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Chemical Coordination and Integration – Class 11 Biology notes, important questions and MCQs

NCERT Class 11 Biology, chapter 19. Notes, key terms, important questions with answers and MCQs.

Chapter overview

Endocrine glands release hormones into the blood to regulate growth, metabolism, reproduction and stress responses. Hormones act on target cells through receptors.

Glands and hormones

Hypothalamus releases releasing/inhibiting hormones; pituitary (master gland) secretes GH, TSH, ACTH, FSH, LH, prolactin; posterior pituitary stores oxytocin and ADH.
Thyroid: thyroxine (metabolism; deficiency causes goitre and cretinism), calcitonin; parathyroid: PTH raises blood Ca²⁺.
Adrenal medulla: adrenaline (fight or flight); adrenal cortex: cortisol, aldosterone; pancreas: insulin lowers, glucagon raises blood glucose.

Mechanism and disorders

Protein hormones act through cell-surface receptors and second messengers (cAMP); steroid hormones enter cells and act on genes.
Excess GH in childhood causes gigantism, in adults acromegaly; deficiency causes dwarfism.
Diabetes mellitus (insulin), Addison's disease (adrenal cortex), Graves' disease (hyperthyroidism).

Key terms

Hormone: chemical messenger secreted into blood that acts on target cells
Second messenger: intracellular molecule like cAMP that relays a hormone signal
Feedback control: regulation in which the level of a hormone or its effect controls further secretion, e.g. high thyroxine reduces TSH

Important questions with answers

Why is the pituitary called the master gland, and what controls it?2 marks

It secretes hormones (TSH, ACTH, FSH, LH, GH, prolactin) that control many other endocrine glands. It is itself controlled by releasing and inhibiting hormones from the hypothalamus.

Explain the antagonistic action of insulin and glucagon.3 marks

When blood glucose rises after a meal, β-cells release insulin, which makes liver and muscle cells take up glucose and store it as glycogen, lowering blood sugar. When glucose falls, α-cells release glucagon, which breaks down glycogen and makes new glucose in the liver, raising blood sugar. Together they keep glucose in a normal range.

Describe the mechanism of action of protein hormones and steroid hormones, with examples, and explain the effects of hypothyroidism in children and adults.5 marks

Protein/amine hormones (insulin, glucagon, adrenaline, FSH) cannot cross the cell membrane. They bind to receptors on the surface, activating second messengers such as cAMP or Ca²⁺, which trigger enzyme changes and cellular responses. Steroid hormones (cortisol, testosterone, oestrogen) and iodothyronines are lipid-soluble; they enter the cell, bind intracellular receptors, and the hormone–receptor complex acts on DNA to change gene expression and protein synthesis. Hypothyroidism: in pregnancy or childhood, lack of thyroid hormone causes cretinism — stunted growth, mental retardation, low IQ, abnormal skin and deafness. In adults it causes myxoedema — low metabolic rate, weight gain, puffiness, tiredness and irregular menstrual cycles; iodine deficiency also causes goitre.

Quick revision

Pituitary is the master gland.
Insulin lowers blood sugar.
Iodine deficiency causes goitre.

Exam tips

Pineal gland secretes melatonin (sleep–wake cycle); thymus secretes thymosins (T-cell maturation).
Make a table: gland → hormone → main function → disorder (excess / deficiency); it covers most questions.

Practice MCQs

Master gland of the body is the
1. thyroid
2. pituitary
3. adrenal
4. pancreas
Show answer
Answer: (b) pituitary. Pituitary.
Insulin is secreted by
1. pancreas (β-cells)
2. liver
3. thyroid
4. adrenal
Show answer
Answer: (a) pancreas (β-cells). Islets of Langerhans.
Deficiency of iodine causes
1. diabetes
2. goitre
3. gigantism
4. Addison's disease
Show answer
Answer: (b) goitre. Thyroid enlargement.
The "fight or flight" hormone is
1. adrenaline
2. insulin
3. thyroxine
4. oxytocin
Show answer
Answer: (a) adrenaline. Adrenal medulla.
Which hormone lowers blood calcium
1. PTH
2. calcitonin
3. aldosterone
4. cortisol
Show answer
Answer: (b) calcitonin. From thyroid parafollicular cells.
Excess GH in adults causes
1. gigantism
2. cretinism
3. dwarfism
4. acromegaly
Show answer
Answer: (d) acromegaly. After growth plates close.
Steroid hormones act by
1. binding surface receptors and cAMP
2. entering the cell and acting on genes
3. blocking enzymes only
4. changing blood pH
Show answer
Answer: (b) entering the cell and acting on genes. Intracellular receptors.
Diabetes insipidus is caused by deficiency of
1. ADH (vasopressin)
2. insulin
3. glucagon
4. thyroxine
Show answer
Answer: (a) ADH (vasopressin). Large volumes of dilute urine.

All chapters of Class 11 Biology

Written by Kundali IQ from standard, well-established facts to help with revision. This is not an official NCERT publication; always read your textbook too.