10th Biology GREEN VALLEY EDUCATIONAL INSTITUTE

Control and Coordination

Control: is the power of restrain and regulation by which something can be
started, slowed down, expedited or stopped.
Coordination: (L. co-joint, ordinates-regulated) is orderly or harmonious
working of different but inter- related parts so as to perform one or more
activities very smoothly.
Need for control and coordination in an organism: The body of a multicellular
organism consists of a number of components and sub-components; each
specialized to perform a particular function. However, all the components are not
required to function all the time at the same speed. A system of controls is
required to function all the time at the same speed. A system of controls is
required to allow them to perform or not to perform, slow down or speed up their
working. Further, most activities require the simultaneous or sequential
functioning of a number of parts, stopping some and stimulation others. During
feeding, eyes locate the food, nose registers its smell, hands pick up the food and
take it to mouth, mouth opens to receive the food, teeth and muscles take part in
its mastication and saliva moistens it. Tongue perceives its taste. It moves the
food below the teeth. Later it pushes the crushed food into pharynx. All this is
possible only through a system of coordination.
Animals Nervous System:
It is the system of nervous organs, nerves and neurons that form a network
throughout the body for conducting information via electrical impulses so as to
coordinate and control activities of different parts as well as provide
appropriate response to both internal and external stimuli.

Functions of Nervous System:

1. Control: Nervous system exerts control over the functioning of different
tissues, organs and parts of the body.
2. Coordination: It coordinates the activity of different but inter-related
organs so as to perform a particular function, e.g., swallowing.
3. Surrounding: It makes an animal aware of its surroundings with the help
of sense organs.
4. Internal Environment: Nervous system gathers information about the
 internal environment of the body.
5. Higher Faculties: Intelligence, reasoning, memory, emotions, will, etc
are due to nervous system.
6. Involuntary Movements: They are movements of internal organs
carried out by a section of nervous system without consulting the will of
the individual, e.g., peristalsis.
7. Reflexes: They are immediate, automatic, protective response to harmful
stimuli.
Structure of Neuron and Nerve Cell:
Neuron or nerve cell is a structural and functional unit of nervous system
that is specialised to receive, conduct and transmit impulses. It is very long,
sometimes reaching 90-100 cm. An individual nerve cell consists of a cellular
head and long thread like tail. The cellular head is the critical non-replaceable
part. The tail can regenerate itself if cut or injured. Most of the heads are located
in the brain or Spinal Cord. The tails or nerve fibres are bundled together into
nerve trunks. From the brain and Spinal Cord, these nerve trunks branch out into
the extremities of the body. A neuron has three parts cell body, dendrites and
axon.
a. Cell Body or Cyton (= Soma, Perikaryon): It is broad, rounded,
pyriform or stellate part of the neuron that contains a central nucleus,
abundant cytoplasm and various cell organelles except centrioles. Because
of the absence of centrioles, neurons cannot divide. Injured neurons are
neither replaced nor repaired. Cytoplasm of cell body is also called
neuroplasm. Nucleus is large with a prominent nucleolus. Special
structures present in cell body of a neuron are small ribosome containing
Nissl granules and fine fibrils called neurofibrils. Cell body maintains the
neuron through its metabolic activity and growth.
b. Dendrites (Dendrons): They are fine short and branched protoplasmic
processes of the cell body that pick up sensations (physical, mechanical,
electrical, chemical) and transmit the same to the cell body. Dendrites
contain Nissl granules and neurofibrils.
c. Axon: It is a long fibre-like cytoplasmic process that carries impulses away
from the cell body. Axon is branched terminally. The terminal branches are
called terminal arborisations. Axon terminals may end in muscle fibres,
glands, other structures or form synapses with dendrites of other neurons.
Axon terminals are often knob-like. Axon is covered by one or two sheaths.
The sheathed axon is called nerve fibre. A number of nerve fibres are
 joined to form a nerve. The cell membrane covering the axon is called
axolemma. Cytoplasm of axon is termed as axoplasm.

Synapse:
It is a narrow gap containing junction between two neurons where an axon
terminal comes in near contact with dendrite terminal of next neuron. Axon
terminal is expanded to form a presynaptic knob. The dendrite terminal is
slightly broadened and depressed to form post-synaptic depression. A narrow
fluid filled space, called synaptic cleft, occurs between the two. As the
impulse reaches the presynaptic knob, it stimulates release of
neurotransmitter into cleft. Neurotransmitter molecules come in contact with
membrane of post-synaptic depression. It functions as stimulus and produces
an impulse in the dendrite part of the second neuron. Because of the release
of neurotransmitter on one side of the synapse, impulse travels through the
neurons only in one direction.
Reflex Action: is an automatic, mechanical and immediate response to a
harmful stimulus. Reflex Action is a nerve mediated, automatic involuntary and
spontaneous response to a stimulus acting on a specific receptor without
consulting the will. It was discovered by Marshall Hall (1833). Reflex action is
an accurate, unconscious, involuntary and instantaneous response to a stimulus
where delay can be harmful. On being pricked or coming in contact with hot
surface or flame, the hand is withdrawn even before pain is perceived by brain.
Reflex Arc: Reflex action requires a stimulus, a receptor organ, sensory
neurons, a part of central nervous system, motor neurons and effect or organ.
The pathway taken by a stimulus to travel from receptor organ to effect or
organ is known as reflex arc. Its components are as follows;
i. Receptor Organ: It is a tissues or organ which receives the stimulus for
initiating nerve impulse, e.g., skin, eye, and ear.
ii. Sensory Neurons: They conduct impulses from receptor to central
nervous system.
iii. Part of Central Nervous System: It is spinal cord or brain. Accordingly,
there are two types of reflexes, spinal reflexes and cerebral reflexes.
Cerebral reflexes include closure of eyes exposed to flash of light,
salivation at sight or smell of salivation at the time of crushing of food.
Peristalsis, inspiration and expiration. In central nervous system the
impulse is transferred from sensory neuron to motor neuron either directly
or through an inter-neuron.
 iv. Motor Neurons: They conduct motor impulse from central nervous system
to the effect or organ.
v. Effect or Organ: It is a muscle, gland or organ. The effector organ is
activated by motor impulse to provide a suitable response to the stimulus.

Importance of Reflex Action:

1. Overloading: It checks overloading and overtaxing of brain.
2. Survival Value: Reflex actions have survival value.
3. Quick Response: There is a immediate response to otherwise harmful
stimuli without the brain having analyzed the same.
4. Conditioned Reflexes: With the help of conditioned reflexes we perform
a number of our activities, e.g., reading, writing, typing, pedaling, playing
a musical instrument.
Difference between Reflex Action and Walking

Reflex Action Walking

Reflex action is inborn and It is acquired through learning
present in an individual right from
birth
It is inherited It is not inherited
It is automatic. An individual cannot It is under control of the
control it. cerebellum part of
the brain.
It cannot be changed It can be changed
It has survival and protective value It has various functions, generally
other than
survival and protection.

Human Nervous System:

Human nervous system has three parts
a) Central Nervous System (CNS)
b) Peripheral Nervous System (PNS)
c) Autonomic Nervous System (ANS)
Central Nervous System (CNS): CNS is hollowed part of nervous system that
lies along the mid dorsal part of the body inside axial Skelton. It has two parts:
i) the Brain ii) the Spinal Cord:
i) Human Brain (Encephalon)
It is the widest and the uppermost part of central nervous system which
weighs 1.2-1.4 kg and constitutes 98% of the total nervous system. Human
brain is the most advanced and well developed of all animals. The brain is
differentiated into three parts-fore brain, mid brain and hind brain. The parts
of the brain can be discussed as under:
1. Olfactory Lobes: They are a pair of wisely separated which occur on
the inferior surface of cerebrum. Each olfactory lobe consists of an
anterior olfactory bulb and a posterior narrow olfactory stalk. Olfactory
lobes relay sense of smell received from olfactory epithelium to the
temporal part of the cerebrum.
2. Cerebrum: It is the largest part of the brain which forms nearly 80% of
the same. Cerebrum occupies the front, lateral and superior parts of the
brain. It has two closely placed cerebral hemispheres separated by a
longitudinal cerebral fissure. The cerebral hemispheres are attached
interiorly by a thick nerve band called corpus callosum. Superior
surface is convex while the inferior surface is concave. Internally, each
cerebral hemisphere has a fluid filled cavity called lateral ventricle.
There is a thick outer layer of grey matter called cerebral cortex. Inner
to it is cerebral medulla of white matter. Grey matter is made of cell
bodies while white matter is formed of my elinated nerve fibres.
Cerebral cortex is thrown up into folds. The deep groves between the
folds are called fissures. A longitudinal fissure divides the cerebrum
into two hemispheres. Right cerebral hemisphere controls the
functioning of left parts of the body while the left cerebral hemisphere
controls the right parts of the body.
3. Diencephalon: It lies on the inferior side of the cerebrum. It has
epithalamus on its roof, thalami on the sides and hypothalamus on
flow. A narrow cavity called third ventricle occurs in diencephalon.
Epithalamus bears pineal body and anterior choroid plexus (for filtering
out cerebrospinal fluid from blood). Thalami (singular thalamus)
relay sensory impulses (except that of smell) from medulla and other
parts to cerebrum. They also regulate activity of smooth muscles.
 Hypothalamus has control centres for hunger, thirst, fatigue, sleep,
sweating, body temperature and emotions. It also secretes a number of
hormones. Ten of them control the functioning of anterior pituitary
while two hormones pass into posterior pituitary to function as its
hormones.
4. Mid Brain: It is small area having two thick fibrous tracts and four
swellings. Fibrous tracts are called cerebral peduncles or crura cerebri.
They connect hind brain with fore brain. The four swellings are known
as corpora quadrigemina or colliculi. They are connected with reflex
movements of head, neck and trunk in response to light, sight and
sound stimuli. The two superior colliculi or corpora quadrigemina have
centes for sight reflexes while the two inferior corpora quadrigemina
have centres of auditory reflexes.

5. Cerebellum: It is second largest part of the brain, constituting about

12.5% of the total. Cerebellum lies behind cerebrum and above
medulla oblongata. It has two large furrowed lateral cerebellar
hemispheres and a central worm like vermis. Cerebellum coordinates
muscular activity of the body. It also maintains equilibrium or posture
of the body as during walking, jumping, lifting, catching, bending, etc.
6. Pons (Pons Varolli): It is a cross-wise bundle of nervous tissue that
lies on the antero-ventral side of medulla oblongata. It connects the
cerebellum, medulla oblongata and cerebrum. Pons functions as relay
centre among different parts of brain. It also possesses pneumotaxic
area of respiratory centre.
7. Medulla Oblangata: It is the hindermost part of the brain which lies
below cerebellum. It continues behind into spinal cord. Medulla
oblongata has a fluid filled cavity called forth ventricle. Its roof bears
posterior choroid plexus (for filtering cerebrospinal fluid from blood)
and three pores for connecting external cerebrospinal fluid with internal
cerebrospinal fluid. Medulla oblongata contains (i) Respiratory centre
for regulating rate of breathing. (ii) Cardiac centre for regulating rate of
heart beat. (iii) Regulation of blood pressure. (iv) Reflex centre for
swallowing, vomiting, coughing, sneezing, salivation, peristalsis, etc.
Pons, medulla oblongata and mid brain are collectively called brain
stem.
Functions of Brain:-
1. Sensory Information: - Brain receives information from all the sensory
receptors and sense organs of the body.
2. Processing:- It processes the information obtained from various
sources and chooses the most appropriate response.
3. Response:- Brain sends instructions to effector organs all over the body
to provide the appropriate response to received stimuli.
4. Control:- It has controls for regulating the functioning of various body
organs.
5. Coordination:- Working of the different organs of a system is coordinated
by brain.
6. Reflexes:- It has centres for reflexes related to sound, sight and
involuntary functioning of many body parts.
7. Faculties:- It is the seat of intelligence, memory, reasoning, learning and
emotions.
ii) Spinal Cord:-
It is a narrow cylindrical lower part of central nervous system which is
43-45cm in length. It lies inside vertebral column that extends from base
of brain upto early part of lumbar region. It begins as continuation of the
medulla oblongata and ends at about the second lumbar vertebra. The cord
is well protected within this bony canal. Protection is also provided by the
meninges and the cerebrospinal fluid.
The spinal cord is a series of 31 sections called segments, each segment
giving rise to a pair of spinal nerves. Each pair of spinal nerves is
connected to a segment of the spinal cord by two points of attachment
called roots.
The posterior or dorsal root contains sensory fibres only and
conducts nerve impulses form the periphery to the spinal cord. Each
dorsal root also has a swelling called the dorsal root ganglion. It
contains the cell bodies of the sensory neurons. The other point of
attachment of a spinal nerve to the cord is the ventral root. It contains
motor neuron axons only and conducts impulses from the spinal cord to
the periphery.
Its cross-section, the spinal cord shows an inner gray matter lying
within a white matter. The gray matter forms an H of the gray matter is
a small space called the central canal. The canal runs the length of the
spinal cord and contains the cerebrospinal fluid.
Functions of Spinal Cord:-
i) It conveys sensory nerve impulses form the periphery to the brain and to
conduct motor impulses from the brain to the periphery.
ii) It serves as a reflex centre.

Peripheral Nervous System (PNS):

The peripheral nervous system is composed of the cranial nerves and
spinal nerve processes that connect the brain and spinal cord with receptor
muscles and glands.
a) Cranial nerves: Out of the 12 pairs of cranial nerves 10 originate from the
brain stem. Some cranial nerves contain only sensory fibres and are called
sensory nerves. The others contain both sensory and motor fibres and are
referred to as mixed nerves.]

b) Spinal nerves: The 31 pairs of spinal nerves are named and numbered
according to the region and level of the spinal cord from which they
emerge. All spinal nerves are mixed nerves.
Autonomic Nervous System (ANS):
It is a special system of ganglia and peripheral motor nerve fibres which
innervates various organs and glands of the body for stimulation, slowing
down and stopping their functions, without consulting the will. Autonomic
nervous system develops from branches of some cranial and spinal nerves
called visceral nerves. Autonomic nervous system has two opposing divisions,
sympathetic and parasympathetic.
1. Sympathetic Nervous System:- It is formed from branches of 12 thoracic
and first three lumbar spinal nerves. The system forms 2 long chains of
ganglia, a few isolated ganglia and long post- ganglionic fibres that
innervate different organs, muscles and glands of the body. The
sympathetic fibres secrete noradrenaline into them for activation.
Sympathetic system is also specialized to prepare the body for any
emergency, like hormone adrenaline. It causes constriction of peripheral
blood vessels, increased blood supply to heart, increased blood supply to
heart, increased heart beat, higher breathing rate, dilation of pupil, etc.
2. Parasympathetic Nervous System:- It is formed from branches of III, VII,
IX and X cranial nerves and sacral spinal nerves II, III and IV. The
ganglia are located over the organs from where short postganglionic fibres
develop to innervate the organs. The organs are influenced by secretion
of neurottansmitter acetycholine. Parasympathetic nervous system
 moderates or reduces heart beat, reduces blood pressure, dilates peripheral
blood vessels, constricts pupil, stimulates excretion and peristalsis.

Difference between Cerebrum and Cerebellum:

Cerebrum Cerebellum
It is a part of fore brain. It is part of hind brain.
Cerebrum constitutes 80% of brain. It constitutes 12.5% of brain.
It forms the front, superior and It lies in the posterior region of
lateral sides of the brain. brain.
Cerebrum is made of two parts
has three parts, two lateral
called cerebral
cerebellar hemispheres and one
hemispheres.
central vermis.
It contains two cavities called lateral
A cavity is nearly absent.
ventricles.
It is seat of intelligence and memory. It coordinates muscular activity.
Cerebrum controls intelligence,
Cerebellum maintains equilibrium of
movements, speech, sight, smell, taste,
the body.
sensations.

How are Nervous Organs Protected?

Both brain and spinal cord are protected from mechanical injury and shock by
bony cases around them. Brain is covered by cranium or brain box of skull.
Spinal cord is similarly covered by vertebral column. Additional protective
coverings called meninges (singular meninx) occur between brain or spinal
cord and the surroundings skeleton.
Layers of fluid around brain and spinal cord protect them from shock.
Duramater prevents slipping of brain and spinal cord from bony covering.

How does Nervous Tissue Cause Action?

Nervous system generally operates through muscles. Axon terminal in
contact with muscle fibre is broadened to function as motor end plate. The
plasmalemma of the muscle fibre is folded and depressed in the region of
neuromuscular junction. A narrow fluid filled gap occurs between the
plasmalemma of muscle fibre and motor end plate of axon terminal.
Whenever, an impulse reaches the motor end plate, it includes the release of
 neurotransmitter (acetylcholine or noradrenaline) into cleft area. The
neurotransmitter sensitizes the chemoreceptor sites of muscle fibre membrane.
Sodium channels of the latter open. The positive potential developed due to
the entry of sodium, results in release of calcium ions open active sites of actin
filaments slide past the myosin filaments producing new cross bridges and
shortening the size of muscle fibre. The arrangement of actin and myosin
filaments is different in striated and unstriated muscle fibres. The results in
their differential contraction.

Chemical Co-ordination In Plants: -

Plants produce certain specific chemical substances, which control its
growth. These accordingly called as plant growth regulators and include auxins,
cytoikinins, gibberellins, and ethylene and absesic acid. Among these the first
four are referred to as plant hormones and the last one as a growth inhibitor.
When a plant hormone is an organic compound, which is synthesized in one
tissue of a plant and migrates to another part or tissues where in a very minute
quantity affects the growth of that plant. A plant hormone is an organic
substance, which is produced in any part of the plant and is transferred or
migrated to another part where it influences a specific physiological process.
Some of the hormones and their physiological effects are as follows:

(i) Auxins: -
Auxins are a group of hormones produced by the root and shoot apices.
These are essential for cell elongation. Auxins were first of all discovered by a
Dutch botanist F. W. Went in 1928 and were chemically found to be Indole
Acetic Acid, which is derived from an amino acid tryptophan. The common
naturally occurring auxin is the indole acetic acid. Synthetic Auxins, the
compounds made in NAA (naphthalene acetic acid) and 2, 4-D (2, 4-
dichlorophenoxy acetic acid).

Functions of Auxins: - The important functions of auxins are as under: -

1. It stimulates cell division in the root and shoot apices.
2. It promotes cell elongation by increasing cell wall elasticity.
3. It stimulates seed germination.
4. It promotes growth of root at lower concentration and of shoot at very high
concentration.
5. It initiates development of xylem.
6. It helps in the production of parthenocarpic fruits.
 7. It affects or retards the growth of lateral buds.
8. It prevents pre harvest fruit fall in apples and pears.
9. It speeds up various physiological processes of a cell e.g. protein synthesis,
respiration etc.
(ii) Cytokinins:-These were first of all isolated in 1955 at Wisconsin
University (USA) from an old stock of nucleic acids. These are also named as
kinetins because of their property to activate the division of cytoplasm During
cell division. These are also obtained from coconut milk, apples and fruits etc.
cytokinesis are the chemicals, which promote cytokinesis in the cells of
various plant origin. They are synthesized in the endosperm of the seeds and
the roots of the plants. The first cytokinin was isolated by Miller et-al (1954).
Zeatin was the first natural cytokinin of plants.
Functions of Cytokinins: - The important functions of cytokinins are as under:

1. It activates cell division by activating DNA and protein synthesis.

2. It promotes the growth of the lateral buds by neutralizing the effects of the
auxins.
3. It counter acts the longitudinal growth in stems induced by the auxins.
4. It helps in the expansion of cotyledon by leaves and foliage leaves.
5. It enhances the growth of the callus.
6. It overcomes ageing and senescence.
(iii) Gibberellins: -
Gibberellins are growth hormones, which promote cell elongation.
Japanese pathologist called Kurosawa in 1926 first of all discovered these
growth hormones. Gibberellins from fungus called gibberella fujikorol.
This fungus secreted a substance, which was found to be responsible for
causing tallness. This substance was called gibberellin or gibberellic acid
(GA,) Later on other three Japanese workers Yabuta, Sumiki, and Hayashi
isolated them from culture filtrate of the fungus, which referred to as
gibberellic acid. Later on, gibberellins were discovered in a variety of
plants and now a day 36 different types of gibberellins are known.
Functions of Gibberellins: - Some of the important uses of the gibberellins are
listed as under:
1. It causes cell elongation in stem.
2. It does not affect the growth of the roots and inhibits the initiation of
adventitious roots.
 3. It stimulates the growth and development of the seedlings and
parthenocarpic fruits.
4. It stimulates cell division especially in cambial region.
5. It helps in breaking dormancy of seed, buds and tubers.
6. It helps in seed germination.
7. It promotes growth of leaves and flowers.

(iv) Ethylene: -
Ethylene is also a growth regulator. It is produced as a gas in the cells of
the higher plants. It is involved in breaking dormancy, induction of growth
of roots and root hairs, fruit ripening and regulation of cell elongation.

(v) Absessic acid: -

The American botanists W.C. Liu and H.R Corns during their
investigation found a substance was abundant at a senescent stage of the
cotton plant. This substance was instrumental in abscission and was
accordingly named as Absessin. Later on, addicott and his co-workers (1965)
found a simple compound called Absesic acid having same properties. It is
now isolated from dormant seeds, buds, and other parts of the plant. It is
primary growth inhibitor or suppressor of growth. Initially the growth
inhibitor was called dormin

Functions of Absessic Acid: -

1. It retards growth, promotes leaf fall and causes dormancy of seeds, buds and
tubers.
2. It causes loss of RNA, proteins and chlorophyll.
3. It causes of closing of the stomata and decreases the loss of water.
4. It inhibits both cell division and cell enlargement.
5. It antagonizes the growth promoting hormones and acts as a growth
inhibitor.
Functions of Plant Hormones
1. Induction of Dormancy: ABA induces dormancy of buds, seeds and
storage organs.
2. Breaking of Dormancy: Gibberellins and cytokinins break dormancy of
seeds, buds and storage organs.
3. Growth: It is mediated by auxin and Gibberellins.
4. Cell Division: Auxins and cytokinins control cell division.
 5. Stomata: Cytokinins bring about opening of stomata while abscisic acid
(ABA) causes their closure.
6. Movements: Movements of growth are caused by differential
distribution of auxin and other growth hormones.
7. Ripening of Fruits: It is controlled by gaseous hormones, ethlylene.
8. Coordination: Plants coordinate their activities and responses with the help
of hormones.
Plant Movements Due to Growth:
Plant movements due to growth are: a) Autonomic b) Paratonic
a) Autonomic Movements of Growth:- They are shown by apical regions of
stems and tendrils. The movements are called nutations (or
circumnutation). While growing the apices of these organs bend in
different directions resulting in their rotation. It helps the climbing stems
and tendrils to find support for climbing or clinging.

b) Paratonic Movements of Growth:-They are growth movements in

response to an external stimulus. Paratonic movements of growth are of
two types, nastic and tropic.
Tropic Movements of Growth:
Tropic movements generally occur in cylindrical organs like stems and
roots. The important tropic movements are phototropism, geotropism,
hydrotropism, thigmotropism and chemotropism.
1. Phototropism:- It is directional growth movement of curvature which
occurs in response to unidirectional exposure to light. The region on
photoperception is shoot apex while the region of response is in blue area
of elongation. Phototropic movement is generally caused by increased
auxin on the dark side and lesser auxin on the illuminated side. It causes
more growth o the dark side in stem causing it to bend towards the source
of light.
2. Geotropism:- It is directional growth movement of curvature which
occurs in response to force of gravity. The region of graviperception is
root cap in root, nodes and apex in shoots. The region of response or
curvature is the zone of elongation in case of stem and root. For nodes the
curvature producing region lies nearby.
3. Hydrotropism:- It is directional growth movement of curvature which
occurs in response to unilateral stimulus. Hydrotropism in generally
shown only by roots. Roots are positively hydrotropic. Positive
hydrotropic response of roots is stronger than their geotropic response.
This can be tested by placing germinating seeds in moist saw dust
contained in a sieve. The radicles will pass down and come out of the
sieve pores under the influence of gravity. However, after some growth,
they bend back and enter the saw dust again showing that hydrotropic
response is stronger than geotropic response.
4. Thigmotropism (Haptotropism):- It is directional growth movement of
curvature which occurs in response to stimulus of contact. Thigmotropism
is found in twiners and tendrils. After initial contact with support due to
mutation, the tendril or twiner shows less growth in the region of contact
and more growth on the other side. As a result they bend over the support.
Later on bending or coiling may occur in lower parts of the tendril as well.

5. Chemotropism:- Chemotropism is directional growth movement of

curvature that occurs in response to a stimulus of contact. Thigmotropism
is found in twiners and tendrils. After initial contact with support due to
mutation, the tendril or twiner shows less growth in the region of contact
and more growth on the other side. As a result they bend over the support.
Later on bending or coiling may occur in lower parts of the tendril as well.

6. Chemotropism:- Chemotropism is directional growth movement of

curvature that occurs in response to a chemical stimulus. It is best seen in
the growth of pollen tube inside style, ovary and ovule. Here every region
produces its own nutrients and chemotactic chemicals for growth and
passage of pollen tube. Chemotropism can be observed by germinating a
number of pollen grains in a minimal medium.

Chemical Co-ordination of Animals: -

In animals the various physiological processes are regulated by hormones,
which are special chemical messengers and help in controlling and
coordinating the various activities of the body. These hormones are
produced by endocrine glands present in the body of human beings.
Hormones are chemical messengers. They are discharged in the blood from
where they reach different parts of the body. A hormone acts as a trigger.
 The hormones in animals show following characteristic features-
1. They are commonly synthesized by ductless glands called as endocrine
glands.
2. They are produced at a place other than the site of action. They travel
through blood to other parts where they cause changes.
3. They are secreted directly into the blood stream.
4. The structures that respond to the hormones are called as target organs,
which are very specific.
5. They are secreted in response to the changes in the external or the
internal environment of the body and are called as chemical messengers
also.
6. They may stimulate or inhibit the activity of the target organ, thus
regulating its activity.
7. They are effective in minute quantities, often in trace amounts, which are
difficult to detect at times.
8. The hormones are rapidly altered or destroyed immediately after their
action is over, i.e. after they have acted on the target tissue.
Endocrine System or Hormonal System:-
It is a system of isolated ductless glands that pour their secretion directly
into circulatory system for passage to different targets in order to control
their metabolism, permeability, growth, differentiation and activity.
Endocrine system is also called hormonal system. Endocrine system often
operates in coordination with nervous system. Endocrine system controls
and coordinates many processes of the body where nervous system has no
role, e.g., cell permeability, cell division, cell growth, cell differentiation,
development of sex organs, secondary sex characters and several other
activities. Any discrepancy can lead to a disorder.
Endocrine glands in human body:-
Hypothalamus: -
It lies at the floor of diencephalon. Hypothalamus produces
neurohormones (formed by secretory neurons) which are passed on the pituitary
gland for controlling its activity. They are of two types, releasing hormones
(RH) and inhibitory hormones (IH), viz. TSH-RH, ACTH-RH, FSH-RH, LH-
RH, P- RH, GH-RH (STH-RH), GH-IH(=somatostatin).
Pituitary Gland: -
It is known as hypothalamic gland. It is a small round pea shaped gland
found as an out growth in the floor of the brain It is also called as the master
gland of the body. It is connected with the brain by a short, thin stock called
infundibullum. It is composed of three lobes – anterior lobe, intermediate
lobe and posterior lobe. The anterior and intermediate lobes are known as
Adenohypophysis and the posterior lobe is known as Neurohypophysis.

ANTERIOR LOBE Six different hormones are secreted from this part, they are

1. Growth hormone or somatotrophin (GH) it promotes the growth of the

body during early life.. it influences the growth of long bones and muscles.
Excess or less secretion of this hormone causes abnormalities in growth.
2. Thyroid Stimulating Hormone:- (TSH) Its primary function is to regulate
the growth of the thyroid gland. It stimulates thyroid gland to produce
Thyroxine.
3. Adrenocorticotrophic hormone (ACTH) It stimulates the adrenal cortex to
grow and secrete all of its normal hormones at an increased rate.
4. Follicle Stimulating Hormone (FSH) It stimulates the growth of ovarian
follicle up to the point of ovulation. It stimulates ovary to produce oestrogen.
While in males it stimulates the development of seminiferous tubules and
maintains spermatogenesis.
5. Luteinising Hormone(LH) In the male it goes to the testes and inside the
testes, it influences the Leydig cells to secrete testosterone. In females, it
works with FSH and is responsible for the final maturation of ovarian
follicles and ovulation.
6. Prolactin or Luteotrophic Hormone (LTH) It helps in the maintenance of
frequency and in the secretion of another female hormone oestrogen and
progesterone
Intermediate Lobe:- The lobe connects the posterior and the anterior lobe of
the pituitary glands . From this part, only one hormone is released. This is called
Melanocyte stimulating hormone (MSH) this hormone is effective in lower
vertebrates where it gives the skin its color. It also regulates the contents of
lipids in hair.
Posterior Lobe:- The posterior part of the pituitary gland is termed
neurohypophysis. This lobe is made of nervous tissues and consists of
termination of many neurosecretory fibres of the neurosecretory cells. From this
part two hormones are released-
1. Oxytocin This hormone brings about contraction in the wall of the uterus at
the time of birth of animal. When oxytocin sets the contraction of the
uterine wall, this causes a kind of pain to the mother, termed labour pain.
2. Vasopressin:- This hormone is also called antidiuretic hormone (ADH) . It
influences the area of nephron so that water may be reabsorbed and brought
back to the blood. In this way, the volume of urine is reduced.

Pineal Glands: - It is a small cone shaped gland lying between the cerebral
hemisphere and the dorsal side of the brain. It secretes a hormone called
Melatonin, which inhibits ovarian growth and ovulation
Thyroid Gland:- The mammalian thyroid gland is composed up of two lobes
that lie together on either side of the trachea just behind the thyroid cartilage .
Human thyroid weighs 25gms. It secretes Thyroxine and thyrocalcitonin
hormones. Thyroxine controls the general metabolism of the body. It accelerates
the energy production and oxygen consumption of the body. It stimulates
absorption of glucose in the intestine and synthesis proteins in the body
Thyrocalcitonin decreases the amount of calcium in the body, by taking excess
calcium to the bone.
Parathyroid Gland:- These are 4 in number and are named so because they
are found on the surface of the thyroid glands. This gland secrets para
thormone, which serves to increase the blood calcium by taking it out of the
bone.
Thymus Gland:- this gland can be seen in the new borne child close to the
heart. It gradually becomes smaller with advancing years. It secretes thymosine
and produces lymphocytes known as T lymphocytes.

Adrenal Gland: - The adrenal glands of man are two small yellowish glands
each lying above or near the kidney. Histologically each gland is composed of 2
distinct regions- an outer cortex and an inner Medulla. The two parts differ in
function and development.
(a) Adrenal cortex:- The main hormones secreted by adrenal by adrenal
cortex are corticoids in the form of gluco, mineral and sex corticoids. The
most important mineralo-cortocoid is aldosterone, which is concerned with
the water balance of the body. Glucocorticoids regulate the metabolism of
carbohydrates fat and proteins and come stress by increasing blood
glucose level.
(b) Adrenal medulla: it produces two main hormones, adrenaline
(Epinephrine) and noradrenaline (nor- epinephrine). Adrenal is also known
as emergency hormone because it increases the
Conversation of glycogen to provide extra energy to the body during
emergency situation. It also helps the body to handle situations of extreme
danger by increasing heart rate, blood pressure, increasing blood glucose
level by selective contraction and dilation of blood vessels.

(c) Pancreas:- The pancreas is double gland consisting of exocrine position,

which secretes various digestive enzymes of the pancreatic juice and round
or oval patches of cells called Islet of Langerhans. Each Islet consists of
two types of cells. Alpha cells and beta cells. Alpha cells secrete a hormone
called glycogen, which increases the blood sugar level from low to normal,
and beta cells secrete a hormone called insulin, which decreases the blood
sugar, level from high to normal and also induced protein synthesis.
Ovaries:- Ovaries are female sex glands. These are chiefly concerned with
the production of the female sex hormone oestrogen and progesterone. The
developing follicles before ovulation secrete oestrogen. It is associated with
the development of the female sex hormones and the secondary
characteristics at puberty. Progesterone on the other side promotes the
growth of mammary glands up to the full maturity. During pregnancy, it is
also associated with the contraction of uterus and swelling of mammary
glands.

Testis:- Testes are male sex glands. These are associated with the production
of the male sex hormones testosterone, which is secreted by the interstitial
cells; it promotes the development of male sex organs, secondary characters
and developing of sexual desire.
Feed back system: - is a regulatory mechanism in which presence of certain
level of substance promotes or inhibits its further formation. Regulation of
thyroxine production by its concentration in blood is an example of hormonal
feed back system. Concentration of thyroxine in blood is detected by
hypothalamus. If it is low, hypothalamus produces TSH-RH. The latter
passes into anterior lobe of pituitary through hypophyseal portal vein. TSH-
RH stimulates pituitary gland to produce TSH or thyroid stimulating
hormone. TSH passes into circulatory system and reaches thyroid. Thyroid
begins to secrete more thyroxine. It concentration of thyroxine rises above its
optimum level, hypothalamus stops producing TSH-RH. The unstimulated
pituitary also stops producing TSH (thyroid stimulating hormone). Non-
availability of TSH results in failure of thyroid to produce thyroxine. Non-
formation of new thyroxine will automatically result in reduction in level of
blood thyroxine to suboptimum level when hypothalamus will be again
stimulated.
Some important terms:-
Hermaphrodite:- An organism in which both the male and female sex
organs are present is called hermaphrodite or bi-sexual. Hydra and
earthworm are such organisms.
Gamete:- Two types of r reproductive cells produced in males and females
are called gametes. Female gametes are larger in size than the male gametes
but are non- motile. The male gametes are motile.
Puberty:- In humans , reproductive organs become functional only after
attaining sexual maturity. This is attained at the age of 13- 14 years. In males,
and 10-11 years in females, the age of attaining sexual maturity is called
puberty. It leads to development of secondary sexual characters
Placenta:- From the outer most membrane of the embryo, a number of out
pushing’s arise and get inserted into the inner wall of uterus of mother to
form placenta. This device draws nutrition from the maternal blood.
Umbilical cord:- It serves a link between the fetal and maternal circulation.
Homeostasis:- One hormone accelerate the function of a particular organ,
but the other hormone puts a brake on it. This system of opposing effects
leads to a proper control and balance in the working of the organs. When
there is too much of acceleration of the effect organ, the later sends a
message back to the endocrine gland asking to stop secreting the hormone.
This is a kind of feed back information, which serves to bring about a steady
state or a stable state. This steady state of body function is called
Homeostasis.