You are currently viewing 10th Science Guide Unit 16 Plant and Animal Hormones

10th Science Guide Unit 16 Plant and Animal Hormones

10th Science Guide Unit 16 Plant and Animal Hormones

10th Standard Science Biology Lesson 16 Plant and Animal Hormones Book Back Answers | Samacheer Kalvi Guide

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10th Standard Science Book Solution Lesson 16 Plant and Animal Hormones


I. Choose the best answer

1. Gibberellins cause:

  1. Shortening of genetically tall plants
  2. Elongation of dwarf plants
  3. Promotion of rooting
  4. Yellowing of young leaves

Ans ; Elongation of dwarf plants

2. The hormone which has positive effect on apical dominance is:

  1. Cytokinin
  2. Auxin
  3. Gibberellin
  4. Ethylene

Ans ; Auxin

3. Which one of the following hormones is naturally not found in plants:

  1. 2, 4–D
  2. G A 3
  3. Gibberellin
  4. IAA

Ans ; 2, 4–D

4. Avena coleoptiles est was conducted by

  1. Darwin
  2. Smit
  3. Paal
  4. W. Went

Ans ; F.W. Went

5. To increase the sugar production in sugarcanes they are sprayed with _______

  1. Auxin
  2. Cytokinin
  3. Gibberellins
  4. Ethylene

Ans ; Ethylene

6. LH is secreted by

  1. Adrenal gland
  2. Thyroid gland
  3. Anterior pituitary
  4. Hypothalamus

Ans ; Anterior pituitary

7. Identify the exocrine gland

  1. Pituitary gland
  2. Adrenal gland
  3. Salivary gland
  4. Thyroid gland

Ans ; Salivary gland

8. Which organ acts as both exocrine gland as well as endocrine gland

  1. Pancreas
  2. Kidney
  3. Liver
  4. Lungs

Ans ; Pancreas

9. Which one is referred as “Master Gland”?

  1. Pineal galnd
  2. Pituitary gland
  3. Thyroid gland
  4. Adrenal gland

Ans ; Pituitary gland

II. Fill in the blanks

  1. __________ causes cell elongation, apical dominance and prevents abscission. Ans ; Auxin

  1. __________ is a gaseous hormone involved in abscission of organs and acceleration of fruit ripening. Ans ; Ethylene

  1. __________ causes stomatal closure.Ans ; Abscisic acid

  2. Gibberellins induce stem elongation in __________ plants.Ans ; Rosette

  3. The hormone which has negative effect on apical dominance is __________.Ans ; Cytokinin

  4. Calcium metabolism of the body is controlled by __________.Ans ; Parathormone

  5. In the islets of Langerhans, beta cells secrete __________.Ans ; Insulin

  6. The growth and functions of thyroid gland is controlled by __________. Ans ; Thyroid Stimulating Hormone (TSH)

  1. Decreased secretion of thyroid hormones in the children leads to __________. Ans ;  Cretinisms

III a) Match Column I with Columns II and III

Column I

Column II

Column III


Gibberella fujikuroi



Coconut milk

Internodal elongation

Abscisic acid

Coleoptile tip

Apical dominance






Cell division

Ans ; 1 – C – C, 2 – E – D, 3 – D – A, 4 – B – E, 5 – A – B

III b) Match the following hormones with their deficiency states



1. Thyroxine


2. Insulin


3. Parathormone

Simple goitre

4. Growth hormone

Diabetes insipidus

5. ADH

Diabetes mellitu

Ans ; 1 – C, 2 – E, 3 – B, 4 – A, 5- D

IV. State whether true or false, if false write the correct statement

  1. A plant hormone concerned with stimulation of cell division and promotion of nutrient mobilization is cytokinin. ( True )
  2. Gibberellins cause parthenocarpy in tomato. ( True )
  3. Ethylene retards senescence of leaves, flowers and fruits. ( False )
  • Ethylene hastens senescence of leaves, flowers and fruits.
  1. Exopthalmic goiter is due to the over secretion of throxine. ( True )
  2. Pituitary gland is divided into four lobes. ( False )
  • Pituitary gland is divided into two lobes.
  1. Estrogen is secreted by corpus luteum. ( False )
  • Estrogen is secreted by Graafian follicles.

V Assertion and Reasoning

  1. Assertion is correct and reason is wrong.
  2. Reason is correct and the assertion is wrong.
  3. Both assertion and reason are correct.
  4. Both assertion and reason are wrong.

1. Assertion : Application of cytokinin to marked vegetables can keep them fresh for several days.

Reason : Cytokinins delay senescence of leaves and other organs by mobilisation of nutrients.

Ans : (a) Both A and R ture and R is correct explanation of A

2. Assertion (A) : Pituitary gland is referred as “Master gland”.

Reason (R) : It controls the functioning of other endocrine glands.

Ans : (a) Both A and R are true and R is correct explanation of A

3. Assertion (A) :- Diabetes mellitus increases the blood sugar levels.

Reason (R) :- Insulin decreases the blood sugar levels.

Ans : (b) Both A and R are true but R is not the correct explanation of A


VI Answer in a word or sentence

1. Which hormone promotes the production of male flowers in Cucurbits?

  • Gibberellins hormone promotes the production of male flower in Cucurbits.

2. Write the name of a synthetic auxin.

  • 2,4 D – (2,4 Dichlorophenoxy Acetic Acid) is a synthetic auxin.

3. Which hormone induces parthenocarpy in tomatoes?

  • Gibberellins hormone induces parthenocarpy in tomatoes.

4. What is the hormone responsible for the secretion of milk in female after child birth?

  • Prolactin (PRL) or Lactogenic Hormone is responsible for the secretion of milk in female after child birth.

5. Name the hormones which regulates water and mineral metabolism in man.

  • Aldosterone regulates water and mineral metabolism in man.

6. Which hormone is secreted during emergency situation in man?

  • Adrenaline is secreted during emergency situation in man.

7. Which gland secretes digestive enzymes and hormones?

  • Pancreas is a duel gland. It secretes both digestive enzymes and hormones.

8. Name the endocrine glands associated with kidneys.

  • The endocrine glands associated with kidneys is Adrenal Gland.


10th Science Guide Unit 16 Plant and Animal Hormones

VII Short answer questions

1. What are synthetic auxins? Give examples.

  • Artificially synthesized auxins that have properties like auxins are called as synthetic auxins.
  • Example: 2, 4 D (2,4 Dichlorophenoxy Acetic Acid).

2. What is bolting? How can it be induced artificially?

  • Bolting : Treatment of rosette plants with gibberellin induces sudden shoot elongation followed by flowering. This is called bolting.
  • It is induced by artificial treatment with plant hormone gibberellin. It causes stem elongation in plants under normal condition.

3. Bring out any two physiological activities of abscisic acid.

  • ABA promotes the process of abscission (separation of leaves, flowers and fruits from the branch).
  • ABA promotes senescence in leaves by causing loss of chlorophyll.

4. What will you do to prevent leaf fall and fruit drop in plants? Support your answer with reason.

  • We can spray auxins to prevent leaf fall and fruit drop in plants. Auxins prevent the formation of abscission layer thus delay the abscission of leaves and fruits. So leaf and fruit can remain attached to the stem long time.

5. What are chemical messengers?

  • Hormones are powerful messengers that control and coordinate essential processes such as growth, metabolism and fertility by carrying messges from endocrine glands to target cells and tissues.

6. Write the differences between endocrine and exocrine gland.

Endocrine gland

Exocrine gland

1. They secrete hormones

They secrete enzymes, saliva and milk

2. They are ductless gland

They may have or may not have ducts

3. They are transported through blood stream

They are transported through ducts or tubes

4. They control long term activities

They control short term activities

5. Ex: Piyuitary, Thyroid, Adrenal, etc.

Ex: Salivary, Gastric and Sweat glands


7. What is the role of parathormone?

Role of parathormone

  • The parathormone regulates calcium and phosphorus metabolism in the body.
  • They act on bone, kidney and intestine to maintain blood calcium levels

8. What are the hormones secreted by posterior lobe of the pituitary land? Mention the tissues on which they exert their effect.

Hormones secreted by posterior lobe of the pituitary gland

Hormones excert effect on

1. Vasopressin or Antidiuretic hormone

Tissues of kidney tubules

2. Oxytocin

Tissues of uterus and mammary gland

9. Why are thyroid hormones refered as personality hormone?

  • As thyroid hormones (Triiodothyronine (T3) and Tetraiodothyronine (T4) or Thyroxine) are essential for normal physical, mental and personality development, they are also known as personality hormone.

10. Which hormone requires iodine for its formation? What will happen if intake of iodine in our diet is low?

  • Thyroid hormones, Triiodothyronine (T3) and Tetraiodothyronine or Thyroxine (T4) require iodine for its formation.
  • The inadequate supply of iodine in our diet leads to the enlargement of thyroid gland which protrudes as a marked swelling in the neck and is called as goitre.


VIII. Long answer questions

1. a) Name the gaseous plant hormone. Describe its three different actions in plants.

Physiological effects of ethylene :

  • Ethylene promotes the ripening of fruits eg: Tomato, Apple, Mango, Banana, etc.
  • Ethylene inhibits the elongation of stem and root in dicots.
  • Ethylene hastens the senescence of leaves and flowers.
  • Ethylene stimulates formation of abscission zone in leaves, flowers and fruits. This leads to premature shedding.
  • Ethylene breaks the dormancy of buds, seeds and storage organs.

b) Which hormone is known as stress hormone in plants? Why?

  • Abscisic acid (ABA) is the stress hormone. Because it increases tolerance of plants to various kinds of stress. So, it is called as stress hormone.

2. Describe an experiment which demonstrates that growth stimulating hormone is produced at the tip of coleoptile.

  • Frits Warmolt Went (1903–1990), a Dutch biologist demonstrated the existence and effect of auxin in plants.
  • He did a series of experiments in Avena coleoptiles.
  • In his first experiment he removed the tips of Avena coleoptiles.
  • The cut tips did not grow indicating that the tips produced something essential for growth. In his second experiment he placed the agar blocks on the decapitated coleoptile tips.
  • The coleoptile tips did not show any response. In his next experiment he placed the detached coleoptile tips on agar blocks.
  • After an hour, he discarded the tips and placed this agar block on the decapitated coleoptile.
  • It grew straight up indicating that some chemical had diffused from the cut coleoptile tips into the agar block which stimulated the growth.
  • From his experiments Went concluded that a chemical diffusing from the tip of coleoptiles was responsible for growth, and he named it as “Auxin” meaning ‘to grow”.

3. Write the physiological effects of gibberellins.

Physiological effects of Gibberellins:

  • Application of gibberellins on plants stimulate extraordinary elongation of internode. eg: Corn and Pea.
  • Treatment of rosette plants with gibberellin induces sudden shoot elongation followed by flowering. This is called bolting.
  • Gibberellins promote the production of male flowers in monoecious plants (Cucurbits).
  • Gibberellins break dormancy of potato tubers.
  • Gibberellins are efficient than auxins in inducing the formation of seedless fruit – Parthenocarpic fruits (Development of fruits without fertilization) eg: Tomato.

4. Where are estrogens produced? What is the role of estrogens in the human body?

  • Estrogens are produced by the Graafian follicles of the ovary.

Functions of estrogens :

  • It brings about the changes that occur during puberty.
  • It initiates the process of cogenesis.
  • It stimulates the maturation of ovarian follicles in the ovary.
  • It promotes the development of secondary sexual characters (breast development, high pitched voice etc).

5. What are the conditions which occur due to lack of ADH and insulin? How are the conditions different form one another?

  1. i) The conditions occur due to lack of ADH and insulin
  • Deficiency of ADH causes Diabetes insipidus.
  • The deficiency of insulin causes Diabetes mellitus.
  1. ii) Differences between Diabetes insipidus and Diabetes mellitus

Diabetes insipidus

Diabetes mellitus

1. It reduces reabsorption water in kidney tubules

It increases blood sugar level (Hyperglycemia)

2. Sympoms :

  1. Frequenty and excessive urination (polyuria)
  2. Dehydration
  3. Increased thirst (Polydipsia)

Symptoms :

  1. Excretion of excess glucose in the urine (Clycosuria)
  2. Frequenty urination (Polyuria)
  3. Increased thirst (Polydipsia)
  4. Increase in appetite (Polyphagia)

10th Science Guide Unit 16 Plant and Animal Hormones

IX Higher Order Thinking Skills (HOTS)

1. What would be expected to happen if :

  1. Gibberellin is applied to rice seedlings.

If Gibberellins is applied to rice seedlings, then the rice seedlings will exhibit internode-elongation and increase in height.

  1. A rotten fruit gets mixed with unripe fruits.

If rotten fruits get mixed with unripe fruits, then the Ethylene produced from the rotten fruits will hastens the ripening of the unripe fruits.

  1. When cytokinin is not added to culture medium.

When cytokinin is not added to culture medium, it slows down the cell division and there by prevent thefomation of new organs from the callus (Organogenesis) in the tissue culture.

2. A plant hormone was first discovered in Japan when rice plants were suffering from Bakanae disease caused by Gibberella fujikoroi. Based on this information answer the following questions:

  1. Identify the hormone involved in this process.

The hormone involved in this process is Gibberellins.

  1. b. Which property of this hormone causes the disease?

Gibberellins has the property of stimulating the extraordinary elongation of internode.

  1. Give two functions of this hormone.

Gibberellins promote the production of male flowers in monoecious plants (Cucurbits).

Gibberellins break dormancy of potato tubers.

3. Senthil has high blood pressure, protruded eyeball and an increased body temperature. Name the endocrine gland involved and hormone secretion responsible for this condition.

High blood pressure, protruded eyeball and an increased body temperature are the symptoms of Grave’s disease. It is caused due to the excess secretion (Hyperthyroidism) of the thyroid hormones.

  1. a) The endocrine gland involved for this condition is Thyroid gland.
  2. b) Hormones responsible for this condition are Thyroid hormones such as
  • Triiodothyronine (T3).
  • Tetraiodothyronine or Thyroxine (T4).

4. Sanjay is sitting in the exam hall. Before the start of the exam , he sweats a lot, with increased rate of heart beat. Why does this condition occur?

In stressful situations, such as before and during an exam, the body releases “Emergency hormones” called Epinephrine (Adrenaline) and Norepinephrine (Noradrenaline). Secretion of these hormones leads to conditions such as more sweating and increased rate of heart beat.

5. Susan’s father feels very tired and frequently urinates. After clinical diagnosis he was advised to take an injection daily to maintain his blood glucose level. What would be the possible cause for this? Suggest preventive measures.

Feeling very tired and frequent urination are the symptoms of Diabetes mellitus. It is caused due to deficiency of insulin.

Prevention of Diabetes mellitus

  • Performing physical activity on a regular basis may help prevent diabetes.
  • Lose excess body fat – Being overweight is a big risk factor for diabetes.
  • Follow a plant-based, low-calorie diet.
  • Foods to avoid are those rich in trans fats (also called hydrogenated fat), saturated fat, and sugar.
  • Stress less : The stress response triggers the release of several hormones that increase blood sugar.
  • Sleep well : Chronic sleep deprivation and poor quality sleep increase the risk for diabetes and obesity.

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