TOPIC 3: COORDINATION
Concept
of Coordination.
The
Concept of Coordination in Organisms
Explain the concept of coordination in organisms
Coordination is the working together of the various
organs of an organism in a systematic manner so as to produce a proper response
to the stimuli. Without coordination the body becomes disorderly and it may fail
to function properly.
The
Ways in Which Coordination is Brought About
Outline the ways in which coordination is brought
about
The coordination in simple multicellular animals
takes place through nervous systemonly. The control and coordination in higher
animals called vertebrates (including humanbeings) takes place through nervous
system as well as hormonal system called endocrinesystem. Coordination in
plants is under the control of hormones.
All the living organisms (plants and animals)
respond and react to changes in the environment around them. The changes in the
environment to which the organisms respond and react are called stimuli
(singular: stimulus). The living organisms show response to stimuli such as
light, heat, cold, sound, smell, taste, touch, pressure, pain,water, and force
of gravity, etc. The ability to perceive, interpret and respond to stimuli is
called irritability or sensitivity.
There are two types of stimuli: external and
internal. External stimuli are associated with the surrounding environment such
as wind temperature, light, pressure, touch, water and gravity. Internal
stimuli occur within the organism, for example, a decrease or an increase in
the amount of water and glucose in the blood.
When an organism detects a stimulus, it initiates a
response. A response is a behavioural,physiological or muscular activity
initiated by a stimulus. For example, if a man touches a very hot utensil
accidentally, he quickly pulls his hand away from the hot utensil. Here,heat is
the stimulus and the man reacts (responds) by moving his hand away from the hot
utensil. Similarly, when the sun is bright, we close our eyes. In this case,
light is the stimulus and we react by closing our eyes. Likewise, when the
amount of water in the blood drops, the pituitary gland secretes an
anti-diuretic hormone (ADH) which stimulates the reabsorption of water in the
kidneys.
Multicellular organisms detect stimuli through
sense organs called receptors. A receptor is a sense organ (e.g. eye) or
sensory nerve ending (e.g. in the skin or internal organ) which receives
stimuli and sets nervous impulses. Impulses are electrical transmissions or
chemical stimuli that are sent from the receptor to the coordinating system in
the organism. The organs that respond to the stimuli are called effectors. A
coordinator is an organ (e.g. the brain and spinal cord) that receives messages
from the receptors,translates them and sends the information back to an
effector for action. An effector is a muscle or gland which receives impulses
from nerves, brain or spinal cord and responds to them. Response is the
end-action, such as a muscle contracting to cause the movement of the arm. The
diagram below illustrates the five components of coordination in mammals.
Nervous
Coordination in Human, Neurons
The
Structure of Motor Sensory and Relay Neurons
Describe
the structure of motor sensory and relay neurons
Neurones
Neurones are nerve cells. They carry information as
tiny electrical signals. A neuroneconsists of a cell body (with a nucleus and cytoplasm),
dendrites that carry electricalimpulses to the cell, and a long axon that
carries the impulses away from the cell. Theaxon of one neurone and the
dendrites of the next neurone do not actually touch eachother. The gap between
neurones is called the synapse
Structure
and functions of neurones
The diagram below shows a typical neurone: in this
case, a motor neurone. It has tinybranches at each end (dendrites) and a long
fibre (axon) that carries the signals or nervousimpulses. The axon is surrounded
by a fatty layer known as the myelin sheath. Thishelps to protect the neurone
and allow impulses to travel faster. The sheath is produces bySchawnn cells.
The myelin sheath has nodes (Nodes of Ranvier) that speed uptransmission of
nervous impulses. The cell body consists of cytoplasm enclosing thenucleus.
There are also other organelles in the cytoplasm such as mitochondria
thatsupply energy to for metabolic functions.
Synapses
Where two neurones meet, there is a tiny gap called
a synapse. Signals cross this gap using chemicals (neurotransmitters) released
by a neurone. When the chemical diffuses across the gap it makes the next
neurone transmit an electrical signal. The transmission of nervous impulses
across synapses occurs thus:
§
An
electrical impulse travels along an axon.
§
This
triggers the nerve-ending of a neuron to release chemical messengers
calledneurotransmitters.
§
These
chemicals diffuse across the synapse (the gap) and bind with receptor molecules
on the membrane of the next neuron.
§ The receptor molecules on the second neuron bind
only to the specific chemicals released from the first neuron. This stimulates
the second neuron to transmit the electrical impulse.
Types of Neurones:
There are three types of neurones namely motor
neurone, sensory neurone and relay(or intermediate) neurone. Each of these
neurones has a different structure and performsdifferent functions.
Motor
neurone
A motor neurone is a nerve cell that transmits
impulses from the central nervous system(CNS) to the effector organs such as
muscles or glands where response is made. The cell body of a motor neurone is
at one end of the neurone and lies entirely within the central nervous system
(see the diagram above).
Sensory
neurone
A sensory neurone is a nerve cell that transmits
impulses from the receptors to the CNS.Sensory neurones have their cell bodies
off the axon and outside the central nervoussystem.
Relay
(intermediate or inter) neurone
A relay neurone conveys messages between neurones
in the CNS. Relay neurones are located in the CNS between the sensory and the
motor neurones.
Central
Nervous System (CNS)
The
Meaning of Central Nervous System
Give
the meaning of central nervous system
The CNS is the part of the nervous system
consisting of the brain and spinal cord. Itcoordinates all the neural
functions. The chart below shows subdivisions of the nervoussystem.
The brain
The human brain is a specialized organ that is
ultimately responsible for all thought and movement that the body produces.
This allows humans to successfully interact with their environment, by
communicating with others and interacting with inanimate objects near their
surroundings. If the brain is not functioning properly, the ability to move,
generate accurate sensory information or speak and understand language can be
damaged as well.
The brain has many different parts. Each part has a
unique function that allows humansobserve and interact with their environment
effectively. The following are parts of thehuman brain and their functions:
Cerebrum
The cerebrum is the largest portion of the brain,
and contains tools which are responsible for most of the brain's function. It
is divided into four sections: the temporal lobe, the occipital lobe, parietal
lobe and frontal lobe.
Parietal Lobe: Located in the cerebral hemisphere,
this lobe focuses on comprehension.Visual functions, language, reading,
internal stimuli, tactile sensation and sensory comprehension are monitored
here.
Temporal Lobe: The temporal lobe controls visual
and auditory memories. It includesareas that help manage some speech and
hearing capabilities, behavioural elements, andlanguage. It is located in the
cerebral hemisphere.
Occipital Lobe: the occipital lobe is located in
the cerebral hemisphere in the back of thehead. It helps to control vision.
Cerebellum
This is commonly referred to as "the little
brain‖. The cerebellum controls essential bodyfunctions such as balance,
posture and coordination, allowing humans to move properlyand maintain their
posture.
Limbic
system
The limbic system contains glands which help relay
emotions. Many hormonal responses that the body generates are initiated in this
area. The limbic system includes the amygdala, hippocampus, hypothalamus and
thalamus.
Amygdala: The amygdala helps the body responds to
emotions, memories and fear.
Hippocampus: This portion of the brain is used for
learning memory, specificallyconverting temporary memories into permanent
memories which can be stored within thebrain.
Hypothalamus: The hypothalamus region of the brain
controls mood, thirst, hunger and temperature. It also contains glands which
control the hormonal processes throughout the body.
Thalamus: The thalamus is located in the centre of
the brain. It helps to control theattention span, sensing pain and monitors
input that moves in and out of the brain to keeptrack of the sensations the
body is feeling.
Brain stem
All basic life functions originate in the brain
stem, including heartbeat, blood pressure and breathing. In humans, this area
contains the medulla, midbrain and pons.
Midbrain: This part of the brain helps regulate
body movement, vision and hearing.
Pons: The pons interprets information that is used
in sensory analysis or motor control.The pons also creates the level of
consciousness necessary for sleep.
Medulla: The medulla or medulla oblongata is an
essential portion of the brain stemwhich maintains vital body functions such as
the heart rate and breathing.
The diagram below shows and summarizes the basic
functions of different parts of thebrain.
The
Components of the Central Nervous System and their Functions
Identify
the components of the central nervous system and their functions
The table below summarizes the structure and
functions of the major components of the brain.
The
Structure of the Spinal Cord and Brain
Describe the structure of the spinal cord and brain
Spinal cord
The spinal cord functions primarily in the
transmission of neural signals between the brain and the rest of the body but
also contains neural circuits that can independently control numerous reflexes
and central pattern generators. It carries out two main functions:
§
It
connects a large part of the peripheral nervous system to the brain.
Information(nerve impulses) reaching the spinal cord through sensory neurons is
transmitted up into the brain. Signals arising in the motor areas of the brain
travel back down the cord and leave in the motor neurones.
§ The spinal cord also acts as a minor coordinating
centre responsible for some simplereflexes like the withdrawal reflex.
The intermediate neurones carrying impulses to and
from specific receptors and effectors are grouped together in spinal tracts.
The diagram shows various sections of the spinal
cord and the functions of each section.
Peripheral
Nervous System (PNS)
The
Meaning of Peripheral Nervous System
Give the meaning of peripheral Nervous System
The peripheral nervous system is made up of a
network of nerves linking various parts of the body to the brain and spinal
cord. It includes the cranial nerves, spinal nerves and their roots and branches,
peripheral nerves, and neuromuscular junctions.
The peripheral nervous system (PNS) has two
components: the somatic nervous systemand the autonomic nervous system. The PNS
consists of all of the nerves that lie outsidethe brain and spinal cord.
The
Components of the Peripheral Nervous System and Their Functions
Identify the components of the peripheral nervous
system and their functions
The somatic nervous system is made up of nerves
that connect to voluntary skeletal muscles and to sensory receptors. It is
composed of afferent nerves that carry information to the central nervous
system (spinal cord) and efferent nerves that carry neural impulses away from
the central nervous system. This system is responsible for the involuntary
control of the skeletal muscles, bones and sense organs.
The autonomic nervous system is further subdivided
into sympathetic andparasympathetic nervous system.
§ The sympathetic nervous system activates the ‗fight
or flight' response under sudden or stressful circumstances, for instances by
raising the heart rate and dilating the pupils.
§ The parasympathetic nervous system helps the body
return to normal activity after an emergency, which conserve energy and
replenishes the system.
Together, these two systems regulate homeostasis
within the body - one preparing the body for action, and the other repairing
the body afterward.
Reflex
Action
The
Meaning of Reflex Action
Give the meaning of reflex action
When a receptor is stimulated, it sends a signal to
the central nervous system, where thebrain co-ordinates the response. But
sometimes a very quick response is needed, one thatdoes not need the
involvement of the brain. This is a reflex action.
The reflex action is a rapid, involuntary response
to a certain stimulus. The route that is followed by impulses during a reflex
action is called a reflex arc.
Reflex actions are rapid and happen without us
thinking. For example, you would pully our hand away from a hot flame without
thinking about it. The diagram below shows a simplified reflex arc.
This is what happens:
§
receptor
detects a stimulus - change in the environment
§
sensory
neurone sends signal to relay neurone
§
motor
neurone sends signal to effector
§ effector produces a response
The above process appears to be a long one but, in
reality, the process takes a very shorttime. It happens within seconds.
The way the iris in our eye adjusts the size of the
pupil in response to bright or dim lightis also a reflex action. It happens
without our thinking and beyond our control.
The
Neuronic Path of a Reflex Action
Describe the neuronic path of a reflex action
A reflex action can either be simple or conditioned
reflex.
Simple reflex action
An example of a simple reflex found in humans is
the pupil reflex, where the pupil of the eye gets larger in dim light and
smaller in bright light.The eye needs to control the amount of light entering
it in different light conditions. In dim conditions, more light is allowed to
enter so that a clear image can be formed on the retina. In bright conditions,
less light is allowed to enter so that the retina is not damaged.
Conditioned
reflex action
A conditioned reflex is some action or feeling that
is learned in response to a specificsituation or stimulus.
A Russian scientist called Pavlov trained dogs to
expect food whenever he rang a bell.The dogs eventually produced saliva when
they heard the bell ring. The dog salivates naturally when given food. Pavlov
rung a bell every time the dogs were to be given food.After much repetition the
dogs salivated when they heard the bell ringing, even when there was no food.
This is an example of a conditioned reflex.
The dogs were conditioned to salivate when the bell
rang. A ringing bell does not normally cause salivation in dogs. However, when
the ringing bell becomes a secondary stimulus, it does cause salivation, even
though the dog will not be able to eat the bell as food.
This is now called a conditioned reflex. In a
conditioned reflex the final response(salivation) has no direct connection with
the stimulus (ringing bell).
Another example of a conditioned (learned) reflex
is when the driver comes across a hurdle on the road such as a ditch or a
pedestrian. In such circumstances, the first thing the driver will do is to
move his leg towards the brake pedal to apply the brakes. He has learned to do
this action for so long that he finds himself applying the brake in any of such
circumstances.
The
Difference between Simple Reflex and Conditioned Reflex Action
Distinguish simple reflex from conditioned reflex
action
Differences between conditioned
reflex action and simple reflex action
|
Conditioned reflex |
Simple reflex |
|
|
1 |
It involves more than one stimuli |
Requires only one stimulus |
|
2 |
Involves the brain |
Mostly involve the spinal cord |
|
3 |
It is an immediate action (no time to learn) |
It is an immediate action (no time to learn) |
|
4 |
It is acquired in one‘s life |
It is inborn |
Modifying
a reflex response
In some circumstances the brain can modify a reflex
response. It does this by sending an impulse along a motor neuron of the reflex
arc. This enables us, for example, to hold a hot dinner plate when normally we
would drop it.
Sense
Organs
The
Meaning of a Sense Organ
Explain the meaning of a sense organ
Sense organs are organs of the body that detect and
respond to changes in the environment (stimuli) so as to survive.
Types
of Sense Organs and Their Relative Position
Identify types of Sense organs and their relative
position
There are five sense organs in our body: eyes,ears,
nose, tongue and skin. We receive a variety of information from the
environmentaround us through the sense organs. The sense organs contain
receptors. A receptor is acell (or a group of cells) in a sense organ which is
sensitive to a particular type ofstimulus (or a particular type of change in
the environment) such as light, sound, smell,taste, heat, pressure, etc. The
different sense organs contain receptors for detectingdifferent stimuli.
The eyes have light receptors (which can detect
light), ears have sound receptors (which can detect sound), nose has smell
receptors (which can detect smell), tongue has taste receptors (which can
detect taste) whereas skin has receptors for detecting touch,pressure, heat (or
cold) and pain, etc.
The
Structure of Each Sense Organ
Describe the structure of each sense organ
The human eye
The eye is the organ for vision. The eye is one of
the most complex parts of the body.The different parts of the eye allow the eye
to take in light and perceive objects around usin the proper colour, detail and
depth. This allows people to make more informeddecisions about their
environment. If a portion of the eye becomes damaged, you may notbe able to see
effectively. You may even lose your vision completely.Parts of the eye and
their functionsThere are several physical and chemical elements that make up
the eye. The table belowshows different parts of the human eye and their
functions.Eye part Description and function(s)Cornea The cornea is the outer,
transparent covering of the eye. This layerprotects the eye from elements that
could cause damage to the innerparts of the eye. The cornea also helps to focus
light on the retina at theback of the eye.Sclera The sclera is commonly
referred to as the "white" of the eye. It protectsthe eye and
maintains the shape of the eye ball.Pupil The pupil appears as a black dot in
the middle of the eye. This blackarea is actually a hole that takes in light to
enable the eye focus on theobjects in front of it. The pupil, thus, controls
the amount of light thatenters the eye.Iris The iris contains the pigment which
gives the eye its colour. It has radialInternal structure
Parts
of the eye and their functions
There are several physical and chemical elements that
make up the eye. The table belowshows different parts of the human eye and
their functions.
|
Eye
part |
Description
and function(s) |
|
Cornea |
The cornea is the outer, transparent covering of
the eye. This layer protects the eye from elements that could cause damage to
the inner parts of the eye. The cornea also helps to focus light on the
retina at the back of the eye. |
|
Sclera |
The sclera is commonly referred to as the
"white" of the eye. It protects the eye and maintains the shape of
the eye ball. |
|
Pupil |
The pupil appears as a black dot in the middle of
the eye. This black area is actually a hole that takes in light to enable the
eye focus on the objects in front of it. The pupil, thus, controls the amount
of light that enters the eye. |
|
Iris |
The iris contains the pigment which gives the eye
its colour. It has radial and circular muscles that control the size of the
pupil by dilation and contraction. This allows the eye to take in more or
less light depending on how bright it is around. The iris allows more light
into the eye when the environment is dark and allows less light into the eye
when the environment is bright. |
|
Conjunctiva |
This is a membrane that covers the cornea. It is
thin and transparent so as to allow light to enter the eye. It is tough and
protects the eye from mechanical damage. |
|
Lacrimal glands |
These glands are located on the outer corner of
each eye. They produce tears which help moisten the eye when it becomes dry,
and flush out particles which irritate the eye. As tears flush out
potentially dangerous irritants, it becomes easier to focus properly. |
|
Lens |
This is a transparent structure filled with a
jelly-like substance. The lens focuses light into the retina. It is held in
place by the suspensory ligaments attached to the ciliary muscles, which
allow the lens to change shape depending on the amount of light entering the
eye. Through the ciliary muscles, the lens becomes thicker to focus on nearby
objects and thinner to focus on distant objects. |
|
Retina |
Retina is the sensory tissue that lines the inner
layer of the eye. It is the layer of the eye where images are formed, and it
is connected to the optic nerve that transmits the images to the brain to be
interpreted. The retina is made up millions of photoreceptors known as rods
and cones. |
|
Ciliary body |
Ciliary body, also called ciliary muscles, is a ring-shaped tissue which holds
and controls the movement of the eye lens, and thus, it helps to control the
shape of the lens. The ciliary body contains glandular cells which secrete
the aqueous humour. |
|
Suspensory ligaments |
The suspensory ligaments attach the lens to the
ciliary muscles. When the ciliary muscles contract, they pull the suspensory
ligaments and the lens gets long and thin to accommodate rays of light from
distant objects. When the ciliary muscles relax, there is less tension on the
suspensory ligaments and the lens becomes more spherical in shape. This
enables the accommodation of light rays from near objects. |
|
Choroid |
The choroid lies between the retina and the
sclera, which provides blood supply to the eye. Just like any other portion
of the body, the blood supply gives nutrition to the various parts of the
eye. |
|
Vitreous humour |
The vitreous humour is the gel located in the
back of the eye which helps it hold its shape. This gel takes in nutrients
from the ciliary body, aqueous humour and the retinal vessels so the eye can
remain healthy. The gel in the vitreous humour is transparent to allow light
to get to the retina and also helps maintain the shape of the eyeball. |
|
Aqueous Humor |
The aqueous humour is a watery substance that
fills the eye. The aqueous humour gives the front of the eye its shape as
well as nourishes the cornea and lens. This liquid is drained through the
Schlemm canal so that any build-up in the eye can be removed. If the person’s
aqueous humour is not draining properly, s/he can develop glaucoma. |
|
Optic nerve |
Optic nerve is a cranial nerve which contains
sensory neurones. The neurones transmit impulses from the rods and cones of
the retina to the brain for interpretation. The optic nerve exits the eye at
the blind spot. |
|
Blind spot |
It is located at the point where the optic nerve
leaves the eye. The blind spot is not sensitive to light because it has no
rods or cones. |
|
Fovea |
The fovea is the centremost part of the macula*.
This tiny area is responsible for our central, sharpest vision. A healthy
fovea is important for reading, watching television, driving, and other
activities that require the ability to see detail.*Small and highly sensitive
part of the retina responsible for detailed central vision. The retina is the
very centre of the macula. |
Adaptations of the eye to its functions
The eye is adapted to its functions by possessing
the following features:
§
Conjunctiva,
cornea and lens are transparent to allow light to pass through them.
§
Sclerotic
layer is made up of (collagen) fibres; it maintains shape of
eyeball/protectsthe eye from mechanical damage.
§
Cornea
is transparent and curved thus refracts light rays and allows light to
passthrough.
§
Choroid
(a layer of a tissue) has black or dark pigments that prevent
internalreflections of light in the eye.
§
The
eye contains blood vessels in the choroids layer that supply oxygen and
nutrientsto the eye, giving the eye energy to perform its function, and removes
the metabolicwastes from the eye.
§
Retina
is made of photoreceptors known as rods and cones, which trap light rays
toenable the eye to do its function of vision.
§
Yellow
spot (fovea) has the highest concentration of cones for accurate and
sharp,central vision.
§
Optic
nerve has sensory neurones for transmission of nerve impulses to the brain
(forinterpretation).
§
Lens
is biconvex and made up of elastic, transparent material which adjusts to
focusfar or near objects and allows light rays to pass through.
§
Suspensory
ligaments are fibrous to hold the lens in place.
§
. The
ciliary body contains ciliary muscles which are contractile to for controlling
thecurvature and hence focal length of the lens. It also contains glands that
secrete theaqueous and vitreous humours.
§
The
iris is opaque and contractile for controlling the amount of light entering the
eye(by adjusting the size of the pupil).
§
Ocular
muscles coordinate eye movement so that both eyes can follow a movingobject
together.
§
The
eyelid covers an eye and prevents it from mechanical damage and invasion
byforeign bodies.
§
Eye
lashes help to prevent dust and small insects or particles from entering the
eyeby trapping them on their hairs.
§ The presence of aqueous and vitreous humours helps
the eye to bend light raystoward retina to process the signal and send impulse
to the brain.
The
Functions of Sense Organs and their Adaptive Features
Explain the functions of sense organs and their
adaptive features
Adaptations of the eye to its functions
The eye is adapted to its functions by possessing
the following features:
§
Conjunctiva,
cornea and lens are transparent to allow light to pass through them.
§
Sclerotic
layer is made up of (collagen) fibres; it maintains shape of
eyeball/protectsthe eye from mechanical damage.
§
Cornea
is transparent and curved thus refracts light rays and allows light to
passthrough.
§
Choroid
(a layer of a tissue) has black or dark pigments that prevent
internalreflections of light in the eye.
§
The
eye contains blood vessels in the choroids layer that supply oxygen and nutrientsto
the eye, giving the eye energy to perform its function, and removes the
metabolicwastes from the eye.
§
Retina
is made of photoreceptors known as rods and cones, which trap light rays
toenable the eye to do its function of vision.
§
Yellow
spot (fovea) has the highest concentration of cones for accurate and
sharp,central vision.
§
Optic
nerve has sensory neurones for transmission of nerve impulses to the brain
(forinterpretation).
§
Lens
is biconvex and made up of elastic, transparent material which adjusts to
focusfar or near objects and allows light rays to pass through.
§
Suspensory
ligaments are fibrous to hold the lens in place.
§
. The
ciliary body contains ciliary muscles which are contractile to for controlling
thecurvature and hence focal length of the lens. It also contains glands that
secrete theaqueous and vitreous humours.
§
The
iris is opaque and contractile for controlling the amount of light entering the
eye(by adjusting the size of the pupil).
§
Ocular
muscles coordinate eye movement so that both eyes can follow a movingobject
together.
§
The
eyelid covers an eye and prevents it from mechanical damage and invasion
byforeign bodies.
§
Eye
lashes help to prevent dust and small insects or particles from entering the
eyeby trapping them on their hairs.
§ The presence of aqueous and vitreous humours helps
the eye to bend light raystoward retina to process the signal and send impulse
to the brain.
The
human ear
The ear is the organ of hearing and maintaining
balance and posture. The outer earprotrudes away from the head and is shaped
like a cup to direct sound waves toward thetympanic membrane, which transmits
vibrations to the inner ear through a series of smallbones (ossicles) in the
middle ear called the malleus, incus and stapes. The inner ear, orcochlea, is a
spiral-shaped chamber covered internally by nerve fibres that react to
thevibrations and transmit impulses to the brain via the auditory nerve. The
brain combinesthe input of our two ears to determine the direction and distance
of sounds.
The inner ear has a vestibular system formed by
three semicircular canals that areapproximately at right angles to each other
and which are responsible for the sense ofbalance and spatial orientation. The
inner ear has chambers filled with a viscous fluid andsmall particles
(otoliths) containing calcium carbonate. The movement of these particlesover
small hair cells in the inner ear sends signals to the brain that are
interpreted asmotion and acceleration. The figure below shows the internal
structure of themammalian ear.
Adaptations
of the mammalian ear to its functions
The ear is adapted to its functions by possessing
the following features:
§ The outer ear (pinna) is a flap of tissue which
collects sound waves and directs theminto the inner ear via the auditory canal.
§ The lining of auditory canal contains wax-secreting
cells which produce wax. Thewax in the canal traps dust particles and other
foreign bodies and hence protects theinner delicate parts of an ear from
mechanical damage or microbial infections.
§ The ear drum is thin and membranous, a fact that
enables it to vibrate when soundwaves hit it before converting the waves into
vibrations and passing them on to theear ossicles in the middle ear.
§ The ear ossicles (malleus, incus and stapes) act as
a lever system which can moveforward and backward to amplify and transmit
vibrations to the oval window.
§ The Eustachian tube is hollow, a fact which allows
air in and out of the middle ear toequalize the pressure between the inside and
outside of the ear drum—whichimproves the drum‘s ability to vibrate
§ The cochlea is coiled to increase the surface area
for sound reception. It also cariesauditory nerves which transmit sound
impulses to the brain for interpretation.pinnaear drumskull bonesemi-circular
canalsauditory canaleustachian tuberound windowcochleaauditory nerveInternal
structure of the human earoval window
§ The presence of fluid-filled vestibular apparatus
(semi-circular canals, sacculus, andutriculus) in the inner ear facilitates
balancing of sound when the fluid is displaced.
The tongue
The tongue is an organ responsible for taste. It is
the primary organ of taste (gustation), asmuch of its upper surface is covered
in taste buds. The tongue's upper surface is alsocovered with numerous lingual
papillae. The tongue is sensitive and kept moist by saliva,and is richly
supplied with nerves and blood vessels.
The receptors for taste, called taste buds, are
situated chiefly in the tongue, but they arealso located in the roof of the
mouth near the pharynx. They are able to detect four basictastes: salty, sweet,
bitter, and sour.
Generally, the taste buds close to the tip of the
tongue are sensitive to sweet and saltytastes, whereas those in the back of the
tongue are sensitive to bitter tastes. The taste budsin the sides of the tongue
are sensitive to sour tastes. At the base of each taste bud there isa nerve
that sends the sensations to the brain. The sense of taste functions in
coordinationwith the sense of smell.
The number of taste buds varies substantially from
individual to individual, but greaternumbers increase sensitivity. Women, in
general, have a greater number of taste budsthan men. As in the case of colour
blindness, some people are insensitive to some tastes.
Adaptation
of the tongue to its functions (as a sense organ)
The tongue is adapted to its functions by
possessing the following features:
§ The tongue has taste buds which help it to respond
the stimuli such as sweet, bitter,sour and salty.
§ At the base of each taste bud there is a nerve that
sends the sensations to the brain.
The
human nose
The nose is the organ responsible for the sense of
smell. The cavity of the nose is linedwith mucous membranes that have smell
receptors connected to the olfactory nerve. Thesmells themselves consist of
vapours of various substances. The smell receptors interactwith the molecules
of these vapours and transmit the sensations to the brain. The smellreceptors
are sensitive to seven types of sensations that can be characterized as
camphor,musk, flower, mint, ether, acrid, or putrid. The sense of smell is
sometimes temporarilylost when a person has a cold. Dogs have a sense of smell
that is many times moresensitive than man's.
When we want to ―smell‖ food we draw air high up
into the nasal cavity where thechemicals come into contact with hairs on the
sensory cells. Different chemicalsstimulate different sensory cells and nervous
impulses are set up which pass along theverves to the brain to be interpreted.
When our nose is blocked with cold, our food may
become ―tasteless‖ because we nolonger smell it.
Adaptations
of the nose to its functions
The nose is adapted to its functions by possessing
the following features:
§
There
are olfactory nerves, which carry impulse from the nose to the olfactory
lobesof the brain for interpretation.The human nose
§
Presence
of mucus-secreting cells, which produce mucus that keep the surface of thenose
moist.
§ Presence of hairs in the nose helps the nose to
trap dust particles and other foreignbodies. When the mucus is blown out from
the nose, it carries the dust and otherforeign bodies with it, thus preventing
the olfactory organs from damage.
The
human skin
The skin is the outer covering of the body. In
humans, it is the largest organ of the integumentary system. The skin has
multiple layers of ectodermal tissue and guards the underlying muscles, bones,
ligaments and internal organs. It protects us from microbes and the elements;
helps regulate body temperature; and permits the sensations of touch,heat, and
cold.
The skin has three layers:
§ The epidermis, the
outermost layer of skin, provides a waterproof barrier andcreates our skin tone
§ The dermis, beneath the epidermis, contains
tough connective tissue, hairfollicles, and sweat glands
§
The
deeper subcutaneous layer (hypodermis) is made
of fat and connectivetissue.
The skin‘s colour is produced by special cells
called melanocytes, which produce thepigment melanin. Melanocytes are located
in the epidermis.
The skin contains sensory nerve endings which are
receptors. They are sensitive to pain,pressure, touch, heat and coldness. When
the nerve endings are stimulated they set upnervous impulses which are sent to
the spinal cord or brain to be interpreted.
Functions
of skin
§
Regulation:
The skin plays an important role in regulation of body temperature inan
organism thus helping to keep the body temperature constant (endothermic).
§
The
skin manufactures vitamin D through exposure to sunlight. Ergosterol in thefatty
layer of the skin converts into vitamin D under the influence of sunlight.
§
The
skin produces melanin that protects the body from ultra violet radiationswhich
can cause skin cancer.
§
The
skin acts as sensory organ due to the presence of various nerve endings.
§
Protection:
It prevents micro-organism and other foreign materials from enteringthe body.
§
Excretion:
Sweat glands produce sweat, which gets rid of excess heat, water, salts,some
carbon dioxide and urea.
§
Storage:
Fat is a food store in the dermis.
Adaptations
of the skin to its functions (as a sense organ)
The human skin is adapted to its sensory functions
by having the following features:
§
It has
the hair erector muscle which controls whether the hair stands erect or lies
down depending on the temperature of the surrounding.
§
It is
supplied with nerves which convey impulses to the CNS to be interpreted.
§
Presence
of blood vessels (in the dermis) which dilate when the body temperature ishigh
to facilitate heat loss by radiation and constrict when the temperature is low
toreduce heat loss. The blood vessels also supply nutrients and oxygen to the
skin andremove excretory products.
§ The skin has sweat glands which produce sweat to
help cool the body. During a hot day, the glands produce sweat (through sweat pores).
Evaporation of the sweat uses the body heat and hence helps to cool down the
body.
Drugs
and Drug Abuse in Relation to Nervous Coordination
The
Meaning of Drugs and Drug Abuse, in Relation to Nervous Coordination
Explain the meaning of drugs and drug abuse, in
relation to nervous coordination
Drugs
A drug is any chemical substance, natural or
synthetic, that has known physiologicaleffects on humans or other animals.
Foods are generally excluded from this definition, inspite of their
physiological effects on animal species.
Most drugs, both useful and harmful, may affect the
body (especially the brain), byaltering the nerve cells' natural reaction to
these chemicals, or by mimicking the body'snormal compounds.
Some drugs slow down the passage of stimuli by
affecting nerve cell membranes, andothers act like neurotransmitters, perhaps
passing stronger or longer-lasting impulses. Assuch they may alter the way
sensory information is processed, or affect the thinkingprocess.
Stimulants are drugs which speed up the action of
the brain e.g. caffeine, found in tea andcoffee. Sedatives are drugs which slow
down the action of the brain e.g. alcohol. Evenone alcoholic drink will have
some effect on the brain.
Proper
Ways of Handling and Using Drugs
Outline proper ways of handling and using drugs
Proper use and handling of drugs
When using and handling drugs the following
precautions must be observed:
§
Avoid
taking any drug without diagnosing the disease and prescription by the doctor.
§
Always
stay away from peer pressures and drug addicts to avoid copying their
badhabits.
§
Keep
yourself busy with a number of activities such as sports and games,
readingbooks, etc. Remember ‗an idle mind is the devil‘s workshop‘!
§
Report
any case of drug abuse or trafficking to concerned authorities.
§
Form a
counselling club to advise people especially youths on how to keep off
fromdrugs.
§
If one
feels addicted, s/he should seek advice from health officials.
§
Never
take a dose more or less that what has been prescribed by the doctor.
§ Complete the prescribed dose even after you start
feeling well or after the symptomsof the disease has disappeared.9. Keep all
drugs out of reach of children and drug addicts.
Drug
addiction
Drug addiction refers to the compulsive and
repeated use of increasing amounts of drugswith the appearance of withdrawal
symptoms when drug use ceases. While drug use oftenbegins as a way to seek
recreation, the addictive properties of the drug make an addictcrave for it
permanently. This compulsion is uncontrollable and may interfere with aperson‘s
everyday life. Even when the effects of drugs are damaging to a person‘s
bodyand relationships with friends, family members and co-workers, the constant
need for adrug often overcomes any rational thinking.
The human body has its own ability to produce some
chemicals for its proper functioning. The continued use of the drug suppresses
the body‘s ability to produce these chemicals or diminishes its production
because these chemical are replaced by the drug.The body thus uses the drug as
a substitute for its own natural chemicals. Since these chemicals are no longer
produced, the body perceives that it needs the drug for its functioning.
Therefore, a person craves for the drug so much that s/he feels cannot live
without taking it. At this level the drug abuser becomes addicted to the drug.
This is called drug addiction.
Causes
and Effects of Drug Addiction
Explain causes and effects of drug addiction
Like many mental health disorders, several causes
may contribute to development of drugaddiction and dependence. Some of the
causes of drug abuse and addiction include thefollowing:
§
Some
people take drugs to avoid physical or emotional pain, discomfort,
stress,boredom, anxiety and depression.
§
Some
people also take drugs as a way to forget problems and life hardships
theyexperience in life.
§
Recreation:
Drug users believe that taking drugs make them ‗feel better‘ and lively.
§
Peer
pressure leads people to drug so as to create a sense of belonging and fitting
inthe peer group. It‘s often said that teens use drugs when their friends do.
Using drugsallows these young people to fit in with their peers and blend in
with the crowd
§
.
Desire for a new experience and arousal: Some people just take drugs as
an‗experiment‘ to find out the experience the drug users feel, but badly end
upbecoming drug addicts.
§ Lack of life and social skills, for example drug
resistance skills that would help aperson learn how to say no or avoid bad
influence. People who are easy to copyhabits from others, irrespective of the
outcome of the given habit, can easily get intodrug use.
Effects of drug abuse and addiction
Effects of drug abuse and addiction
Many illegal chemicals have extreme effects on the
function of the brain, e.g. some drugscause hallucinations - objects around you
may change colour, shape and size, or you maysee and experience things that are
not there at all. Such experiences may cause fear,depression, and mental
disorders. Mostly, these substances alter one's perception ofreality.
Drugs produce a variety of short-term effects, but
the most common ones includeincreased heart rate, high blood pressure,
dizziness, tremors, mood changes and paranoia.In high dosages, the risk for
more dangerous effects increases, and the potential for heartattack, stroke,
respiratory failure and coma increases. The various effects of drug
abuseinclude the following:
§
Drugs
confuse the mental faculties so that many drug users die in accidents,
oroverdose on the chemicals. Drugs can also induce them do dangerous activities
suchas unsafe sex or reckless driving.
§
Many
drugs induce a feeling of dependency (addiction) and are linked with
criminalactivity.
§
Solvent
abuse (sniffing glue, lighter fuel, etc.) - on which one can easily overdose
-can cause death by heart failure.
§
Other
substances can incidentally affect the body's "thermostat" - located
in thehypothalamus (refer to a topic on homeostasis and osmoregulation) and
cause death,following disruption of the body's temperature control and
regulation of the body'swater content. Even "legal" chemicals, such
as alcohol (a "social" drug!), haveadverse effects on the body.
§
They
can lead to aggressiveness, crime, violence and divorce.
§
Sharing
of needles used to inject drugs into the bloodstream cause HIV infections
andhepatitis among the addicts. Likewise, because drugs impair one‘s judgement,
it canlead to unprotected sex and hence become the cause of contracting other
sexuallytransmitted diseases like syphilis, gonorrhoea, chlamydia and herpes.
§
Drugs
are very expensive to purchase. Therefore, the addicts spend much of theirmoney
on drugs at the expense of other family needs.
§
Many
drug addicts are weak and so they cannot participate in in-come
generatingactivities. This leads to poverty, a fact which can lead to failure
to meet one‘s basicneeds.
§
Drug addiction
among women can lead to birth defects which include giving birth tosmall or
premature babies or cause the baby to have withdrawal symptoms, birthdefects or
learning and behavioural problems. Additionally, illicit drugs may
containimpurities that may be harmful to unborn baby
§ Medical concerns like depression and anxiety can
severely interrupt the addict‘s social and professional life, leading to mood
swings, chronic fatigue and a diminished interest in former hobbies and
important life events.
Preventive
and Control Measures of Drug Abuse
Suggest preventive and control measures of drug
abuse
Drug abuse is a serious psycho-sociological problem
often difficult to be cured. The bestway to avoid these tragedies is to never
start taking drugs. However, nowadays specifictreatments are available for
different types of mental illness. A regular, prolonged andsincere treatment is
required .Social therapy or rehabilitation has got a very significantrole. The
following activities can be done for the control of drug addiction:
§
Early
detection, treatment and rehabilitation of drug addicts can help minimize
theproblem.
§
Parents
should set a warm and friendly atmosphere at home so that the drug users
canfeel easy to cooperate with.
§
Motivation
of the addicts to make up for detoxification.
§
The
youth should be motivated to get involved in the fight against drug abuse.
§
Educating
the community about the problems of drug addiction.
§
Enforcement
of laws, rules and regulation for the control and supply of drugs.
§
The
school curricula should contain courses about the drug addiction and drug
abusein detail (like the topic you are reading now).
§
Various
effects of drug addiction must be advertised through newspapers,
radio,television, magazine, social media, and many other media so as to make
the problemknown to as many people as possible.
§ The experience of drug users can be advertised to
the people through media to makethe general public aware of the effects of
drugs so as to discourage those who mightthink of starting taking drugs.
Location
of the Different Endocrine Glands in the Mammalian Body
Identify location of the different endocrine glands
in the mammalian body
THE ENDOCRINE SYSTEM
The endocrine system is a collection of glands that
produce hormones which regulate metabolism, growth and development, tissue
function, sexual function, reproduction,sleep, and mood, among other functions.
The glands are located in various parts of the human body. The function of
these glands is to release various hormones, and as a whole,they are most
commonly referred to as the endocrine system. These glands are pituitary gland,
hypothalamus, thymus, pineal gland, testes, ovaries, thyroid, adrenal
glands,parathyroid and pancreas. The location of these glands in the human body
is as shown in the diagrams below.
The
role of Hormones produced by each Endocrine gland
Explain the role of hormones produced by each
endocrine gland
The hormones released by glands of the endocrine
system regulate the functions of many cells and organs as indicated in the
following table.
Disorders
of Hormonal Coordination in Mammals
Outline disorders of hormonal coordination in
mammals
Causes of endocrine disorders
The causes of endocrine disorders are typically
grouped into two categories:
§
Endocrine
disease that results when a gland produces too much or too little of
anendocrine hormone, called a hormone imbalance.
§ Endocrine disease due to the development of lesions
(such as nodules or tumours) inthe endocrine system, which may or may not
affect hormone levels.
The endocrine's feedback system helps control the
balance of hormones in thebloodstream. If your body has too much or too little
of a certain hormone, the feedbacksystem signals the proper gland or glands to
correct the problem. A hormone imbalancemay occur if this feedback system has
trouble keeping the right level of hormones in thebloodstream, or if your body
doesn't clear them out of the bloodstream properly.
Increased or decreased levels of endocrine hormone
may be caused by:
§
A
problem with the endocrine feedback system.
§
Disease.
§
Failure
of a gland to stimulate another gland to release hormones (for example,
aproblem with the hypothalamus can disrupt hormone production in the
pituitarygland).
§
A
genetic disorder, such as multiple endocrine meoplasia or congenitalhypothyroidism.
§
Infection.
§
Injury
to an endocrine gland.
§ Tumour of an endocrine gland.Most endocrine tumors
and nodules (lumps) are non-cancerous. They usually do notspread to other parts
of the body. However, a tumor or nodule on the gland may interferewith the
gland's hormone production.
Types of endocrine disorders
There are many different types of endocrine
disorders. Majority of endocrine disorderscause the endocrine glands to produce
too much (hypersecretion) or too low(hyposecretion) of a given hormone from a
particular gland. Common problems thatresult from oversecretion
(hypersecretion) or undersecretion (hyposecretion) of givenhormones from given
endocrine glands are explained below.
PITUITARY GLAND
Hypersecretion of growth hormone: Gigantism in children
and acromegaly in adults.If the pituitary gland produces too much growth
hormone, a child's bones and body partsmay grow abnormally fast.
Hyposecretion of growth hormone:
Pituitary dwarfism - if the condition occurs duringchildhood, it slows down long
bone growth.
Hypersecretion of ADH:
Causes increased reabsorption of water in the kidney tubulesleading to
production of a little urine but which is more concentrated.
Hyposecretion of ADH: Less water is absorbed from
the glomeruli filtrate back to thebody, leading to production of large volumes
of dilute urine. This is called diuresis and isa symptom of diabetes inspidus.
THYROID GLAND
Hyperthyroidism
§
Grave's
disease: The most common cause for an overactive thyroid is an
autoimmunedisorder called Grave's disease. Grave's disease, considered an
autoimmune disease,shows elevated weight loss, nervousness, excessive
perspiration, nervousness, highmetabolic rate and rapid, irregular heartbeat.
§
Exophthalmos:
protrusion of the eyeballs caused by oedematous tissue behind theeyes.
Hypothyroidism
§
Cretinism
(infantile hypothyroidism) - shows stunted growth, thickened facialfeatures,
abnormal bone development and mental retardation.
§
Myxedema
- low metabolic rate, lethargy (a condition characterized by extremefatigue or
drowsiness, or prolonged sleep patterns.), weight gain, increase in bodyfluids.
§
Goitre
- abnormal growth of the thyroid gland.
PARATHYROID GLAND
Hyperparathyroidism: demineralization of bone
resulting in possible bone deformityand fracture, and stones in the urinary
tract
Hypoparathyroidism: decreased plasma calcium levels
which can lead to severe muscletetany (a condition characterized by or
resulting from uncontrolled muscle spasms).
PANCREAS
Hyperinsulinism: The liver is overstimulated to
convert excess glucose to glycogen andfats for storage. This leads to low
glucose concentration in the blood, a condition calledhypoglycemia. This
condition results in lack of glucose delivery to the brain
causingdisorientation, unconsciousness and even death (usually the result of an
overdose ofinsulin).
Hypoinsulinism: Under-secretion of isulin causes
very little glucose to be converted toglycogen and fats. This results in
elevated glucose levels in the blood and urine. Thecondition is called
hyperglycaemia, and is a symptom of diabetes mellitus. Over time,diabetics
experience vascular and neural problems. Secondarily, poor circulation maylead
to gangrene, blindness, kidney damage and impotence.
ADRENAL GLAND
Hypersecretion of corticosteroids: Cushing's
syndrome - changes in carbohydrate andprotein metabolism resulting in a puffy
appearance.
Hyposecretion of glucocorticoids and
mineralocorticoids: Addison‘s disease -symptoms of the disease include fatigue,
stomach upset, hypoglycaemia, sodium andpotassium imbalance, dehydration,
hypotension, and rapid weight loss. Death occurs withlack of treatment.
Hypersecretion of adrenaline: hypertension,
obesity, headache, increased heartbeat,weak bones, hyperglycaemia, nervousness,
sweating and early onset of sexualdevelopment.
Hyposecretion of adrenaline: low blood pressure,
fatigue, muscular weakness, musclewasting, inability to withstand stress, and
increased dark pigmentation of the skin.
OVARIES
Hypersecretion of oestrogen: Causes decreased
sexual desire, heavy menstrual flow andincreased weight in females.
Hyposecretion of oestrogen: Causes failure of
females to develop some secondarysexual characteristics, poor development of
the reproductive organs, liver, kidney andlungs.
TESTES
Hypersecretion of testosterone: Causes males to
have female features such as enlargedbreasts and a wide pelvis.
Hyposecretion of testosterone: Causes failure of
males to develop some secondarysexual characteristics, poor development of the
reproductive organs and weak bones andmuscles.
THYMUS
Not responsible for any effects of hypo or hyper
secretion of thymosin.
PINEAL
Not responsible for any effects of hypo or hyper
secretion of melatonin.
Coordination
in Plant, Concept of Tropic and Nastic Responses
The
Concept of Tropic and Nastic Responses
Explain the concept of tropic and nastic responses
COORDINATION IN PLANTS
Both, plants and animals react (or respond) to
various stimuli around them. But the method of reacting to stimuli is not
similar in plants and animals. They react to stimuli indifferent ways. For
example, plants bend towards light but animals do not bend towards light. The
animal amoeba reacts to the presence of food by moving towards the food
particle.
The plants do not have a nervous system and sense
organs like eyes, ears, or nose, etc.,like the animals, but they can still
sense things. The plants can sense the presence of stimuli like light, gravity,
chemicals, water, and touch, etc., and respond to them. They sense these
stimuli by using hormones in them.
The stimuli like light, gravity, chemicals, water,
and touch, etc., are called environmental changes. So, we can also say that the
plants coordinate their behaviour against environmental changes by using
hormones. The hormones in plants do not act the same way as in animals.
The hormones in plants coordinate their behaviour
by affecting the growth of a plant.And the effect on growth of the plant can
result in the movement of a part of the plantlike shoot (stem) or root, etc
towards a certain stimulus.
Experiments
to Investigate the Effects of Tropic and Nastic Responses in Plants
Carry out experiments to investigate the effects of
tropic and nastic responses in plants
Plants receive and respond to a variety of stimuli
that are important to their survival in the environment. These responses allow
the plants to survive, grow, develop and reproduce.The movement of plants in
the direction of stimulus is known as 'tropism'. Tropisms are growth responses
of plants that result in curvatures of plant organs toward or away from certain
stimuli. Tropisms can be positive, in which case the plant will bend toward a
stimulus, or negative, in which case the plant will bend away from a stimulus.
The other movements shown by the plants are
associated with the growth of the plants.For example, the shoot system moves
towards sunlight and the root system towards earth.Thus, the plants also
respond to their environment.
Important tropisms in plants include phototropism,
geotropism, hydrotropism,chemotropism and thigmotropism.
Phototropism
Phototropism is the tendency for plant organs to
bend in response to a directional lightsource. For example, light streaming in
a window from one direction will often cause thestems of plants placed nearby
to bend toward the window, a positive phototropism.
Most plant shoots are positively phototropic
because they tend to grow towards light.Most roots are negatively phototropic
because they away from light.
The
Importance of Tropic and Nastic Responses
Explain the importance of tropic and nastic
responses
Importance of phototropism
Phototropism is important to plants because of it
enables the plant leaves to be placed under direct sunlight to absorb maximum
light so as to carry out photosynthesis effectively.
Geotropism
Geotropism is the movement of a part of the plant
towards gravity. In most plants, rootsgrow downward with gravity while shoots
grow upward against gravity. Within hours,the shoot of a plant placed on its
side will usually bend upward and the roots will benddownward as the plant
reorients its direction of growth in response to gravity.
Most plant roots grow towards gravity and are said
to be positively geotropic. Mostshoots grow away from gravity and are said be
negatively geotropic.
Importance
of geotropism
Geotropisms are important to plants because of the
following reasons:
§
It
enables the plants to send roots into the ground hence anchoring the plant
firmlyinto the soil.
§
It
enables plant roots to absorb water and mineral salts from the soil.
§ Negative geotropism exhibited by the shoot enables
the shoot to grow upwards, andin so doing, exposes the plant leaves to maximum
sunlight for effectivephotosynthesis
Hydrotropism
Hydrotropism is the movement of a plant or part of
a plant towards water. Plant rootsnormally grow towards moisture. They are
therefore positively hydrotropic. If you plant aplant near a water source such
as porous pot or river, the roots will always grow towardswater.
Importance
of hydrotropism
It enables the plants to absorb dissolved minerals
and water. Water is necessary forvarious functions such as:
§
Photosynthesis
§
Numerous
physiological reactions that take place within plant cells.
§
Turgor
pressure, which aids in plant support.
§ Dissolution of mineral salts.
Chemotropism
An example of positive and negative chemo-tropism
is shown by a plant‘s roots; the rootsgrow towards useful minerals displaying
positive chemo-tropism, and grow away fromharmful acids displaying negative
chemo-tropism.
Chemotropism is the movement or growth of an
organism or part of an organism inresponse to a chemical stimulus. During the
process of fertilization the movement ofpollen tube towards ovule due to
secretion of a sugary chemical in the ovary is anexample of chemotropism
Importance
of chemotropism
§
It
enables the plant to absorb mineral salts from the soil when the roots grow
towardsbeneficial chemicals such as fertilizers.
§
Negative
geotropism, such as when plant roots grow away from the toxins, enablesthe
plant to survive by avoiding contact with such harmful chemicals.
§
. It
facilitates the fertilization process in flowering plants.
Thigmotropism
or haptotropism
Thigmotropsim refers to non-directional movements
which take place neither towards noraway from the stimulus. The best example of
nastic movement is folding and drooping ofleaves of Mimosa pudica plant when its
leaves are touched with fingers or any object.The leaves fold even when swayed
about by wind. Also the specialized touch-sensitivetendrils of many vining
plants, such as pea, will bend toward the side receiving a touchstimulus.
Continual stimulation can lead to the coiling of the tendril around an
object,which enables vining plants to grasp objects on which they can climb
Importance
of thigmotropism
§
Thigmotropism
enables crawling plants to climb up higher plants and expose theirleaves to
sunlight for optimum photosythesis.
§
It
enables the insectivorous plants such as the Venus flytrap to trap insects and
digest them to obtain nutrients.