CBSE Important Questions

Electrostatics

Terminology:

Stimuli: The changes in the environment or environmental factors to which the organisms respond and react are called stimuli.
The reaction to stimuli is the characteristic feature of the living organism. The animals can react to stimuli in many different ways. Example; Light, heat, cold, sound, smell, taste, touch, pressure and force of gravity.
The plants however react to stimuli in a very limited way.

Coordination: The working together of the various organs of an organism in a systematic manner so as to produce proper reaction to the stimuli is called coordination.

• In Plants coordination takes place through hormones. The plants respond to various stimuli very slowly by growing
• In lower animals coordination takes place through nervous system while in higher animals coordination takes place through nervous system as well as hormonal system called endocrine system

Control and coordination in plants

Plant hormones or phytohormones: Plant hormones are also called phytohormones or growth substances because they control the aspects of growth. The growth of a plant can be divided into three stages

1. Cell division
2. Cell enlargement and
3. Cell differentiation.
   

These three stages as well as promotion of dormancy, breaking of dormancy, stomata control, falling of leaves, fruit growth, ripening of fruits, and ageing in plants are controlled by various plant hormones.

Types of plant hormones:

1. Auxins
2. Gibberellins
3. Cytokinins
4. Abscisic acid
5. Ethene or ethylene
   

Hormone	Function
Auxins	Promote cell enlargement, cell differentiation, fruit growth.
Gibberellins	Promote cell enlargement, cell differentiation in presence of Auxins. Help in breaking the dormancy in seeds and buds. Promote growth in fruits.
Cytokinins	Promote cell division, opening of stomata, fruit growth, help in breaking the dormancy of seeds and buds, and delay the ageing in leaves.
Abscisic acid	Promote the dormancy in seeds and buds, closing of stomata.
Ethene	Promotes ripening of fruits, help in breaking bud dormancy.

Plant movement: The plants are fixed at one place, however movement of parts of plants like root, shoot etc are possible when they are subjected to some external stimuli like light, force of gravity, chemical substances, water etc. Due to these movements there is an unequal growth in its structure. For example; if one side of the stem has more Auxins than the other side, then the side of the stem having more Auxins hormone will grow faster than the other side. This will cause the stem to bend. The movement in any part of the plant is usually a growth movement.

Tropism: The movement of a part of a plant in response to external stimuli is called tropism.
(i) If the growth is towards the stimulus it is called positive tropism.
(ii) If the growth is away from the stimulus it is called negative tropism.
Tropism is a directional movement.

Types of tropism:

1. Phototropism.(response to light)
2. Geotropism.(response to gravity)
3. Chemotropism (response to chemical stimulus)

Phototropism: The movement of a part of a plant in response to light is called photo tropism. When a growing plant is illuminated by unidirectional light it responds by bending towards the light. In phototropism the shoot shows positive phototropism while the roots show negative phototropism.

Geotropism: The movement of a part of a plant in response to gravity is called Geotropism. In a growing plant the root shows positive geotropism while the shoot shows negative geotropism.

Chemotropism: The movement of a part of a plant in response to chemical stimulus is called Chemotropism. The ripe stigma secretes a chemical substance which passes towards the ovary through style. This substance acts as stimulus for the pollen grains and it makes the pollen tube to move towards the ovaries which carry out fertilization.

Nastic movements: In some plants the movement is neither towards, nor away from the stimulus such movements are called nastic movements. E.g.; touch me not (Mimosa pudica) in which leaves bend and droop on touching.

Photoperiodism: Flowering and germination in plants are regulated by the duration of light. This phenomenon is called Photoperiodism. Example;

1. The tobacco plant never flower in the long days of summer but flower only in autumn season. This is due to photoperiodic response.
2. The seeds of lettuce germinate only if exposed to sunlight for a particular period of time.

Phytochrome: It is a blue green pigment present in plants and works when light falls on
Plant parts. For example; seeds of many plants germinate only if they are exposed to light.

Note: Phytochrome and phytohormones together are involved in the control and coordination between environment and plant responses.

Coordination in animals: Animals respond to stimuli through a specialized cell called neuron .Neurons are present in multicellular organisms except sponges.

Neuron: It is a structural and functional unit of nervous system. Nervous system includes brain, spinal cord and nerves

Nervous system in Hydra: The nervous system of Hydra consists of a network of nerve cells joined to one another and spread through out the body. When an external stimuli acts on the body the impulses spread out in all the directions of the tbody through the network of nerve cells. These impulses make some other cells in the body of Hydra to respond to the stimulus in appropriate manner. The nervous system of Hydra does not contain a brain.(central organ)

Ganglion: A mass of nerve cells is called ganglion.(singular = ganglia)

Note:

1. In insects, nervous system consists of ganglion, nerve cord and a bilobed ganglion (brain). E.g.; grasshopper.
2. Animals receive a variety of information with the help of specialized organs called sense organs.(receptors)
3. Photoreceptors are sensitive to light.
4. Phonoreceptors are sensitive to sound.
5. Olfactoreceptors are sensitive to smell.

Sensory neurons: This passes information to the brain from various parts of the body.

Motor nerve: This passes information from the brain to the various parts of the body.

Receptors: It is a cell or group of cells which is sensitive to a particular type of stimulus.

Effectors: The part of the body which responds to the stimulus is called effectors. These are mainly muscles and glands.

Nervous system of grasshopper: The nervous system of grasshopper has a long nerve cord (ventral nerve cord) which runs along the body of grasshopper just below the alimentary canal. The nerve cord has ganglion at intervals to which are attached small nerve branches which reaches all parts of the body. At the anterior end of the nerve cord a bilobed ganglion called brain is attached.(cerebral ganglion). There are specialized sense organs called antennae (feelers) which are sensitive to smell and feeling.

Vertebrate nervous system: It consists of two parts:

1. Central nervous system (brain and spinal cord).
2. Peripheral nervous system (all types of nerves which includes cranial nerves, spinal nerves and visceral nerves)

Human nervous system: It controls all our actions thinking and behaviour. It coordinates the activities of our body.

Structure of neuron: It is the structural and functional unit of the nervous system. It is the largest cell in our body which looks like an electric wire. Neuron carries messages in the form of electrical signals called nerve impulses. It consists of three components.

1. Cell body.
2. Dendrites
3. Axon

Cell body: The cell body consists of granular cytoplasm and nucleus. A number of long and thin fibres called nerve fibres.

Dendrites: The shorter fibres on the body of neuron are called dendrites. The dendrite picks up the nerve impulses from other neurons lying near by. They pass the impulses to the cell body and then along the axons.

Axon: The longest fibre in the cell body is called the axon. The axon has an insulating and protective sheath of myelin around it. The axon passes the impulse to another neuron through a junction called SYNAPSE.

Type of neuron	Function
Sensory neuron	Transmits impulses from the sensory cells towards the central nervous system.
Motor neuron	Transmits impulses from the central nervous system towards the muscle cells. (effectors)
Relay neurons	Occurs in the central nervous system where they serve as links between other neurons.

Synapse: A microscopic gap between a pair of adjacent neurons over which nerve impulses pass when going from one neuron to the next.

Brain

1. It is the highest coordinating centre in the body. It is located inside the skull which is protected by cranium.
2. It is surrounded by three membranes called meninges. It helps to protect the brain.
3. The space between the membranes is filled with cerebro spinal fluid which protects the brain from mechanical shocks.
4. Pairs of cranial nerves arise from the brain.
5. Brian is broadly divided into three parts namely: (i) fore – brain (ii) mid – brain and (iii) hind brain.
   

Name of the part	Components	Functions
Fore – brain	Olfactory bulb	Sense of smell.
	Cerebrum	Mental function, intelligence and regulation of impulses.
	Thalamus	Animal driver
	Hypothalamus	Body temperature, Appetite, sleepiness and water balance.
Mid – brain	Optic lobes	Sense of sight and hearing
	Crura cerebri
Hind – brain	Cerebellum	Muscular co – ordination and balancing.
	Medulla oblongata	Vital involuntary functions of the body such as visceral control..

Structure of Cerebrum: Cerebrum is dome shaped roof of the brain. It is the largest part, most important, most complex and most specialized part of brain. It is divided into two hemispheres called cerebral hemisphere. Different areas have different functions.

Functions of cerebrum:

1. It has sensory areas which receive impulses from eyes, ears, tongue, nose and skin and give us the sensation of feeling.
2. Similarly cerebrum has motor areas which control our muscles during the movement of our body parts.
3. Occipital lobe region is for sight, temporal lobe is the region for hearing, frontal lobe is the region for speech, facial muscular activities and higher mental activities, and parietal lobe is the region for taste, smell, touch, temperature and conscious association.

Functions of mid – brain:

1. It controls reflex movements of head, neck and trunk in response to visual and auditory stimuli.
2. It also controls the reflex movements of eye muscles, changes in pupil size and the shape of the eye lens.

Functions of hind brain:

1. Pons takes part in regulating respiration.
2. Cerebellum controls the coordination of body movements and postures (balance).
3. Medulla oblongata controls heart beat, breathing, blood pressure. It is also the regulating centre for swallowing, coughing, sneezing and vomiting.

Spinal cord:

1. It is a cylindrical structure begins in continuation with medulla oblongata and extends downwards till the last vertebrae. It is enclosed in a bony cage called vertebral column.
2. It is also surrounded by membranes called meninges which protect it. It contains 31 pairs of nerves. It is concerned with spinal reflex action and the conduction of nerve impulses to and from the brain.

Function of brain:

1. The brain receives information in the form of impulses from all the sensory organs of the body.
2. The brain responds to the impulses brought by sensory organs by sending instructions (through motor nerves) to the muscles and glands to act accordingly.
3. The brain correlates the various stimuli from different sense organs and produces the most appropriate and intelligent response.
4. It also coordinates the body activities so that the mechanisms and chemical reactions of the body work together efficiently. It stores information so that the behaviour can be modified according to the past experiences.

Peripheral nervous system: All the nerves of the body together constitute peripheral nervous system. They all enter and leave the central nervous system. It is divided into two
(i) Based on origin (cranial nervous and spinal nerves)
(ii) Based on innervation (somatic nerves and visceral nerves)

Cranial nerves: They arise from the brain and spread through out the head. They carry both sensory and motor neurons.

Spinal nerves: They arise from the spinal cord along most of the length of the spinal cord spread through out the body except head. They all carry both sensory and motor neurons.

Somatic nerves: They are associated with skeletal muscles and conduct the impulses received by the receptor organs present in the skin and muscles.

Visceral nerves: They arise from the spinal cord. They are connected to the visceral organs present in the digestive tract. They are both sensory and motor.

Autonomic nervous system: This comprises of two sub - divisions
(i) Sympathetic nervous system and
(ii) Parasympathetic nervous system.

The term ‘’auto’’ means self and ‘’nomous’’ means governing. It controls the activities of the organs inside our body automatically. The organs receive nerves from both sympathetic and parasympathetic nerve fibres. They have opposite effects on the organs; if one is stimulatory the other is inhibitory.

Effects of sympathetic and parasympathetic nervous system

Organ	Sympathetic system	Parasympathetic system
Heart	Increase contraction and rhythm.	Decrease contraction and rhythm.
Blood vessels	Constriction	Dilation
Bronchi	Dilation	Constriction
Eye	Dilation of pupil	Constriction of pupil.
Gastric secretion	Inhibition	Stimulation
Urinary bladder	Relaxation	Contraction

Reflex action: It is defined as an unconscious and involuntary response of infectors (muscles and glands) to a stimulus. In reflex action a message from receptors is relayed by sensory nerves to the spinal cord which sends information for response via motor nerves to effectors. The pathway is called reflex arc. Example; blinking of eyes, movement of diaphragm, withdrawal of hands or legs on pricking a pin or touching a hot or cold substance.

Hormones: Hormones are the chemical substances which coordinate the activities of living organisms and also their growth.

Characteristics of hormones:

1. The hormones are secreted in small amounts by the endocrine glands.
2. They are poured directly into the blood and carried through out the body by blood circulatory system.
3. They have their effects at the sites different from the sites where they are produced so they are called chemical messengers.
4. The hormones acts on specific tissues or organs called target organs.
5. They coordinate the activities of the body and its growth.

Endocrine glands: These are ductless glands which secretes different hormones. A gland is made up of group of cells or tissues which secretes specific substance. There are two types of glands in the body:

1. Exocrine glands (have ducts example; salivary glands)
2. Endocrine glands.(ductless glands which produces hormones in the body)

Endocrine system: A group of glands which produces various hormones constitute endocrine system. The endocrine glands are:

1. Pineal gland
2. Hypothalamus gland
3. Pituitary gland (hypophysis)
4. Thyroid gland
5. Parathyroid gland
6. Pancreas (it is both endocrine and exocrine gland)
7. Adrenal gland
8. Testis
9. Ovaries
   

Gland and location	Secretion	Function
Pineal gland (Brain)	Secretes melatonin	Responsible for colouration and smooth muscle contraction.
Hypothalamus (Brain)	Releasing hormones	Regulation of the secretion of hormones from pituitary glands.
Pituitary (Just below the brain)	Growth hormone or Somatotrophic hormone (STH)	Controls the growth of somatic cells. Promote protein synthesis.
	Thyroid stimulating hormone (TSH)	Regulates the growth of thyroid glands and secretion of Thyroxine.
	Adreno -corticotrophic hormone (ACTH)	Controls secretion of adrenal cortex.
	Follicle stimulating hormone (FSH)	Controls spermatogenesis in males and stimulate the growth of Graafian follicles in ovary of female.
	Luteinizing hormone(LH)	Stimulates interstitial cells to secrete testosterone, influences growth of male accessory sex organs.
	Luteotrophic hormone (LTH)	Initiates milk secretion and stimulates corpus luteum to secrete progesterone.
	Melanocytes stimulating hormone (MSH)	Regulates melanin in the Melanocytes.
	Vasopressin or Antidiuretic hormone (ADH)	It elevates blood pressure and promotes tubular reabsorption of water.
	Oxytocin hormone	Helps in constriction of uterine wall during parturition, stimulates lactation to increase milk secretion.
Thyroid (in the neck)	Thyroxine	Controls metabolic rates of carbohydrates, protein and fat, heat production.
Parathyroid (near the wind pipe)	Calcitonin	Lowers blood calcium level
	Parathormone (PTH)	Increases plasma calcium and decreases plasma phosphate.
Adrenal (i) cortex (above the kidneys)	Mineral corticoid (aldosterone)	Controls reabsorption of sodium and excretion of potassium.
	Glucocorticoid (cortisone)	Controls metabolism, glucogenesis, anti – inflammatory and anti – allergic actions.
	Sex corticoids	Influences change in muscles, bones, external sex characters and sexual behaviour.

 

Adrenal (ii) medulla	Epinephrine (adrenaline)	Increases heartbeat rate, blood pressure, reduces volume of urine, during stress by glycogenolysis raises blood glucose level.
	Norepinephrine	Increases systolic and diastolic pressure, controls normal blood circulation.
Islets of Langerhans (just below the stomach)	Insulin	Decreases blood glucose by converting into glycogen.
	Glucagons	Increases blood sugar level by glycogenolysis.
(a) Testis (cells of Leydig) (scrotum)	Androgen (Testosterone)	Stimulates spermatogenesis, controls development of male secondary sexual characters.
(b) Ovary (Beside uterus)	Estrogen	Controls development of female sex organs and ovulation.
(i) Graafian follicle (in ovary)	Progesterone	Initiates development of secondary sexual characters, maintains pregnancy, and prevents abortion.
(ii) Corpus luteum (in ovary)	Relaxin	Softens pubic symphysis, facilitates birth.
Thymus (below thyroid gland)	Thymosin	Produces lymphocytes and immunity.

Pancreas: It is present just below the stomach in the body. It secretes two hormones namely insulin and glucagon. The function of insulin is to lower the blood sugar. Deficiency of insulin causes diabetes. The function of glucagon is to increase blood sugar. These hormones are actually secreted by a gland called islets of Langerhans present in the pancreas.

Differences between hormones and enzymes

Hormone	Enzyme
They are produced by glands which lack ducts.(endocrines)	They are generally produced by glands which bear the ducts.(exocrine)
They may be steroids, amines or proteins in chemical nature.	They are always proteinic in nature.
They are consumed during metabolism.	They act as catalysts and are produced in the same quantity at the end of reaction.