NCERT Solutions for Class 11 Biology Chapter 19: Chemical Coordination and Integration (NCERT 2026–27)

These Class 11 Biology Chapter 19 solutions cover Chemical Coordination and Integration from the NCERT textbook (session 2026–27). The chapter explains how the endocrine system uses hormones — non-nutrient chemical messengers produced in trace amounts — to coordinate and regulate body functions alongside the neural system. Below you will find every NCERT Exercises question reproduced verbatim and answered in exam-ready prose, plus extra questions, MCQs, assertion–reason items, exam tips and FAQs.

Class: 11 Subject: Biology Chapter: 19 Title: Chemical Coordination and Integration Unit: Human Physiology Session: 2026–27
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Class 11 Biology Chapter 19 Solutions – Overview

Chapter 19, Chemical Coordination and Integration, describes the second great coordinating system of the body. While the neural system gives fast, short-lived, point-to-point control, the endocrine system provides slower but longer-lasting, widespread regulation through hormones. The chapter surveys the organised endocrine glands — hypothalamus, pituitary, pineal, thyroid, parathyroid, thymus, adrenal, pancreas, testis and ovary — and the hormone-secreting cells of the heart, kidney and gastrointestinal tract. It explains each gland’s hormones and their functions, common disorders linked to hyper- or hypo-secretion (such as goitre, diabetes mellitus, gigantism and Addison’s disease), and finally the mechanism of hormone action through membrane-bound receptors (using second messengers) and intracellular receptors (regulating gene expression).

Key Concepts & Definitions

Endocrine gland: a ductless gland that secretes hormones directly into the blood, which carries them to distant target organs.

Hormone: a non-nutrient chemical that acts as an intercellular messenger and is produced in trace amounts.

Hypothalamus: the basal part of the diencephalon; its neurosecretory nuclei produce releasing and inhibiting hormones that control the pituitary.

Pituitary parts: pars distalis (anterior pituitary — GH, PRL, TSH, ACTH, LH, FSH), pars intermedia (MSH), pars nervosa (posterior pituitary — stores oxytocin and vasopressin made by the hypothalamus).

Thyroid hormones: thyroxine (T4) and triiodothyronine (T3) regulate the basal metabolic rate; thyrocalcitonin (TCT) lowers blood Ca2+.

Parathyroid hormone (PTH): a hypercalcemic hormone that raises blood Ca2+ by acting on bones, kidney and the gut.

Islets of Langerhans: the endocrine pancreas — α-cells secrete glucagon (hyperglycemic) and β-cells secrete insulin (hypoglycemic).

Mechanism of hormone action: peptide hormones bind membrane-bound receptors and trigger second messengers (cyclic AMP, IP3, Ca++); steroids and iodothyronines bind intracellular receptors and regulate gene expression.

NCERT Exercises — Solutions

All questions below are reproduced verbatim from the NCERT textbook. Answers are original and written in CBSE exam-ready style.

1. Define the following: (a) Exocrine gland (b) Endocrine gland (c) Hormone

ANSWER (a) Exocrine gland: A gland that possesses ducts and pours its secretion through these ducts onto a surface or into a cavity. Examples include the salivary glands, sweat glands and the exocrine part of the pancreas, which release saliva, sweat and digestive enzymes respectively. (b) Endocrine gland: A ductless gland whose secretions (hormones) are released directly into the blood and carried to distantly located target organs. Examples include the pituitary, thyroid and adrenal glands. (c) Hormone: A non-nutrient chemical that acts as an intercellular messenger and is produced in trace amounts by endocrine glands or certain cells. It is transported by blood to target tissues, where it binds specific receptors to regulate physiological functions.

2. Diagrammatically indicate the location of the various endocrine glands in our body.

ANSWER A labelled human-outline diagram should show the endocrine glands in the following positions (drawing this from memory in the exam is expected): Hypothalamus and pituitary — in the brain; the hypothalamus is the basal part of the forebrain and the pituitary lies just below it in the bony sella tursica. Pineal gland — on the dorsal side of the forebrain. Thyroid and parathyroid — in the neck region; the thyroid’s two lobes lie on either side of the trachea and the four parathyroids are embedded on the back of the thyroid. Thymus — in the thoracic cavity, between the lungs behind the sternum on the ventral side of the aorta. Adrenal glands — one above each kidney. Pancreas — in the abdomen between the stomach and duodenum. Gonads — the testes in the scrotal sac (males) and the ovaries in the abdomen (females).

3. List the hormones secreted by the following: (a) Hypothalamus (b) Pituitary (c) Thyroid (d) Parathyroid (e) Adrenal (f) Pancreas (g) Testis (h) Ovary (i) Thymus (j) Atrium (k) Kidney (l) G-I Tract

ANSWER
SourceHormones secreted
(a) HypothalamusReleasing hormones (e.g. GnRH) and inhibiting hormones (e.g. somatostatin)
(b) PituitaryGH, PRL, TSH, ACTH, LH, FSH (anterior); MSH (pars intermedia); oxytocin and vasopressin/ADH (posterior, stored)
(c) ThyroidThyroxine (T4), triiodothyronine (T3) and thyrocalcitonin (TCT)
(d) ParathyroidParathyroid hormone (PTH)
(e) AdrenalAdrenaline (epinephrine) and noradrenaline (medulla); glucocorticoids (cortisol), mineralocorticoids (aldosterone) and small amounts of androgenic steroids (cortex)
(f) PancreasGlucagon (α-cells) and insulin (β-cells)
(g) TestisAndrogens, mainly testosterone
(h) OvaryEstrogen and progesterone
(i) ThymusThymosins
(j) AtriumAtrial natriuretic factor (ANF)
(k) KidneyErythropoietin
(l) G-I TractGastrin, secretin, cholecystokinin (CCK) and gastric inhibitory peptide (GIP)

4. Fill in the blanks:

ANSWER
HormonesTarget gland
(a) Hypothalamic hormonesPituitary gland (anterior pituitary)
(b) Thyrotrophin (TSH)Thyroid gland
(c) Corticotrophin (ACTH)Adrenal cortex
(d) Gonadotrophins (LH, FSH)Gonads (testis in males, ovary in females)
(e) Melanotrophin (MSH)Melanocytes (pigment cells of the skin)

5. Write short notes on the functions of the following hormones: (a) Parathyroid hormone (PTH) (b) Thyroid hormones (c) Thymosins (d) Androgens (e) Estrogens (f) Insulin and Glucagon

ANSWER (a) Parathyroid hormone (PTH): A hypercalcemic peptide hormone that raises blood Ca2+ levels. It stimulates bone resorption (demineralisation), promotes reabsorption of Ca2+ by the renal tubules, and increases Ca2+ absorption from digested food. With thyrocalcitonin it maintains calcium balance. (b) Thyroid hormones (T4, T3): They regulate the basal metabolic rate and the metabolism of carbohydrates, proteins and fats. They support red blood cell formation, help maintain water and electrolyte balance, and aid development and maturation of tissues. Thyrocalcitonin from the thyroid lowers blood calcium. (c) Thymosins: Peptide hormones from the thymus that promote differentiation of T-lymphocytes, providing cell-mediated immunity, and also promote the production of antibodies for humoral immunity. Their decline in old age weakens the immune response. (d) Androgens (testosterone): They regulate development, maturation and function of the male accessory sex organs, stimulate spermatogenesis and the male secondary sex characters (facial/axillary hair, low-pitched voice, muscular growth), influence male sexual behaviour, and produce anabolic effects on protein and carbohydrate metabolism. (e) Estrogens: They stimulate growth and activity of female secondary sex organs, development of growing ovarian follicles, appearance of female secondary sex characters (high-pitched voice etc.), mammary gland development, and regulate female sexual behaviour. (f) Insulin and Glucagon: Insulin (from β-cells) is hypoglycemic — it enhances cellular glucose uptake and utilisation and promotes glycogenesis, lowering blood glucose. Glucagon (from α-cells) is hyperglycemic — it stimulates glycogenolysis and gluconeogenesis in the liver, raising blood glucose. Together they maintain glucose homeostasis.

6. Give example(s) of: (a) Hyperglycemic hormone and hypoglycemic hormone (b) Hypercalcemic hormone (c) Gonadotrophic hormones (d) Progestational hormone (e) Blood pressure lowering hormone (f) Androgens and estrogens

ANSWER (a) Hyperglycemic hormone — glucagon; hypoglycemic hormone — insulin. (b) Hypercalcemic hormone — parathyroid hormone (PTH). (c) Gonadotrophic hormones — luteinizing hormone (LH) and follicle stimulating hormone (FSH). (d) Progestational hormone — progesterone. (e) Blood pressure lowering hormone — atrial natriuretic factor (ANF). (f) Androgens — testosterone; estrogens — estradiol (estrogen).

7. Which hormonal deficiency is responsible for the following: (a) Diabetes mellitus (b) Goitre (c) Cretinism

ANSWER (a) Diabetes mellitus: deficiency of insulin (and/or insulin resistance), leading to prolonged hyperglycemia, loss of glucose in urine and formation of ketone bodies. (b) Goitre: deficiency of thyroid hormones, usually caused by a dietary lack of iodine, which leads to hypothyroidism and enlargement of the thyroid gland. (c) Cretinism: deficiency of thyroid hormones during pregnancy/early childhood (hypothyroidism), causing stunted growth, mental retardation, low IQ, abnormal skin and deaf-mutism.

8. Briefly mention the mechanism of action of FSH.

ANSWER FSH (follicle stimulating hormone) is a gonadotrophin secreted by the anterior pituitary. Being a peptide/protein hormone, it cannot enter the target cell, so it acts through membrane-bound receptors on the target gonadal cells. Binding of FSH to its specific receptor on the cell membrane forms a hormone–receptor complex, which activates the generation of second messengers (such as cyclic AMP) inside the cell. These second messengers trigger a cascade of biochemical changes that regulate cellular metabolism. As a result, in males FSH (with androgens) stimulates spermatogenesis, while in females it stimulates the growth and development of the ovarian follicles.

9. Match the following:

ANSWER
Column IColumn II
(a) T4(ii) Thyroid
(b) PTH(iv) Parathyroid
(c) GnRH(i) Hypothalamus
(d) LH(iii) Pituitary

Extra Practice Questions

Short Answer Type Questions

Q1. Why is the posterior pituitary not considered a true endocrine gland?

ANSWERThe posterior pituitary (pars nervosa) does not synthesise its own hormones. Oxytocin and vasopressin are actually made by the hypothalamus and transported axonally to the posterior pituitary, which only stores and releases them. Hence it acts as a storage-and-release site rather than a true secretory gland.

Q2. Distinguish between the action of glucagon and insulin on blood glucose.

ANSWERGlucagon is hyperglycemic: it stimulates glycogenolysis and gluconeogenesis in the liver and reduces cellular glucose uptake, raising blood sugar. Insulin is hypoglycemic: it enhances glucose uptake and utilisation by hepatocytes and adipocytes and promotes glycogenesis, lowering blood sugar. Together they maintain glucose homeostasis.

Q3. What is diabetes insipidus and how is it caused?

ANSWERDiabetes insipidus is a condition in which the kidney loses its ability to conserve water, leading to excessive water loss in urine and dehydration. It is caused by impaired synthesis or release of ADH (vasopressin), which normally promotes water reabsorption by the distal tubules.

Q4. Name the hormones of the adrenal medulla and state why they are called emergency hormones.

ANSWERThe adrenal medulla secretes adrenaline (epinephrine) and noradrenaline (norepinephrine), together called catecholamines. They are called “fight or flight” or emergency hormones because they are rapidly released under stress and increase alertness, heart rate, strength of heart contraction, respiration rate, pupillary dilation, piloerection, sweating, and blood glucose to prepare the body for emergencies.

Q5. List the four hormones secreted by the gastrointestinal tract and one function of each.

ANSWERGastrin stimulates secretion of hydrochloric acid and pepsinogen from gastric glands; secretin stimulates the exocrine pancreas to secrete water and bicarbonate ions; cholecystokinin (CCK) stimulates the pancreas and gall bladder to release pancreatic enzymes and bile; and gastric inhibitory peptide (GIP) inhibits gastric secretion and motility.

Long Answer Type Questions

Q1. Describe the structure of the pituitary gland and the hormones secreted by its different parts.

ANSWERThe pituitary gland lies in a bony cavity called the sella tursica and is attached to the hypothalamus by a stalk. Anatomically it is divided into an adenohypophysis and a neurohypophysis. The adenohypophysis has two portions — pars distalis and pars intermedia. The pars distalis (anterior pituitary) secretes six hormones: growth hormone (GH), prolactin (PRL), thyroid stimulating hormone (TSH), adrenocorticotrophic hormone (ACTH), luteinizing hormone (LH) and follicle stimulating hormone (FSH). The pars intermedia secretes only melanocyte stimulating hormone (MSH), and in humans it is almost merged with the pars distalis. The neurohypophysis (pars nervosa or posterior pituitary) stores and releases oxytocin and vasopressin, which are actually synthesised by the hypothalamus. Disorders of GH secretion lead to gigantism, dwarfism or acromegaly, showing the gland’s central role in growth and the regulation of other endocrine glands.

Q2. Explain the structure of the adrenal gland and the functions of the hormones secreted by its medulla and cortex.

ANSWEREach adrenal gland sits above a kidney and consists of two tissues: a centrally located adrenal medulla and an outer adrenal cortex. The medulla secretes the catecholamines adrenaline and noradrenaline, the emergency “fight or flight” hormones that raise heart rate, respiration, alertness and blood glucose. The cortex is arranged in three layers (zona glomerulosa, zona fasciculata and zona reticularis) and secretes corticoids. Glucocorticoids (mainly cortisol) stimulate gluconeogenesis, lipolysis and proteolysis, maintain the cardiovascular system and kidney function, produce anti-inflammatory effects and stimulate RBC production. Mineralocorticoids (mainly aldosterone) act on the renal tubules to reabsorb Na+ and water and excrete K+ and phosphate, helping maintain electrolytes, body fluid volume and blood pressure. The cortex also secretes small amounts of androgenic steroids. Underproduction of cortical hormones causes Addison’s disease.

Q3. Explain the mechanism of hormone action for protein hormones and for steroid hormones.

ANSWERHormones act only on target tissues that possess specific hormone receptors; each receptor is specific to one hormone. Protein/peptide hormones (e.g. insulin, glucagon, FSH) and amino-acid derivatives such as epinephrine bind to membrane-bound receptors on the cell surface. They normally do not enter the cell; instead, the hormone–receptor complex generates second messengers such as cyclic AMP, IP3 or Ca++, which trigger biochemical changes that regulate cellular metabolism. In contrast, steroid hormones (e.g. cortisol, testosterone, estradiol, progesterone) and iodothyronines are lipid-soluble and enter the target cell to bind intracellular (mostly nuclear) receptors. The hormone–receptor complex then interacts with the genome to regulate gene expression and chromosome function. In both pathways, the cumulative biochemical actions produce the physiological and developmental effects of the hormone.

MCQs

1. Endocrine glands are also called:

(a) ducted glands    (b) ductless glands    (c) exocrine glands    (d) mixed glands

2. Which gland is known as the “master gland”?

(a) thyroid    (b) adrenal    (c) pituitary    (d) pineal

3. The hormone melatonin is secreted by the:

(a) thyroid gland    (b) pineal gland    (c) thymus    (d) pancreas

4. Deficiency of iodine in the diet causes:

(a) diabetes mellitus    (b) Addison’s disease    (c) goitre    (d) acromegaly

5. Insulin is secreted by the:

(a) α-cells of Islets of Langerhans    (b) β-cells of Islets of Langerhans    (c) adrenal cortex    (d) Leydig cells

6. The hormone that increases blood Ca2+ level is:

(a) thyrocalcitonin    (b) parathyroid hormone    (c) insulin    (d) aldosterone

7. The “fight or flight” hormones are secreted by the:

(a) adrenal cortex    (b) adrenal medulla    (c) thyroid    (d) thymus

8. Which hormone is also known as the anti-diuretic hormone (ADH)?

(a) oxytocin    (b) vasopressin    (c) prolactin    (d) MSH

9. Atrial natriuretic factor (ANF) is secreted by the heart and it:

(a) increases blood pressure    (b) decreases blood pressure    (c) raises blood glucose    (d) lowers blood calcium

10. Steroid hormones act mainly by:

(a) generating cyclic AMP    (b) binding membrane receptors only    (c) binding intracellular receptors and regulating gene expression    (d) opening ion channels on the cell surface

Answer key: 1-(b), 2-(c), 3-(b), 4-(c), 5-(b), 6-(b), 7-(b), 8-(b), 9-(b), 10-(c).

Assertion–Reason Questions

For each Assertion–Reason question, choose: (A) Both true and the Reason correctly explains the Assertion; (B) Both true but the Reason is not the correct explanation; (C) Assertion true, Reason false; (D) Assertion false, Reason true.

A-R 1. Assertion: Vasopressin is called the anti-diuretic hormone.

Reason: It stimulates resorption of water by the distal tubules of the kidney, reducing water loss in urine.

A-R 2. Assertion: Glucagon is a hyperglycemic hormone.

Reason: Glucagon stimulates glycogenolysis and gluconeogenesis in the liver, increasing blood glucose.

A-R 3. Assertion: The posterior pituitary synthesises oxytocin and vasopressin.

Reason: The posterior pituitary stores and releases hormones made by the hypothalamus.

A-R 4. Assertion: Deficiency of iodine can lead to goitre.

Reason: Iodine is essential for the normal synthesis of thyroid hormones.

A-R 5. Assertion: Peptide hormones can freely enter their target cells.

Reason: Peptide hormones act through second messengers such as cyclic AMP generated at the cell membrane.

Answer key: 1-(A), 2-(A), 3-(D), 4-(A), 5-(D).

Common Mistakes to Avoid

Watch out for these

  • Confusing exocrine (ducted) with endocrine (ductless) glands — the pancreas is both.
  • Saying the posterior pituitary makes oxytocin and vasopressin — the hypothalamus makes them; the posterior pituitary only stores and releases them.
  • Mixing up PTH (raises Ca2+) with thyrocalcitonin (lowers Ca2+).
  • Reversing insulin (hypoglycemic) and glucagon (hyperglycemic), or the cells that make them (β-cells vs α-cells).
  • Confusing adrenal cortex hormones (corticoids) with adrenal medulla hormones (catecholamines).
  • Thinking all hormones enter the cell — only steroids and iodothyronines do; peptide hormones act via membrane receptors and second messengers.

Exam tips for this chapter

Make a single revision table of gland → hormone → function → disorder — most questions are drawn from it. Remember the pituitary’s six anterior hormones with the mnemonic “GP-TALF” (GH, PRL, TSH, ACTH, LH, FSH). For disorders, link the symptom to hyper- or hypo-secretion (e.g. excess GH → gigantism/acromegaly; low GH → dwarfism). When asked about mechanism of action, always classify the hormone first (peptide vs steroid) and then describe membrane receptor + second messenger or intracellular receptor + gene expression accordingly.

Frequently Asked Questions

What is Class 11 Biology Chapter 19 about?

Chapter 19, Chemical Coordination and Integration, explains how the endocrine system uses hormones to coordinate and regulate body functions. It covers the major endocrine glands and their hormones, hormone-secreting tissues of the heart, kidney and gut, related disorders, and the mechanism of hormone action.

What is the difference between an exocrine and an endocrine gland?

An exocrine gland has ducts and releases its secretion onto a surface or into a cavity (e.g. salivary glands), whereas an endocrine gland is ductless and releases hormones directly into the blood, which carries them to distant target organs (e.g. the thyroid).

Which hormones raise and lower blood glucose?

Glucagon (from the α-cells of the pancreas) raises blood glucose by stimulating glycogenolysis and gluconeogenesis, while insulin (from the β-cells) lowers blood glucose by promoting glucose uptake and glycogenesis. Together they maintain glucose homeostasis.

Are these Class 11 Biology Chapter 19 solutions free?

Yes. All ClearStudy NCERT Solutions for Class 11 Biology are free and follow the official NCERT textbook for session 2026–27.

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