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Section 6 - Organisms respond to changes in their environments - Coggle…
Section 6 - Organisms respond to changes in their environments
14 Response to stimuli
Internal and external stimuli
Receptors
Pacinian corpuscle
Layers of connective tissue surrounding a neurone ending
Specific to detecting mechanical pressure
Converts mechanical energy into a generator potential
Stretch-mediated sodium channels are deformed when pressure is applied
Influx of sodium ions depolarises the membrane of the neurone
Rods and cones in retina
Distribution in retina (periphery and fovea)
Cone cells are sensitive to wavelength and colour
Retinal convergence with rods
Different light sensitives
Visual activity
Heart rate
Myogenic - contraction is initiated from within heart itself
Sino-atrial node
Electrical wave is transmitted throughout heart
Autonomic nervous system
Parasympathetic - decreases heart rate
Sympathetic - increases heart rate
Chemoreceptors and baroreceptors
CO2, pH, and pressure changes
External stimuli
Responses
Motile organisms
Kinesis
Change in speed of movement or rate of turning
Taxis
Movement (not growth) of an organism in response to a stimulus
Increases chance of survival
Three neurone reflex
Stimulus - receptor - sensory neurone - intermediate neurone - motor neurone - effector - response
Plants
IAA, an auxin, controls plant cell elongation
Gravitropism
Negative gravitropism in shoots - grow away from force of gravity
Positive gravitropism in roots
IAA is produced in tip of root an moves to the lower side of the root
IAA inhibits cell elongation in roots
Phototropism
Negative phototropism in roots
IAA synthesised in the tip moves down to the shaded side of the shoot
Shoots grow and bend towards light - positive phototropism
Stimulus - a change that is detected and leads to a response
15 Nervous coordination and muscles
Nervous coordination
Nerve impulses
Action potential
Stimulus opens voltage-gated sodium channels
Influx of sodium ions cause depolarisation of axon, which reaches a threshold
All-or-nothing principle
Action potential - wave of depolarisation
At +40mV, sodium channels close and potassium channels open
Repolarisation
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Resting membrane potential
Around - 65mV, in a polarised state
Sodium-potassium pump in axon membrane
3 sodium ions out, 2 potassium ions in
Protein channels allow ions to diffuse in and out
Membrane is more permeable to K+ ions, so some K+ ions diffuse back out
Neuron = nerve cell
Structure
Schwann cells
Cell body
Dendrites - carry nerve impulses towards cell body
Axon - single fibre that carries impulses away from cell body
Axons can be myelinated
Myelin sheath and nodes of Ranvier between
Adapted to carry rapid nerve impulses
Synaptic transmission
Synapse
Neuromuscular junction - between motor neurone and muscle end plate
Junction between 2 neurons
Inhibitory synapses
Chloride ion enter postsynaptic neurone
Hyperpolarisation
Summation
Spatial - multiple presynaptic neurones
Temporal - one presynaptic neurone firing many times
Undirectionality
Always from presynaptic neurone to postsynaptic neurone
Skeletal muscle
Muscle fibres
Fast twitch
e.g. bicep
Thicker myosin filaments
Glycogen
Strong, fast contractions for a short period of time
Phosphocreatine to generate ATP rapidly
Slow twitch
Calf and back muscles
Slow, sustained contractions
Store of myoglobin to provide oxygen
Aerobic respiration
Mitochondria
Muscle contraction
Sliding filament mechanism
Sarcomeres shorten
Neuromuscular junction
Motor unit = group of muscle fibres supplied by a single motor neurone
Action potential enters T-tubules
Release of calcium ions into sarcoplasm
Calcium binds to tropomyosin
Uncovers actin binding sites
Myosin heads bind to actin
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Structure
Sarcomere - unit of muscle
Myofibrils consist of sarcomeres
Z-line - boundary of sarcomere
Muscle contains bundles of muscle fibres
Skeletal muscle is responsible for voluntary movement of the skeleton
Sarcoplasm around muscle fubres
Contains mitochondria and endoplasmic reticulum
Muscle fibres contain many myofibrils
Actin (thin) and myosin (thick) protein filaments
I-band - length of actin filament
Lighter than the A-band
A-band - length of myosin filament
Darker due to overlap of filaments
H-zone - in the centre of the A-band
Myosin heads
16 Homeostasis
Homeostasis
Homeostasis
Maintaining an internal environment within set limits
Temperature
Detected by hypothalamus
Too hot - vasodilation, sweating, seeking shade
Too cold - shivering, vasoconstriction, raising hairs on skin
Need to control to maintain enzyme activity
pH
Need to control to maintain enzyme activity
Changes in water potential in blood and cells can lead to shrinkage or bursting
Negative feedback
Positive feeback
The change detected leads to a further deviation away from the normal value
The change detected leads to a reduction in the stimulus, turning the system off or restoring to original level
Example - control of blood glucose
Blood glucose
Liver
Glycogenesis
Gluconeogenesis
Glycogenolysis
Insulin
Regulates channel proteins and glucose uptake in cells
Pancreas
Activates enzymes to convert glucose into glycogen
Decreases blood glucose concentration
Glucagon
Activates enzymes to convert amino acids and glycerol into glucose
Increases blood glucose concentration
Activates enzymes to convert glycogen into glucose
Adrenaline
Second-messenger model of hormone action
Diabetes
Type 1 and type 2
Insulin-dependent or insulin independent
Blood glucose is controlled to ensure the cells have enough respiratory substrates
Osmoregulation
Kidney
Cortex and medulla
Water potential of blood detected in hypothalamus
Nephron = functional unit of kidney
Glomerular filtrate - forms in Bowman's capsule
Glucose and water are reabsorbed in the proximal convoluted tubule
Loop of Henle - maintenance of sodium ion gradient
Counter-current multiplier
Water is reabsorbed in the distal convoluted tubule and collecting duct
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