Clear and concise Cornell styled notes for Unit 6 Biology A Level - Organisms respond to changes in their internal and external environments. The notes include diagrams and colours to make revision more visually appealing. The whole course is covered by my notes and is written in a detailed way tha...
Responses in Plant & Animals Eve Holland
Key Points: Notes:
Stimuli:
Changed to the environment = stimuli
- All organisms need to respond to changes in the environment
(stimuli) in order to survive
Organism detract changes in both - Organisms can detect changes in:
internal and external environment 1. External environment (e.g. temperature of surroundings).
2. Internal environment (e.g. blood glucose concentration).
Coordinating a response requires:
Timulus, receptor and effectors - Coordinating a response to the environment involves three
components:
1. Stimulus - change in the environment.
Plant responses are called tropisms 2. Receptors - detect the change in the environment.
3. Effectors - initiate the response.
Plants have growth factors called
Plant Responses:
Indoleacetic acid (IAA) a type of auxin
- Tropisms are directional growth responses in plants
which either:
- Plants respond to directional stimuli using specific growth factors,
Stimulates growth in shoots which move to regions where they are needed from growing
Inhibits growth in roots regions
- indoleacetic acid (IAA) is a type of auxin - growth factor in plants, it
IAA is produced in the tips of the causes elongation of shoot cells, while it also inhibits root cell
shoots and diffuses were it needs to elongation
go - IAA is produced in the shoots of the tips and DIFFUSES to where it
needs to go.
Gravitropism is plants response to
gravity, IAA gathers downwards in - Phototropism is growth in response to direction of light:
shoots due to gravity Shoots are positively phototropic - they grow towards light. (IAA DIFFUSES
to shaded side)
Roots are negatively phototropic - they grow away from light.
Phototropism is plants response to
light, IAA gathers in shaded side - Phototropism is growth in response to direction of light:
Shoots are positively phototropic - they grow towards light.
Roots are negatively phototropic - they grow away from light. (IAA
There are 2 types of animal DIFFUSES to base side)
responses;: taxes and kinesis
Animal responses :
Taxes is a response that requires There are two ways in which simple animals respond:
movement in a specific direction Taxes (tactic response) Kinesis (kinetic movement response)
The stimulus is positively or The stimulus is non-directional, e.g.
Kinesis is a response that involve negatively directional, e.g. light. humidity. E.g. Woodlice move more
movement but in random directions E.g. Woodlice move away from light slowly and turn less in high humidity
Summary:
, Reflexes & receptors Eve Holland
Key Points: Notes:
Reflexes = automatic response Reflexes:
- Reflexes are an automatic response to a stimulus
- Reflexes are good because they are:
They are quick and automatic so thus 1. Quick
are better at helping avoid harm 2. Automatic
This is good because they often help an organism respond quickly to a harmful
Reflex arcs involve 3 neuron, sensory, stimulus, e.g. heat.and the information is not processed in the brain and no
relay and motor decision is made about the response.
Reflex Arcs:
How a reflex arc works: - The pathway of neurons involved in a reflex response is called a reflex arc
1. Receptor - There are 3 types of neurons in a reflex arc:
2. Sensory neuron 1. Sensory
3. Relay neuron 2. Relay
4. Motor neuron 3. Motor
5. Effector (muscle or gland) Example of how a reflex arc works - touching a hot surface
1. Thermoreceptors in the skin detect the heat stimuli
2. Sensory neuron send impulse from thermoreceptors to relay neuron
3. Relay neuron send impulses to motor neuron
Receptors 2 important features 4. Motor neuron sends impulses to effectors in the arm (muscles)
1. Stimuli specific
Receptors:
2. Can create a generator - Receptors have 2 important features
potential Specificity: receptors only respond to specific stimuli e.g light, temperature and
pressure. This also means that a light receptor will NOT respond to changes in
Pacinian corpuscle = temperature
mechanoreceptor in skin that detects Generator Potentials: receptors connect with sensory neurons and when
stimulated the receptor creates a generator potential in the sensory neurons e.g
pressure changes parcipian corpuscule
They work by: Pacinian Corpuscle:
1. pressure on connective tissue - The pacinian corpuscle is a mechanoreceptor found in the skin which
2. Push on sensory neuron respond to changes in pressure
- It is made from rings of connective tissue around a sensory neuron.
3. Stretch mediated Na+ ion
- When non stimulated its in resting state (-70mV) and is more negative
channels inside the neuron than outside because there are more Na+ outside
4. Sensory neuron becomes more
positive than outside - When a pressure stimuli is applied the rings press on the sensory neuron
5. Generator potential reached and push open the stretch mediated Na+ channels
6. Voltage gated Na+ ion channels - Na+ flood into the sensory neuron so charge inside sensory neuron is
more positive than the outside so a generator potential occurs
open and action potential is - If generator potential reaches the threshold (-50mV) then an action
reached potential happens
Summary:
, The Human Retina Eve Holland
Key Points: Notes:
Light passes through: The Eye:
1. Cornea Step 1: Light enters the eye through the cornea. ...
Step 2: The pupil adjusts in response to the light. ...
2. Pupil Step 3: The lens focuses the light onto the retina. ...
3. Retina Step 4: The light is focused onto the retina. ...
4. Receptors Step 5: The optic nerve transmits visual information to the brain.
5. Optic nerve → brain
- There are 2 types of receptors in the eye: rods and cones
Rods:
Rods: - Highly sensitive to light
- Very light sensitive - Low visual acuity (ability to distinguish between close objects)
- Black and white - There are lots of rod cells, evenly distributed along the retina however
- Low visual acuity not on the fovea
- Everywhere by fovea - Rod cells contain a pigment called rhodopsin which detects light and dark
thus gives a monochromatic image (only detect one wavelength of light)
- Contain rhodopsin - SEVERAL rod cells synapse with a singular bipolar neuron thus spatial
- Sever rods per 1 bipolar summation can happen where the combined stimulation of multiple rods
(spatial summation → retinal can cause the action potential. (retinal convergence)
convergence)
Cones:
- Less sensitive to light
Cones:
- High visual acuity (ability to distinguish between close objects)
- Less light sensitive - Fewer cone cells and mainly distributed on one point on the retina (fovea)
- Colours - Cone cells use iodopsin pigment which detects colour
- Higher visual acuity - Cone cells are trichromatic which means they are divided into 3 types
- Concentrated on fovea which each respond to a different wavelength of colour: red, blue, green
- Single cone per 1 bipolar - SINGULAR cone synapses with a Single bipolar neuron so sufficient light is
needed to stimulate the cone cell
How light causes impulse: Converting Light to Electrical Impulses:
1. Pigment absorbs light Rod and cone cells are a type of photoreceptor, when they detect light a
2. Light absorbed changes generator potential is created and an impulse travels along the neuron
permeability of membrane
- Rhodopsin or iodopsin absorb light
3. Na+ ions flood in and change
- This changes the permeability of their membranes
the charge - Na+ flood into the cell and generator potential is established
4. Generator potential happens - If generator potential reaches the threshold then a nerve impulse flows
5. If threshold reached action down the bipolar neuron
potential happens and impulse
goes to the bipolar neuron → Each photoreceptor synapses with relay neuron (BIPOLAR NEURON), then with a
sensory neuron (GANGLION CELL), then axons of the ganglion cells leave the eye
ganglion cells → ganglion via the optic nerve and send impulses to the brain.
axons → optic nerve → brain
Summary:
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