10th Science Unit 16 Plant and Animal Hormones Book Back Answers

Gibberellins stimulate extraordinary elongation of internodes, as seen in corn and pea.

So dwarf plants treated with gibberellin grow tall.

Auxins produced by the apical bud suppress the growth of lateral buds, which is called apical dominance.

Cytokinin has the opposite effect, as it promotes lateral bud growth.

2,4-D (2,4 Dichlorophenoxy Acetic Acid) is an artificially synthesized auxin.

IAA and gibberellins (GA3) are natural plant hormones.

F. W. Went performed a series of experiments on Avena coleoptiles using agar blocks.

He concluded that a chemical diffusing from the tip causes growth and named it auxin.

Luteinizing hormone is a gonadotropic hormone.

Gonadotropic hormones (FSH and LH) are secreted by the anterior lobe of the pituitary (adenohypophysis).

Exocrine glands have ducts to carry their secretions.

Salivary glands have ducts; pituitary, adrenal and thyroid are ductless endocrine glands.

The exocrine part of the pancreas secretes pancreatic juice for digestion through a duct.

The endocrine part, the Islets of Langerhans, secretes insulin and glucagon into the blood.

The pituitary gland regulates and controls the other endocrine glands.

Hence it is called the "Master gland".

Auxins are produced at the tip of stems and roots and migrate to the zone of elongation.

They promote elongation of stems, cause apical dominance (apical bud suppresses lateral buds) and prevent formation of the abscission layer.

Ethylene is the only gaseous plant hormone.

It stimulates formation of the abscission zone in leaves, flowers and fruits and promotes ripening of fruits like tomato, apple and banana.

Abscisic acid (ABA) is a growth inhibitor called the stress hormone.

During water stress and drought conditions ABA causes closure of stomata to reduce water loss.

Application of gibberellins stimulates extraordinary elongation of internodes.

This effect is clearly seen in genetically dwarf plants, which grow tall like normal plants.

Apical dominance is the suppression of lateral buds by the apical bud, caused by auxin.

Cytokinin promotes the growth of lateral buds even in the presence of the apical bud, so it opposes apical dominance.

The parathyroid glands secrete parathormone from their chief cells.

Parathormone regulates calcium and phosphorus metabolism by acting on bone, kidney and intestine to maintain blood calcium level.

Islets of Langerhans of the pancreas have alpha and beta cells.

Alpha cells secrete glucagon, while beta cells secrete insulin, which lowers blood glucose.

The anterior lobe of the pituitary secretes thyroid stimulating hormone (TSH).

TSH controls the growth of the thyroid gland, coordinates its activities and its hormone secretion.

Decreased secretion of thyroid hormones is hypothyroidism.

In children it causes cretinism — stunted growth, mental defect, lack of skeletal development and deformed bones.

Auxin – Coleoptile tip – Apical dominance: Went obtained auxin from Avena coleoptile tips, and auxin of the apical bud suppresses lateral buds (apical dominance).

Ethylene – Fruits – Ripening: ethylene is a gaseous hormone whose maximum synthesis occurs during ripening of fruits like apple, banana and melon.

Abscisic acid – Chloroplast – Abscission: ABA is found in the chloroplast and promotes abscission (fall of leaves, flowers and fruits).

Cytokinin – Coconut milk – Cell division: cytokinin is abundant in the liquid endosperm of coconut and induces cytokinesis (cell division).

Gibberellins – Gibberella fujikuroi – Internodal elongation: the fungus Gibberella fujikuroi caused the Bakanae (foolish seedling) disease with excess internodal elongation in rice.

a) Thyroxine – deficiency due to inadequate iodine in the diet enlarges the thyroid gland, seen as a swelling in the neck called Simple goitre.

b) Insulin – deficiency of insulin raises blood sugar and causes Diabetes mellitus (hyperglycemia, glycosuria, polyuria, polydipsia, polyphagia).

c) Parathormone – decreased secretion (as after removal of parathyroid glands during thyroidectomy) causes sustained muscle spasm called Tetany.

d) Growth hormone – excess secretion of GH in adults causes abnormal enlargement of head, face, hands and feet, known as Acromegaly.

e) ADH (Vasopressin) – deficiency reduces reabsorption of water in kidney tubules, causing excess urine output; this disorder is Diabetes insipidus.

Cytokinins (cytos = cell, kinesis = division) induce cell division or cytokinesis in plant cells in the presence of auxins.

They also cause cell enlargement, promote growth of lateral buds and delay ageing (Richmond Lang effect).

Gibberellins are more efficient than auxins in inducing the formation of seedless fruits.

Parthenocarpy is the development of fruits without fertilization, e.g. tomato.

Ethylene is a growth inhibitor concerned with maturation and ripening of fruits.

It hastens (speeds up), not retards, the senescence of leaves and flowers and also forms the abscission zone leading to premature shedding.

Excess secretion of thyroid hormones (hyperthyroidism) leads to Grave's disease.

Its symptoms include protrusion of the eyeballs (exophthalmia), increased metabolic rate, high body temperature, profuse sweating and loss of body weight.

The pituitary gland is anatomically composed of two lobes – the anterior lobe (adenohypophysis) and the posterior lobe (neurohypophysis).

The intermediate lobe is non-existent in human beings.

Estrogen is produced by the Graafian follicles of the ovary.

The corpus luteum, formed from the ruptured follicle after ovulation, secretes progesterone.

Assertion is true: cytokinin application keeps vegetables fresh for many days, because cytokinin delays ageing in plants (Richmond Lang effect).

Reason is true: cytokinins delay senescence of leaves and other organs by mobilising nutrients towards the treated part.

The delay of senescence stated in the Reason is exactly why the vegetables stay fresh, so R correctly explains A.

Assertion is true: the pituitary gland is called the "Master gland".

Reason is true: it secretes TSH, ACTH and gonadotropins which regulate and control the other endocrine glands.

Since its control over other glands is the very reason for the name "Master gland", R correctly explains A.

Assertion is true: diabetes mellitus is caused by deficiency of insulin and is marked by increase in blood sugar level (hyperglycemia).

Reason is true: insulin converts glucose into glycogen and promotes entry of glucose into cells, so it decreases blood glucose concentration.

When insulin is deficient this lowering action is lost, so blood sugar rises — the reason correctly explains the assertion.

Gibberellins act on monoecious plants like cucurbits (Cucumber, Pumpkin).

They increase the number of male flowers produced.

Artificially made auxin-like chemicals are called synthetic auxins.

Example: 2,4-D (2,4-Dichlorophenoxy Acetic Acid); NAA and IBA are others.

Parthenocarpy is the development of fruits without fertilisation.

Gibberellins are more efficient than auxins in inducing seedless (parthenocarpic) fruits in tomato.

Prolactin (PRL), also called lactogenic hormone, is secreted by the anterior pituitary.

It develops the mammary glands during pregnancy and stimulates milk production after child birth.

Vasopressin (ADH) of the posterior pituitary increases reabsorption of water in kidney tubules.

Aldosterone, a mineralocorticoid of the adrenal cortex, reabsorbs sodium ions, excretes potassium ions and regulates electrolyte and fluid balance.

The adrenal medulla secretes epinephrine (adrenaline) and norepinephrine (noradrenaline).

They are called emergency hormones or the "flight, fright and fight" hormones, released during stress and emotion.

The pancreas is both exocrine and endocrine in nature.

Its exocrine part secretes pancreatic juice containing digestive enzymes, while the Islets of Langerhans secrete the hormones insulin and glucagon.

The adrenal glands lie above each kidney.

Hence they are also called supra renal glands; they consist of adrenal cortex and adrenal medulla.

Auxins are of two types – natural auxins produced by the plant itself, and synthetic auxins.

Synthetic auxins are artificially synthesized chemicals that have properties like natural auxins.

Examples: 2,4-D (2,4 Dichlorophenoxy Acetic Acid), IBA (Indole-3 Butyric Acid), NAA ($\alpha$-Naphthalene Acetic Acid), 2,4,5-T (2,4,5 Trichlorophenoxy Acetic Acid), Indole-3-Propionic Acid.

Rosette plants have very short internodes, so their leaves appear crowded near the ground.

When such rosette plants are treated with gibberellin, there is a sudden elongation of the shoot followed by flowering. This is called bolting.

It can be induced artificially by external application (spraying) of gibberellins on rosette plants.

Abscisic acid promotes abscission – the separation of leaves, flowers and fruits from the branch.

During water stress and drought conditions, ABA causes closure of stomata, so it is called the stress hormone.

(It also promotes senescence by loss of chlorophyll and induces bud dormancy in winter.)

Leaf fall and fruit drop occur due to the formation of an abscission layer at the base of the leaf or fruit stalk.

To prevent this, auxins should be sprayed on the plants.

Reason: Auxins prevent the formation of the abscission layer, so leaves and fruits are not shed.

Auxin spray also helps to retain fruits on the plant till they mature.

Chemical messengers are the hormones secreted by the specialized endocrine (ductless) glands.

They are produced in very minute quantities and diffuse directly into the blood stream.

The blood carries them to distant parts of the body where they act on specific organs called target organs.

They control physiological processes such as digestion, metabolism, growth, development and reproduction.

Ducts: Exocrine glands have specific ducts to carry their secretions; endocrine glands are ductless glands.

Mode of transport: Exocrine secretions pass through ducts to the site of action; endocrine secretions diffuse into the blood stream and are carried to distant parts.

Secretion: Endocrine glands secrete hormones in minute quantities which act on target organs; exocrine glands secrete enzymes, sweat, milk, saliva etc.

Examples: Exocrine – salivary glands, mammary glands, sweat glands; Endocrine – pituitary, thyroid, adrenal glands.

Parathormone is secreted by the chief cells of the parathyroid glands.

It regulates calcium and phosphorus metabolism in the body.

It acts on bone, kidney and intestine to maintain the blood calcium level.

Its decreased secretion (as after thyroidectomy) causes tetany – muscle spasm and painful cramps of limb muscles.

The posterior lobe (neurohypophysis) secretes two hormones – vasopressin (ADH) and oxytocin.

Vasopressin (Antidiuretic hormone) acts on the kidney tubules, where it increases the reabsorption of water and reduces water loss in urine. Its deficiency causes diabetes insipidus.

Oxytocin acts on the smooth muscles of the uterus, helping in its contraction during child birth.

Oxytocin also acts on the mammary glands causing milk ejection after child birth.

Thyroid hormones (T3 and T4) control the growth of the body and bone formation.

They influence the activity of the central nervous system and regulate cell metabolism.

They are essential for normal physical, mental and personality development of a person.

Since their deficiency affects mental and physical development (cretinism, myxoedema), they are called personality hormones.

Thyroid hormone (thyroxine, T4) requires the amino acid tyrosine and iodine for its formation; the gland needs about 120 µg of iodine daily.

If the iodine content of the diet is low, the thyroid gland cannot make enough thyroxine.

The gland then enlarges and protrudes as a marked swelling in the neck – this condition is called goitre (simple goitre / hypothyroidism).

It is common in Himalayan regions where the soil has a low iodine content.

a. Gibberellin applied to rice seedlings: it causes extraordinary elongation of the internodes, so the seedlings grow abnormally tall and thin — the same symptom seen in Bakanae (foolish seedling) disease.

b. A rotten fruit mixed with unripe fruits: the rotten fruit releases ethylene gas, which promotes ripening; so the unripe fruits also ripen quickly and may start to rot.

c. Cytokinin not added to the culture medium: cell division (cytokinesis) will not take place properly and new organs will not be formed from the callus, so morphogenesis in tissue culture fails.

a. The hormone is Gibberellin (gibberellic acid), discovered by Kurosawa in 1926 from the fungus Gibberella fujikuroi.

b. Its property of causing extraordinary elongation of internodes makes the rice plants grow abnormally tall and weak — the foolish seedling (Bakanae) symptom.

c. Functions: (i) induces bolting — sudden shoot elongation followed by flowering in rosette plants; (ii) induces parthenocarpic (seedless) fruits, e.g. tomato. It also breaks dormancy of potato tubers and promotes male flowers in cucurbits.

The symptoms — protrusion of eyeballs (exophthalmia), high body temperature and increased metabolic rate with high blood pressure — point to hyperthyroidism.

The gland involved is the thyroid gland, situated on either side of the trachea.

The condition is due to excess secretion of the thyroid hormones triiodothyronine (T3) and thyroxine (T4).

This condition of hyperthyroidism is called Grave's disease; other signs are profuse sweating, loss of body weight and nervousness.

Fear and tension before the exam is a condition of stress and emotion.

During stress the adrenal medulla secretes epinephrine (adrenaline) and norepinephrine.

These are called emergency hormones or 'flight, fright and fight' hormones.

Adrenaline increases the heart beat and blood pressure, raises the rate of respiration and causes profuse sweating — hence Sanjay's symptoms.

Tiredness and frequent urination (polyuria) with the need for a daily injection to control blood glucose show that he is suffering from Diabetes mellitus.

The cause is deficiency of insulin secreted by the beta cells of the Islets of Langerhans of the pancreas; without insulin glucose is not converted into glycogen, so blood sugar rises (hyperglycemia) and glucose is excreted in urine (glycosuria).

Preventive measures: take a balanced diet low in sugar and fat, and avoid oily and junk foods.

Do regular exercise, walking or yoga and maintain normal body weight; avoid stress.

Check blood glucose regularly and take insulin injection or medicines exactly as advised by the doctor.