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Summary Topic 6 - Organisms respond to changes - AQA A-level biology $13.54   Add to cart

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Summary Topic 6 - Organisms respond to changes - AQA A-level biology

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  • June 7, 2024
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  • 2023/2024
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Plant Tropisms
organisms respond tochangesintheir environment to increase chanceof survival
Tropism The growth of a floweringplantin response to awediond snnulus

Phototropism response to light

IAA Indoleacetic acid growthfactor typeofauxin madein hpofshoots root


positive phototropism in shoots IAA causes cell elongation

Cells in tip of shootproduce IAA
IAA diffusesdownshootevenly andthenlightcauses it to diffusefromlight toshady
side
Greater conc IAA onshaded side
IAA causes cell elonsation moreelongation onshaded side
shoot grows towards light positivephototropism




Negative phototropism in roots IAAinhibits cellelongation

IAA produced in tipof root
It diffuses into rootevenly andthendiff fromlightside toshadyside
HigherconeIAAinshadedside of root
IAAinhibitscellelongation in roots cellselongatemore on lightside
root grows awayfromlight negativephototropism

, againstgravity
y
Negative Gravotropism in shoots IAA causes cell elongation


cells in tip of shoot produce IAA
IAA diffuserintoshootdeny thengravitycauses diffusiontolowerside
HigherconeIAAon lowerside
IAA causes cen elongation morecellelongation onlower side
shootgrowsupwards negativegravonopism




Positive gravonopism in roots IAA inhibits cell elongation

Cells in lipof root produce IAA
IAA diffuses intorootevenly and thendiffuses to lower side due to gravity
Higher cone IAA on lowerside of root
IAAinhibits cell elongation less onlowerside more onupper side
rootgrowsdownwards positivegravowopism

, Simple responses
Reflex are


Importance advantages

Only 3 neurons rapid
innate not learnt
protects against damage totissues helps
escape from predators
Involuntary

ater




rear


Iigsopogy
Effector
muscleou sad
intermediate




steps

Receptordetectsstimulus
Receptorsends electricalimpulses to spendcord ens via sensory neuron
impulse moves fromsensory synapse intermediates synapses motor
Impulse moves to effector through motor neuron
effectorbringsaboutresponse

, In's reflex
circular
antagonistic

radial


Bright Light pupilconstricts
circular muscles contract
radid musclesrelax


Dimlight pupil dilates
Ciraulo muscles relax
radiomuscles contract

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