Previous year questions: Chemical Coordination and Integration

These ten questions come from the NCERT Exemplar chapter on chemical coordination and integration, the only official previous year source available for Class 11 Biology. The set covers the adrenal cortex, the gonads, the pancreas, the pineal gland, erythropoiesis, the pars intermedia, calcitonin, thyroid disorders and the mechanism of hormone action. Marks follow the book convention: 1 mark MCQ, 2 marks very short answer, 3 marks short answer and 5 marks long answer. Each heading quotes the Exemplar chapter and question number.

Q1 (NCERT Exemplar, 1 mark; Chapter 22, MCQ 4)

Which steroid maintains the water and electrolyte balance of the body?

Answer: Aldosterone keeps the water and the electrolyte balance of the body. It is a mineralocorticoid from the adrenal cortex, and it acts on the distal tubules of the kidney, where it promotes the reabsorption of sodium and water and the excretion of potassium. Sodium retention pulls water along with it, so the blood volume and the blood pressure rise, while the potassium leaves the body in the urine.

Q2 (NCERT Exemplar, 1 mark; Chapter 22, Multiple Choice 7)

Leydig cells produce a group of hormones called what?

Answer: Leydig cells produce androgens. They are the interstitial cells of the testis, and their androgens, mainly testosterone, control the development of the male reproductive organs and the male secondary sexual characters. The other cells of the testis, the Sertoli cells, do not secrete androgens; they support the developing sperm instead.

Q3 (NCERT Exemplar, 1 mark; Chapter 22, Multiple Choice 8)

Corpus luteum secretes a hormone called what?

Answer: The corpus luteum secretes progesterone. It is the progesterone that prepares the uterus for the implantation of the embryo and maintains the pregnancy in its early stages. If pregnancy does not occur, the corpus luteum breaks down and the progesterone level falls, which allows a new cycle to begin.

Q4 (NCERT Exemplar, 1 mark; Chapter 22, Multiple Choice 9)

Cortisol is secreted by which gland?

Answer: Cortisol is secreted by the adrenal cortex. It is the main glucocorticoid of the body, and it acts on carbohydrate metabolism by raising the blood glucose level and also suppresses the inflammatory response.

Q5 (NCERT Exemplar, 1 mark; Chapter 22, Multiple Choice 10)

The hormone responsible for the normal sleep and wake cycle is what?

Answer: Melatonin is the hormone responsible for the regulation of the twenty four hour rhythm of the body, including the normal sleep and wake cycle. It is secreted by the pineal gland, and it also influences body temperature, metabolism, pigmentation and the menstrual cycle.

Q6 (NCERT Exemplar, 2 marks; Chapter 22, Very Short Answer 3)

What is erythropoiesis and which hormone stimulates it?

Answer: Erythropoiesis is the formation of red blood cells in the bone marrow. It is stimulated by erythropoietin, a hormone secreted by the kidney. When the oxygen supply to the tissues falls, the kidney releases more erythropoietin, the bone marrow makes more red cells and the oxygen carrying capacity of the blood rises. This is another example of a hormone acting as a feedback signal between an organ and the tissue it controls.

Q7 (NCERT Exemplar, 2 marks; Chapter 22, Very Short Answer 4)

Name the only hormone secreted by the pars intermedia of the pituitary.

Answer: The only hormone secreted by the pars intermedia is melanocyte stimulating hormone, or MSH. It acts on the melanocytes, the melanin containing cells of the skin, and controls their pigmentation. In humans this part is almost merged with the pars distalis of the anterior pituitary.

Q8 (NCERT Exemplar, 2 marks; Chapter 22, Very Short Answer 5)

Name the endocrine gland that produces calcitonin and mention its function.

Answer: The thyroid gland produces calcitonin, also called thyrocalcitonin. Its function is to lower the level of calcium in the blood. It therefore acts in the opposite direction to parathyroid hormone, and the two hormones together keep the blood calcium within a narrow range.

Q9 (NCERT Exemplar, 3 marks; Chapter 22, Short Answer 8)

Mention the difference between hypothyroidism and hyperthyroidism.

Answer: Hypothyroidism is the condition in which the thyroid gland secretes too little thyroid hormone. The metabolic rate falls, the person gains weight and feels cold and tired, the gland may enlarge as goitre because iodine is deficient, and in a pregnant woman or an infant the deficiency causes stunted growth and mental retardation, which is cretinism. Hyperthyroidism is the condition in which the gland secretes too much hormone. The metabolic rate rises, the person loses weight, feels hot and anxious and has a rapid heartbeat, and exophthalmic goitre is a form of hyperthyroidism in which the eyes bulge out.

Q10 (NCERT Exemplar, 5 marks; Chapter 22, Long Answer 4)

Illustrate the differences between the mechanism of action of a protein hormone and a steroid hormone.

Answer: The two mechanisms differ mainly in the location of the receptor and in the way the message is carried inside the cell.

A protein hormone is water soluble and cannot cross the lipid membrane of the cell. Its receptor is therefore on the outer surface of the membrane. When the hormone binds the receptor, the receptor is activated and it makes a second messenger, such as cyclic AMP, inside the cell. The second messenger activates enzymes that speed up or slow down particular reactions, and these reactions produce the physiological response. The hormone itself never enters the cell, and the response is quick but short lived because the second messenger is soon destroyed.

A steroid hormone is lipid soluble and can pass through the membrane. Its receptor is therefore inside the cell, in the cytoplasm or the nucleus. The hormone binds the receptor, the hormone-receptor complex enters the nucleus and binds to a specific region of the DNA, particular genes are switched on, mRNA is made and the mRNA is translated into proteins. The new proteins then carry out the response. The hormone is not a second messenger itself, and the response develops slowly but lasts longer. Because the effect depends on the genes that are switched on, different tissues can respond to the same steroid in different ways.

A table with the hormone type, the receptor location, the messenger and the speed of response in the two columns is the clearest way to present the difference. The protein mechanism is used by insulin and growth hormone, and the steroid mechanism by cortisol, aldosterone and the sex hormones. A single table with the receptor location, the messenger and the speed of response in the two columns is enough to answer most of the short questions on this topic.

Answer habits for this set

Hormone questions are marked on names and on the direction of the effect. Always write the gland, the hormone and its target in one line, for example the adrenal cortex, cortisol, liver and muscle. When a pair of hormones is asked, write them as opposites with their directions, such as insulin lowering and glucagon raising blood glucose, or calcitonin lowering and parathyroid hormone raising blood calcium. When a disorder is asked, name the deficient or excess hormone before the symptoms, because that order keeps the answer logical. For the mechanism questions, state the receptor location first and let the rest follow from it. These habits make even a short answer look complete to the examiner.

Ten facts to revise last

One, endocrine glands are ductless and pour their hormones into the blood. Two, the hypothalamus controls the pituitary through releasing and inhibiting hormones. Three, the posterior pituitary only stores oxytocin and vasopressin, which the hypothalamus makes. Four, growth hormone excess gives gigantism in children and acromegaly in adults. Five, iodine deficiency produces goitre, and thyroid deficiency in pregnancy produces cretinism. Six, parathyroid hormone raises blood calcium while calcitonin lowers it. Seven, cortisol comes from the adrenal cortex and adrenaline from the adrenal medulla. Eight, the beta cells of the pancreas make insulin and the alpha cells make glucagon. Nine, melatonin from the pineal gland sets the sleep and wake rhythm. Ten, protein hormones act through membrane receptors and second messengers, while steroid hormones act through intracellular receptors and gene expression. These ten statements cover most of the one and two mark questions of the chapter and can each be expanded for a longer answer.