Stimuli And Response

Question 1

Phototropism

Answer 1

Cells in tip of shoot produce IAA
IAA travels down shoot and increases in concentration on the shades side
Promotes cell elongation
Causing the shoot to bend towards the light

Question 2

Tropism

Answer 2

The growth of a plant in response to a directional stimulus

Question 3

Positive vs negative responses

Answer 3

Positive- growth/ movement towards

Negative- growth/ movement away

Question 4

Gravitropism

Answer 4

IAA produced by cells in shoot tip 
IAA transported down shoot into root
IAA increases in conc on the lower side of roots
Inhibits cell elongation 
Roots curve downwards towards gravity

Question 5

Define a stimulus

Answer 5

A detectable change in an organism’s environment that leads to a response

Question 6

Importance of a reflex arc

Answer 6

3 neurones, few synapses so rapid
Automatic does not involve the brain, does not have to be learnt
Response able to be carried out quickly, protect against harm

Question 7

Taxes

Answer 7

Directional response ( movement towards or away) made by simple mobile organisms to a stimulus

Question 8

Kineses

Answer 8

Non- directional responses by simple mobile organism to a non- directional stimulus
altering their speed or direction of movement

Question 9

Benefits of taxis/ kinesis

Answer 9

Increases changes of finding a favourable environment to increase chances of survival

Question 10

How a pacinian corpuscle produces a generator potential

Answer 10

Mechanical stimuli deforms lamellae and stretch meditated sodium-ion channels
Opens sodium ion channels
Sodium ions diffuse into sensory neurone, depolarising it
Forming a generator potential
If threshold reached- action potential

Question 11

Rod cells

Answer 11

Black and white vision
One type
Low visual acuity
Highly sensitive to light

Question 12

Where are rod cells found?

Answer 12

Periphery of the retina

None at fovea

Question 13

Why do rod cells have the high sensitivity to light?

Answer 13

Many rod cells are connected to one bipolar neurone
Spatial summation occurs! Many impulses converge to one bipolar neurone
More likely to collectively reach the threshold and cause an action a potential

Question 14

Why do cone cells have high visual acuity?

Answer 14

One cone cell connected to one bipolar neurone
If 2 adjacent cones are stimulated the brain will receive 2 discrete different impulses
Therefore able to distinguish between two different sources of light

Question 15

Resting potential

Answer 15

Sodium potassium pump 
Active transport 
3 NA+ out
2 K+ in
Membrane more permeable to K+
K+ diffuses out via facilitated diffusion down electrochemical gradient 
Polarised

Question 16

Generation of an action potential

Answer 16

Stimulus detected,
Membrane becomes more permeable to NA+, NA+ channels open
NA+ diffuse in down electrochemical gradient through facilitated diffusion
Depolarised
If pd threshold reached, action potential generated
Voltage gated NA+ channels open
Influx of NA+ into axon
Then voltage gated K+ channels open, membrane becomes more permeable to K+, NA+ begin to shut
K+ diffuse out of axon
Repolarised, becoming more negative
Hyper polarisation occurs as K+ channels are slow to close, so slight overshoot in number of K+ that leave
Refractory period- during which non action p can be gen ( uni, discrete impulses)
Restring potential then restored by sodium-potassium pump

Question 17

Effect of myelination

Answer 17

Faster nervous transmission as depolarisation only has to occur at nodes of ranvier
Saltatory conduction, impulses jump
Depolarisation does not need to occur across the whole length of the axon

Question 18

Cone cells

Answer 18

Coloured vision 
3 types, dependant on wavelength of light 
Low sensitivity 
High visual acuity 
One cone to one bipolar neurone 
Found at fovea

Question 19

Where are rods distributed?

Answer 19

Periphery of retina, except fovea and blind spot

Question 20

Where are cones found?

Answer 20

High concentration around fovea

Question 21

How is resting heart rate maintained

Answer 21

Cardiac muscle myogenic
SAN acts as a pacemaker and sends out regular waves of impulses
Impulse reached SAN, causes atria to contract simultaneously
Impulse travels to AVN
Impulse is delayed
Impulses travel down bundles of his and purkyne fibres
Ventricles contract from the bottom upwards

Question 22

Where in the brain is in charge of controlling heart rate?

Answer 22

Medulla, cardio-vascular centre

Question 23

Role of sympathetic neurones

Answer 23

Increase frequency of impulses sense to SAN

When bp is too low / CO2 con too high

Question 24

How bp is increased

Answer 24

Low bp detected by baroreceptors in the aorta
More freq impulses sent to medulla
More freq impulses sent to SAN via sympathetic neurones
More frequent impulses sent from SAN
Cardiac muscle contracts more frequently

Question 25

Response to high blood ph ( low CO2)

Answer 25

Chemoreceptors in Aorta detect
Increased frequency of impulses sent to medulla
Increased frequency of impulses sent to SAN via parasympathetic neurone
SAN sends out impulses less frequently
Cardiac muscles contract less frequently

Question 26

Effect of temperature on speed of nervous transmission

Answer 26

Increased temperature= increased rate of impulse transmission
K+ and Na+ ions move faster as more kinetic energy
Active transport quicker as faster rate of respiration, faster rate of ATP production
Temp gets too high- proteins like sodium potassium pump denature- rate slows

Question 27

Effect of axon diameter on rate of nervous transmission

Answer 27

Bigger the diameter
Faster the rate of transmission
Bigger so less leakage of ions

Question 28

Neuromuscular junction vs normal synapse

Answer 28

Neuro neurone to muscle, nor neurone to neurone
Neuro always excitatory
Neuro has more receptors on post synaptic membrane
Neuro’s post synaptic membrane if highly folded into clefts

Question 29

Role of acetylcholine

Answer 29

Excitatory neurotransmitter

Released from neuromuscular junctions

Question 30

Role of AchE

Answer 30

Enzyme released from post-synaptic membrane to break down acetylcholine
So the neurotransmitter cannot keep binding to receptors
So response does not keep occurring

Question 31

Refractory period

Answer 31

Period it takes to restore resting potential after hyper polarisation
No action potentials can be generated
Ensures impulses are uni directional and discrete

Question 32

Unidirectionality due to synapses

Answer 32

Neurotransmitter only released from pre-synaptic neurone

Neurotransmitter receptors only found on post-synaptic membrane

Question 33

Inhibition by synapses

Answer 33

Hyperpolarise post-synaptic neurone
K+ diffuse out
Cl- diffuse in
No action potentials can form as depolarisation cannot occur/ reduces effect of any sodium ions entering sp reaching of pd threshold for ap less likely

Question 34

Use of the refractory period

Answer 34

period in which no action potentials can be generated
makes nervous impulses discrete and unidirectional
lists frequency of impulses

once maximum frequency of impluse reached any further increase in the strength of the stimuli will not lead to a stronger response- all seem the same

Question 35

What is the purpose of the refractory period?

Answer 35

limits frequency of impulses, thus intensity of response

ensures impulse are unidirectional, action potential can not be propagated in a hyper polarised region

implies are discrete, action ponytails cannot overlap

Question 36

the passage of an action potential along a non-myelinated neurone

Answer 36

action potential passes along as waves of depolarisation

the influx of sodium ions into one region causes the voltage-gated sodium ion channels of the adjoining region to open

causing sodium ions to diffuse into the neurone and depolarise it