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All living organism respond & react to their surrounding or environmental changes. The organism respond to change in light, heat, cold , pressure, presence or absence of their organisms, availability of food etc e.g. Amoeba move towards food, aggregate in moderately saline water, avoid mechanical obstructions, some organism move towards or against light source.

It is important to know the following terminologies:

Stimulus:- The changes in the environment of an organism which tend to make the organism respond and react is called Stimulus( plural Stimuli). For example pricking of a pin, touching of hot or cold object etc.

Response:- Reaction to the various stimuli by the organism is called response. For example movement of organs(limbs) while pricking of a pin, touching of hot or cold object etc.

Co-ordination:- The process in which various organs or parts of an organism work together properly in order to give response to the various stimuli is called Co-ordination.

There are two systems to control and co-ordinate various functions of the body

(1)        Nervous system

(2)        Endocrine System

The coordination in Plants and Animals are different from each other. So it would be comfortable to discuss them separately.

Coordination in Animals( In human)

  • Control and coordination in simple multicellular animals takes place only through the nervous system.
  • Control and coordination in higher animals, called vertebrates, takes place through nervous System as well as hormonal system called endocrine system.

Unit of Nervous System :

The basic unit of the nervous system is the neuron. Neuron or nerve cell is the structural and functional unit of nervous system. It is specialised to receive, conduct and transmit electrical impulses. Neuron is the largest cell in the body.

A neuron (or nerve cells) has three components:

  1. Cell body,
  2. Dendrites, and
  3. Axons

Functions of the Nervous System

  • It controls and coordinates voluntary muscular activities.
  • It regulates involuntary actions.
  • It enables us to think, reason and remember.
  • It controls all the reflex actions in our body.

The cell body of a neuron is like a typical animal cell which contains cytoplasm and a nucleus. A number of long and thin nerve fibres stretch out form the neuron are called dendrites. The longest nerve fibre of the neuron is called axon. The axon is covered by a fat covering called the myelin sheath. This sheath helps in insulation of the axon and fast conduction of nerve impulses. One neuron is connected to the other through a junction known as synapse.

Electrical impulses or nerve impulses are the messages that are transmitted in the nervous system. The dendrites pick these impulses form receptors (sense organs) that pass the impulses to the cell body (cyton) and then along the axon to another neuron through a synapse. The cyton transmits only strong impulses. Weak impulses are not further transmitted.

Neurons are of three types:

  1. sensory neurons,
  2. motor neurons and
  3. relay (connector) neurons.

A receptor is a cell or a group of cells of a sense organ that is sensitive to a particular stimulus (or a particular change in the environment) such as light, heat , pressure , touch etc. The different sense organs contain different receptors to detect different stimuli.


Human nervous system is classified in to three broad categories-

  1. Central Nervous System
  2. Peripheral Nervous System
  3. Autonomous Nervous System


Central nervous system consists of (I) Brain (II) Spinal Cord

Brain is the highest co-coordinating centre in the body protected by a bony box called cranium  (a body born in the skull)

Brain & Spinal cord are covered by three membranes called Meninges. The space between the membranes is filled with a fluid called cerebrospinal  fluid which protects the brain from mechanical shocks.

The brain is divided into three regions –

(i) forebrain (ii) Midbrain (iii) Hind brain

The forebrain is the largest and highly specialized part of brain consist of cerebrum and olfactory lobes


The forebrain consist of cerebrum & olfactory lobes

The cerebrum is the most specialized part consist of two cerebral hemisphere.

The cerebrum consist of two areas

(a)        Sensory area to receive impulses from sense organs.

(b)        Motor area from where impulse or message is sent to muscles or effective organs.           In the cerebrum, particular regions are present for each kind of stimulus.

Cerebrum consist of following four lobes

Occipital Lobe –Region for visual reception

Temporal lobe – auditory reception

Parietal Lobe – touch smell, temperature and conscious association.

Frontal Lobe – Co-ordinate muscular activities and highly mental activities

MID BRAIN :- Mid brain control the movement of head, neck and trunk in response to light and sound.


It consist of three main parts :-

(I) Cerebellum     (II) Pons            (III) Medulla Oblongata

Co-ordination        take part in            Regulating centre for

and adjustment      regulation of        Swallowing, Coughing,

of movement &     respiration              Sneezing and Vomiting


  • Spinal Cord is a cylindrical structure. It begins in Continuation with the medulla oblongata and extends downward.
  • Spinal Cord is enclosed with in the Vertebral Column or backbone
  • Like brain, it is also covered with a protective covering called meninges.
  • From spinal cord, 31 pains of spinal nerve arise.


Peripheral nervous system consists of the nerves emerging from central nervous system i.e brain and spinal chord. These are of two types-

Cranial Nerves:- There are 12 pairs of cranial nerves which originate from Brain

Spinal Nerves:- These are 31 in pair and originate from spinal chord

Autonomic Nervous System :-

Autonomic Nervous System is a part   of peripheral Nervous System which regulate the activities of the internal organs like heart blood vessels and glands, smooth muscles and uterus in the body.

Autonomic Nervous System is divided into

(I)        Sympathetic

(II)       Parasympathetic

Each organ receive supply of nerve fibres from both parts of Autonomic nervous System i.e. Sympathetic & Parasympathetic.

Sympathetic & Parasympathetic: Nervous system have opposite effects on the body. Usually sympathetic system, is stimulatory while parasympathetic system is  inhibitory with some exception

How do we feel a hot or cold object? How do we feel pain?

  • All sensations or stimuli are felt through thousands of receptor cells that are present in the sense organs. They detect stimuli such as heat, cold, pain, smell and taste e.g. algesireceptors (for pain), tangoreceptors (for touch), gustatoreceptors (for taste), phonoreceptors(for sound), photoreceptors (for light) .
  • The stimulus received by a receptor is passed on in the form of electrical signals through the dendrites of a neuron to the cyton of the neuron. When it reaches the end of the axon, it causes the axon bulb to release a chemical that diffuse across the synapse and stimulates the dendrites of the adjacent neuron. These dendrites in turn send electrical signals to their cell body, to be carried along the axon.
  • In this way, the sensation from the receptors is passed on to the brain or spinal cord. In response to the signal received, a signal from the brain is similarly passed on to the neurons and is further carried to the effectors (glands or muscles) for appropriate action or response.


Reflex action is a spontaneous and involuntary (unconscious or without a will) response of an effector (muscles or glands) to a stimulus. It is an extremely quick action that does not involve any thinking by the brain. Blinking of eyes, movement of diaphragm during respiration , coughing , yawning, watering of mouth on seeing the food, are examples of a reflex action.

 What Happens in Reflex Actions?

  • In reflex action, fine tips (dendrites) of receptors (sensory neurons) quickly relay a message (electrical impulse) via motor nerves to effectors (muscles or glands). The path taken by nerve impulses in a reflex action is called reflex arc.
  • Thus, reflex actions generally involve spinal cord for quick response to specific stimulus. However, information input also goes on to reach the brain where thinking process occurs. Withdrawal of hand after coming in contact with hot surface, thorn or needle is an example of reflex action.
  • When our hand accidentally touches a hot object, the heat is sensed by thermoreceptors present in the skin of hand. The receptor triggers nerve impulse in sensory (receptor) neuron. It transmits the instruction to a muscle in our arm. The arm muscle contracts and pulls our hand.


We have three types of glands in our body

  1. Exocrine glands:- Also called duct glands and transport their secreted material through ducts. These secrete various types of substances like enzyme, sweat, oil.

Eg. Liver, sweat glands, gastric glands etc.

  1. Endocrine glands:- These glands secrete only hormones and also known as ductless glands as these don’t have any duct to transport their secreted material i.e. hormones to the required organ/cells. These glands pour the hormones in the blood which transport the hormones to the target organ. Eg. Pituitary, thyroid etc.
  2. Heterocrine glands:- Those glands perform both the functions above two types of glands i.e. exocrine and endocrine. E.g. Pancreas, testis and ovary

Various endocrine glands form the endocrine system which help in hormonal coordination in our body

General characters of hormones:

  • They are organic compounds.
  • They are effective in very low concentration.
  • They act away from the site of production.
  • They are generally slow in action.
  • They are uses in the regulatory action.
  • They do not initiate a reaction but can influence the rate of a reaction (or act as a catalyst).
  • They are poured directly into the blood by the endocrine glands and carried throughout the body by blood circulatory system.
  • They coordinate the growth of the organism.


Endocrine glands Hormones Functions
1.    Hypothalamus Releasing hormone Stimulates pituitary to secrete (TSH)
2.    Pituitary gland (i)     Growth Hormone

(ii)   Prolactin

(iii) Vasopressin

(iv)  Oxytocin

Controls the growth of human body.

Regulates the function of mammary glands.

Regulates water and electrolyte balance in the body.

Regulates the release of milk during lactation.

3.    Thyroid gland Thyroxine Controls the rate of metabolism of carbohydrates, fats and proteins in the body.
4.    Parathyroid Parathormone Regulates calcium and phosphate levels in the blood.
5.    Pancreas (i)   Insulin

(ii)  Glucagon

To lower the blood glucose.

To increase the blood glucose.

6.    Thymus Thymosin Develops immune system till puberty.
7.    Adrenal gland (i)   Adrenalin

(ii) Corticoids

Regulate heart beat  rate, breathing rate, blood pressure carbohydrate metabolism and mineral balance.
8.    Tastes Testosterone Regulates male accessory sex organs and male feature like deeper voice, moustache, body hair.
9.    Ovaries (i)   Estrogen

(ii) Progesterone

Regulate female accessory sex organs and female feature like mammary glands, menstrual cycle, maintenance of pregnancy.
10. Pineal Melatonin Influences skin colouration and may delay sexual development.

Controls biological clock of body.


Involuntary Actions Reflex Actions
1.They are controlled by brain

2.They involved autonomic nervous system


3. Example, Beating of heart

 1. Controlled by spinal cord.

2.They involve all parts of voluntary nervous system though they do not consult the will

3. Example, removal of hand on touching hot place.


                       Nervous System                                     Hormonal System
1.       Made of neurons (nerve cells)

2.       Messages transmitted in the form of electrical impulses                               .

3.       Messages transmitted along nerve fibers.

4.       Message travel very quickly.

5.      Effect of message usually last for a vary short time.

1.       Made of secretory cells (glands).

2.      Messages transmitted in the form of chemicals called hormones.

3.      Messages transmitted through blood stream

4.      Messages travel slowly.

5.      Effect of message usually lasts longer



Movement in Sensitive Plant Movement in Legs
1.      It occurs in response to an external stimulus like touch (shock)

2.      Nerves. No nerves are involved

3.      Movement. It is bought about by turgor in specific  cells

1.       It occurs in response to our requirement (will)


2.       Nerves carry the message for movement of legs

3.       It is brought about by bending and Muscle changes contraction and revaluation

 Control of Hormone Secretion:– The hormone secretion and balance in the body is maintained by the feedback mechanism. This mechanism regulates the precise quantity and timing of hormone secretion. For example, when we take a meal, our blood sugar level rises immediately. To regulate or lower this increased level, the secretion of insulin is stimulated. The insulin carries glucose to the tissues. As a result, the blood sugar level falls. As the blood sugar level normalizes, the insulin secretion is reduced. This mechanism helps in maintaining the state of balance in the body.

Response and Coordination in Plants

Plants do not have any special organ to respond external stimulus. But they are respond to light, touch gravitational force and other stimuli.Growth & Development in plants are regulated by both external and internal factors.Nervous system is absent in plants. The control and co-ordination is brought about by some chemical substances called phytohormones.

Movements in the plants:- There are two types of movements which represent coordination in plants.

(A)Tropic Movements (Tropism)

 (B)Nastic Movements.

Tropism. The movement of plant in the direction of stimulus is known as tropism.

Depending on the type of the stimulus, tropic movements are of different types. Growth-related movement of plants is quite slow.

Phototropism. Phototroposm (Photo; light, Tropism: movement) is the response of the plants to light. When a young green plant receives light from one direction (unidirectional), the stem grows towards the source of light. This can be tested by placing a plant in a dark box with a hole that acts a source of light. The stem is said to be positively phototropic as it grows in the direction of light. The root is said to be negatively phototropic as it moves away from the light.

Sunflower buds exhibit a special type of phototropism in which the buds move according to the direction of the sun and turn slowly through the day to face the sun. This movement is caused by turgor changes.

Geotropism:- Geotropism (Geo: gravity, Tropism: movement) is the response of the plants to gravity. This can be tested by placing the growing portion of the plant horizontally; the stem tip grows away from the pull or gravity, white the root tip grows towards it. Thus, the stem is said to be negatively geotropic and the root positively.

Hydrotropism:-Hydrotropism (Hydro: water. Trpism: movement) is the response of the plant parts towards or away from water. The stem is said to be negatively hydrotropic as it grows away from the soil and the root is said to be positively hydrotropic as it grows towards water in the soil.

Chemotropism:- Chemotropism (Chemo; chemical, Tropism: movement) is the response of the plants to certain chemicals. For example, during fertilization pollen tubes grow towards a chemical produced by the ovule.

Thigmotropism:-Thigmotropism (Thigmo: touch, Tropism: movement) is the response of the plants to touch or contact with a solid surface. When the parts of the plant touches a support, the side of its apical meristem comes in contact with the support and grows slower than the other side, e.g., tendrils coil around a support.

Photoperiodism:- Photoperiodisn (Photo: light, Period: regular episode) is the regulation of flowering and seed germination by duration of light. This occurs with the help of specialized pigments called phytochromes.

Nastic movements- When the movement of the plant is neither towards nor away from the stimulus, it is known as nastic movements. They are also known as Quick Movements. These movements are uncommon in plants, but some plants do display such movements in response to certain stimuli such as touch.

  • In Mimosa pudica (touch-me-not) plant, the leaflets fold up quickly on touching. This occurs due to a sudden and rapid loss of water (turgor changes) from cells at the base of the leaflets.
  • Stomatal Movements:- The opening and closing of stomata are known as stomatal movements. They are controlled by changes in the turgor change of the guard cells and are coordinated with light.


They are chemical substances that are responsible for the responses and growth in plants. They are also known as phytohormones. These hormones are found in very minute quantities in plant tissues. While some plant hormones such as auxins, gibberellins and cytokinins stimulate growth, some others such as abscisic acid retard it.

Functions of plant Hormones

  • Germination of seeds or breaking the dormancy of seeds
  • Growth of root, stem and leaves
  • Flowering of plants
  • Ripening of fruits
  • Movement of stomata in leaves, and thus, exchange of gases.
  • Photoropism, geotropism, chemotropism and nastic movements.

There are five types of plant hormones or phytohormones which help in coordination in the plants

1.Auxins(Indole 3-acetic acid):- Auxins are synthesized in the apical meristerm of the root tips and shoot tips.

Major functions of auxins are as follows:

  • Cell Enlargement. They promote growth of cells.
  • Root Formation. They are essential for root formation on stem cuttings.
  • They stimulate respiration and provide energy for various active processes.
  • They mediate plant movements due to their differential distribution e.g. geotropism, phototropism.
  • Inhibition of Abscission. They prevent premature falling of leaves and fruits.
  • Fruit Growth. They promote fruit growth.
  • Induce parthenocarpy(formation of seedless fruits without fertilization) in number plants
  1. Gibberellins(Gibberellic acid):-
  • Promote cell enlargement and cell differentiation in plants in the presence of auxins.
  • Promote growth in stems and fruits.
  • Rosette plants(i.e., plants that show profuse leaf developments but reduced internode’s growth) show bolting(stimulation in the internode growth just before reproduction) and flowering when treated with gibberellins.
  1. Cytokinins:-
  • Promote cell division in plants.
  • Play vital role in the morphogenesis in plants.
  • Help in breaking the dormancy of seeds and buds.
  • Delay the ageing in leaves.
  • Promote the opening of stomata
  • Also promote fruit growth.


  • Promotes growth and ripening of fruits.
  • Helps in breaking the dormancy in buds and seeds.
  • Stimulates the formation of separation layer (abscission zone) in leaves, flowers and fruits.
  • Promotes yellowing and senescence of leaves.
  1. Abscisic Acid:-
  • It promotes the dormancy in seeds and buds and thus inhibits growth.
  • Promotes the closing of stomata and thus effects wilting of leaves.
  • Promotes the falling of leaves (abscission) and senescence in leaves.

Photoperiodism:- The plant response like flowering & seed germination regulated by the duration of light period is called photoperiodism.

Phytochrome:- Phytochrome is a protein pigment presence in very small quantity, responsible for photoperiodic response. Phytohormones and phytochromes together are involved in the control and co-or-dination between environment and plant responses.


  • Coordination is the working of various systems in the body together.
  • Coordination is controlled by the nervous and the endocrine systems.
  • Chemical coordination is seen in plants and animals.
  • Stimulus (Plural – stimuli) are the changes in the environment to which an organism responds and reacts. The response to stimuli is characteristic in each living organisms.
  • Response and coordination in animals is controlled and regulated by the sense organs, nervous system and endocrine system (through hormones).
  • Plants, however, react to stimuli in a very limited way as they do not have a nervous system like animals. The plants use only the chemical substances called plant hormones to respond and react to external stimuli.
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