SAMACHEER CLASS 10 UNIT16 NOTES

 

UNIT 16

  samacheer SCIENCE
CLASS 10

BIOLOGY

PLANT & ANIMAL HORMONES

INTRODUCTION

·     Word ‘Hormone’ – derived from Greek word ‘hormon’ à ‘to excite’

PLANT HORMONE

·     Control & co-ordination in plants – performed by chemical substances – called Plant hormones

·     Plants – several cells – produce hormones

·     Phytohormones – transported to different plant parts – perform various physiological functions

ANIMAL HORMONES

·     Endocrine glands (Vertebrate animals) – communication system – to co-ordinate physiological & metabolic functions – by chemical integration

·     Endocrine system – acts through chemical messengers – ‘Hormones’ – produced by specialised glands

·     Physiological processes – Digestion, metabolism, growth, development. Growth, development & reproduction – controlled by Hormones

PLANT HORMONES

·     Plant hormones – organic molecules – produced at low concentration in plants

·     They control – morphological, physiological & biochemical responses

 

TYPES OF PLANT HORMONES

·     5 major classes of plant hormones

o   Auxins

o   Cytokinins

o   Gibberellins

o   Abscisic acid (ABA)

o   Ethylene

·     Auxins, Cytokinins & Gibberellins – promote plant growth

·     Abscisic acid & Ethylene – inhibit plant growth

AUXINS

·     Auxin (Gk. Auxin = to grow)

·     Auxin – first plant hormone discovered

·     Term ‘auxin’ – introduced by Kogl & Haagen-Smith (1931)

·     Auxin – produced at – tips of stems & roots – they migrate from there to zone of elongation

·     Charles Darwin (1880) – observed unilateral growth & curvature of canary grass (Phalaris canariensis) Coleoptiles

·     Darwin concluded – some ‘influences’ – transmitted from the tip of coleoptile – to basal region

·     This ‘influence’ – later identified as ‘Auxin’ – by Went

WENT’S EXPERIMENTS

·     Frits Warmolt Went (1903 - 1990) – Dutch biologist – demonstrated effect of Auxin in plants

·     He did experiments with – Avena coleoptiles

1^ST EXPERIMENT

·     Removed the tips of Avena coleoptiles

·     Cut tips – did not grow

·     Indicates – tips produce – something essential for growth

2^ND EXPERIMENT

·     Cut coleoptile tip – placed agar block – on decapitated coleoptile tip

·     No response

3^RD EXPERIMENT

·     Placed detached coleoptile tip on agar block

·     After 1 hour – discarded tip – placed agar block on decapitated coleoptile tip

·     It grew straight up

·     Indicates – some chemical – diffused from cut coleoptile tip – into agar block – stimulates growth

CONCLUSION

·     A chemical – diffuse from tips of coleoptile – responsible for growth

·     Named it – ‘Auxin’ – meaning ‘to grow’

·     TYPES OF AUXINS

·     2 types of Auxins

·     (i) Natural Auxins &              – (ii) Synthetic Auxins

NATURAL AUXINS

·     Produced by plants – natural auxins

·     Eg: IAA (Indole – 3 – Acetic Acid)

SYNTHETIC AUXINS

·     Artificially produced auxins

·     Have properties like auxins – called ‘Synthetic auxins’

·     Eg: 2,4,D (2,4, Dichlorophenoxyl Acetic Acid)

 

PHYSIOLOGICAL EFFECTS OF AUXINS

·     Auxins – bring different physiological effects – in different plant parts

·     promote elongation of stems & coleoptiles – make them grow

·     Low concentration of auxin – induce root formation; Higher concentration – inhibit root formation

·     Auxin produced by – apical buds – suppress growth of – lateral buds – called ‘Apical dominance’

·     Seedless fruits – without fertilisation – induced by – applying auxins externally – Parthenocarpy – Eg: Watermelon, grapes, lime, etc

·     Prevents – formation of Abscission layer

DO YOU KNOW?

·     Natural Auxins

·     Phenyl Acetic Acid (PAA)

·     Indole 3 Acetonitrile (IAN)

·     Synthetic Auxins

·     Indole 3 Butyric Acid (IBA)

·     Indole 3 Propionic Acid (IPA)

·     α – Naphthalene Acetic Acid (NAA)

·     2,4,5 – T (2,4,5 Trichlorophenoxy Acetic Acid)

CYTOKININS

·     Cytos – Cell; Kinesis – Division

·     Cytokinins (plant hormone) – promotes cell division / Cytokinesis – in plant cells

·     First isolated from – Herring fish sperm

·     Zeatin (cytokinin) – isolated from Zeamays

·     Cytokinin – abundant in coconut milk

PHYSIOLOGICAL EFFECTS OF CYTOKININS

·     Induce cell division – in the presence of auxin

·     Also cause – cell enlargement

·     Both auxin & cytokinin – essential for organ formation – from callus in tissue culture (Morphogenesis)

·     Promote growth of lateral buds – even when apical bud is present

·     Application of Cytokinin – delays ageing in plants – called Richmond Lang effect

GIBBERELLINS

·     Gibberellins – abundant plant hormone

·     Hurosawa (1926) – observed Bakanae disease or foolish seedling disease (Rice crops)

·     Internodal elongation in rice – caused by fungus – Gibberella fujjikuron

·     Active substance – Gibberellic acid

PHYSIOLOGICAL EFFECTS OF GIBBERELLINS

·     Application of Gibberellins – stimulate elongation of internode – Eg: Corn & Pea

·     Rosette plants – treated with gibberellin – induce sudden shoot elongation – flowering follows – called Bolting

·     Promotes – production of male flowers – in monoecious plants (Cucurbits)

·     Breaks dormoncy – potato tubers

·     Gibberellins – efficient than auxins – in inducing seedless fruit formation – parthenocarpic fruits (Development of fruits without fertilisation) – Eg: Tomato

ABSCISIC ACID (ABA)

·     ABA – growth inhibitor, regulates abscission & dormancy

·     Increases – tolerance of plants to different stress

·     Also called stress hormone

·     Found in – Chloroplast

PHYSIOLOGICAL EFFECTS OF ABA

·     Promotes – abscission process (separation of leaves, flowers & fruits from the branch)

·     During water stress & drought – ABA causes stomatal closure

·     Promotes senescence in leaves (cause loss of chlorophyll)

·     Induce bud dormancy (by the approach of winter) – Eg: Birch trees

·     Powerful inhibitor of lateral bud growth (Tomato)

ETHYLENE

·     Gaseous plant hormone – growth inhibitor

·     Helps – maturation & ripening of fruits

·     Ethylene synthesis – maximum during – ripening of fruits – like apples, bananas & melons

PHYSIOLOGICAL EFFECTS OF ETHYLENE

·     Promotes – ripening of fruits – Eg: Tomato, apple, mango, banana, etc

·     Inhibits – elongation of stem & root – in Dicots

·     Hastens – senescence of leaves & flowers

·     Stimulates – formation of abscission zone (leaves, flowers & fruits) – leads to premature shedding

·     Breaks – dormancy of buds, seeds & storage organs

HUMAN ENDOCRINE GLANDS

·     Endocrine glands (animals) – communication system – coordinates biological functions

·     2 kinds of glands in animals

·     Endocrine Glands &            

·     Exocrine glands

·     Endocrine glands – animals & human beings

·     Also called ductless glands

·     Endocrine secretions – ‘hormone’ – produced in minute quantities

·     Secretions diffuse in blood stream – carried to distant parts of the body

·     Act on specific organs – ‘Target organs’

·     Exocrine glands – have specific ducts to carry secretions

·     Eg: Salivary glands, mammary glands, sweat glands

DO YOU KNOW?

·     Endocrinology – study of Endocrine glands & its physiology

·     Thomas Addison – Father of Endocrinnolgy

·     W.M. Bayliss & E.H. Starling (English Physiologists) – introduced the term ‘Hormone’ (1909)

·     They first discovered – Secretin hormone

·     Endocrine glands – present in Humans & other vertebrates are

o   Pituitary gland

o   Thyroid gland

o   Parathyroid gland

o   Pancreas (Islets of Langerhans)

o   Adrenal gland (Adrenal Cortex & Adrenal Medulla)

o   Gonads (Testes & Ovary)

o   Thymus gland

(A)PITUITARY GLAND

·     Pituitary gland / Hypophysis – pea shaped compact mass of cells

·     Located – base of midbrain – attached to hypothalamus – by Pituitary stalk

·     Pituitary gland – has 2 lobes – perform different functions

o   Anterior lobe (Adenohypophysis)

o   Posterior lobe (Neurohypophysis)

·     Intermediate lobe – absent in humans

·     Pituitary gland – major endocrine gland in most vertebrates

·     Regulates & controls – other endocrine glands – so called ‘Master gland’

HORMONES SECRETED BY ANTERIOR LOBE OF PITUITARY GLAND (ADENOHYPOPHYSIS)

·     Anterior pituitary – different type of cells – secrete hormones – stimulates production of hormones by other endocrine glands

·     Hormones secreted by – anterior pituitary

o   Growth hormone

o   Thyroid stimulating hormone

o   Adrenocorticotropic hormone

o   Gonadotropic hormone – Follicle stimulating hormone + Luteinizing hormone

o   Prolactin

    (I) GROWTH HORMONE (GH)

·     Promotes – development & enlargement of all body tissues

·     Stimulates – growth of muscles, cartilage & long bones

·     Controls – Cell metabolism

·     Improper secretion of GH – leads to

o   Dwarfism     

o   Gigantism    

o   Acromegaly

 

IMPROPER SECRETION OF GROWTH HORMONE

DWARFISM

·     Caused by – decreased secretion of GH – in children

·     Characteristics – stunted growth, delayed skeletal formation & mental disability

GIGANTISM

·     Caused by – over secretion of GH – in children

·     Characteristics – over growth of all body tissues & organs

·     Individuals with Gigantism – attain abnormal increase in height

ACROMEGALY

·     Caused by – excess secretion of GH – in adults

·     Characteristics – abnormal enlargement of head, face, hands & feet

(II) THYROID STIMULATING HORMONE

·     Controls – growth of thyroid gland, co-ordinates – thyroid activities & hormone secretion

(III) ADRENOCORTICOTROPHIC HORMONE (ACTH)

·     Stimulates – adrenal cortex of adrenal gland – to produce hormone

·     Influences – protein synthesis – in adrenal cortex

(IV) GONADOTROPHIC HORMONES (GTH)

·     Follicle stimulating hormone & Luteinizing hormone – Gonadotrophic hormone

·     FSH & LH – essential for development of Gonads

FOLLICLE STIMULATING HORMONE (FSH)

·     In males – stimulates – germinal epithelium of testes – to form sperms

·     In females – initiates – growth of ovarian follicles & its development in ovary

LUTEINIZING HORMONE (LH)

·     In males – promotes – Leydig cells of Testes – to secrete Testosterone (Male sex hormone)

·     In females – causes ovulation (rupture of mature graffian follicle) – responsible for – development of Estrogen & Progesterone (Female sex hormones)

(V) PROLACTIN (PRL)

·     Also called Lactogenic hormone

·     Initiates – development of mammary glands (during pregnancy)

·     Stimulates – milk production (after child birth)

 

HORMONES SECRETED BY POSTERIOR LOBE OF PITUITARY (NEUROHYPOPHYSIS)

·     Hormones secreted by – posterior pituitary

o   Vasopressin or Antidiuretic hormone

o   Oxytocin

VASOPRESSIN / ANTIDIURETIC HORMONE (ADH)

·     In kidney tubules – increases reabsorption of water

·     Reduce loss of water – through urine – so named antidiuretic hormone

·     Deficiency of ADH – reduces reabsorption of water – increases urine output (Polyuria) – deficiency disorder – Diabetes insipidus

OXYTOCIN

·     Helps in contraction of smooth muscles – in uterus (during child birth) & in mammary gland (during milk ejection after child birth)

(B) THYROID GLAND

·     Has 2 distinct lobes – on either side of trachea

·     2 lobes – connected by – narrow band of tissue – isthmus

·     This gland – composed of – glandular follicles - & lined by cuboidal epithelium

·     Follicles – filled with – colloidal material – ‘Thyroglobulin’

·     An amino acid (Tyrosine) & iodine – helps in formation of thyroid hormone

·     Hormones – secreted by thyroid gland

o   Tri iodothyronine (T₃)

o   Tetra iodothyronine (T₄)

FUNCTIONS OF THYROID HORMONES

·     Increases – O₂ consumption – in tissues

·     Helps in production of energy – by maintaining BMR (Basal Metabolic Rate) of the body

·     Helps maintain – normal body temperature

·     Influences – CNS activity

·     Controls – growth of body, bone formation & gonad development

·     Essential for – normal physical, mental & personality development – also called personality hormone

·     Regulates – Carbohydrate, protein & fat metabolism

MORE TO KNOW

·     Edward C.Kendal (1914) – first crystallised – thyroxine hormone

·     Charles Harrington & George Barger – identified molecular structure of Thyroxine (1927)

·     Thyroid gland – requires 120µg of iodine everyday – for thyroxine production

THYROID DYSFUNCTION

·     When thyroid gland – fails to secrete hormones – at normal level

·     This condition – ‘Thyroid dysfunction’

·     Leads to

o   Hypothyroidism

o   Hyperthyroidism

HYPOTHYROIDISM

·     Caused due to – less secretion of thyroid hormone

·     Abnormal conditions are

o   Goitre

o   Cretinism

o   Myxoedema

GOITRE

·     Caused due to – inadequate supply of iodine – in diet

·     Common in – Himalayan regions – low level of iodine in soil

·     Enlargement of thyroid gland – marked as swelling in the neck – called Goitre

CRETINISM

·     Caused due to – less thyroid hormone secretion – in children

·     Symptoms – stunted growth, mental defect, lack of skeletal development & deformed bones – called Cretins

MYXOEDEMA

·     Caused by – thyroid hormone deficiency – in adults

·     Mentally sluggish, increase in body weight, puffiness of face & hand Oedematous appearance

HYPERTHYROIDISM

·     Caused due to – excess secretion of thyroid hormone

·     Leads to Grave’s disease

·     Symptoms – protrusion of eye balls (Exopthalmia), increased metabolic rate, high body temperature, profuse sweating, loss of body weight & nervousness

(C) PARATHYROID GLAND

·     They are – 4 small oval bodies – situated on – posterior surface of thyroid lobes

·     Chief cells of the gland – secretes parathormone

FUNCTIONS OF PARATHORMONE

·     Regulates – Calcium & Phosphorus metabolism

·     Acts on – bone, kidney & intestine – to maintain blood calcium levels

PARATHYROID DYSFUNCTION

·     Secretion of parathyroid hormone – altered due to following conditions

·     Removal of parathyroid glands – during thyroidectomy (removal of thyroid) – decreases secretion of parathormone

·     The conditions are

·     Muscle spasm – Tetany (sustained contraction of muscles – face, larynx, hands & feet)

·     Painful cramps (limb muscles)

(D) PANCREAS (ISLETS OF LANGERHANS)

·     Elongated, yellowish gland

·     Situated in – loop of stomach & duodenum

·     Exocrine & endocrine in nature

·     Exocrine pancreas – secretes pancreatic juice – plays a role in digestion

·     Endocrine portion – made of Islets of Langerhans

·     Islets of Langerhans – 2 types of cells – alpha cells & beta cells

·     Alpha Cells – secrete glucagon

·     Beta Cells – secrete insulin

 

FUNCTIONS OF PANCREATIC HORMONES

·     Balance between insulin & glucagon – necessary to maintain – blood glucose concentration

INSULIN

·     Helps in – conversion of glucose into glycogen – stored in liver & skeletal muscles

·     Promotes – transport of glucose into cells

·     Decreases – glucose concentration in blood

GLUCAGON

·     Helps in – breakdown of glycogen to glucose – in liver

·     Increases – blood glucose levels

DIABETES MELLITUS

·     Deficiency of insulin – causes Diabetes Mellitus

 

DIABETES MELLITUS - CHARACTERISTICS

·     Increase in blood sugar level (Hyper-glycemia)

·     Excretion of excess glucose in urine (Glycosuria)

·     Frequent urination (Polyuria)

·     Increased thirst (Polydipsia)

·     Increase in appetite (Polyphagia)

DO YOU KNOW?

·     Human insulin – first discovered by – Fredrick Banting, Charles Best & Mac Leod (1921)

·     Insulin – first used in Diabetes treatment – on 11^th January 1922

(E) ADRENAL GLAND

·     Located above each kidney

·     Also called supra renal glands

·     Outer part – adrenal cortex; inner part – adrenal medulla

·     2 distinct parts – structurally & functionally different

ADRENAL CORTEX

·     Consists of 3 layers

·     Zona glomerulosa

·     Zona fasciculata &

·     Zona reticularis

HORMONES OF ADRENAL CORTEX

·     Hormones secreted by adrenal cortex  - Cortico steroids

·     Classified into

o   Gluco corticoids

o   Mineralocorticoids

FUNCTIONS OF ADRENOCORTICAL HORMONES

GLUCOCORTICOIDS

·     Secreted by – Zona fasciculata

·     Glucocorticoids are – cortisol & corticosterone

·     Regulate – carbohydrate, protein & fat metabolism

·     Stimulates – formation of glucose from glucogen – in liver

·     Anti-inflammatory & anti-allergic agent

FUNCTIONS OF ADRENOCORTICAL HORMONES

MINERALO CORTICOIDS

·     Secreted by Zona glomerulosa

·     Hormone – Aldosterone

·     Helps – reabsorb sodium ions – from renal tubules

·     Causes – increased excretion of potassium ions

·     Regulates – electrolyte balance, body fluid volume, osmotic pressure & blood pressure

MORE TO KNOW

·     Cortisol hormone à maintain the body in living condition

·     Recover body – from severe effects of stress

·     Increased output of cortisol – life saving in shock conditions

·     Also called Life saving hormone

ADRENAL MEDULLA

·     Composed of – Chromaffin cells

·     Richly supplied with – sympathetic & parasympathetic nerves

HORMONES OF ADRENAL MEDULLA

·     Secretes 2 hormones

o   Epinephrine (Adrenaline)

o   Norepinephrine (Noradrenaline)

·     Together called – Emergency hormones

·     Produced during – Stress & emotion

·     Also called – ‘Flight, fright & fight hormone’

 

 

FUNCTIONS OF ADRENAL MEDULLARY HORMONES

EPINEPHRINE (ADRENALINE)

·     Promotes – conversion of glycogen to glucose (in liver & muscles)

·     Increases – heart beat & blood pressure

·     Increases – rate of respiration – by dilation of bronchi & trachea

·     Causes – dilation of pupil in eye

·     Decrease – blood flow through skin

NOREPINEPHRINE (NORADRENALINE)

·     Most actions – similar to epinephrine

(F) REPRODUCTIVE GLANDS (GONADS)

·     Sex glands – 2 types

·     (i) Testes                       – (ii) Ovaries

·     Testes – present in males

·     Ovaries – present in female

TESTES

·     Reproductive glands – in males

·     Composed of – seminiferous tubules, Leydig cells – form endocrine part of testes

·     Secrete – male sex hormone – Testosterone

FUNCTIONS OF TESTOSTERONE

·     Influences – spermatogenesis process

·     Stimulates – protein synthesis

·     Controls – muscular growth

·     Responsible for – development of secondary sexual characters (distribution of hair on body, face, deep voice, etc.,)

OVARY

·     Female gonads – located in pelvic cavity of abdomen

·     Secretes – female sex hormones

·     (a) Estrogen                            – (b) Progesterone

·     Estrogen – produced by Graafian follicle

·     Progesterone – produced by Corpus Luteum – formed in Ovary – from ruptured follicle – during ovulation

FUNCTIONS OF ESTROGENS

·     Brings the changes – occurs during puberty

·     Initiates – oogenesis (Production of Ovum)

·     Stimulates – maturation of ovarian follicles – in ovary

·     Promotes – development of secondary sexual characters (breast development, high pitched voice, etc.,)

FUNCTIONS OF PROGESTERONE

·     Responsible for – premenstrual changes of uterus

·     Prepares uterus – for implantation of embryo

·     Maintains pregnancy

·     Essential for – formation of placenta

 

THYMUS GLAND

·     Partly endocrine & partly lymphoid gland

·     Located in – upper part of chest – covering lower end of trachea

·     Thymosin – hormone secreted

FUNCTIONS OF THYMOSIN

·     Has stimulatory effect – on immune function

·     Stimulates – production & differentiation of lymphocytes