone causes earlier seed germination by removing the dormancy of seeds?

Answer

Abscisic acid (ABA) hormone helps in earlier seed germination by removing the dormancy of seeds.

Question 23

What is the full name of GA? 

Answer

The full name of GA is Gibberellic Acid.

Question 24

What is the term used for a growing movement in response to the direction of light? 

Answer

The term used for a growing movement in response to the direction of light is phototropism.

Question 25

What is phytohormone ? 

Answer

Phytohormones, also known as plant hormones, are chemical messengers produced naturally by plants that regulate various physiological processes such as growth, development, and response to environmental stimuli.

Question 26

Mention the place of action of auxins.

Answer

The primary site of auxin action is in the apical meristem, which is the growing tip of the plant.

Question 27

Is there any ductless gland present in plant?

Answer

Yes, plants have ductless glands called endocrine glands that produce and release hormones directly into the bloodstream or surrounding tissues.

Question 28

Name one hormone which is gaseous in nature.

Answer

Nitric oxide (NO) is a hormone that is gaseous in nature.

Short Answer (SA) type questions

Question 1

What is hormone ? 

Answer

Hormones are chemical messengers produced by glands in the endocrine system that regulate various physiological processes in the body. They are transported through the bloodstream to target organs and tissues, where they bind to specific receptors and initiate a response. Hormones play a crucial role in growth and development, metabolism, reproduction, and stress response, among other functions.

Question 2

Name two important characteristics of hormones (plant hormones). 

Answer

Two important characteristics of hormones are:

1. Plant hormones occur in extremely low concentrations.
2. Plant hormones cannot be stored.

Question 3

Mention differences between Hormone and Vitamin. 

Answer

Hormones	Vitamins
Produced by endocrine glands or cells	Obtained from food or dietary supplements
Serve as chemical messengers that regulate physiological processes	Required for various metabolic and biochemical reactions in the body
Act on specific target cells or organs via receptors	Not specific to target cells or organs
Released into the bloodstream to travel to distant target tissues	Act locally within cells or tissues
Examples include insulin, testosterone, and estrogen	Examples include vitamin A, vitamin C, and vitamin D

Question 4

What do you mean by ‘growth regulators’ ? 

Answer

Growth regulators, also known as plant hormones or phytohormones, are chemical substances produced naturally by plants that regulate various aspects of plant growth and development. They control cell division and elongation, differentiation of tissues and organs, seed germination, flowering, fruit ripening, and other processes.

Question 5

What is phytohormone? 

Answer

Phytohormones, also known as plant hormones or growth regulators, are natural chemical substances produced by plants that regulate various physiological processes, such as growth, development, reproduction, and response to stimulus.

Question 6

Name one natural and one artificial plant hormone. 

Answer

1. Natural plant hormone: Auxin
2. Artificial plant hormone: 1-Naphthaleneacetic acid (NAA)

Question 7

What are the chemical name and chemical constituents of Auxin ? 

Answer

Auxins are a group of plant hormones, with Indole-3-acetic acid (IAA) being the most common and well-studied. IAA, with the chemical formula C10H9NO2, is synthesized from the amino acid tryptophan through the indole-3-acetic acid biosynthesis pathway.

Question 8

Mention two important functions of Auxin. 

Answer

The two important functions of Auxin

1. Cell elongation: Auxins promote cell elongation in the elongation zone of the plant, particularly in stems, by loosening cell walls and allowing expansion.
2. Apical dominance: Auxins play a role in apical dominance by suppressing the growth of lateral buds, allowing the main stem to grow taller and outcompete surrounding plants for sunlight.

Question 9

Mention the sources of Gibberellin and Kinin. 

Answer

Source of Gibberellins: Young tissues, seeds, and developing fruits.

Source of Kinin: In the root apical meristems of plants.

Question 10

State two sites of production and two functions of Gibberellin. 

Answer

Sites of production:

1. Shoot apical meristems
2. Root apical meristems

Functions:

1. Promote cell elongation
2. Seed germination:

Question 11

Mention the sites of production and functions of Kinins. 

Answer

Sites of production:

1. Root apical meristems
2. Developing embryos, young leaves, and fruits.

Functions:

1. Cell division and differentiation
2. Apical dominance regulation

Question 12

Distinguishes between Gibberellin and Kinin. 

Answer

Gibberellins	Cytokinins
Primarily synthesized in shoot apical meristems and root apical meristems	Mainly produced in root apical meristems, but also in developing embryos, young leaves, and fruits
Promote stem elongation, seed germination, and fruit development	Stimulate cell division and differentiation, regulate apical dominance and promote lateral bud growth
Gibberellins can delay leaf senescence	Cytokinins can actively delay senescence, particularly in leaves, by reducing the rate of protein degradation

Question 13

What is the chemical name and chemical constituents of Gibberellins? 

Answer

Gibberellin are colourless acids, diterpenoids, consisting of C, H and O. [Formula GA₃ is C₁₉H₂₂O₆]

Question 14

Write short notes on Indole Acetic Acid. 

Answer

Indole-3-acetic acid (IAA) is the most common and well-studied auxin, a class of plant hormones that regulate growth and development. IAA is synthesized from the amino acid tryptophan through the indole-3-acetic acid biosynthesis pathway in plants. It plays crucial roles in processes such as cell elongation, apical dominance, root initiation, and tropisms (directional growth in response to environmental stimuli).

Question 15

State the role of auxin in abscission.

Answer

Auxin plays a critical role in the regulation of abscission, which is the process where plants shed leaves, flowers, or fruits in response to environmental or developmental signals. Auxins produced in young, actively growing organs can suppress the formation of the abscission zone, thereby preventing premature organ shedding

Question 16

Why are lateral branches developed when tip of stem is sectioned ? 

Answer

When the tip of a stem is sectioned or removed, lateral branches develop due to the disruption of apical dominance. Apical dominance is a phenomenon in which the main shoot’s terminal (apical) bud inhibits the growth of lateral (axillary) buds, allowing the main stem to grow taller and outcompete surrounding plants for sunlight.

Question 17

What is parthenocarpic fruit. How it is formed? 

Answer

Parthenocarpic fruit is a type of fruit that develops without fertilization, meaning it is seedless. Parthenocarpy occurs when the ovary of a flower develops into a fruit without undergoing the process of fertilization, which typically involves the fusion of male and female gametes.

Question 18

How plant hormone controls weed? 

Answer

Plant hormones, specifically synthetic auxins, are employed as herbicides to control weeds. These synthetic auxins, such as 2,4-dichlorophenoxyacetic acid (2,4-D), disrupt normal hormonal balance, leading to uncontrolled growth and plant death. They are particularly effective on broadleaf weeds, making them useful in agricultural settings where grass crops are grown.

Question 19

Write short notes on Auxin. 

Answer

Auxins are a class of plant hormones that play essential roles in regulating growth and development processes in plants. The most common auxin, Indole-3-acetic acid (IAA), is synthesized from the amino acid tryptophan. Key functions of auxins include promoting cell elongation, regulating apical dominance, and initiating root formation in response to environmental stimuli.

Question 20

What is Auxin ? Mention the site of secretion and the place of action of auxin.

Answer

Auxin is a class of plant hormones that play a critical role in regulating growth and development processes in plants. The primary site of auxin secretion is the shoot apical meristem, the growing tip of the plant, where it is synthesized from the amino acid tryptophan. Auxin acts in various parts of the plant, including stems, roots, and lateral buds, influencing processes such as cell elongation, apical dominance, root initiation, and directional growth in response to environmental stimuli.

Question 21

Write short notes on Gibberellins.

Answer

Gibberellins are a large family of diterpenoid plant hormones that regulate various aspects of plant growth and development. They are synthesized primarily in shoot apical meristems and root apical meristems. Gibberellins play crucial roles in stem elongation, seed germination, and fruit development, among other growth processes.

Question 22

Write short notes on cytokinins.

Answer

Cytokinins, also known as kinins, are a class of plant hormones that regulate cell division, differentiation, and various developmental processes in plants. They are primarily synthesized in the root apical meristems and are also found in developing embryos, young leaves, and fruits. Cytokinins play vital roles in promoting lateral bud growth, regulating apical dominance, and delaying senescence in leaves.

Question 23

Mention the role of Auxin in rooting and cutting in the plant body. 

Answer

Auxin plays a crucial role in rooting and cutting processes in plants. When stem cuttings are taken from a plant for vegetative propagation, the application of auxin-containing rooting hormone powders or solutions can promote the formation of adventitious roots at the cut site. This occurs because auxins stimulate cell division and elongation in the undifferentiated cells near the cut, leading to the initiation and growth of roots that help the cutting establish itself as a new, independent plant.

Question 24

What do you mean by parthenocarpy? How does plant hormone help in parthenocarpy?

Answer

Parthenocarpy refers to the development of fruit without fertilization, resulting in seedless fruits. It occurs when the ovary of a flower grows into a fruit without the need for fertilization, which typically involves the fusion of male and female gametes.

Plant hormones play a role in promoting parthenocarpy. The application of certain hormones, such as auxins, gibberellins, and cytokinins, can induce parthenocarpy in some plants. These hormones stimulate the growth and development of the ovary, bypassing the requirement for fertilization, and ultimately leading to the formation of seedless fruit

Long Answer (LA) type questions

Question 1

(a) Name one animal and one plant hormones with their site of secretion. (b) What are the general functions of hormone? 

Answer

(a) Animal hormone: Insulin, secreted by the beta cells of the pancreatic islets in the pancreas. Plant hormone: Auxin, primarily secreted by the shoot apical meristem (growing tip of the plant).

(b) Hormones are chemical messengers that regulate various physiological processes in organisms. Their general functions include:

1. Coordination and regulation of growth and development
2. Maintaining homeostasis, or internal balance, within the body
3. Regulating metabolic processes and energy production
4. Facilitating response and adaptation to environmental changes and stressors
5. Mediating communication between cells, tissues, and organs
6. Influencing reproductive processes, sexual development, and behaviors

Question 2

Mention four characteristics of hormone.

Answer

The four characteristics of hormone are

1. Hormones are chemical messengers that are produced by glands or specialized cells in the body.
2. Hormones are transported through the bloodstream to target tissues and organs, where they exert their effects by binding to specific receptors.
3. Hormones are usually present in very low concentrations in the body, but they can have powerful and widespread effects on physiological processes.
4. Hormones often act in a coordinated fashion with other hormones to regulate complex processes in the body, such as growth and development, metabolism, and stress responses.

Question 3

Explain why hormones are known as chemical messenger?

Answer

Hormones are known as chemical messengers because they are signaling molecules that are produced by glands or specialized cells in the body and are transported through the bloodstream to target tissues and organs, where they exert their effects by binding to specific receptors.

Like messengers carrying a message from one person to another, hormones carry information from one part of the body to another to coordinate and regulate various physiological processes. This enables hormones to communicate with distant cells and organs and allows them to affect a wide range of physiological functions, such as growth and development, metabolism, and stress responses.

Question 4

What are the differences between hormones and enzymes?

Answer

Hormones	Enzymes
Produced by glands or specialized cells in the body	Produced by cells in the body
Typically proteins or steroids in nature	Usually proteins in nature
Serve as chemical messengers to regulate physiological processes in the body	Catalyze biochemical reactions in the body
Bind to specific receptors on target cells to exert their effects	Act on specific substrates to catalyze chemical reactions
Typically present in low concentrations in the body	Can be present in high concentrations in the body

Question 5

Name the site of secretions and functions of the following hormones-Plant hormones-(i) Auxin (ii) Gibberellin (iii) Cytokinin or Kinin. 

Answer

Site of secretion and functions of plant hormones:

(i) Auxin

• Site of secretion: Shoot apical meristem
• Functions:
  1. Promotes cell elongation in stems, leaves, and flowers
  2. Regulates apical dominance by suppressing lateral bud growth
  3. Stimulates root initiation and growth
  4. Plays a role in phototropism and gravitropism
  5. Helps in the formation of adventitious roots in cuttings.

(ii) Gibberellin

• Site of secretion: Shoot and root apical meristem
• Functions:
  1. Promotes stem elongation and cell division
  2. Stimulates seed germination and fruit development
  3. Helps in the breaking of dormancy in seeds and buds
  4. Regulates flower development and sex determination
  5. Increases tolerance to abiotic stress.

(iii) Cytokinin or Kinin

• Site of secretion: Root apical meristem
• Functions:
  1. Stimulates cell division and differentiation
  2. Regulates apical dominance by promoting lateral bud growth
  3. Delays senescence in leaves and other organs
  4. Helps in the formation of chloroplasts and thylakoid membranes
  5. Increases tolerance to abiotic stress.

Question 6

Name three hormones of plant. Mention the parts of the plant from where these hormones are produced.

Answer

Question 7

What is auxin ? In which part of the plant auxin is manufactured ? How does auxin work.

Answer

Auxin is a class of plant hormones that play a crucial role in regulating various growth and development processes in plants. The most common auxin is Indole-3-acetic acid (IAA), which is synthesized primarily in the shoot apical meristem, the growing tip of the plant.

Auxin works by binding to specific receptors on the surface of plant cells, which triggers a signal transduction pathway that ultimately leads to changes in gene expression and cellular responses. Auxin promotes cell elongation, regulates apical dominance, stimulates root initiation, and plays a role in tropisms, which are directional growth responses in plants in response to environmental stimuli. Auxin also helps in the formation of adventitious roots in cuttings and plays a role in fruit development.

Question 8

What are Gibberellin ? Mention their sources of secretions and important functions.

Answer

Gibberellins are a class of plant hormones that regulate various growth and developmental processes in plants. They are diterpenoid compounds that are synthesized primarily in the shoot and root apical meristems, young leaves, and developing seeds.

Some important functions of Gibberellins include:

1. Promoting stem elongation and cell division
2. Stimulating seed germination and breaking of dormancy in seeds and buds
3. Regulating flower development and sex determination
4. Stimulating fruit development and seedless fruit formation through parthenocarpy
5. Improving fruit quality by increasing fruit size and reducing ripening time
6. Enhancing tolerance to environmental stressors such as drought and cold temperatures

Question 9

Write the differences between Auxins and Gibberellins.

Answer

Auxins	Gibberellins
Indole-3-acetic acid (IAA) is the primary auxin found in plants	Gibberellins are diterpenoid compounds synthesized from isopentenyl pyrophosphate
Produced primarily in the shoot apical meristem and young leaves	Produced in the shoot and root apical meristems, young leaves, and developing seeds
Promote cell elongation, regulate apical dominance, stimulate root initiation, and play a role in tropisms and fruit development	Promote stem elongation and cell division, stimulate seed germination and dormancy breaking, regulate flower development and sex determination, and enhance tolerance to environmental stressors
Act by binding to specific receptors on the surface of plant cells and triggering a signal transduction pathway	Bind to specific receptors and regulate gene expression and cellular responses
Examples – Indole-3-acetic acid (IAA), 2,4-dichlorophenoxyacetic acid (2,4-D)	Examples – Gibberellic acid (GA), gibberellin A3 (GA3

Question 10

What is cytokinin ? Name the sources from which it is secreted. Mention its function.

Answer

Cytokinins, also known as kinins, are a class of plant hormones that regulate various developmental processes in plants. They are primarily synthesized in the root apical meristem and are also found in developing embryos, young leaves, and fruits.

Some important functions of cytokinins include:

1. Stimulating cell division and differentiation
2. Regulating apical dominance by promoting lateral bud growth
3. Delaying senescence in leaves and other organs
4. Promoting the formation of chloroplasts and thylakoid membranes
5. Increasing tolerance to abiotic stress such as drought, salinity, and high temperature.

Cytokinins work in conjunction with other plant hormones such as auxins and gibberellins to regulate various physiological processes in plants.

Question 11

Distinguish between Gibberellin and Kinin.

Answer

Gibberellins	Cytokinins
Diterpenoid compounds synthesized from isopentenyl pyrophosphate	Adenine derivatives
Produced in the shoot and root apical meristems, young leaves, and developing seeds	Produced in the root apical meristem, developing embryos, and young leaves
Promote stem elongation and cell division, stimulate seed germination and dormancy breaking, regulate flower development and sex determination, and enhance tolerance to environmental stressors	Stimulate cell division and differentiation, regulate apical dominance by promoting lateral bud growth, delay senescence in leaves and other organs, promote the formation of chloroplasts and thylakoid membranes, and increase tolerance to abiotic stress
Used to promote elongation and cell division in stem cuttings and tissue culture	Used to promote shoot formation and organogenesis in tissue culture
Gibberellic acid (GA), gibberellin A3 (GA3)	Zeatin, isopentenyladenine (iP), kinetin

Question 12

Discuss briefly about the practical application of plant hormone in agriculture. Or, Discuss the practical application of Auxin hormones in agriculture.

Answer

Auxin hormones have several practical applications in agriculture. Some of the key applications of auxins in agriculture are:

1. Rooting of stem cuttings: Auxin-containing rooting hormone powders or solutions are used to promote the formation of adventitious roots in stem cuttings, which can be then used for vegetative propagation of plants.
2. Fruit thinning: Auxin sprays are used to reduce the number of fruit on a tree by inducing fruit drop. This helps in increasing the quality and size of the remaining fruit.
3. Weed control: Auxin-like herbicides, such as 2,4-dichlorophenoxyacetic acid (2,4-D), are used to control broadleaf weeds in crops such as corn, soybeans, and wheat.
4. Delaying fruit ripening: Synthetic auxins, such as 2,4-D, are used to delay the ripening of fruit such as apples and pears to extend their shelf life and improve their marketability.
5. Controlling plant growth: Auxins are used to control the growth and development of ornamental plants, such as bonsai trees and roses, by regulating apical dominance and promoting lateral branching.

Question 13

We are benefited by application of hormones in agriculture. Mention three such hormones and show their usefulness.

Answer

Here are three plant hormones used in agriculture and their benefits:

1. Auxins:

• Benefit: Used to promote root formation in cuttings and to thin fruit, which improves fruit quality and size.
• Example: Indole-3-acetic acid (IAA)

2. Gibberellins:

• Benefit: Used to promote stem elongation, increase seed germination rates, and stimulate flowering, which can improve crop yields.
• Example: Gibberellic acid (GA)

3. Cytokinins:

• Benefit: Used to stimulate cell division and differentiation, which can promote overall plant growth and development.
• Example: Kinetin

Question 14

Mention the sources of Gibberellin and Kinin. Discuss the practical application of plant hormones in agriculture.

Answer

Sources of Gibberellin and Kinin:

• Gibberellins are primarily synthesized in the shoot and root apical meristems, young leaves, and developing seeds.
• Cytokinins are synthesized in the root apical meristem, developing embryos, and young leaves.

Practical applications of plant hormones in agriculture:

• Rooting of stem cuttings: Auxin-containing rooting hormone powders or solutions are used to promote the formation of adventitious roots in stem cuttings, which can be then used for vegetative propagation of plants.
• Fruit thinning: Auxin sprays are used to reduce the number of fruit on a tree by inducing fruit drop. This helps in increasing the quality and size of the remaining fruit.
• Weed control: Auxin-like herbicides, such as 2,4-dichlorophenoxyacetic acid (2,4-D), are used to control broadleaf weeds in crops such as corn, soybeans, and wheat.
• Delaying fruit ripening: Synthetic auxins, such as 2,4-D, are used to delay the ripening of fruit such as apples and pears to extend their shelf life and improve their marketability.
• Controlling plant growth: Plant growth regulators, such as gibberellins, are used to regulate plant growth and development to improve crop yields and plant quality.