stimuli/reflexes/nervous Co-ordination

Question 1

What are the benefits of response to stimuli

Answer 1

-increase chance of survival
-move towards beneficial stimuli
-move away from harmful stimuli

Question 2

What is tropism?

Answer 2

-plant response to a directional stimulus
-meristem cells

Question 3

What tropism do roots and shoot display?

Answer 3

-roots display positive gravitropism and negative phototropism
-shoots display positive phototropism and negative gravitropism

Question 4

What is taxes?

Answer 4

-Invertebrates and single cell organisms use this
-simple response
-move towards beneficial stimuli
I.e daphnia (water fleas) moving towards light

Question 5

Give examples of taxes

Answer 5

-Daphnia moving towards light = positive phototaxis
-bacteria moving towards higher glucose conc. = positive chemotaxis

Question 6

What is kineses?

Answer 6

-a more complex response that not only involves movement, but the rate of movement (acceleration) and direction change
I.e woodlice moving quickly and randomly until they find suitable conditions

Question 7

What is IAA

Answer 7

Indoleacetic acid

Question 8

Mechanism of IAA

Answer 8

-IAA produced in shoot tips
-IAA move through shoot
-IAA moves to shaded side
-higher conc. of IAA causes ELONGATION of CELLS at a faster rate
-in roots, IAA inhibits cell elongation

Question 9

What is the acid growth hypothesis? (Why does IAA affect cell elongation)

Answer 9

-increases the plasticity of the cell walls as:
-H+ ions actively transported into space between cell walls
-changes the H bonding within the cellulose layers in cell wall

Question 10

Benefits of a reflex arc?

Answer 10

-prevents injury to body
-naturally occurring
-rapid
-involuntary, so doesn’t overload the brain

Question 11

Describe the difference between voluntary nervous system and autonomic nervous system:

Answer 11

-autonomic is reflex actions such as breathing or blinking
-completed by muscles or glands
-voluntary nervous system is for conscious control
-carries impulses to body muscles

Question 12

Describe a reflex arc if a hand came in contact with a flame

Answer 12

-heat stimulus from candle
-sensory nerve cell receives impulse from receptor
-impulses carried by sensory neurone to the CNS via an intermediate neurone
-impulses then move towards motor neurone
-effector receives impulse i.e a muscle and contracts hand

Question 13

2 features of sensory receptors:

Answer 13

-specific to a type of stimulus
-acts as a transducer

Question 14

What is the mechanism of the pacinian corpuscle:

Answer 14

-pressure disrupts and distorts the tissue layers.
-opens stretch mediated Na+ channel proteins
-gel containing Na+ ions move through the channel via facilitated diffusion
-Na+ diffuse into axon to produce a generator potential that may or may not turn into an action potential

Question 15

Describe the structure of rods in the eye:

Answer 15

-3 rod cells connected to one bi-polar neurone (retinal convergence)
-each rod cells contains rhodopsin

Question 16

Characteristics of rods:

Answer 16

-low visual acuity (resolution is lower)
-high sensitivity to light
-monochromatic
-along the retina edges

Question 17

Mechanism of rods:

Answer 17

-in low light, rhodopsin is hydrolysed and causes a generator potential in the bi-polar neurone. If action potential reached then sensory neurone will carry impulse

Question 18

Difference between generator and action potential:

Answer 18

-generator potential comes from when cells begin to become depolarised
-action potential is all or nothing and is where an impulse is made

Question 19

Structure of a cone?

Answer 19

-single cone cell with iodopsin inside
-connected to a bi-polar neurone and then sensory neurone

Question 20

Characteristics of cones

Answer 20

-trichromatic (red, green and blue)
-fovea
-only had 1:1 ratio of neurone to cone cell
-low sensitivity to light
-high visual acuity

Question 21

Mechanism of cones:

Answer 21

-light stimulates the cone cells to hydrolyse iodopsin which causes a generator potential that may become an action potential if the threshold is met

Question 22

Pro and con of cones and rods

Answer 22

Cones:
-pro: each rod has its own bi-polar neurone so separate impulses can be sent, high visual acuity
-con: more energy needed to break down iodopsin and reach the threshold potential

Rods:
-pro: each rod cell has a retinal convergence, less light needed to cause an impulse
-con: retinal convergence doesn’t allow brain to differentiate angles of light, low visual acuity

Question 23

EQ: Explain how the fovea enables an eagle to see its prey in detail.

Answer 23

-high visual ACUITY
-each cone connected to a single bi-polar neurone
-sends individual impulses to the brain

Question 24

EQ: The retina of an owl has a high density of rod cells.
Explain how this enables an owl to hunt its prey at night

Answer 24

-rods cells have retinal convergence
-several rods connected to a single bi-polar neurone
-release enough neurotransmitter to reach threshold and cause an action potential

Question 25

What organelles are useful in nerve cell bodies?

Answer 25

-rough endoplasmic reticulum produces neurotransmitters and proteins

Question 26

what helps to produce the myelin sheath in myelinated neurones?

Answer 26

shwann cells, which produce myelin that wraps around itself

Question 27

describe how resting potential is reached/maintained:

Answer 27

-Higher concentration of potassium ions inside and higher
concentration of sodium ions outside the neurone
-membrane less permeable to sodium ions
-3Na+ ions are actively transported out and 2K+ ions in

Question 28

Why is the speed of impulse faster along a myelinated neurone than a non-myelinated one?

Answer 28

-myelination provides insulation
-allows saltatory conduction and so impulse can jump from each node of Ranvier to the next
-non-myelinated neurones have smaller localised electric currents where depolarisation must take place across the entire axon

Question 29

what factors affect the speed of impulse?

Answer 29

-myelination, a myelinated neurone is faster
-diameter of the axon, larger diameter is quicker due to less leakage of ions from membrane
-temperature, higher temps allow faster impulse, but too high can denature proteins

Question 30

What is the all-or-nothing principle?

Answer 30

-all stimuli above a certain threshold value will generate the same size of action potential

Question 31

How does the size of a stimulus affect impulses?

Answer 31

-a strong stimulus will send more frequent impulses, but they will be at the same strength.

Question 32

Describe how depolarisation and action potentials occur:

Answer 32

-Sodium ion channels in the axon membrane open
-sodium ions move down the electrochemical gradient via facilitated diffusion
-if -55mV is reached, then depolarisation occurs, where more sodium ion channels open to allow more sodium ions in
-reaches peak of +40mV, causing the K+ ion gated channel proteins to open and Na+ ion gated channel proteins to close
-start of refractory period, K+ ions diffuse out of the axon and causes hyperpolarisation at -70mV
-K+ ion gated channels close again and Na+ ion gated channels open, end of refractory period

Question 33

what is the purpose of the refractory period?

Answer 33

-keeps impulse unidirectional
-produces discrete impulses (impulses don’t overlap)
-limits the number of action potentials

Question 34

EQ: Explain how the atrioventricular valve maintains a unidirectional flow of blood

Answer 34

-Pressure in left ATRIUM is greater than in ventricle so atrioventricular valve opens and lets blood into ventricle
-pressure in left VENTRICLE is now greater than in the atrium so valve shuts

Question 35

sympathetic vs parasympathetic nervous system

Answer 35

-sympathetic nervous system stimulates effectors
-parasympathetic nervous system inhibits effectors

Question 36

what does the heart being myogenic mean?

Answer 36

-controls and produces its own contractions

Question 37

describe how the SAN produces a contraction for the heart:

Answer 37

-SAN (sinoatrial node) produces wave of electrical activity that travels around the walls of the atrium
-signal passes down the atrial septum
-atrioventricular node (AVN) receives signal as electrical activity travels around wall of the ventricle, causes the atria to contract.
-Bundle of His conducts signal to the base of the ventricles
-impulse passes up along the purkinje fibres and causes the ventricles to contract from the apex up

Question 38

why is there a delay between the signal moving from the atrial septum to the atrioventricular node?

Answer 38

to allow the atria to fully empty before the ventricles contract

Question 39

where is the SAN found?

Answer 39

in the right atrium

Question 40

what are the two nerves used in the medulla oblongata?

Answer 40

-accelerator nerve for the sympathetic nervous system, increases the heart rate
-vagus nerve for the parasympathetic nervous system, decreases the rate of the heart.

Question 41

what are the three chemoreceptors/two baroreceptors?

Answer 41

chemoreceptors-aorta, carotid artery and medulla oblongata
baroreceptors-aorta and carotid artery

Question 42

describe how an increase in CO2 level is detected by the body

Answer 42

-Increase in CO2 in the blood causes increase in carbonic acid, so pH decreases.
-chemoreceptors in the aorta, carotid artery detect the change and send IMPULSES to the medulla oblongata
-medulla oblongata sends impulses down the sympathetic nervous system via the accelerator nerve which increases the heart rate by sending more impulseS to the SAN

Question 43

what is the difference between temporal and spatial summation

Answer 43

-temporal summation, one presynaptic neurone releases neurotransmitters over a period of time to cause an action potential
-spatial summation, multiple presynaptic neurones release neurotransmitters together to cause an action potential in the postsynaptic neuron.

Question 44

Describe how an inhibitory synapse works

Answer 44

-neurotransmitter binds to chloride ion channels
-chloride ions enter, K+ ions leave
-causes hyperpolarisation so action potential less likely

Question 45

How does synaptic transmission occur?

Answer 45

-impulse reaches presynaptic knob
-causes voltage gated Ca2+ ion channels to open so calcium ions enter presynaptic knob
-causes the vesicles to move towards the presynaptic membrane and fuse with it
-this releases the neurotransmitters and allows them to diffuse across the synaptic cleft
- bind to ligand gated sodium ion channels on postsynaptic membrane
-allows Na+ ions to enter the postsynaptic knob and can cause another action potential

Question 46

How does acetylcholinesterase (AChE) hydrolyse acetylcholine (ACh) and recycle it?

Answer 46

-After the ACh has binded to the ligand gated sodium channels on the postsynaptic knob, AChE hydrolyses the ACh into choline and acetate (ethanoic acid)
-these products can be actively transported back into presynaptic neurone via ENERGY from ATP from mitochondria