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Biology: Responding to Change - Coggle Diagram
Biology: Responding to Change
Reflexes
Stimuli
Receptors
Effectors
Internal: Bllood Glucose concentration
External: Temperature
Thermoreceptors
Quick, Automatic and Protective
Brain is not involved
Reflex Arc
The pathway of neurons involved in the reflex are:
Relay
Carries impulse from sensory to the motor neuron
Motor
Carries impulse from the CNS to the effector
Sensory
Carries impulse from receptors to CNS
Plant Responses
Phototropism = the growth in reponse to the direction of light
Shoots = Positive phototropic
If a shoot is exposed to an uneven light source, IAA is transported to the more shaded part. Shaded parts elongate due to IAA. Shoot bends towards the light
Roots = Negatively phototropic
If root is exposed to uneven light source IAA moved to the shaded part. IAA in the shaded part inhibits cell elongation and the root bends away from the light.
Gravitropism = the growth in response to the direction of gravity
Shoots = Negatively gravitropic
If a shoot is exposed to an uneven gravitational pull IAA is transported to the underside. A higher concentration of IAA in the underside causes cells in the underside to elongate. Cell elongation causes the shoot o bend away from the gravitational pull
Roots = Positivley gravitropic
If the root is exposed to uneven gravitational pull IAA is transported to the underside. A higher concentration of IAA prevents cell elongation on the lower side. The root bends towards the gravitational pull.
Indoleacetic Acid (IAA) = a type of auxin that controls response in plants
Distribution
can be transported over short distances by diffusion or active transport, or longer distances through the phloem
When a plant detects a stimuli, IAA is transported to different parts of the plant creating an uneven distribution
Where the distributon of IAA is uneven a directional growth response occurs
Responses in Animals
Tactic Responses (Taxes)
The stimuli is positively or negatively directional e.g. light
Woodlice move away from light: dark environments = safety from predators.
Kinetic Responses (Kineses)
The stimulus is non directional e.g. humidity
Woodlice more slowly and turn less in high humidity but move faster and turn more in low humidity
Neurones/Nerve Cells
Structure
Myelinated or Non Myelinated
Motor Neurons in vertebrates are usually myelinated
Schwann cells are wrapped around the axon of the neurone. These form the myelin sheath
Gaps between adjacent Schwann cells are called nodes of Ranvier
Dendrites - Carries nervous impulses towards a body cell
Axons - carries nervous impulses away from the cell body
Cell Body - Where the nucleus is normally located
Resting Potential
Potential Difference
At resting state there is a difference in change across the neurone membrane: the inside of the neurone is more negativley charged than the outside
There are more positive ions outside the cell than inside
The difference in charge is called potential difference
When a neuron has not been stimulated it is at resting state
Sodium-Potassium Pumps
The resting potential is maintained by sodium-potassium pumps in the neurone membrane
Three Na+ ions are activly transported out of the neurone by the pumps fro every two K+ ions that are transport in
This leads to a build up of positive ions outside the cell
Potassium Ion Channels
There are potassium ion channels in the neurone membrane. This means it is permeable to K+ ions.
When K+ ions are transported into neurones, they can diffuse back out
The neurone membrane is also impermeable to Na+ ions so the ions cannot diffuse back into the cell after they have been transported out
Together the action of sodium-potassium pumps and potassium ion channeld lead to a potetnial difference across the neurone membrane.
This potential difference is called the resting potential = the neurone is polarised.
Resting potential is about -70mV
Both combined = Action Potential
Sodium Ions
When an action potential is generated there are more Na+ ions inside the neurone than outside
Some Na+ ions diffuse sideways along the neurone axon
Sodium ion Channels
The presence of Na+ ion creates a change in potetnial differnce further along the nuerone membrane
if this reaches the threshold value, sodium ion channels at this part of the membrane open
Na+ ions diffuse into the neurone
this part of the neurone now becomes depolarised
Wave of depolarisation
Na+ diffuse all along the neurone in this way
Depolarisation takes place along the neurone membrane. This creates a wave of depolarisation
Refractory period
The period of hyperpolarisation in an action potential is called the refractory period
The ion channels are recovering during the refractory period. This means an action cannpt be stimulated again instantly
This ensured that the wave of depolarisation travels in one direction
Depolarisation of the Neurone Cell Membrane
Stimulation
Na+ ions channels in the cell membrane open when a neuron is stimulated
Na+ ions flood into the neurone
The Potential difference across the membrane changed to become more positive inside the neurone
Depolarisation
If the potential difference increases above the threshold value (about -55mV) then the membrane will become depolarised
More sodium channels open and there is a sharp increase in potential difference to about +30mV
All-or-Nothing
If the threshold is reached the change in potential difference will occur if not nothing will happen.
If the stimulus is stronger, actioon potentials will be produced more frequently but their size will not decrease
Repolarisation
After the neurone membrane has been depolarised to +30mV, the sodium ion channels close and potassium ion channels open.
K+ ions are transported back out of the neurone and the potential difference becomes more negative
Hyperpolarisation
There is a short period after repolarisation of a neurone where the potential difference becomes slightly more negative than the resting potential.
Hyperpolarisation prevents the neurone from being restimulated instantly = the refractory period
After the refractory period the potassium channels close and the membrane reterns to resting potential.