Co-ordinating a Response
Coordination and Response -2j
Part 1
Coordination and Response
2-j
• All control systems that carry out a coordinated responses require the
following:
• A stimulus (a change in the environment e.g. a change in glucose levels
in the blood, a change in body temperature etc.)
• A receptor (receptor cells that detect stimuli).
• A coordination centre (such as the brain, spinal cord and pancreas),
which receives and processes information from receptors.
• An effector (a muscle or gland), which brings about responses to restore
optimum levels.
Plant CoordinationPlant tropic Responses
A co-ordinated response (such as that required when there is not enough water in the blood)
requires a stimulus, a receptor and an effector
A Tropism is a movement or growth
response by a plant , in response to a
directional stimulus.
What is a
Tropism?
Plants’ responses are usually much slower than
animals.
Plants need to respond to changes in
environment (stimuli) for survival, e.g. light,
water, gravity.
Phototropism
Phototropism is a response in
which parts of a plant grow
towards or away from the
direction from which light is
coming from.
They grow either towards a stimulus (known as
a positive response) or away from a
stimulus (known as a negative response)
Positive and Negative
Phototropism
Positive and negative phototropism
Geotropism
Positive and Negative
Gravitropism
• Geotropism is a
response in which
parts of a plant grow
towards or away from
gravity.
Comparison of Gravitropism and
Phototropism
Phototropism and gravitropism of a shoot are examples of the
chemical control of plant growth.
Investigating Phototropism
Investigating
Tropisms
Method
Three identical plants A,B and C are set up as
shown .
A-Light was allowed to come in one direction only
(unilateral).
B- Light was allowed to come in one direction
only. Plant was kept on a *clinostat.
C- Plant was kept in complete darkness.
* A clinostat is a device which uses rotation to cancel off
gravitropism and phototropism and their effects.
Investigating Gravitropism
Investigating Phototropism
Observations
• Seedlings in A was bent towards the light source.
• Seedlings in B had grown straight up and showed uniform growth. They have not
bent towards any direction.
• Seedlings in C has grown straight up. Plants have grown tall and slender with
yellowing leaves.
Conclusions
• Seedlings in A has curved towards light.
• For the seedlings in B, the clinostat removes the effect of unilateral light, since it
is rotating slowly and uniformly. All the sides of the seedlings get uniform light.
So they grow straight up without curving towards light.
• Seedlings in C grows tall, looking for light ,which they are not getting. Leaves are
yellow and plants are slender due to absence of light.
Method
• Add some damp cotton wool to two
petri dishes
• Place 3 bean seedlings in the cotton
wool in each petri dish
• A – radicle facing downwards
• B – horizontally
• C – radicle (root grows from here)
facing upwards
• Cover each dish with a lid
• Attach one petri dish to a support so
that it’s on its side
• Attach the second petri dish to a
clinostat.
• Place both in a light-proof boxes (so
that the seedlings are in complete
darkness), leave for two days and then
observe the growth of the seedlings
Investigating Gravitropism
Investigating
Gravitropism
• In the first petri dish all radicles (roots) have grown downwards (positive
gravitropic response) regardless of which way they were initially facing
(horizontal, up or down) and all plumules (shoots) have grown
upwards (negative gravitropic response).
• In the second petri dish, all radicles and all plumules have all
grown neither up nor down but straight outwards in whichever direction
they were placed as the effect of gravity has been cancelled out by the
revolving of the clinostat – they have shown no gravitropic response at
all.
• The experiment needs to be done in a lightproof box in order to cancel
out the effect of light on the growth of the seedlings.
Observations
• In setup A all the radicles have
grown downwards and all
plumules have grown upwards
irrespective of the initial way
it was kept.
• In setup B ,all radicles and
plumules have grown
according to whatever the
direction they were kept.
The role of Auxin
• Plants produce plant growth regulators (similar to hormones in animals)
called auxins to coordinate and control directional growth responses
such as phototropisms and geotropisms.
• Auxins are produced in the tips of the shoots and the roots; they diffuse
to the cells below the tips and have the following effects:
• In the shoots, auxins promote cell elongation (growth); more auxin =
more cell elongation = more growth
• In the roots, auxins inhibit cell elongation (growth); more auxin = less
cell elongation =less growth
• The distribution of auxin in the shoots is affected by light and gravity,
whereas the distribution in the roots is primarily affected by gravity
alone.
The role of Auxin
• If a shoot or root is placed on its side, auxins will accumulate
along the lower side as a result of gravity; so the uppermost side
has a lower auxin concentration.
• In the shoots, the lower side grows faster than upper side (more
auxin = more cell elongation), so the shoot grows upwards
• In the roots, the lower side grows slower than the upper side (as
auxin inhibits cell elongation and growth in roots), so the root
grows downwards .
• Unequal distributions of auxin cause unequal growth rates in
plant roots and shoots
The difference in the geotropic response of roots and shoots
results from their different
sensitivities to auxin
How Plants bend towards light
The role of Auxin in phototropism
• If light shines all around the tip, auxin is
distributed evenly throughout and the cells in
the meristem grow at the same rate – this is
what normally happens with plants growing
outside.
• When light shines on the shoot predominantly
from one side though, the auxin produced in the
tip concentrates on the shaded side, making
the cells on that side elongate and grow faster
than the cells on the sunny side.
* This unequal growth on either side
of the
shoot causes the shoot to bend and grow in the
direction of the light.
Structure & Role of the
Mammalian Nervous System
Mammalian Nervous System
2j
• The human nervous system consists of the:
• central nervous system (CNS) - the brain and the spinal cord
• peripheral nervous system (PNS) - all of the nerves in the body
• It allows us to
• Make sense of our surroundings and respond to them
• Coordinate and regulate body functions
• Information is sent through the nervous system as nerve impulses electrical signals that pass along nerve cells known as neurones
• A bundle of neurones is known as a nerve
Adaptations of Neurones
• Neurones have a cell body (where the nucleus and main organelles are found) and cytoplasmic extensions
from this body called axons and dendrites.
• The axon is the main long fibre of the neurone.
• Some human neurones have axons over a metre in length (but only 1 - 4 micrometres wide).
• This is far more efficient than having multiple neurones to convey information from the CNS to
effectors – less time is wasted transferring electrical impulses from one cell to another.
• The axon is insulated by a fatty myelin sheath with small uninsulated sections along its length
(called nodes).
• This means that the electrical impulse does not travel down the whole axon, but jumps from one node
to the next.
• Many extensions called dendrites extend out from the cell body of the neurone and at the far end of the
axon.
• This means neurones can connect to many other neurones and receive impulses from them, forming
a network for easy communication
The structure of a myelinated neurone
Types of neurones
• There are three main types of neurones: sensory neurones, relay neurones and motor
neurons.
1.
Sensory neurones carry impulses from sense organs to the CNS (brain or spinal
cord).
2.
Relay neurones are found inside the CNS and connect sensory and motor
neurons.
3.
Motor neurones carry impulses from the CNS to effectors (muscles or glands).
• Sensory neurones are long and have a cell body
branching off the middle of the axon.
• Relay neurones are short and have a small cell body
at one end with many dendrites branching off it.
• Motor neurones are long and have a large cell body
at one end with long dendrites branching off it.
The Human Nervous System: Function
• The pathway through the nervous system;
• stimulus → Receptor→ sensory neurone → coordinator/relay neurone → motor neurone
→ effector → response
• First, a stimulus is received by a sensory (receptor) neurone.
From stimulus to response:
an example of a nerve
pathway showing how an
electrical impulse travels
through sensory, relay and
motor neurones
• Most receptors are specialised to detect particular stimuli.
• When a receptor is stimulated, it produces electrical impulses.
• These impulses then travel along a sensory neurone to the central nervous system (the
coordinator is either the brain or the spinal cord).
• In the CNS, the impulses are passed on to a relay neurone.
• The relay neurone links to a motor neurone, along which the impulses travel until they reach
the effector.
• The effector is what carries out the response (the effector may be a muscle or gland).
Voluntary Vs involuntary responses
1. A voluntary response is where you make a conscious
decision to carry out a particular action.
2. Therefore, it starts with your brain.
Ex: picking up a cup of coffee.
3. An involuntary/ reflex response does not involve the brain not undern conscious control.
4. Involuntary actions are usually protective.
5. Voluntary responses are usually slow while reflex actions are
rapid.
6. Reflex actions are automatic.
The reflex arc
• A reflex arc is the pathway of a reflex response (specifically, the pathway taken by electrical impulses as they travel
along neurones).
• An example of a reflex response is the pain-withdrawal reflex that occurs when someone steps on a pin.
• The reflex arc for this response is outlined below:
1.
2.
3.
4.
5.
6.
7.
The pin (the stimulus) is detected by a (pain/pressure/touch) receptor in the skin
on the person's foot.
A sensory neurone sends electrical impulses to the spinal cord (the coordinator).
An electrical impulse is passed to a relay neurone in the spinal cord (part of
the CNS).
A relay neurone synapses with a motor neurone.
A motor neurone carries an impulse to a muscle in the leg (the effector).
When stimulated by the motor neurone, the muscle will contract and pull the foot
up and away from the sharp object (the response)
This all occurs within a fraction of a second.
Example of a reflex arc- Withdrawing the hand from a hot object
Reflex Arc
• A reflex action
follows this
general
sequence and
does not
involve the
conscious part
of the brain.
This is why the
response is so
fast.
Reflex Arc of moving your hand away from a hot object
Withdrawing the hand away from a sharp object
Example of a reflex arc- Withdrawing the hand from a hot object
• Receptor in the skin detects a stimulus (the change in temperature).
• Sensory neuron sends electrical impulses to a relay neuron, which is
located in the spinal cord. Relay neurons connect sensory neurons to
motor neurons.
• Motor neuron sends electrical impulses to an effector.
• Effector produces a response (muscle contracts to move hand away).
• Receptors In hand → Sensory Neuron→ Spinal cord→ Relay
Neuron→ Motor Neuron→ Muscle in upper arm/Biceps→
contraction of biceps/withdrawing the hand
Reflex Arc of moving your hand away from painful object
Differences between Voluntary/conscious/ actions and Involuntary/reflex actions
The neurones of the reflex arc
• There are three main types of neurone in a reflex arc: sensory, relay
and motor.
• Sensory neurones carry impulses from sense organs to the CNS (brain or
spinal cord).
• Relay neurones are found inside the CNS and connect sensory and motor
neurons.
• Motor neurones carry impulses from the CNS to effectors (muscles or
glands).
SYNAPSE
1. Neurones do not touch each other.
2. The gap between two neurones is called a synapse (synaptic
cleft).
3. The chemical molecules that diffuses across this gap are
called neurotransmitters.
4. Once these neurotransmitters cross the synaptic cleft and
meet the neurone on the opposite side, this chemical signal
is converted back into an electrical impulse.
5. This impulse moves along the next neurone.
Voluntary Action
Involuntary Action
Involves the brain
Doesn’t involve the brain most of the time
Takes more time
Takes very less time
For the same stimulus, the response may vary
For the same stimulus the response is the same
The effector is a muscle.
The effector is a muscle or a gland.
Voluntary movements according to our will.
Involuntary movements not according to our will.
Voluntary movements occur when needed and are under
our control
Involuntary movements occur continuously and are not
under our control
e.g. eating, walking reading
e.g. Breathing, heartbeat, digestion
How an impulse is passed across a synapse
• The electrical impulse travels along the first axon (of the first neurone, known as the presynaptic neurone).
• This triggers the end of the presynaptic neurone to release chemical messengers called neurotransmitters from vesicles.
• These vesicles fuse with the presynaptic membrane, releasing their contents into the synaptic cleft.
• The neurotransmitters diffuse across the synaptic cleft and bind with receptor molecules on the membrane of the
second neurone (known as the postsynaptic membrane).
• This stimulates the second neurone to generate an electrical impulse (which then travels down the second axon).
• The neurotransmitters are then destroyed to prevent continued stimulation of the second neurone (otherwise the
neurotransmitters would cause repeated impulses to be sent).
• Synapses ensure that impulses only travel in one direction, avoiding the confusion that would be caused within the
nervous system if impulses were able to travel in both directions.