Control and Coordination PYQs – Biology, SSC & Railway

Correct Answer: Option 1 — By changing the amount of water in them
Plants have no nervous system and no muscles, so they cannot move the way animals do. Instead, plant cells change shape by changing the amount of water in them. The classic example is the touch-me-not plant (Mimosa pudica), whose leaves fold and droop immediately when touched.
When the plant is touched, the stimulus travels as an electrochemical signal from cell to cell. In the swollen cushion-like pulvinus at the base of each leaf, some cells lose water and become flaccid, while others gain it. This change in turgor pressure alters the shape of the cells, so the leaflets fold up and the leaf drops. Since it is not caused by growth and has no relation to the direction of the stimulus, it is a nastic (thigmonastic) movement, not a tropic one.
❌ Why the other options are incorrect
✗ By changing the amount of protein in them — proteins act as enzymes and structural material; they do not swell or shrink cells to cause movement.
✗ By changing the amount of nucleic acid in them — DNA and RNA carry and express genetic information; their amount does not change for a quick response.
✗ By changing the amount of lipid in them — lipids are storage and membrane molecules; they play no role in this rapid leaf movement.
📌 SSC & Railway Exam Facts
• Plant movements are of two kinds — growth-dependent (tropic) and growth-independent (nastic).
• Mimosa pudica shows seismonasty/thigmonasty; the folding of leaves at dusk is nyctinasty (sleep movement).
• The swollen leaf base that controls the movement is the pulvinus.
• Tendrils coiling round a support is thigmotropism, which is growth-dependent.
• Plants use chemical (hormonal) coordination — auxin, gibberellin, cytokinin, abscisic acid, ethylene.

Correct Answer: Option 4 — chemotropism
Chemotropism is the directional growth movement of a plant part in response to a chemical stimulus. The standard NCERT example is exactly the one in this question: the growth of the pollen tube towards the ovule.
After pollination, the pollen grain lands on the stigma and germinates. Chemical substances (sugars and calcium compounds) secreted by the stigma, style and ovule guide the growing pollen tube downwards through the style so that it reaches the ovule inside the ovary and delivers the male gametes for fertilisation. As with all tropic movements, the direction of the growth is decided by the direction of the stimulus — here, the chemical gradient.
❌ Why the other options are incorrect
✗ hydrotropism — growth in response to water; roots bending towards moisture in the soil, not the pollen tube's guidance.
✗ phototropism — growth in response to light; shoots bend towards light (positive) and roots away (negative).
✗ geotropism — growth in response to gravity; roots grow downwards (positive) and shoots upwards (negative), as already stated in the question itself.
📌 SSC & Railway Exam Facts
• Tropic movements — photo-, geo-, hydro-, chemo- and thigmotropism (touch, as in tendrils).
• Tropic movements are slow and growth-dependent, controlled by auxin.
• Nastic movements are non-directional — e.g. Mimosa pudica folding on touch.
• The pollen tube was first observed by Giovanni Battista Amici.
• Fertilisation in flowering plants is double fertilisation, discovered by S. G. Nawaschin.

Correct Answer: Option 4 — Geotropism
Geotropism (gravitropism) is the directional growth movement of a plant part in response to the pull of gravity. It explains both the upward and the downward growth of a plant:
• The stem grows upward, away from gravity — this is negative geotropism.
• The root grows downward, towards gravity — this is positive geotropism.
The response is controlled by the plant hormone auxin. Under gravity, auxin collects on the lower side of the organ. In the stem, extra auxin makes the lower side elongate faster, bending the shoot up; in the root, the same high concentration inhibits growth on the lower side, so the root curves down.
❌ Why the other options are incorrect
✗ Phototropism — growth towards or away from light; the shoot is positively phototropic and the root negatively phototropic. It explains bending towards a window, not up-and-down growth.
✗ Chemotropism — growth towards a chemical; the classic example is the pollen tube growing towards the ovule through the style.
✗ Hydrotropism — growth towards water; roots bend towards a moist region of soil. It relates to moisture, not to gravity.
📌 SSC & Railway Exam Facts
• Tropic movements are directional and growth-dependent; nastic movements (e.g. the drooping of *Mimosa pudica* leaves) are non-directional and not due to growth.
• Auxin was the first plant hormone discovered; Charles Darwin and Francis Darwin did the pioneering phototropism experiments.
• Gibberellin — stem elongation; Cytokinin — cell division; Abscisic acid (ABA) — stress/growth inhibitor, closes stomata.
• Ethylene is the only gaseous plant hormone; it ripens fruits.
• Thigmotropism is growth in response to touch — seen in the tendrils of climbers like pea and grapevine.

Correct Answer: Option 3 — Menstrual cycle
The ovary is the female gonad. It is a mixed gland — it produces the ova (eggs) and also secretes the female sex hormones oestrogen and progesterone.
These hormones regulate the menstrual cycle, the roughly 28-day cycle in which the uterine lining (endometrium) thickens to receive an embryo. Oestrogen rebuilds the lining and triggers ovulation around day 14; progesterone, from the corpus luteum, maintains the thickened lining. If fertilisation does not occur, both hormones fall, the lining breaks down and is shed as menstruation. Oestrogen also brings about the female secondary sexual characters.
❌ Why the other options are incorrect
✗ Regulates metabolism — the metabolism of carbohydrates, proteins and fats is regulated by thyroxine from the thyroid gland, which needs iodine.
✗ Stimulates pituitary glands — the pituitary is stimulated by releasing hormones from the hypothalamus, not by the ovary; in fact the pituitary's FSH and LH control the ovary.
✗ Stimulates growth in all organs — that is the work of growth hormone (GH) secreted by the anterior pituitary gland.
📌 SSC & Railway Exam Facts
• Ovary → oestrogen and progesterone; Testis → testosterone; both are mixed glands making gametes and hormones.
• Menarche is the first menstruation; menopause (about 45–50 years) is its permanent stopping.
• Ovulation occurs around the 14th day of a 28-day cycle; the ovum survives about 24 hours.
• Progesterone is called the pregnancy hormone; it is secreted by the corpus luteum and later by the placenta.
• Pituitary is the master gland, but it is itself controlled by the hypothalamus.

Correct Answer: Option 3 — It stimulates growth in all organs.
Growth hormone (GH or somatotropin) is secreted by the pituitary gland, the pea-sized "master gland" lying at the base of the brain. As its name says, it regulates the growth and development of the whole body — it stimulates cell division, protein synthesis, elongation of bones and muscle growth in all organs.
Its secretion has to be finely balanced. A deficiency of growth hormone in childhood causes dwarfism (very short stature with normal body proportions), while over-secretion causes gigantism in children and acromegaly (thickened jaw, hands and feet) in adults.
❌ Why the other options are incorrect
✗ It regulates metabolism for body growth — that is the work of thyroxine from the thyroid gland, which controls carbohydrate, protein and fat metabolism.
✗ It regulates the blood sugar level — this is done by insulin and glucagon from the pancreas; lack of insulin causes diabetes mellitus.
✗ It regulates the menstrual cycle — controlled by oestrogen and progesterone from the ovary, along with FSH and LH.
📌 SSC & Railway Exam Facts
• The pituitary is called the master gland because it controls the other endocrine glands.
• Thyroxine needs iodine; its deficiency causes goitre.
• Adrenaline from the adrenal gland is the emergency (fight-or-flight) hormone.
• Testosterone (testes) and oestrogen (ovary) are the chief sex hormones.
• Hormones are chemical messengers poured directly into the blood by ductless (endocrine) glands.

Correct Answer: Option 4 — Pituitary gland
The pituitary gland is a small, pea-sized endocrine gland attached to the base of the brain below the hypothalamus. It secretes growth hormone (GH), which controls the growth and development of bones, muscles and all the organs of the body. Because it also directs the other endocrine glands, it is called the master gland.
A deficiency of growth hormone in childhood causes dwarfism, while over-secretion causes gigantism in children and acromegaly in adults. The pituitary also produces FSH, LH, TSH, ACTH, prolactin and vasopressin (ADH).
❌ Why the other options are incorrect
✗ Thyroid gland — lies in the neck and secretes thyroxine, which regulates the metabolism of carbohydrates, fats and proteins; it needs iodine.
✗ Testes — the male gonads; they secrete testosterone, responsible for male secondary sexual characters such as a beard and a deep voice.
✗ Adrenal gland — sits above each kidney and secretes adrenaline, the fight-or-flight (emergency) hormone, which raises heart rate and blood pressure.
📌 SSC & Railway Exam Facts
• The pituitary is the master gland, lodged in the sella turcica at the base of the brain.
• Iodine deficiency causes goitre; excess thyroxine causes exophthalmic goitre.
• Insulin from the pancreas lowers blood sugar; its deficiency causes diabetes mellitus.
• The pancreas is a mixed gland — both exocrine and endocrine.
• Hormones are poured by ductless glands directly into the blood.

Correct Answer: Option 4 — Thyroid gland
The thyroid gland is a butterfly-shaped endocrine gland lying in the neck in front of the trachea. It secretes the hormone thyroxine (T4) and tri-iodothyronine (T3), and iodine is essential for making them — each molecule of thyroxine carries four iodine atoms.
Thyroxine regulates the metabolism of carbohydrates, proteins and fats in the body and thereby controls the rate at which energy is released. If iodine in the diet is insufficient, the gland cannot make enough thyroxine, enlarges, and the person develops goitre — a visibly swollen neck. This is why iodised salt is recommended.
❌ Why the other options are incorrect
✗ Pineal gland — a tiny gland in the brain that secretes melatonin and regulates the sleep–wake cycle; it does not need iodine.
✗ Pancreas — a mixed gland; its endocrine part secretes insulin and glucagon to control blood sugar, not thyroxine.
✗ Thymus — secretes thymosin and helps in the maturation of T-lymphocytes for immunity; it shrinks after puberty.
📌 SSC & Railway Exam Facts
• The thyroid is the largest endocrine gland in the human body.
• Iodine deficiency causes goitre; in children it causes cretinism (stunted growth, mental retardation).
• Excess thyroxine causes Grave's disease / hyperthyroidism; deficiency in adults causes myxoedema.
• The thyroid is stimulated by TSH from the anterior pituitary.
• The parathyroid glands, embedded behind the thyroid, secrete parathormone, which controls calcium balance.

Correct Answer: Option 3 — peripheral nervous system
The Peripheral Nervous System (PNS) is made of all the nerves that branch out of the central nervous system to every part of the body. It comprises 12 pairs of cranial nerves arising from the brain and 31 pairs of spinal nerves arising from the spinal cord.
The PNS is the communication link of the body: its sensory (afferent) nerves carry impulses from receptors in the skin, eyes, ears, nose and tongue to the brain and spinal cord, while its motor (efferent) nerves carry commands from them to the muscles and glands, which act as effectors.
❌ Why the other options are incorrect
✗ central nervous system — made of only the brain and spinal cord; it processes information, and the nerves leaving it are not part of it.
✗ autonomic nervous system — a subdivision of the PNS that controls involuntary actions such as heartbeat, breathing and digestion through its sympathetic and parasympathetic parts.
✗ endocrine system — the system of ductless glands that coordinates the body chemically through hormones, not through nerve impulses.
📌 SSC & Railway Exam Facts
• Human nervous system = CNS (brain + spinal cord) + PNS (cranial + spinal nerves).
• 12 pairs of cranial nerves; 31 pairs of spinal nerves.
• The neuron is the structural and functional unit of the nervous system — the longest cell of the body.
• Reflex arc is completed at the spinal cord, which is why the reaction is so quick.
• Cerebrum — thinking and memory; cerebellum — balance and posture; medulla — heartbeat, breathing, blood pressure.

Correct Answer: Option 3 — 1-d, 2-a, 3-b, 4-c
Hormones are chemical messengers secreted in tiny amounts by endocrine (ductless) glands directly into the blood, which carries them to their target organs.
1 – d. Thyroxin, from the thyroid gland, regulates the metabolism of carbohydrates, proteins and fats; iodine is essential for its formation.
2 – a. Growth hormone, from the anterior pituitary, controls the overall growth and development of the body, especially of bones and muscles.
3 – b. Testosterone, from the testes, brings about development of the male sex organs and the secondary sexual characters at puberty.
4 – c. Insulin, from the beta cells of the pancreas, lowers and thereby controls the level of blood sugar (glucose).
❌ Why the other options are incorrect
✗ 1-a, 2-c, 3-b, 4-d — wrong; thyroxin does not control growth (that is GH), and insulin does not control fat–protein metabolism (that is thyroxin).
✗ 1-b, 2-a, 3-d, 4-c — wrong; thyroxin has no role in male sex organ development, which is the work of testosterone.
✗ 1-d, 2-b, 3-c, 4-a — wrong; growth hormone is not linked to male sex organs, and testosterone does not control blood sugar.
📌 SSC & Railway Exam Facts
• Deficiency of insulin causes diabetes mellitus; insulin was discovered by Banting and Best.
• Excess GH in childhood → gigantism; deficiency → dwarfism; excess in adults → acromegaly.
• Iodine deficiency → goitre; the thyroid is the largest endocrine gland.
• Oestrogen is the female sex hormone from the ovary; testosterone is the male one from the testes.
• Adrenaline, from the adrenal gland, is called the emergency / fight-or-flight hormone.

Correct Answer: Option 3 — Only (i) and (ii)
Adrenaline is the emergency hormone (the "fight or flight" hormone) secreted by the adrenal medulla of the adrenal glands, which sit on top of the kidneys. It is poured directly into the blood and reaches the heart, lungs, muscles and blood vessels.
Its effects prepare the body for sudden action — the heart beats faster so that more oxygen reaches the muscles, the breathing rate increases because the diaphragm and rib muscles contract faster, blood is diverted away from the skin and digestive system to the skeletal muscles, and the blood pressure rises. Statement (iii) is therefore false; adrenaline raises, never lowers, blood pressure.
❌ Why the other options are incorrect
✗ Only (ii) and (iii) — includes the false statement (iii); adrenaline increases blood pressure.
✗ Only (i) and (iii) — again wrongly accepts (iii) and drops the true statement (ii).
✗ (i), (ii) and (iii) — cannot be correct because (iii) contradicts the actual action of adrenaline.
📌 SSC & Railway Exam Facts
• Adrenaline (epinephrine) is secreted by the adrenal medulla; the cortex secretes cortisol and aldosterone.
• It is called the 3F hormone — fight, flight and fright.
• Thyroxine (thyroid) needs iodine; its deficiency causes goitre.
• Insulin from the pancreas lowers blood sugar; its deficiency causes diabetes mellitus.
• Growth hormone comes from the pituitary, the "master gland".

Correct Answer: Option 3 — smell
Olfactory receptors are the specialised sensory receptors for smell. They lie in the olfactory epithelium in the roof of the nasal cavity. Odour molecules dissolve in the mucus, stimulate these receptors, and the impulse travels through the olfactory nerve to the brain, where the smell is identified.
When the nose is blocked (as in a cold), air carrying the odour molecules cannot reach the olfactory epithelium, so the receptors are not stimulated and smell cannot be detected. Because flavour depends largely on smell, food also seems tasteless at that time — but the taste receptors themselves are still working.
❌ Why the other options are incorrect
✗ walking — walking is a voluntary movement controlled by the cerebellum and skeletal muscles; no receptor "detects" it as a stimulus.
✗ hearing — sound is detected by the phonoreceptors in the cochlea of the ear, not by olfactory receptors.
✗ taste — taste is detected by gustatory receptors in the taste buds on the tongue.
📌 SSC & Railway Exam Facts
• Receptors: olfactory (smell), gustatory (taste), photoreceptors (light), phonoreceptors (sound), thermoreceptors (heat).
• The olfactory nerve is the first cranial nerve.
• The cerebellum maintains posture and balance; the medulla controls heartbeat, breathing and blood pressure.
• The four basic tastes sensed by the tongue are sweet, sour, salty and bitter.
• The neuron is the structural and functional unit of the nervous system.

Correct Answer: Option 3 — Roots
Roots always grow downwards, into the soil and towards the pull of gravity. This directional growth movement in response to gravity is called geotropism (gravitropism). Because the root grows towards gravity it shows positive geotropism, while the shoot grows away from gravity and shows negative geotropism.
Such tropic movements are growth-dependent and are controlled by the plant hormone auxin. Auxin collects on the lower side of a horizontally placed root and there it inhibits root growth, so the upper side grows faster and the root bends downward. Roots are also positively hydrotropic, bending towards water.
❌ Why the other options are incorrect
✗ Branches — branches are part of the shoot system and grow upwards and outwards, showing negative geotropism and positive phototropism.
✗ Buds — buds develop on the stem into shoots, flowers or leaves and grow upwards/outwards, towards light.
✗ Leaves — leaves are borne on the stem, spread outwards and turn towards light (positive phototropism) to trap maximum sunlight.
📌 SSC & Railway Exam Facts
• Geotropism — response to gravity; root = positive, shoot = negative.
• Phototropism — response to light; shoot = positive, root = negative.
• Hydrotropism — response to water; roots are positively hydrotropic.
• Chemotropism — growth of the pollen tube towards the ovule.
• Auxin promotes shoot elongation but inhibits root growth; other plant hormones are gibberellin, cytokinin, abscisic acid (ABA) and ethylene.

Correct Answer: Option 2 — By changing the amount of water in them
The folding of the leaves of the touch-me-not plant (Mimosa pudica) is a nastic movement — it is independent of growth and does not depend on the direction of the stimulus. The plant has no nerves and no muscles, so it must move the leaf in some other way.
At the base of each leaflet there is a swollen cushion called the pulvinus. When the plant is touched, an electrochemical signal passes through the cells; water moves out of the pulvinus cells on one side, they lose their turgidity (turgor pressure) and shrink, while the cells on the other side stay swollen. This change in the amount of water makes the leaf fold and droop. Growth-independent movements of this kind are reversible — the leaf opens again when water returns.
❌ Why the other options are incorrect
✗ lipid — lipids are stored fat and membrane material; their quantity does not change quickly enough to bend a leaf.
✗ nucleic acid — DNA and RNA store and express genetic information; they play no part in this rapid mechanical movement.
✗ protein — proteins build enzymes and structures, and animals use contractile proteins for movement, but plant cells have no such contractile machinery.
📌 SSC & Railway Exam Facts
• Nastic movement — non-directional and growth-independent (Mimosa leaves).
• Tropic movement — directional and growth-dependent (phototropism, geotropism).
• Mimosa pudica is the touch-me-not (chhui-mui) plant; the response is thigmonasty (seismonasty).
• Electrical-chemical signals travel from cell to cell in plants; plants have no nervous tissue.
• Plant movement is controlled by hormones — auxin, gibberellin, cytokinin, abscisic acid, ethylene.

Correct Answer: Option 3 — Helps the cells to grow longer
Auxin is a plant hormone (phytohormone) synthesised at the tip of the shoot. It promotes cell elongation — the cells behind the growing tip take in more water and grow longer, so the shoot gets taller.
This single property explains phototropism. When light falls on one side of a shoot, auxin diffuses towards the shady side. The cells on the shady side elongate more than those on the lighted side, and the unequal growth makes the shoot bend towards the light. Auxin also causes apical dominance and is used to make rooting hormones and weedicides.
❌ Why the other options are incorrect
✗ Make plants insect resistant — insect resistance comes from alkaloids, resins and Bt genes, not from auxin.
✗ Induce flowering — flowering is controlled mainly by florigen and gibberellins along with photoperiod, not by auxin.
✗ Increases stem width — increase in girth is secondary growth caused by the cambium, not by auxin.
📌 SSC & Railway Exam Facts
• Auxin was studied by Charles Darwin and named by F. W. Went.
• Gibberellin causes stem elongation; cytokinin promotes cell division.
• Abscisic acid (ABA) is the stress / growth-inhibitor hormone that causes wilting and closes stomata.
• Ethylene is the only gaseous plant hormone; it ripens fruits.
• 2,4-D is a synthetic auxin used as a weedicide.

Correct Answer: Option 3 — Auxin, Cytokinins and Gibberellins
Plant hormones (phytohormones) are chemicals produced in one part of a plant that control its growth, development and responses to the environment. They are of two functional kinds — growth promoters and growth inhibitors.
The three growth-promoting hormones are:
• Auxin — made at the shoot tip; it causes cell elongation and is responsible for phototropism, as the cells on the shaded side elongate faster and the shoot bends towards light.
• Cytokinins — promote cell division; they are present in high concentration in fruits and seeds and delay the ageing of leaves.
• Gibberellins — cause stem elongation, seed germination and bolting.
Abscisic acid (ABA) is the exception; it inhibits growth, closes stomata, and causes wilting and dormancy of buds and seeds.
❌ Why the other options are incorrect
✗ Gibberellins, Cytokinins and Abscisic acid — includes abscisic acid, which is an inhibitor, not a promoter.
✗ Auxin, Abscisic acid and Gibberellins — again wrongly places abscisic acid among the growth promoters.
✗ Auxin, Cytokinins and Abscisic acid — same mistake; ABA is the growth-inhibiting stress hormone.
📌 SSC & Railway Exam Facts
• Auxin was discovered by F. W. Went; IAA (Indole-3-Acetic Acid) is the natural auxin.
• Gibberellin was isolated from the fungus Gibberella fujikuroi.
• Ethylene is the only gaseous hormone and ripens fruits; ABA is the stress hormone.
• Growth towards light is phototropism, towards gravity is geotropism, towards water is hydrotropism, towards chemicals is chemotropism.
• Plants have no nervous system, so all coordination is done by hormones.

Correct Answer: Option 1 — Pulling hand from the flame
A reflex action is a sudden, automatic and involuntary response to a stimulus, made without the conscious thinking of the brain. Withdrawing the hand on touching a flame is the standard example.
The pathway followed is called the reflex arc:
• Receptor in the skin detects the heat (stimulus).
• Sensory neuron carries the impulse to the spinal cord.
• Relay (inter) neuron in the spinal cord immediately passes it on.
• Motor neuron carries the impulse to the effector, the arm muscle, which contracts and pulls the hand away.
Because the decision is taken in the spinal cord and not in the brain, the response is extremely fast and prevents injury; the brain only comes to know of it afterwards.
❌ Why the other options are incorrect
✗ Walking on the street — a voluntary action planned and controlled by the cerebrum, with balance maintained by the cerebellum.
✗ Talking to a child — a voluntary action involving thinking, memory and speech centres of the fore-brain.
✗ Dancing on the stage — a learned voluntary activity needing precise control of posture and balance by the cerebellum.
📌 SSC & Railway Exam Facts
• Other reflexes — blinking, sneezing, coughing, knee-jerk, salivation on smelling food, and the pupil narrowing in bright light.
• The reflex arc is completed in the spinal cord; reflex arcs evolved because thinking is slower.
• Neuron is the structural and functional unit of the nervous system; the gap between two neurons is the synapse.
• Voluntary actions — controlled by the cerebrum; involuntary actions such as heartbeat and breathing — by the medulla.
• Humans have 31 pairs of spinal nerves and 12 pairs of cranial nerves.

Correct Answer: Option 3 — Both cranial and spinal nerves
The nervous system is divided into the Central Nervous System (CNS) — the brain and spinal cord — and the Peripheral Nervous System (PNS), which is made of the nerves arising from the CNS.
The PNS consists of both cranial nerves and spinal nerves:
• Cranial nerves — 12 pairs, arising from the brain, supplying the sense organs and muscles of the head and neck (e.g. the optic nerve for sight, the auditory nerve for hearing).
• Spinal nerves — 31 pairs, arising from the spinal cord, supplying the trunk and limbs.
These nerves carry sensory impulses from receptors to the CNS and motor impulses from the CNS to muscles and glands, so the PNS is the communication link between the body and the CNS.
❌ Why the other options are incorrect
✗ Neither cranial nor spinal nerves — completely wrong; these are exactly the two sets of nerves forming the PNS.
✗ Only cranial nerves — incomplete; the 31 pairs of spinal nerves are equally a part of the PNS.
✗ Only spinal nerves — incomplete; the 12 pairs of cranial nerves also belong to the PNS.
📌 SSC & Railway Exam Facts
• CNS = brain + spinal cord; PNS = cranial nerves + spinal nerves.
• The autonomic nervous system (sympathetic + parasympathetic) controls involuntary organs such as the heart and gut.
• 12 pairs of cranial nerves and 31 pairs of spinal nerves are present in humans.
• The vagus nerve is the longest cranial nerve; the sciatic nerve is the longest and thickest nerve in the body.
• The spinal cord is protected by the vertebral column, and the brain by the cranium and cerebrospinal fluid.

Correct Answer: Option 1 — Adrenaline
Adrenaline (epinephrine) is secreted by the adrenal glands, which sit like caps on the top of the two kidneys. It is called the emergency hormone or the fight-or-flight hormone, because it is poured into the blood the instant an animal such as a squirrel senses danger.
Adrenaline makes the heartbeat and breathing rate faster, raises blood pressure, diverts blood from the skin and digestive system to the skeletal muscles, makes the liver release stored glucose, and widens the pupils. Together these changes supply the extra oxygen and energy the animal needs either to fight or to run away.
❌ Why the other options are incorrect
✗ Oestrogen — a female sex hormone secreted by the ovary; it develops the female secondary sexual characters and controls the menstrual cycle.
✗ Testosterone — a male sex hormone secreted by the testes; it develops the male secondary sexual characters such as a deep voice and facial hair.
✗ Thyroxin — secreted by the thyroid gland; it regulates carbohydrate, protein and fat metabolism and needs iodine for its synthesis.
📌 SSC & Railway Exam Facts
• The adrenal gland is also called the supra-renal gland; its medulla secretes adrenaline and noradrenaline.
• The adrenal cortex secretes cortisol (the stress hormone) and aldosterone (salt and water balance).
• Adrenaline is used as a life-saving medicine in cardiac arrest and in severe allergy (anaphylaxis).
• The pituitary is the master gland; the pancreas is a mixed gland (both exocrine and endocrine).
• Insulin deficiency causes diabetes mellitus; thyroxin deficiency causes goitre.

Correct Answer: Option 2 — Gibberellins : Help in the growth of the stem; Cytokinins : Promote cell division; Abscisic acid : Inhibits growth
Plant hormones (phytohormones) are chemical compounds made in one part of a plant, carried to another part, and there they control growth, development and the response to stimuli.
• Gibberellins — cause elongation of the stem and of the internodes, break seed dormancy and induce flowering; a sprayed plant becomes unusually tall.
• Cytokinins — promote cell division (cytokinesis); they are present in greatest amount in fruits and seeds and they delay the ageing of leaves.
• Abscisic acid (ABA) — a growth inhibitor; it causes wilting, closing of stomata and falling of leaves, so it is called the stress hormone.
Only Option 2 pairs each of the three hormones with its true function.
❌ Why the other options are incorrect
✗ Option 1 — it makes gibberellins an inhibitor and abscisic acid a stem-growth promoter; these two roles are exactly interchanged.
✗ Option 3 — it gives cell division to gibberellins and stem growth to cytokinins; cell division is the special work of cytokinins.
✗ Option 4 — it wrongly makes cytokinins an inhibitor and abscisic acid a promoter of cell division.
📌 SSC & Railway Exam Facts
• Auxin is made at the shoot tip; it causes cell elongation and is responsible for phototropism.
• Ethylene (ethene) is the only gaseous plant hormone; it ripens fruits.
• Gibberellic acid was first obtained from the fungus Gibberella fujikuroi, which causes the bakanae (foolish seedling) disease of rice.
• Auxin, gibberellin and cytokinin are growth promoters; abscisic acid and ethylene are growth inhibitors.
• The term hormone was coined by Bayliss and Starling; the study of auxin began with the experiments of Charles Darwin on coleoptiles.

Correct Answer: Option 4 — Helps the cells to grow longer
Auxin is a plant hormone synthesised at the tip of the shoot. Its basic action is cell elongation — it makes the cell wall loose and stretchable so that the cell takes in water and grows longer. This lengthwise growth of cells is what makes the stem grow taller.
Auxin also explains phototropism. When light falls on one side of a shoot, auxin moves away to the shaded side; the cells there elongate more, so the shoot bends towards the light. In roots auxin acts in the opposite way, which is why roots bend away from light and towards gravity.
❌ Why the other options are incorrect
✗ Increases stem width — increase in girth is secondary growth, done by the lateral meristem (cambium), not by auxin's elongation action.
✗ Induce flowering — flowering is mainly controlled by gibberellins and by the photoperiod (florigen concept); it is not the defining function of auxin.
✗ Make plants insect resistant — resistance to insects comes from alkaloids, resins, tannins and modern Bt genes, not from a growth hormone.
📌 SSC & Railway Exam Facts
• Auxin means 'to grow'; Charles Darwin and Francis Darwin began the work, and F. W. Went isolated it from oat coleoptiles.
• IAA (Indole-3-acetic acid) is the commonest natural auxin.
• Auxin causes apical dominance — the shoot tip suppresses the growth of side buds; that is why gardeners prune the tip.
• 2,4-D is a synthetic auxin used as a weedicide.
• Tropic movements: phototropism (light), geotropism (gravity), hydrotropism (water), chemotropism (chemicals, e.g. pollen tube growth).

Correct Answer: Option 3 — Change in the directions that plant parts grow in
Plants have no nervous system, so they respond to the environment by changing the direction of their growth. Such a directional, growth-dependent movement towards or away from a stimulus is called a tropic movement (tropism).
• Phototropism — response to light: the shoot bends towards light (positively phototropic) while the root bends away from it.
• Geotropism (gravitropism) — response to gravity: the root grows downwards (positively geotropic) and the shoot grows upwards.
• These bends occur because the hormone auxin collects unevenly on the two sides, so one side elongates more than the other.
❌ Why the other options are incorrect
✗ Change in the branching pattern of their roots — branching is decided mainly by the genetic plan and by soil water and nutrients, and it is not a directional response to light or gravity.
✗ Change in the size of ovary and anther — the size of floral parts is a genetically fixed feature of the species, not a tropic response.
✗ Change in the shape of the leaves and fruits — shape of leaves and fruits is again largely inherited; light and gravity change the direction of growth, not the basic shape.
📌 SSC & Railway Exam Facts
• Tropic movements are directional; nastic movements are non-directional, e.g. the folding of Mimosa pudica (touch-me-not) leaves on touch.
• Hydrotropism — roots grow towards water; Chemotropism — growth of the pollen tube towards the ovule.
• Thigmotropism — response to touch, seen in the coiling of tendrils.
• Movement in Mimosa is caused by a rapid change of water content in the cells at the leaf base, not by growth.
• The plant hormone responsible for tropic bending is auxin.

Correct Answer: Option 4 — Thyroxin hormone
Thyroxin (T₄) is secreted by the thyroid gland, a butterfly-shaped gland lying in front of the trachea (windpipe) in the neck. It controls the basal metabolic rate, that is, the speed at which carbohydrates, proteins and fats are oxidised in the body, and so it decides growth, body heat and general body balance.
Iodine is an essential raw material: the thyroid takes iodine from the blood and attaches it to the amino acid tyrosine to build thyroxin. If the diet is deficient in iodine, thyroxin cannot be made, the gland enlarges and a swelling of the neck called goitre appears. This is why we are advised to use iodised salt.
❌ Why the other options are incorrect
✗ Adrenaline hormone — from the adrenal gland; it is the emergency (fight-or-flight) hormone that raises heartbeat and blood pressure; it needs no iodine.
✗ Insulin hormone — from the beta cells of the pancreas; it lowers blood glucose; its deficiency causes diabetes mellitus.
✗ Testosterone hormone — from the testes; it develops male secondary sexual characters and sperms, and has nothing to do with iodine.
📌 SSC & Railway Exam Facts
• The thyroid is the largest endocrine gland in the human body.
• Deficiency of thyroxin in children causes cretinism (stunted growth, mental retardation); in adults it causes myxoedema.
• Excess thyroxin causes Grave's disease (exophthalmic goitre).
• The thyroid also secretes calcitonin, which lowers blood calcium.
• The thyroid gland is stimulated by TSH (Thyroid Stimulating Hormone) from the anterior pituitary.

Correct Answer: Option 4 — the brain and the spinal cord
The human nervous system has two main divisions. The Central Nervous System (CNS) is made of the brain and the spinal cord; the Peripheral Nervous System (PNS) is made of the cranial and spinal nerves that connect the CNS with the rest of the body.
The CNS is the integrating centre. Information picked up by receptors travels along sensory (afferent) neurons to the brain and the spinal cord, where it is analysed and a decision is taken; the instruction then travels along motor (efferent) neurons to the effectors — muscles and glands. The brain is protected by the cranium (skull) and the spinal cord by the vertebral column, and both are cushioned by cerebrospinal fluid.
❌ Why the other options are incorrect
✗ only the brain — incomplete; the spinal cord is equally a part of the CNS and independently controls reflex actions.
✗ only the heart — the heart is a muscular pumping organ of the circulatory system; it has no role in receiving or integrating nerve impulses.
✗ only the spinal cord — incomplete; thinking, memory, vision, hearing and balance are handled by the brain.
📌 SSC & Railway Exam Facts
• Parts of the brain: fore-brain (cerebrum), mid-brain and hind-brain (cerebellum, pons, medulla).
• Cerebrum — the seat of thinking, memory and intelligence; it is the largest part of the brain.
• Cerebellum — maintains posture and balance; medulla controls blood pressure, salivation and vomiting.
• A reflex arc is completed in the spinal cord, so the response is quick and does not wait for the brain.
• The structural and functional unit of the nervous system is the neuron; the gap between two neurons is the synapse.

Correct Answer: Option 1 — tendrils
Tendrils are slender, thread-like, coiling structures formed by the modification of a leaf, leaflet or stem. In the pea plant the terminal leaflets are modified into tendrils. When a tendril touches a support, the side of the tendril away from the support grows faster than the side touching it, so the tendril coils around the support and the weak stem is held up.
This growth response to touch is called thigmotropism, and it is a good example of a tropic (directional) movement in plants brought about by unequal growth, controlled by the hormone auxin.
❌ Why the other options are incorrect
✗ Prickles — small, sharp outgrowths of the epidermis, as in rose; they give protection from grazing animals and may give a slight hold, but they do not coil or climb.
✗ Sepals — the green outermost whorl of a flower; they only protect the flower bud, and have no role in climbing.
✗ Roots — they absorb water and minerals and fix the plant in soil; climbing roots occur in money plant and betel, but the pea plant climbs by tendrils.
📌 SSC & Railway Exam Facts
• Pea — leaflet tendril; Cucumber, pumpkin and grapevine — stem tendrils.
• Thigmotropism = response to touch; Phototropism = light; Geotropism = gravity; Hydrotropism = water; Chemotropism = chemicals.
• In Mimosa pudica the drooping of leaves on touch is a nastic (non-directional) movement, not tropism.
• Pisum sativum (pea) is the plant used by Gregor Mendel in his classic heredity experiments.
• Tendrils are a modification for climbing; thorns of Bougainvillea are modified stems while spines of cactus are modified leaves.

Correct Answer: Option 2 — Salivation
The medulla oblongata is the lowest part of the hind-brain; it joins the brain to the spinal cord. It controls the involuntary actions of the body — those that go on by themselves without our thinking. These include salivation, vomiting, swallowing, coughing, sneezing, blood pressure, heart rate and the rhythm of breathing.
Because the medulla governs such life-supporting functions, it is called the vital centre of the body, and any serious injury to it is usually fatal.
❌ Why the other options are incorrect
✗ Riding a bicycle — a learnt, voluntary skill needing precise coordination and balance; it is controlled by the cerebellum together with the cerebrum.
✗ Maintaining balance and posture — this is the special work of the cerebellum, which keeps the body steady and the movements smooth.
✗ Walking — a voluntary muscular activity initiated by the cerebrum (motor area) and smoothed by the cerebellum, not by the medulla.
📌 SSC & Railway Exam Facts
• The hind-brain has three parts — cerebellum, pons and medulla oblongata.
• The fore-brain has the cerebrum (thinking, memory, intelligence and the seat of all sensory areas).
• The mid-brain controls reflexes of the eye (pupil size) and of the ear.
• The hypothalamus in the fore-brain controls hunger, thirst, sleep and body temperature.
• The brain floats in cerebrospinal fluid (CSF) inside the cranium, which absorbs shocks; the covering membranes are the meninges.

Correct Answer: Option 4 — Pituitary
The pituitary gland is a tiny, pea-sized endocrine gland attached to the base of the brain in a bony cavity of the skull called the sella turcica. Its anterior lobe secretes Growth Hormone (GH), also called somatotropin.
GH controls the overall growth and development of the body. By increasing protein synthesis and cell multiplication, it stimulates the growth of bones, cartilage, muscles and soft tissues in all organs. Its own release is controlled by GHRH sent down from the hypothalamus, making the whole system a neat example of feedback regulation.
❌ Why the other options are incorrect
✗ Thyroid — secretes thyroxine (T₄), which regulates carbohydrate, protein and fat metabolism; it needs iodine and is stimulated by pituitary TSH.
✗ Adrenal — secretes adrenaline, the fight-or-flight (emergency) hormone, and cortisol; it raises heartbeat and blood pressure but does not control growth.
✗ Pancreas — a mixed gland; its endocrine part secretes insulin and glucagon to regulate blood sugar, and its exocrine part pours pancreatic juice into the intestine.
📌 SSC & Railway Exam Facts
• The pituitary is called the master gland, yet it is itself controlled by the hypothalamus.
• Deficiency of GH in childhood causes dwarfism, excess causes gigantism, and excess in adults causes acromegaly.
• The pituitary also secretes TSH, ACTH, FSH, LH and prolactin; its posterior lobe releases ADH (vasopressin) and oxytocin.
• Deficiency of ADH causes diabetes insipidus — do not confuse it with diabetes mellitus, caused by lack of insulin.
• Hormones are carried by the blood, act on specific target organs, and are needed only in very small amounts.

Correct Answer: Option 1 — They detect taste.
Receptors are specialised nerve endings located in our sense organs that detect information from the environment. Gustatory receptors are present in the taste buds of the tongue and they detect taste.
When food dissolves in saliva and touches these receptors, they set up an electrical impulse in the sensory neuron. The impulse travels along the dendrite → cell body → axon, crosses the synapse by releasing chemicals, and finally reaches the fore-brain, where the sensation of taste is recognised. Taste and smell work together, which is why food seems tasteless when we have a cold.
❌ Why the other options are incorrect
✗ They detect smell — that is the work of olfactory receptors, located in the lining of the nose.
✗ They detect sound — sound is detected by phonoreceptors in the inner ear (cochlea), which also maintains balance.
✗ They detect light — light is detected by photoreceptors, the rods and cones in the retina of the eye.
📌 SSC & Railway Exam Facts
• Gustatory → tongue (taste); Olfactory → nose (smell); Photoreceptor → eye (light); Phonoreceptor → ear (sound); Thermoreceptor → skin (heat).
• An adult tongue has about 10,000 taste buds.
• The fore-brain is the main thinking part and contains centres for hearing, smell, sight and taste.
• Rods detect dim light, cones detect bright light and colour; lack of cones causes colour blindness.
• The gap between two neurons is called a synapse; the gap between a neuron and a muscle is a neuromuscular junction.

Correct Answer: Option 3 — All plant hormones except cytokinins promote cell division.
This statement is INCORRECT, and in fact says the exact opposite of the truth. Cytokinins are the hormones that most strongly promote cell division; NCERT states that they are present in greater concentration in areas of rapid cell division, such as fruits and seeds.
Plant hormones (phytohormones) are chemical compounds made in one part of the plant that help to coordinate growth, development and responses to the environment. The four main groups are auxins (cell elongation, phototropism), gibberellins (stem elongation), cytokinins (cell division) and abscisic acid (growth inhibitor, closes stomata, causes wilting and dormancy).
❌ Why the other options are incorrect
✗ Different plant hormones help to coordinate responses to the environment — correct; plants have no nervous system, so hormones alone control tropic responses such as bending towards light.
✗ All plant hormones except abscisic acid help in promoting growth — correct; auxin, gibberellin and cytokinin promote growth, while abscisic acid inhibits it and is called the stress hormone.
✗ Different plant hormones help to coordinate growth and development — correct; this is NCERT's own definition of the role of phytohormones.
📌 SSC & Railway Exam Facts
• Auxin was discovered by F. W. Went; it causes phototropism by faster elongation on the shaded side.
• Gibberellin causes bolting and increases stem length; it was isolated from the fungus Gibberella fujikuroi.
• Cytokinin promotes cell division and delays ageing of leaves.
• Abscisic acid (ABA) is the stress hormone; it closes stomata during water shortage.
• Ethylene is the only gaseous plant hormone and is used for the ripening of fruits.

Correct Answer: Option 1 — the medulla in the hind-brain
The hind-brain has three parts — the cerebellum, the pons and the medulla oblongata. The medulla is the part that controls involuntary actions, that is, actions which go on without our thinking about them, such as blood pressure, salivation and vomiting.
Because it also runs heartbeat, breathing, coughing, sneezing and swallowing, the medulla is called the vital centre of the body; an injury to it is usually fatal. These involuntary actions are carried out through the autonomic nervous system, whose sympathetic and parasympathetic nerves connect the medulla to the heart, blood vessels and glands.
❌ Why the other options are incorrect
✗ The cerebellum in the fore-brain — doubly wrong: the cerebellum is part of the hind-brain, not the fore-brain, and its job is posture, balance and precision of voluntary movement, e.g. walking in a straight line or picking up a pencil.
✗ Only the spinal cord — the spinal cord conducts impulses and controls reflex actions, but blood pressure, salivation and vomiting are governed by the medulla.
✗ Only the heart — the heart is a pumping organ; it is itself controlled by the medulla and cannot control salivation or vomiting.
📌 SSC & Railway Exam Facts
• Brain regions — Fore-brain: cerebrum; Mid-brain; Hind-brain: cerebellum, pons, medulla.
• Cerebrum is the largest part and the seat of thinking, memory, intelligence and voluntary action.
• Medulla controls heartbeat, breathing, blood pressure, vomiting, coughing and sneezing.
• The brain is protected by the cranium (skull), three meninges and the shock-absorbing cerebrospinal fluid (CSF).
• Humans have 12 pairs of cranial nerves and 31 pairs of spinal nerves.

Correct Answer: Option 3 — water
Plants have no muscles and no nervous system, so they move their parts by changing the amount of water in their cells. When water enters a cell it becomes turgid (swells), and when water leaves it becomes flaccid (shrinks). This change in turgor pressure changes the shape of the cell and hence the position of the plant part.
The classic example is the sensitive plant, *Mimosa pudica* (touch-me-not). On being touched, water moves out of the cells at the base of the leaflets, those cells shrink, and the leaves fold up and droop immediately. This is a nastic (non-directional) movement, independent of growth. The opening and closing of stomata by guard cells works on exactly the same principle.
❌ Why the other options are incorrect
✗ chlorophyll — the green pigment in chloroplasts that traps sunlight for photosynthesis; its amount does not swell or shrink cells.
✗ fat — a stored food (energy reserve) in seeds and in animal adipose tissue; it plays no role in changing cell shape.
✗ carbon dioxide — the raw material taken in through stomata for photosynthesis; it is a gas, not the cell's shape-controlling content.
📌 SSC & Railway Exam Facts
• Plant movements are nastic (touch-me-not, independent of growth) and tropic (growth-dependent, directional).
• Tropic movements — phototropism (light), geotropism (gravity), hydrotropism (water), chemotropism (chemicals).
• Auxin promotes cell elongation; gibberellin causes stem growth; cytokinin promotes cell division.
• Abscisic acid (ABA) is the stress/inhibitor hormone — it closes stomata and causes wilting.
• Loss of turgor pressure in herbaceous plants causes wilting; excess water loss from a cell in a strong salt solution causes plasmolysis.

Correct Answer: Option 4 — geotropism
Geotropism (gravitropism) is the directional growth movement of a plant part in response to the stimulus of gravity. The root grows towards gravity, i.e. downwards — this is positive geotropism; the shoot grows away from gravity, i.e. upwards — this is negative geotropism.
The response is controlled by the plant hormone auxin, which collects on the lower side of a horizontally placed seedling. In the stem, auxin promotes cell elongation, so the lower side grows faster and the shoot curves upward; in the root, a high concentration of auxin inhibits elongation, so the upper side grows faster and the root curves downward.
❌ Why the other options are incorrect
✗ chemotropism — growth towards a chemical, e.g. the pollen tube growing down the style towards the ovule.
✗ hydrotropism — growth of roots towards water (moisture) in the soil; the stimulus here is water, not gravity.
✗ phototropic movement — growth in response to light; shoots are positively phototropic and roots negatively phototropic.
📌 SSC & Railway Exam Facts
• Tropic (directional) movements — phototropism, geotropism, hydrotropism, chemotropism, thigmotropism (touch, as in tendrils).
• Nastic (non-directional) movements — the folding of Mimosa pudica (touch-me-not) leaves.
• Auxin was the first plant hormone discovered; F. W. Went isolated it.
• Gibberellin — stem elongation; Cytokinin — cell division; Abscisic acid — inhibits growth, causes wilting.
• Ethylene is the only gaseous plant hormone and is used for ripening of fruits.

Correct Answer: Option 3 — Cytokinin
Cytokinins are plant hormones (phytohormones) that promote cell division (cytokinesis) — the very word cytokinin comes from *cytokinesis*. They are naturally present in greater concentration in regions of rapid cell division, such as fruits, seeds, root tips and shoot apices.
Besides triggering division, cytokinins delay the ageing of leaves, help in opening of stomata, and break the apical dominance imposed by auxins so that lateral buds can sprout. Zeatin, obtained from maize, is the best-known natural cytokinin, and the hormone is largely synthesised in the root tips and carried upward through the xylem.
❌ Why the other options are incorrect
✗ Abscisic acid (ABA) — the only growth inhibitor among these; it causes wilting, closure of stomata, dormancy of buds and seeds, and abscission (fall) of leaves. It is the stress hormone.
✗ Gibberellins — cause elongation of the stem, bolting, breaking of seed dormancy and parthenocarpy; discovered from the fungus *Gibberella fujikuroi*.
✗ Auxins — synthesised at the shoot tip; they cause cell elongation (not division) and are responsible for phototropism and apical dominance.
📌 SSC & Railway Exam Facts
• Five main plant hormones: Auxin, Gibberellin, Cytokinin, Abscisic acid and Ethylene.
• Ethylene is the only gaseous plant hormone; it ripens fruits.
• Auxin was the first plant hormone discovered; F. W. Went isolated it.
• ABA is the stress / anti-transpirant hormone; cytokinin is the anti-ageing hormone.
• Gibberellin makes dwarf plants grow tall; cytokinin is widely used in tissue culture media.

Correct Answer: Option 3 — Oestrogen
Oestrogen is the female sex hormone, secreted mainly by the ovary. It brings about the growth and development of the female reproductive organs — uterus, fallopian tubes and vagina — and produces the secondary sexual characters at puberty: enlargement of the breasts, broadening of the hips, a high-pitched voice and growth of hair in the armpits and the pubic region.
Together with progesterone, oestrogen also regulates the menstrual cycle: it rebuilds the uterine lining (endometrium) every month after menstruation and prepares it to receive a fertilised egg. The whole process is under the control of FSH and LH from the pituitary gland.
❌ Why the other options are incorrect
✗ Testosterone — the male sex hormone from the testes; it develops male reproductive organs and male secondary characters such as a deep voice and facial hair.
✗ Thyroxin — from the thyroid gland; it regulates the metabolism of carbohydrates, fats and proteins and needs iodine for its formation.
✗ Adrenaline — the emergency or fight-or-flight hormone from the adrenal gland; it raises heart rate, breathing rate and blood pressure in fear or stress.
📌 SSC & Railway Exam Facts
• Progesterone is the pregnancy hormone; it maintains the uterine lining after fertilisation.
• The menstrual cycle lasts about 28 days; ovulation occurs around the 14th day.
• Deficiency of thyroxin causes goitre; iodised salt prevents it.
• Insulin from the pancreas lowers blood sugar; its deficiency causes diabetes mellitus.
• The pituitary is the master gland, but it is itself controlled by the hypothalamus.

Correct Answer: Option 4 — Phototropism – movement towards water
Phototropism is movement in response to light, not water. The shoot bends towards light, which is positive phototropism, while the root bends away from light, which is negative phototropism. The bending is caused by the hormone auxin: it accumulates on the shaded side of the shoot and makes those cells elongate more, so the tip curves towards the light. Hence statement 4 is incorrect.
A tropic movement is a directional growth movement of a plant part in response to an external stimulus, and it is always slow because it is brought about by growth, not by muscles.
❌ Why the other options are incorrect
✗ Hydrotropism – movement towards water — a correct match; roots grow towards a source of water, showing positive hydrotropism.
✗ Chemotropism – movement towards chemical — a correct match; the classic example is the growth of the pollen tube towards the ovule through the style.
✗ Geotropism – response to the pull of earth or gravity — a correct match; the root grows downward (positive) and the shoot upward (negative) geotropism.
📌 SSC & Railway Exam Facts
• Thigmotropism — growth movement in response to touch, seen in the tendrils of climbers.
• Nastic movements are non-directional, e.g. the drooping of Mimosa pudica (touch-me-not) leaves — that is thigmonasty, not tropism.
• Auxin is the hormone behind phototropism; it is made at the shoot tip.
• Plants show no nervous system; they coordinate through chemicals (hormones) and electrical-chemical signals.
• Movement in *Mimosa* occurs by a change in the water content of the cells, and it is much faster than a tropic movement.

Correct Answer: Option 3 — Hypothalamus
The hypothalamus lies at the base of the brain and is the master controller of the endocrine system. When the blood level of growth hormone falls, the hypothalamus secretes Growth Hormone Releasing Hormone (GHRH), also called growth hormone releasing factor. GHRH travels to the anterior pituitary and stimulates it to secrete Growth Hormone (GH / Somatotropin).
This is a classic example of feedback regulation — the amount of hormone in the blood itself decides how much more will be released.
❌ Why the other options are incorrect
✗ Pancreas — a mixed gland; secretes insulin and glucagon to control blood sugar, not GHRH.
✗ Adrenal gland — secretes adrenaline (emergency hormone) and cortisol; it is controlled by the pituitary, it does not control it.
✗ Thyroid gland — secretes thyroxine, which regulates carbohydrate, protein and fat metabolism; it needs iodine and is itself stimulated by pituitary TSH.
📌 SSC & Railway Exam Facts
• The pituitary gland is called the master gland, but it is itself controlled by the hypothalamus.
• Excess GH in childhood causes gigantism; deficiency causes dwarfism; excess in adults causes acromegaly.
• The hypothalamus also controls body temperature, hunger, thirst and sleep.
• The pituitary is located in a bony cavity of the skull called the sella turcica.

Correct Answer: Option 3 — It stimulates growth in all organs.
Growth Hormone (GH / Somatotropin) is secreted by the anterior lobe of the pituitary gland. Its main function is to regulate the growth and development of the body, stimulating growth in all organs — bones, cartilage, muscles and soft tissues — by increasing protein synthesis and cell multiplication.
Its secretion is controlled by GHRH from the hypothalamus.
❌ Why the other options are incorrect
✗ Option 1 — development of female sex organs is stimulated by oestrogen, secreted by the ovary.
✗ Option 2 — blood sugar level is regulated by insulin and glucagon from the pancreas.
✗ Option 4 — metabolism of carbohydrates, proteins and fats is regulated by thyroxine from the thyroid gland.
📌 SSC & Railway Exam Facts
• Deficiency of GH in childhood causes dwarfism; excess causes gigantism; excess in adults causes acromegaly.
• Oestrogen — female secondary sexual characters; Testosterone — male secondary sexual characters (from the testis).
• Insulin deficiency causes diabetes mellitus.
• Thyroxine deficiency causes goitre; iodised salt prevents it.
• Adrenaline from the adrenal gland is the fight-or-flight / emergency hormone.

Correct Answer: Option 2 — Menstrual cycle
The ovary is the female gonad. It performs two jobs: it produces the ova (eggs) and it secretes the female sex hormones oestrogen and progesterone.
These hormones control the menstrual cycle — the monthly thickening and shedding of the uterine lining (endometrium) — and also develop the female secondary sexual characters such as breast development, widening of the pelvis and the feminine voice.
❌ Why the other options are incorrect
✗ Stimulates pituitary glands — the pituitary is stimulated by the hypothalamus through releasing hormones; in fact the pituitary (FSH and LH) stimulates the ovary, not the reverse.
✗ Regulates metabolism — done by thyroxine from the thyroid gland.
✗ Stimulates growth in all organs — done by growth hormone from the pituitary gland.
📌 SSC & Railway Exam Facts
• The menstrual cycle lasts about 28 days; ovulation (release of the egg) occurs around the 14th day.
• Progesterone is the pregnancy-maintaining hormone; it prepares the uterus for implantation.
• Testis secretes testosterone, which controls male secondary sexual characters.
• Placenta acts as a temporary endocrine gland during pregnancy.
• FSH and LH are gonadotropic hormones released by the anterior pituitary.

Correct Answer: Option 3 — fore-brain
The fore-brain is the main thinking part of the brain. Its largest region, the cerebrum, has separate sensory areas that receive impulses from receptors for hearing, smell, sight and touch, separate association areas where this information is interpreted and combined with earlier memory, and motor areas that send instructions to voluntary muscles.
The fore-brain also contains centres for hunger, thirst, emotions and body temperature in the hypothalamus. Thus thinking, reasoning, memory, intelligence and voluntary action are all controlled here.
❌ Why the other options are incorrect
✗ mid-brain — controls involuntary reflexes such as changes in pupil size and reflex movements of the head, neck and eyes; it does no thinking.
✗ hind-brain — has the cerebellum (precision of voluntary action, posture and balance), the pons, and the medulla (involuntary control of blood pressure, salivation, vomiting).
✗ spinal cord — a nerve cord that carries impulses to and from the brain and is the centre of reflex arcs; it does not think.
📌 SSC & Railway Exam Facts
• The brain has three parts — fore-brain, mid-brain and hind-brain.
• The cerebrum is the largest part of the human brain; the cerebellum is the second largest.
• The medulla oblongata controls breathing, heartbeat, coughing and sneezing.
• The brain is protected by the cranium (skull) and by three membranes called meninges, cushioned by cerebrospinal fluid (CSF).
• Reflex actions are completed by the spinal cord without waiting for the brain's decision.