6.1 stimulus and response

What is meant by phototropism

Directional growth in response to light

what is meant by gravitropism

Directional growth in response to gravity

what is mean by positive and negative tropisms

are directional growths towards(positive) or away(negative) a stimulus

where is IAA produced

IAA is produced in the tops of the roots and shoots

effects of different IAA concentrations on root growth

inhibits growth

effects of different IAA concentrations on shoot growth

causes cell elongation and promotes growth

How does IAA cause positive phototropism in shoots

IAA is produced in the tip of the shoot and is transported evenly down the plant

Light causes movement of IAA

IAA diffuses to the shady part of the shoot increasing concentration

Promotes cell elongation and growth on this side

Shoot bends to the light

How does IAA cause positive gravitropism in roots

Cells in the top of the roots Produce IAA and transported evenly

Gravity influences movement of IAA from the upper side of the root to the lower side of the root

Greater concentration on the lower side

IAA inhibits elongation on the lower side then the upper side

causes root to bend downwards

how does IAA cause positive gravitropism in shoots

Greater concentration of IAA on lower side increases cell elongation

Causes side to elongate more than the upper side

Shoot grows upwards away from the force of gravity

What is meant by taxis

A directional response to a stimulus

What is meant by kinesis

When an organism changes the speed and rate it changes direction in to find a more favourable environment

Role of reflexes and why they are important

Reflexes are rapid involuntary responses

Produce against damage

Enable homeostatic control

Enable escape from predators

Role of sensory, intermediate and motor neurones in a reflex arc

simple reflex arcs only involve 3 neurones this limits number of synapse

sensory neurones carry electrical nerve impulses from the receptor to the central nervous system

intermediate neurones synapse with the sensory neurone and then with a motor neurone

features of a sensory reception which are common to all receptors

respond to one type of stimulus

acts as a transducer creating a generator potential

receptors in nervous system convert the energy of the stimulus into a nervous impulse known as a generator potential

structure of the Pacinian corpuscle

single sensory neurone is at the centre of layers of tissue called lamellae each separated by a gel

a capsule surrounds the layers

the sensory neurone at the centre has a stretch mediated sodium channel in its membrane

what stimulus does the Pacinian corpuscle respond to

mechanical stimuli such as pressure

how does the Pacinian corpuscle produce a generator potential in response to a specific stimulus

increased pressure deforms lamella

deforms stretch mediated sodium ion channels in the membrane

sodium ion channels open

sodium ions diffuse in

causes inside of the neutron to be more positive called depolarisation

a generator potential is produced

pigment in rod cells and what they’re sensitive to

rhodospin-sensetive to low light intensity

pigment in cone cells and what theyre sensetive to

iodosin- not sensetive to low light intensity

why do rod cells have low visual acuity

a number of rod cells ae connected to a single bipolar neurone

why do rod cells have a sensitivity to light

rhodopsin can be broken down in low light intensity

why do rod cells only create images in black and white

rhodopsin cannot distinguish between different wavelengths as its broken down by all wavelengths

why do cone cells have high visual acuity

each cone cell is connected to a singular bipolar neurone

why are cone cells not sensitive to light

iodopsin can only be broken down in bright light

stimulation cannot be combined to reach threshold

why are cone cells sensitive to colour

three types of cone cells with different types of iodopsin

each type of iodopsin is sensitive to different wavelengths of light

role of the medulla oblongata

contains the cardio regulatory centre which consists of two parts

the acceleratory centre responsible for speeding up heart rate and the inhibitory centre responsible for slowing down the heartbeat

what is meant by sympathetic nervous system

activating the acceletory centre in the medulla sends impulses along the sympathetic nervous system this system initiates a fight or flight response

what is meant by parasympathetic nervous system

activating the inhibitory centre in the medulla sends impulses along the parasympathetic nervous system this system helps your body to relax

events which take place which produce an electrical wave to cause your heart to beat

SAN sends out regular electrical waves across atria

causes atria to contract

non conducting tissue between the atria and ventricle prevents impulses from passing from walls of atria to ventricles

this delay ensures atria empty of blood before ventricles contract

AVN detects electrical activity in the atria and after the delay sends out electrical waves down the bundle of his to the apex of the ventricle

impulses travel up the smaller purkyne fibres and ventricles contract from the apex upwards

Explain the roles of SAN

the sequence of muscle contraction is initiated by the SAN, it sends out regular waves of electrical activity across the atria

Explain the roles of AVN

the AVN after a short delay begins electrical activity in tissues called purkyne tissue to cause contraction of ventricles

Explain the role of bundle of his

Purkyne tissue is initially grouped together in a structure called the bundle of his and then branches into smaller fibres. This conducts electrical activity down the wall between the ventricles and the upwards from the base this ensures that it contract from the bottom of the ventricle upwards.

what does it mean if the heart is myogenic

The heart can contract without any nervous stimulation

Location and the role played by chemoreceptors

Detects changes in CO2 that occur after changes to respiration rate

found in the aorta close to the heart and the carotid arteries

location and the role played by pressure receptors

Detect changes in pressure

found in the aorta close to the heart and the carotid arteries

the role of autonomic nervous system in controlling heart rate(sympathetic)

increased respiration in cells increases CO2 and so causes a fall in PH

detected by chemoreceptors

sends impulses to the CNC in the medulla

acceleratory centre in the medulla sends more impulses to SAN by sympathetic nervous system

at the synapse with the SAN a neuro transmitter in released which causes increase frequency of impulses sent out by SAN across atria

the role of autonomic nervous system in controlling heart rate(parasympathetic)

decreased respiration in cells decreased CO2 concentration in blood

detected by chemoreceptors

send less impulses to the CNC in the medulla

Inhibitory Centre in the medulla sends more impulses to SAN by parasympathetic nervous system

at the synapse with the SAN a neurotransmitter in released which causes decrease in frequency of impulses sent out by SAN across the atria