NCERT Solutions for Class 11 Biology Chapter 19: Chemical Coordination and Integration – Free PDF Download

Chapter 19, Chemical Coordination and Integration, is the last chapter of the NCERT Class 11 Biology textbook. It explains how the human endocrine system works alongside the nervous system to coordinate body functions, covering the major endocrine glands (hypothalamus, pituitary, pineal, thyroid, parathyroid, thymus, adrenal, pancreas, and gonads), the hormones they secrete, their mechanism of action at the cellular level, and disorders caused by hypo- or hyper-secretion of hormones.

Last Updated: September 23, 2026

Exercises

Q1. Define the following:
(a) Exocrine gland (b) Endocrine gland (c) Hormone

(a) Exocrine gland: An exocrine gland is a gland that secretes its products (enzymes, mucus, sweat, etc.) through a duct onto an epithelial surface or into a body cavity rather than directly into the blood. Examples include salivary glands, sweat glands, sebaceous glands, and the digestive glands of the gut.

(b) Endocrine gland: An endocrine gland is a ductless gland that secretes its chemical products, called hormones, directly into the bloodstream. These hormones are then carried by the blood to distant target organs where they produce a specific physiological response. Examples include the pituitary, thyroid, parathyroid, adrenal glands, and pancreas (islets of Langerhans).

(c) Hormone: A hormone is a non-nutrient chemical messenger, usually a small peptide, protein, steroid or amine, produced by an endocrine gland or specialised cells and released in very small (trace) amounts into the blood. It travels to a distant target organ and regulates its physiological activity, growth, or metabolism.

Q2. Diagrammatically indicate the location of the various endocrine glands in our body — The major endocrine glands are distributed throughout the human body as shown in Figure…

The major endocrine glands are distributed throughout the human body as shown in Figure 19.1 of the NCERT textbook. Their approximate locations are summarised below for quick revision:

Q3. 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

Q4. Fill in the blanks:
Hormones — Target gland
(a) Hypothalamic hormones (b) Thyrotrophin (TSH) (c) Corticotrophin (ACTH) (d) Gonadotrophins (LH, FSH) (e) Melanotrophin (MSH)

Q5. Write short notes on the functions of the following hormones:
(a) Parathyroid hormone (b) Thyroid hormones (c) Thymosins (d) Androgens (e) Estrogens (f) Insulin and Glucagon

(a) Parathyroid hormone (PTH): PTH is a peptide hormone secreted by the parathyroid glands. It is a hypercalcemic hormone — it increases blood calcium levels by stimulating bone resorption (release of calcium from bone), increasing calcium reabsorption and reducing phosphate reabsorption in the renal tubules, and indirectly increasing calcium absorption from digested food in the intestine. Its secretion is controlled by circulating calcium levels through negative feedback.

(b) Thyroid hormones: Thyroxine (T4) and tri-iodothyronine (T3) regulate the basal metabolic rate (BMR), support the metabolism of carbohydrates, proteins and fats, help maintain water and electrolyte balance, and are essential for normal growth and development, including the development of the nervous system. The thyroid also secretes calcitonin, which lowers blood calcium (a hypocalcemic effect) and regulates blood phosphate levels.

(c) Thymosins: Secreted by the thymus gland, thymosins play a central role in the immune system. They promote the differentiation and proliferation of T-lymphocytes (cell-mediated immunity) and stimulate the production of antibodies by plasma cells (humoral immunity). The thymus is fully functional only until puberty, after which it gradually shrinks.

(d) Androgens: Produced mainly by the Leydig (interstitial) cells of the testis, androgens (chiefly testosterone) regulate the development, maturation and function of the male accessory sex organs (epididymis, vas deferens, seminal vesicles, prostate), stimulate spermatogenesis, and are responsible for secondary sexual characters such as facial/body hair, muscular growth, and a deeper voice. They also influence male sexual behaviour and have anabolic effects on protein metabolism.

(e) Estrogens: Secreted mainly by the growing ovarian follicles, estrogens stimulate the growth and activity of the female secondary sex organs, are responsible for female secondary sexual characters, and regulate the female reproductive (menstrual) cycle. They also promote growth of the mammary glands and influence female sexual behaviour.

(f) Insulin and Glucagon: Both are secreted by the islets of Langerhans of the pancreas and act antagonistically to maintain glucose homeostasis. Insulin (from beta cells) is a hypoglycemic hormone — it lowers blood glucose by increasing cellular uptake and utilisation of glucose and promoting glycogenesis (conversion of glucose to glycogen) mainly in liver and muscle cells. Glucagon (from alpha cells) is a hyperglycemic hormone — it raises blood glucose by stimulating glycogenolysis (breakdown of glycogen) and gluconeogenesis in the liver. Their secretion is regulated directly by blood glucose levels through negative feedback.

Q6. 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

(a) Hyperglycemic hormone — Glucagon; Hypoglycemic hormone — Insulin.

(b) Hypercalcemic hormone — Parathyroid hormone (PTH).

(c) Gonadotrophic hormones — Follicle-stimulating hormone (FSH) and Luteinising hormone (LH).

(d) Progestational hormone — Progesterone.

(e) Blood pressure lowering hormone — Atrial natriuretic factor (ANF).

(f) Androgens — Testosterone; Estrogens — Estradiol.

Q7. Which hormonal deficiency is responsible for the following?
(a) Diabetes mellitus (b) Goitre (c) Cretinism

(a) Diabetes mellitus is caused by a deficiency of (or reduced sensitivity to) insulin, resulting in persistently high blood glucose levels (hyperglycemia) and glucose appearing in the urine (glycosuria).

(b) Goitre is caused by a deficiency of thyroid hormones (T3/T4), most commonly due to iodine deficiency in the diet, leading to abnormal enlargement of the thyroid gland.

(c) Cretinism is caused by a deficiency of thyroid hormones during foetal life and early childhood, resulting in stunted physical growth, mental retardation, low intelligence, and abnormal skin.

Q8. Briefly mention the mechanism of action of FSH — Follicle-stimulating hormone (FSH) is a glycoprotein (peptide) hormone secreted by the…

Follicle-stimulating hormone (FSH) is a glycoprotein (peptide) hormone secreted by the anterior pituitary. Being a protein, it is not lipid-soluble and therefore cannot cross the plasma membrane of its target cell. Instead, it acts through the second messenger mechanism:

1. FSH (the first messenger) binds to a specific receptor protein present on the surface of the target cell membrane (for example, granulosa cells of the ovarian follicle or Sertoli cells of the testis), forming a hormone–receptor complex.

2. This binding activates the membrane-bound enzyme adenylate cyclase, which converts ATP into cyclic AMP (cAMP), the second messenger.

3. Cyclic AMP activates specific enzymes and protein kinases already present inside the cell, which in turn stimulate particular cellular processes — for example, stimulating the follicular cells to produce estrogen, or supporting spermatogenesis in Sertoli cells.

4. Once the response is produced, the second messenger is broken down, terminating the hormonal signal until the hormone binds again.

This second-messenger (cAMP) pathway is typical of protein, peptide, and catecholamine hormones, in contrast to steroid and thyroid hormones, which are lipid-soluble and act by entering the target cell and directly regulating gene expression (the gene activation mechanism).

Q9. Match the following:

Class 11 Biology Chapter 19 – Notes and Extra Questions

The official NCERT exercise for Chapter 19, Chemical Coordination and Integration, has 9 main questions (Q1–Q9), several of which contain multiple lettered sub-parts — Q1 has 3 parts, Q3 has 12 parts, Q4 has 5 blanks, Q5 covers 6 hormones, Q6 asks for 6 examples, and Q7 has 3 parts — giving well over 30 individually testable items in total. This is the same exercise set used in the pre-2023 edition of the book, where this topic was Chapter 22; the 2023 rationalisation only renumbered it to Chapter 19 (now the final chapter of Class 11 Biology) without trimming or adding any exercise questions. For revision, build a single master table of Gland → Hormone → Target organ → Function, since Q3, Q4, and Q9 are essentially testing the same gland–hormone–target associations in different formats. Also be sure you can clearly explain the difference between the second messenger mechanism (used by peptide/protein hormones like FSH, which bind surface receptors and use cAMP) and the gene activation mechanism (used by lipid-soluble steroid and thyroid hormones, which bind intracellular receptors and directly regulate transcription) — this distinction is a favourite in both board exams and NEET.

Frequently Asked Questions

What is the difference between the mechanism of action of protein hormones and steroid hormones?

Protein/peptide hormones (such as FSH, LH, insulin) are lipid-insoluble, so they bind to receptors on the target cell’s surface and act through a second messenger, usually cyclic AMP, which activates enzymes inside the cell. Steroid hormones and thyroid hormones (such as estrogen, testosterone, cortisol, T3/T4) are lipid-soluble, so they diffuse across the plasma membrane, bind intracellular (cytoplasmic or nuclear) receptors, and the hormone–receptor complex directly regulates gene expression — this is called the gene activation mechanism.

Why is the pituitary gland called the “master gland”?

The pituitary gland is called the master gland because its anterior lobe secretes tropic hormones (TSH, ACTH, LH, FSH) that control the activity of several other endocrine glands, including the thyroid, adrenal cortex, and gonads. However, the pituitary itself is controlled by releasing and inhibiting hormones from the hypothalamus, so it functions as an intermediary rather than the top-level controller of the endocrine system.

What is the difference between a hyperglycemic hormone and a hypoglycemic hormone?

A hyperglycemic hormone raises blood glucose levels — glucagon is the classic example, as it stimulates the breakdown of liver glycogen (glycogenolysis) and gluconeogenesis. A hypoglycemic hormone lowers blood glucose levels — insulin is the example, as it promotes cellular glucose uptake and glycogenesis. Both hormones are secreted by the islets of Langerhans in the pancreas and work antagonistically to maintain blood sugar homeostasis.

How many questions are there in the Class 11 Biology Chapter 19 exercise, and has the list changed after rationalisation?

The chapter has 9 main exercise questions (many with multiple sub-parts), and this set is unchanged from the earlier edition, where the chapter was numbered Chapter 22. After the 2023 NCERT rationalisation, only the chapter number changed (from 22 to 19, now the final chapter of the book) — no exercise questions were added or removed.

Written by Satish

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