CONTROL AND COORDINATION - Class X NTSE Plus

PLANT HORMONES/PHYTOHORMONES

Living organisms respond and react to their external environment. Plants do not have any special structure for perception of stimuli.

In plants control and coordination is performed by chemical substances known as plant hormones or phytohormone. Phytohormones are of five types namely Auxins, Gibberellins, Cytokinins, Abscisic Acid (ABA) and Ethylene.

(a) Auxin :

• Indole acetic acid is the principal naturally occurring auxin found in all plants including fungi.

• Auxin initiate as well as promote cell division, cell elongation, root formation.

• Causes apical dominance and prevents abscission layer.

• Initiation of flowering.

• Synthetic auxins are resistant to oxidation by enzymes some are widely used to regulate various aspects of plant development. They are more effective & have greater stability than indole acetic acid (I.A.A).

e.g. 2, 4 - D

( b) G ib be re ll in s :

• Significant elongation of internodes.

• Leaf expansion • Reversal of dwarfism

• Breaking dormancy • Parthenocarpy

• ^Flowering ( c) Cy tokinin :

• Promote cell division

• Counteraction of apical dominance

• Delay of senescence

• Delay of senescence - Disappearance of chlorophyll and degradation of proteins are two important symptoms of senescence. Cytokinins delay these processes & thus the senescence is also delayed.

This effect of cytokinins is known as Richmond - lang effect.

( d) Et hy le ne :

• Promotes fruit growth and ripening

• Promotes seed germination

• Promotes abscission of leaves, flowers and fruits.

( e ) A bs c is s i c A c id :

• Promotes abscission, senescence, bud dormancy

• Growth inhibition

• ABA suppresses the growth promoting effects of gibberellins and hence is also known as antigibberellins.

PLANT MOVEMENTS

Movement of plant towards the direction of stimulus is called tropism. Bending of plant towards light is called phototropism. Shoot of plants show positive phototropism. Downward movement is in response to gravitational force is called geotropism. Roots of plants shows positive geotropisms, stems show negative geotropism.

Such movements in plants which are caused by external stimuli but are not directional are called nastic movements (such as in touch-me-not plant). - Mimosa pudica

PHOTOPERIODISM

Flowering and germination of seeds in plants is controlled by duration of day light (photoperiod). This phenomenon is called photoperiodism.

On the basis of length of photoperiod requirements of plants, they have been classified into.

(i) Short day plants — Xanthium (ii) Long day plants — Spinach, Radish (iii) Day neutral plants — Cotton, sunflower

Response of plants to photoperiodic stimulus is due to a specialized pigment phytochrome.

Fig : Requirement of light and dark periods during 24 hours for flowering in short day, long day and day neutral plants.

id2013765 pdfMachine by Broadgun Software - a great PDF writer! - a great PDF creator! - http://www.pdfmachine.com http://www.broadgun.com

PAGE # 42 CONTROL AND COORDINATION IN ANIMALS

Animals receive external information through specialized structure called sense organs (receptors). These are photoreceptors for light, phonoreceptor for sound and olfactoreceptors for smell. Control and coordination is achieved by two systems (a) endocrine system (b)) nervous system

Table : Differences Between Exocrine and Endocrine Glands.

Endocrine glands 1 Exocrine glands have ducts . Endocrine glands are ductles s . 2 Thes e glands dis charge their s ecretions into the

ducts .

Thes e glands dis charge their s ecretions directly into the blood.

3 Thes e glands are pres ent near the s ite of action.

Exam ples : Sw eat and oil glands of s kin, s alivary glands , etc.

Thes e glands are pres ent far aw ay from the s ite of action.

Exam ples : Pituitary, thyroid, hypothalam us , etc.

Exocrine glands

Table : Differences Between Hormones and Enzymes.

Enzymes 1 Hormones are peptides, proteins, amino acid

derivatives and steroids in nature.

All enzymes, are complex proteins.

2 They have low molecular weight. They have very high molecular weight.

3 They are secreted by cells at one site and pass into blood to another site to act.

They are secreted by cells and may act in the cells themselves or pass via ducts to act in some cavity in the body.

4 They are used up in their action. They are not used up in their action.

5 Hormone-controlled reactions are not reversible. Enzymes-controlled reactions are reversible.

6 Hormones are effective in low concentration. Their excess or deficiency may cause physiological disorders.

Enzymes also act in low concentration. However, the rate of enzymes-catalysed reactions steadily increase with an increase in their concentration.

7 They may act slowly or quickly. They act slowly.

8 Hormones may accelerate or inhibit specific physiological processes.

Enzymes speed up the biochemical reactions.

Hormones

• Similarities between hormones and enzymes :

1. Both are synthesized in body. 2. Both are not stored in body. 3. Both are required in minute quantities.

Table : Summary of the Effect of Hypersecretion and Hyposecretion of Some Important Endocrine Glands.

Glands and Horm ones Hypersecretion Hyposecretion

1. Pituitary GH ADH

Gigantism In child;

Acrom egaly in adulthood

Dw arfism in child.

Diabetes insipidus 2. Thyroid

Thyroxine

Exophthalm ic Goitre Cretinism in young, Myxoedem a in adults .

3. Parathyroid PTH

Decalcification of bones ; increas e calcium level.

Tetany; low calcium and high phos phate levels .

4. Adrenal

(i) Mineralocorticoid (aldos terone) (ii) Glucocorticoid (cortis one) (iii) Adrenaline (iv) Noradrenaline

Hypertens ion Cushings' disease Hypertens ion

Conn's disease.

Addison's disease.

Increas es blood pres s ure.

5. Pancreas Ins ulin

Decreas e in blood glucos e level.

Increas e in blood glucos e level - hyperglycem ia; diabetes m ellitus.

PAGE # 43 Nervous system in vertebrates is highly evolved and

comprises of

(1) Central Nervous System (2) Peripheral Nervous system (3) Autonomic nervous system

• The central nervous system comprises of : (i) Brain

(ii) Spinal cord

• Peripheral nervous system consists of two sets of nerves :

1. Cranial nerves — 12 pairs 2. Spinal nerves — 31 pairs

• Spinal Nerves

Cervical – 8 Pairs

Thoraic – 12 Pairs

Lumbar – 5 Pairs

Sacral – 5 Pairs

Coccygeal — 1 Pairs

• The Autonomic nervous system comprises of : 1. Sympathetic nervous system — Thoracico-lumbar outflow

2. Parasympathetic nervous system — Cranio sacral outflow

The action of sympathetic and parasympathetic nervous system is antagonistic to each other. Both interact and maintain homeostasis inside the body.

Table : Functions of Autonomic Nervous System.

S.No. Organs Sympathetic system Parasympathetic system

1. Heart accelerates heart beat retards heart beat

Blood vessels constricts all blood vessels except coronary vessels which are dilated

dilates all blood vessels except coronary vessels which are constricted

3. Lungs dilates bronchi and bronchioles constricts bronchi and bronchioles

4. Intestines peristalsis decreased peristalsis increased

5. Urinary bladder sphincter contraction, muscle relaxed sphincter relaxation, muscle contraction (feeling to urinate)

6. Pupil of eye dilation constriction

7. Salivary glands inhibits secretion of saliva (dryness of mouth)

stimulates secretion of saliva 8. Lacrimal (tear) glands stimulates secretion inhibits secretion

9. Arrector (or erector) pili (hair) muscles of skin

stimulates contraction (hairs raised) relaxes (hairs flattened) 10. Body (as a whole) prepares body for action prepares body for relaxation

REFLEX ACTION AND REFLEX ARC

You must have experienced a sudden withdrawl of a body part which comes in contact with objects that are extremely hot, cold, pointed or animals that are scary or poisonous. The entire process of response to a peripheral nervous stimulation, that occurs involuntarily, i.e., without conscious effort or thought and requires the involvement of a part of the central nervous system is called a reflex action.

Diagrammatic Presentation of Reflex Action (Showing Jerk Reflex)

PAGE # 44 Mammals show a wide range of reflexes which can be

broadly classified into two types : unconditioned and conditioned reflexes.

( a) Unc onditioned re fle xe s :

Even when the body has no past experience of a stimulus it still responds spontaneously and such responses or actions are called unconditioned reflexes. These are responses to a natural unconditioned stimulus. The examples of unconditioned reflexes are the blinking of an eye when a particle of dust touches the eyelids, excitement of the salivary glands after seeing the food, etc. Other reflex actions are shown in the Table.

These reflexes are said to be unconditioned or inborn because they are a natural part of an animal’s make up. Another class of reflex produced by the previous experience of an animals is considered below.

( b) Condit ione d re flexe s :

When a reflex which does not naturally exist had becomes a part of the animal behaviour. Such a reflex is said to be conditioned. Conditioned reflex were first demonstrated by the Russian physiologist, Pavlov. The cerebrum controls the conditioned reflexes.

Pavlov’s experiment on dog to show conditional reflex.

Table Showing Different Unconditioned Reflex Actions.

Reflex Stimulus Response

Blinking Swallowing

Sneezing and coughing

Knee-jerk

Foreign in body on surface of eye.

Food touches sensitive spot at back of pharynx.

Foreign particle irritating lining of nose or larynx.

Sharp tap of tendon below knee-cap of crossed leg.

Eyelids close and eye "waters".

Peristaltic waves pass down oesophagus.

Chest muscles and diaphragm contract and relax violently to produce a gust of air.

Leg 'kicks' up.

Differences between Unconditioned and Conditioned Reflexes

Unconditioned reflexes Conditioned reflexes

1. Unconditioned reflexes are inborn (hereditary).

2. Learning does not form the basis of unconditioned reflexes.

3. These are mainly protective in function.

Examples : Breast feeding and swallowing in newly born babies, blinking of eyes, sneezing and coughing and knee-jerk, etc.

1. Conditioned reflexes are acquired after birth.

2. Learning forms the basis of conditioned reflexes.

Examples : Withdrawal of limb when it is touched by hot things, typing, riding a bicycle, knitting, etc.

KNOWLEDGE BOOSTERS

The smallest cranial nerve is trochlear in human.

The largest cranial nerve is trigeminal in human.

Protein hormones are secreted by :

• Parathyroid • ^Pituitary

• Hypothalamus • ^Pancreas

• Steroid hormones are secreted by :

• Adrenal cortex

• ^Gonads

• Amino acids derived hormones are secreted by :

• Thyroid gland

• Adrenal medulla

• Pineal gland

EXERCISE

1. Photoperiodic stimulus is picked up by : (A) Phytochrome (B) Phytohormones

2. Posterior lobe of pituitary gland secretes following hormones :

(A) ADH (B) MSH (C) Oxytocin (D) Both (A) and (C) 3. Smallest cranial nerve is :

(A) Trochlear (B) Trigeminal

PAGE # 45 4. Hormones of pituitary gland are :

(A) All steroids (B) All proteins

(D) Complex substances formed from proteins, steroids, carbohydrates

5. Parasympathetic nervous system is not involved in : (A) Peristalsis

(B) Secretion of Saliva (C) Dilation of pupil

(D) Excitation of reproductive organs 6. Which is not a reflex action ?

(A) Swallowing of food (B) Shivering in cold (C) Both A and B (D) None of these 7. What is common in following substances ?

(i) acetylcholine (ii) noradrenaline (iii) serotonin

(A) All are chemical transmitters (B) All are antidiuretic drugs

8. Conn’s disease is caused due to :

(A) ADH (B) ACTH

9. Which one of the following four glands is correctly matched with the accompanying description ? (A) Thyroid - hyperactivity in young children causes cretinism

(B) Thymus- starts undergoing atrophy after puberty (C) Parathyroid - secretes parathormone which promotes movement of calcium ions from blood into bones during calcification.

(D) Pancreas - Delta cells of the islets of Langerhans secrete a hormone which stimulates glycolysis in liver.

10. Which of the following diseases is not related to thyroid gland ?

(A) Myxoedema (B) Cretinism (C) Acromegaly (D) Goitre

11. The thyroid gland secretes thyroxine hormone.

Function of thyroxine is :

(A) It increases metabolic rate and maintains BMR.

(B) It promotes growth of the body tissues and brain (C) It stimulates differentiation of tissue

(D) All of the above

12. Glucagon is secreted from which cells of islet of Langerhans ?

(A) – cells (B) – cells

is made up of : (A) Grey matter (B) White matter (C) Both A & B (D) None of the above

14. Watering of mouth to see good food is : (A) Unconditioned reflex action

(B) Conditioned reflex action (C) Spinal reflex

(D) None of the above

15. On surgical removal of pituitary gland there is fall in Na⁺ level & rise in K⁺ in serum, this is due to : (A) Oxytocin is no longer available from pituitary (B) Atrophy of adrenal medulla

(D) LTH from pituitary is no longer available 16. Prevention of senescence is not a function of :

(A) Auxins (B) Gibberelins

(A) Bolting of rosette plants

(B) Replacing long day requirement (C) Overcome genetic dwarfism (D) All the above

18. Which of the mammalian cells usually do not divide in adult life ?

(A) Epithelial cells in lung (B) Nerve cell in brain (C) Liver cells (D) Osteoblast cells

19. Receptors for Neurotransmitter are located on the : (A) Cell surface (B) Nucleus

(A) Corn germ oil (B) Gibberella (C) Human urine (D) Rhizopus

21. Which of the following graphs accurately represents the insulin levels (Y-axis) in the body as a function of time (X-axis) after eating sugar and bread/roti ?

[KVPY 2010]

(A) (B)

22. The cell that transfers information about pain to the brain is called a [KVPY 2011]

(A) neuron (B) blastocyst



PAGE # 46

In document Class X NTSE Plus (Page 42-47)