SSLC / 10th - Science - Book Back Answers - Biology Unit 16 - English Medium
Tamil Nadu Board 10th Standard Science - Biology Unit 16: Book Back Answers and Solutions
This post covers the book back answers and solutions for Unit 16 – Biology from the Tamil Nadu State Board 10th Standard Science textbook. These detailed answers have been carefully prepared by our expert teachers at KalviTips.com.
We have explained each answer in a simple, easy-to-understand format, highlighting important points step by step under the relevant subtopics. Students are advised to read and memorize these subtopics thoroughly. Once you understand the main concepts, you’ll be able to connect other related points with real-life examples and confidently present them in your tests and exams.
By going through this material, you’ll gain a strong understanding of Biology Unit 16 along with the corresponding book back questions and answers (PDF format).
Question Types Covered:
- 1 Mark Questions: Choose the correct answer, Fill in the blanks, Identify the correct statement, Match the following
- 2 Mark Questions: Answer briefly
- 3, 4, and 5 Mark Questions: Answer in detail
All answers are presented in a clear and student-friendly manner, focusing on key points to help you score full marks.
All the best, Class 10 students! Prepare well and aim for top scores. Thank you!
Topic: Plant and Animal Hormones
I. Choose the correct Answer
1. Gibberellins cause:(a) Shortening of genetically tall plants
(b) Elongation of dwarf plants
(c) Promotion of rooting
(d) Yellowing of young leaves
Answer Key:
(b) Elongation of dwarf plants
2. The hormone which has a positive effect on apical dominance is _____.
(a) Cytokinin
(b) Auxin
(c) Gibberellin
(d) Ethylene.
Answer Key:
(b) Auxin
3. Which one of the following hormones is naturally not found in plants:
(a) 2, 4-D
(b) GA3
(c) Gibberellin
(d) IAA
Answer Key:
(a) 2, 4-D
4. Avena coleoptile test was conducted by _____.
(a) Darwin
(b) N. Smit
(c) Paal
(d) F.W. Went.
Answer Key:
(d) F.W. Went.
5. To increase the sugar production in sugarcanes they are sprayed with
(a) Auxin
(b) Cytokinin
(c) Gibberellins
(d) Ethylene
Answer Key:
(d) Ethylene
6. LH is secreted by _____.
(a) Adrenal gland
(b) Thyroid gland
(c) Anterior pituitary
(d) Hypothalamus.
Answer Key:
(c) Anterior pituitary
7. Identify the exocrine gland:
(a) Pituitary gland
(b) Adrenal gland
(c) Salivary gland
(d) Thyroid gland
Answer Key:
(c) Salivary gland
8. Which organ acts as both exocrine gland as well as endocrine gland?
(a) Pancreas
(b) Kidney
(c) Liver
(d) Lungs.
Answer Key:
(a) Pancreas
9. Which one is referred to as “Master Gland”?
(a) Pineal gland
(b) Pituitary gland
(c) Thyroid gland
(d) Adrenal gland
Answer Key:
(b) Pituitary gland
II. Fill in the blanks
1. ………. causes cell elongation, apical dominance and prevents abscission.2. …………. is a gaseous hormone involved in abscission of organs and acceleration of fruit ripening.
3. ……… causes stomatal closure.
4. Gibberellins induce stem elongation in ……… plants.
5. The hormone which has negative effect on apical dominance is ………
6. Calcium metabolism of the body is controlled by ………
7. In the islets of Langerhans, beta cells secrete ………
8. The growth and functions of thyroid gland is controlled by ………..
9. Decreased secretion of thyroid hormones in the children leads to ………
Answer Key:
1. Auxin
2. Ethylene
3. Abscisic acid
4. Rosette
5. Ethylene
6. Parathormone
7. Insulin
8. Thyroid Stimulating Hormone (TSH)
9. Cretinism
III.Match the following
1. Match Column
I with Columns II and III
|
Column I
|
Column II
|
Column III
|
|
Auxin
|
Gibberella fujiuroi | Abscission
|
|
Ethylene
|
Coconut milk
|
Internodal elongation
|
|
Abscisic acid
|
Coleoptile tip
|
Apical dominance
|
|
Cytokinin
|
Chloroplast
|
Ripening
|
|
Gibberellins
|
Fruits
|
Cell division
|
Answer Key:
|
Column I
|
Column II
|
Column III
|
|
Auxin
|
Coleoptile tip
|
Apical dominance
|
|
Ethylene
|
Fruits
|
Ripening
|
|
Abscisic acid
|
Chloroplast
|
Abscission
|
|
Cytokinin
|
Coconut milk
|
Cell division
|
|
Gibberellins
|
Gibberella fujikuroi
|
Internodal elongation
|
2.Match the following hormones with their deficiency
states.
|
Hormones
|
Disorders
|
||
|
1
|
Thyroxine
|
i
|
Acromegaly
|
|
2
|
Insulin
|
ii
|
Tetany
|
|
3
|
Parathormone
|
iii
|
Simple
goitre
|
|
4
|
Growth
hormone
|
iv
|
Diabetes
insipidus
|
|
5
|
ADH
|
v
|
Diabetes
mellitus
|
Answer Key:
|
Hormones
|
Disorders
|
||
|
1
|
Thyroxine
|
iii
|
Simple
goitre
|
|
2
|
Insulin
|
v
|
Diabetes
mellitus
|
|
3
|
Parathormone
|
ii
|
Tetany
|
|
4
|
Growth
hormone
|
i
|
Acromegaly
|
|
5
|
ADH
|
iv
|
Diabetes
insipidus
|
a
IV. State whther True or False, If false wirte the correct staement.
2. Gibberellins cause parthenocarpy in tomato.
3. Ethylene retards senescence of leaves,flowers and fruits.
4. Exopthalmic goiter is due to the over secretion of thyroxine.
5. Pituitary gland is divided into four lobes.
6. Oestrogen is secreted by corpus luteum.
Answer Key:
1. True
2. True
3. False – Ascorbic Acid retards senescence of leaves, flowers and fruits.
4. True
5. False – Parathyroid gland is divided into four lobes.
6. False – Oestrogen is produced by the Graffian follicles.
V. Assertion & Reasoning
Direction: In each of the following questions a statement
of assertion (A) is given and a corresponding statement of reason (R) is given
just below it. Mark the correct statement as.
1. Assertion (A): Application of cytokinin to marketed vegetables can keep them
fresh for several days.
Reason (R): Cytokinins delay senescence of leaves and other organs by
mobilisation of nutrients.
(a) If both A and R are true and R is correct explanation of A
(b) If both A and R are true but R is not the correct explanation of A
(c) A is true but R is false
(d) Both A and R are false
Answer Key:
(b) If both A and R are true but R is not the correct explanation of A
2. Assertion (A): Pituitary gland is referred as “Master
gland”.
Reason (R): It controls the functioning of other endocrine glands.
(a) If both A and R are true and R is correct explanation of A
(b) If both A and R are true but R is not the correct explanation of A
(c) A is true but R is false
(d) Both A and R are false
Answer Key:
(a) If 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.
(a) If both A and R are true and R is correct explanation of A
(b) If both A and R are true but R is not the correct explanation of A
(c) A is true but R is false
(d) Both A and R are false
Answer Key:
(a) If both A and R are true and R is correct explanation of A
VI. Answer in a word or sentence
1. Which hormone promotes the production of male flowers in Cucurbits?Answer Key:
Gibberellin promotes the production of male flower in Cucurbits.
2. Write the name of synthetic auxin.
Answer Key:
2, 4 D (2, 4 Dichlorophenoxy Acetic acid).
3. Which hormone induces parthenocarpy in tomatoes?
Answer Key:
Gibberellin induces parthenocarpy in tomatoes.
4. What is the hormone responsible for the secretion of milk in the female after childbirth?
Answer Key:
Prolactin stimulates the production of milk after childbirth. Oxytocin helps milk ejection from the mammary gland after childbirth.
5. Name the hormones which regulates water and mineral metabolism in man.
Answer Key:
Mineralocorticoids hormones of Adrenal cortea maintain the water balance and mineral metabolism in man.
6. Which hormone is secreted during an emergency situation in a man?
Answer Key:
The hormones of Adrenal medulla,
•Epinephrine (Adrenaline)
•Norepinephrine (Noradrenaline) are secreted during an emergency situation in man.
7. Which gland secretes digestive enzymes and hormones?
Answer Key:
Pancreas secretes digestive enzymes and hormones.
8. Name the endocrine glands associated with kidneys.
Answer Key:
Adrenal gland, which is called suprarenal glands is associated with kidneys.
VII. Short answer questions
1. What are synthetic auxins? Give examples.Answer Key:
Artificially synthesized auxin which has the properties of auxins are called Synthetic Auxin. Eg: 2, 4-D
2. What is bolting? How can it be induced artificially?
Answer Key:
Treatment of rosette
plants with gibberellin induces sudden shoot elongation followed by flowering is called bolting. It can be induced artificially before the crop is harvested.
3. Bring out any two physiological activities of abscisic acid.
Answer Key:
The two physiological activities of abscisic acid are:
1.During water stress and drought conditions, Abscisic acid causes stomatal closure.
2.Abscisic acid induces bud dormancy towards the approach of winter in trees like birch.
4. What will you do to prevent leaf fall and fruit drop in plants? Support your Answer Key with reason.
Answer Key:
• Very chill deposition on leaves and fruits cause the drop in plants. Protect the tree from frost providing an overhead cover.
• The plant hormone ethylene controls fruit ripening, flower wilting and leaf fall by stimulating the conversion of starch and acids to sugar.
5. What are chemical messengers?
Answer Key:
Endocrine glands control and coordinate the body functions through secreting certain chemical messengers called hormones.
6. Write the differences between endocrine and exocrine gland.
Answer Key:
|
Exocrine gland |
Endocrine gland |
|
Exocrine glands have specific duct to carry their secretion. |
Endocrine glands are found in different regions of the body . |
|
They have specific duct. |
They do not have specific duct, so they are called ductless gland. |
|
The secretion are produced from the specific duct. |
The secretion diffuse into the blood stream and reach the target organ. |
|
E.g: Salivary glands sweat glands |
E.g: Pituitary Adrenal glands |
7. What is the role of parathormone?
Answer Key:
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 gland? Mention the tissues on which they exert their effect.
Answer Key:
The hormones secreted by the posterior pituitary are:
1.Vasopressin or Antidiuretic hormone: In kidney tubules it increases reabsorption of water.
2.Oxytocin: They exert their effect on the muscles of uterus which helps in the contraction of smooth muscles of uterus at the time of child birth and milk ejection from mammary gland after child birth.
9. Why are thyroid hormones referred to as personality hormone?
Answer Key:
Thyroid hormones are referred to as personality hormone because they are essential for normal physical, mental and personality development.
10. Which hormone requires iodine for its formation? What will happen if intake of iodine in our diet is low?
Answer Key:
The formation of Thyroxine or Thyroid hormone requires iodine. If there is an inadequate supply of iodine in our diet it leads to goitre.
VIII. Long answer questions
1.(a) Name the gaseous plant hormone. Describe its three different actions in plants.(b) Which hormone is known as a stress hormone in plants? Why?
Answer Key:
(a) Ethylene is a gaseous plant hormone. It is a growth inhibitor. The different actions of ethylene are as follows:
• Ethylene promotes the ripening of fruits, eg. Tomato, Apple, Mango, Banana and etc.
• Ethylene inhibits the elongation of stem and root in dicots.
• Ethylene hastens the senescence of leaves and flowers.
• Ethylene stimulates the 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) Abscisic acid (ABA) is a growth inhibitor which regulates abscission and dormancy. It increases the tolerance of plants to various kinds of stress. So, it is also called a stress hormone.
2. Describe an experiment which demonstrates that growth stimulating hormone is produced at the tip of coleoptile.
Answer Key:
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.
Answer Key:
• Application of gibberellins on plants stimulates extraordinary elongation of internodes. eg. Com and Pea.
• Treatment of rosette plants with gibberellin induces sudden shoot elongation followed by flowering, called bolting.
• Gibberellins promote the production of male flowers in monoecious plants like Cucurbits
• Gibberellins break the dormancy of potato tubers.
• Gibberellins is inducing the formation of seedless fruit, termed as Parthenocarpic fruits (Development of fruits without fertilization) eg. Tomato.
4. Where are oestrogens produced? What is the role of oestrogens in the human body?
Answer Key:
Oestrogen is produced by the Graafian follicles of the ovary.
Functions of oestrogens:
1. It brings about the changes that occur during puberty.
2. It initiates the process of oogenesis.
3. It stimulates the maturation of ovarian follicles in the ovaiy.
4. 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 from one another?
Answer Key:
Lack of ADH: Deficiency of ADH (Antidiuretic hormone) reduces the reabsorption of water and causes an increase in urine output (polyuria). This deficiency disorder is called Diabetes insipidus.
Lack of insulin: The deficiency of insulin causes Diabetes mellitus. It is characterised by,
• Increase in blood sugar level (Hyperglycemia).
• Excretion of excess glucose in the urine (Glycosuria).
• Frequent Urination (Polyuria).
• Increased thirst (Polydipsia).
• Increase in appetite (Polyphagia).
Lack of ADH reduces the reabsorption of water and increases the urine output. Lack of insulin causes the Diabetes mellitus, which increases the blood sugar level and excrete the excess glucose in the urine, causing frequent urination.
Insulin:
Deficiency in insulin causes Diabetes mellitus.
Insulin deficiency increase the blood sugar level (Hyperglycemia), excretion of excess glucose in the urine (Glycosuria), frequent urination (Polyuria) increased thirst (Polydipsia), increase in appetite (Polyphagia).
IX. HOTS questions
1. What would be expected to happen if(a) Gibberellin is applied to rice seedlings.
Answer Key:
Causes imemodal elongation in rice.
(b) A rotten fruit gets mixed with unripe fruits.
Answer Key:
If a rotten fruits get mixed with unripe fruit. Then the ethylene produced from the rotten fruit will hasten the ripening of the unripe fruits.
(c) When cytokinin is not added to culture medium.
Answer Key:
Formation of new organs from the callus in tissue culture (Morphogenesis) will not be formed.
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.
2. Which property of this hormone causes the disease?
3. Give two functions of this hormone.
Answer Key:
1. Gibberellins
2. Intermodal elongation
3. Functions:
- promotes the production of male flowers in monoecious plants.
- Gibberellins break the dormancy of potato tubers.
3. Senthil has high blood pressure, protruded eyeball and increased body temperature. Name the endocrine gland involved and hormone secretion responsible for this condition.
Answer Key:
The gland involved is the thyroid gland. The hormone involved in a thyroid hormone. It is due to excess secretion of thyroid hormones called hyperthyroidism which leads to Graver’s disease.
4. Sanjay is sitting in the exam hall. Before the start of the exam, he sweats a lot, with an increased rate of heartbeat. Why does this condition occur?
Answer Key:
This is due to the secretion of the hormone Adrenaline in Adrenal medulla of Adrenal gland.
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.
Answer Key:
A balance between insulin and glucogon production is necessary to maintain blood glucose concentration.
The deficiency of insulin causes Diabetes Mellitus.
Preventive measure:
1. Take proper or balanced diet.
2. Exercise regularly
3. Avoid stress.
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