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What is a stimulus?
A detectable change in the internal or external environment of the organism which produces a response
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Why a response?
To increase chance of survival
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How is the survival chance increased?
Greater chance of having and raising offspring and of passing on their successful alleles to the next generation. SELECTION PRESSURE
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Directional movement
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Non-directional movement - based on the number of turns/rate of movement
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Growth movement of part of a plant in response to a directional stimulus e.g. light. Can be either positive or negative.
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Moving towards/away from light
Positive/Negative phototropism. Positive - for gaining more light for photosynthesis
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Moving towards/away from gravity
Positive/negative geotropism. Negative - roots growing downwards
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Growth hormone, produced in shoot/root tips. Diffuses from tip to other tissues for growth
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What are the 4 steps of shoot growth?
1) Auxin produced in shoot tip 2) Diffuses down the shaded side 3) High % of auxin on shaded side, causes rapid cell growth 4) Cells elongate and the shoot bends towards the light
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What are the 4 steps of root growth?
1) Auxin is produced in root tip 2) Auxin diffuses down the shaded side 3)Inhibits cell growth 4)Side exposed to light, grows faster thus bends away from light
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What does the effect of auxin depend on?
The concentration of auxin present in the region
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What are the 3 main types of neurone?
Sensory, motor and relay
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Conducts the nerve impluse
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Myelin sheath
Made of lipid and surrounds the axon. it is formed from schwaan cells and provides electrical insulation
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Nodes of ranvier
Gaps in the myelin sheath along the axon, allow the impulse to jump along rather than travel the entire distance of the axon
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Sensory Neurone - structure
Myelinated, cell body bulges out of the centre
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Relay Neurone - structure
Situated in the CNS. No myelination, cell body is in the centre
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Motor Neurone - structure
Myelinated, cell body is at the end of the axon.
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What is the reflex arc?
Stimulus > Sensory organ > Sensory Neurone > Relay neurone > Motor neurone > Effector (muscle or gland)
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Nervous responses are ... (3 things)
Rapid, short lived and localised
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5 Advantages of reflexes
1) Avoid damage 2)Rapid, only utilise 3 neurones 3)Rapid evasion from predators 4)Doesn't involve conscious thinking 5)Automatic control of homeostasis
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Endocrine system -
Release of hormones
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Hormones affect ...
widespread physiological effect and is slower
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How do hormones travel, and where to?
In the blood stream to target cells which have complementary receptors
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Peptide hormones
Protein based, such as insulin. Receptors are outside cell membrane, cannot pass through. ACTIVATE ENZYMES through a 2nd messenger system
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Steroid hormones
Lipid based, such as oestrogen. Receptors are inside cell membrane, pass through. ACTIVATE GENES
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Local chemical mediators affect...
Immediate vicinity and have a quicker response
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Name two local chemical mediators and their roles
1)Histamine - released upon allergy or injury. Increased permeability of blood capillaries so white blood cells can move out this causes inflammation. 2)Prostaglandins - cause inflammatory response
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Resting potential of an AXON
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Action Potential of an AXON
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Two ways in which the RESTING POTENTIAL is maintained -
1) Na-K pump using active transport. 3NA+ OUT AND 2K+ IN. 2)Membrane is more permeable to the LOSS of POTASSIUM
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1) Sodium channels open 2) Na+ diffuses IN 3) More Na+ channels open 4)Membrane becomes more positive 5)Membrane is depolarised
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1)Sodium channels close 2) Potassium channels open 3)K+ ions diffuse OUT 4)Membrane becomes negative
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What is propagation of a nerve impulse?
One area of the axon is depolarised, this stimulates the sodium channels to open in the next area of the axon and so on
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What is the refractory period and why is it important?
Time between impulses where nerve impulses are now being produced. It allows the production of DISCRETE impulses - NO OVERLAPPING AND IN ONE DIRECTION
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What is the all or nothing principle?
Stimulus must be above THRESHOLD for an impulse to be generated - the stronger the stimulus the greater frequency of impulses.
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3 Factors effecting nerve impulses (explain)
1) Temperature 2)Myelination/Saltatory conduction 3)Axon diameter
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Receptor, found in the skin. Responds to changes in mechanical pressure - STRETCHES UNDER PRESSURE OPENING STRETCH MEDIATED SODIUM CHANNELS
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Name two photoreceptors in the eye and explain their roles -
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High visual sensitivity - stimulated by dim light, 3 per bipolar neurone, none in the fovea. Spatial summation, additive effect and convergence
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High visual acuity, 1 per 1 bipolar neurone, no convergence and no summation. One impulse per cone.
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Explain the mechanism of transmission across a synapse using these points-
1)Action potential arrives 2)Calcium channels 3)Vesicles 4)Neurotransmitter and receptors 5)EPSP's 6)Depolarisation of post synaptic membrane 7)Neurotransmitter is broken down 8)Components of neurotransmitter
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What is an IPSP
Inhibitory post synaptic potential - caused by Cl- ions which cause hyper-polarisation of the membrane making it less likely for an action potential to be achieved
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Two areas in the medulla which control heart rate
1)cardioacceleratory centre(SYMPATHETIC) 2)Cardioinhibitory centre(PARASYMPATHETIC)
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Increasing heart rate - SYMPATHETIC
1)Exercise increase and CO2 levels increase 2)CHEMORECEPTORS in the atria 3)Impulse sensory neurone to the cardioacceleratory 4)Impulse to SAN via motor neurone 5)Noradrenaline SAN 6)increases heart rate, blood flow, decreased CO2, normal
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decreasing heart rate - PARASYMPATHETIC
1)Pressure up in blood vessels 2)BARRO RECEPTORS 3)Impulse sensory neurone to cardioinhibitory 4)Motor neurones to SAN 5)Acetylcholine 6)slow heart rate
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Why a response?


To increase chance of survival

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How is the survival chance increased?


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