responses to stimuli

what are plant growth factors and where are they produced

-chemicals that regulate plant growth response to directional stimuli
-produced in plant growing regions (apical meristems)
-diffuse from cell to cell/ phloem mass transport

explain why shoots show positive phototropism

1- indoleactic acid diffuses to shaded side of shoot top
2- as IAA diffuses down shaded side, it causes active transport of H+ ions into cell wall
3- Disruption to H-bonds between cellulose molecules and action of expansins make cell more permeable to water
4- cells on shaded side elongate faster due to higher turgor pressure
5- shoot bends towards right

explain why roots show positive gravitotropism

1- gravity causes IAA to accumulate on lower side of the root
2- IAA inhibits elongation of root cells
3- cells on the upper side of the root elongate faster, so the root tip bends downwards

differences between mammalian hormones and plant growth factors

CASTS

define taxis and kinesis, state their advantages

taxis- directional movement in response to external stimulus
kinesis- non-directional response to presence and intensity of external stimulus
-maintain mobile organism in optimum environment

many organisms respond to temperature and humidity via kinesis rather than taxis, why?

less directional stimuli- often no clear gradient from one extreme to another

how could a student recognise kinesis in an organism’s movement

1- organism crosses sharp division between favourable and unfavourable environment: turning increases (return to the original favourable environment

2- if organism moves considerable distance into unfavourable environment: turning slowly decreases, begins to move in long, straight lines, sharper turns lead organism to new environment

outline what happens in a simple reflex arc

receptor detects stimulus, sensory neuron, relay neuron in CNS coordinates response, motor neuron, response by effector

give the advantages of a simple reflex

-rapid response to potentially dangerous stimuli since only 3 neurons involved
-instinctive

what features are common to all sensory receptors

-act as energy transducers which establish a generator potential
-respond to specific stimuli

describe the basic structure of a pacinian corpuscle

-single nerve fibre surrounded by layers of connective tissue which are separated by viscous gel and contained by a capsule
-stretch-mediated Na+ channels on plasma membrane
-capillary runs along base layer of tissue

what stimulus does a pacinian corpuscle respond to, how?

1- pressure deforms membrane, causing stretch-mediated Na + ion channels to open
2- if influx of Na+ raises membrane to threshold potential, a generator potential is produced
3- action potential moves along sensory neuron

name two types of photoreceptor cell located in the retina

cone cells, rod cells

where are rod and cone cells located in the retina

rod- evenly distributed around periphery but not in central fovea
cone- mainly central fovea no photoreceptos at blind spot

compare and contract rod and cone cells

Pigment, visual actuity, colour sensitivity, light sensitivity

outline pathway of light from a photoreceptor to the brain

photoreceptor, bipolar neuron, ganglion cell of optic nerve, brain

define myogenic

contraction of heart is initiated within the muscle itself rather than by nerve impulses

state the name and location of the two nodes involved in heart contraction

sinoatrial node, within the wall of the right atrium

atrioventricular node, near lower end of right atrium in the wall that separates the two atria

describe how heartbeats are initiated and coordinated

-SAN initiates wave of depolarisation
-WOD spread across both atria is atrial systole
-layer of fibrous, non-conducting tissue delays impulse while ventricles fill and valves close
-AVN conveys WOD down septum via bundle of his, which branches into purkinje fibres along ventricles
-causes ventricles to contract from apex upwards

state formula for cardiac output

cardiac outpit= stroke volume x heart rate

what is the autonomic nervous system

-system that controls involuntary actions of glands and muscles
-2 subdivisions, sympathetic and parasympathetic

state the difference between the sympathetic and parasympathetic nervous system

sympathetic involved in fight or flight response, stimulates effectors to speed up activity
parasympathetic involved in normal resting conditions- inhibits effectors to slow down activity

name the receptors involved in changing heart rate