Biology- Internal / External Stimuli, Receptors and Nervous System

Question 1

Define Taxis

Answer 1

A simple response where the direction is determined by the direction of the stimulus.
Positive taxis - Move towards stimulus
Negative taxis - Move away from stimulus

Question 2

Define Kinesis

Answer 2

A response in which the organism does not move to or away from the stimulus (non-directional)

Question 3

Define tropism

Answer 3

The growth movement of a part of a plant in response to a directional stimulus.

Question 4

Define Transducers

Answer 4

Convert energy from one form to another.

E.g Rod and cone cells convert light energy into electrical energy of a nerve impulse.

Question 5

Define Retinal convergence

Answer 5

Where many/several rod cells are connected to one bipolar neurone.

Question 6

Define Generator potential

Answer 6

The depolarisation of a membrane of a receptor cell as a result of a stimulus.

Question 7

Define visual acuity.

Answer 7

The clarity of vision dependent on optical and neural factors.

Question 8

What are Rod cells and where are they located?

Answer 8

• Photoreceptor cells located in the retina of the eye
• Contain Rhodopsin (protein pigment) which absorb light
• Rod cells are stimulated by light at a range of varying intensities (often a lower light intensity)

Question 9

What are Cone Cells and where are they located?

Answer 9

• Photoreceptor cells located in the retina of the eye
• Contain iodopsin (protein pigment) whcih absorbs light.
• Cone Cells are stimulated by light at a higher light intensity.
• Responsible for coloured vision.

Question 10

What is the role of a Transducer?

Answer 10

Role of a transducer is to convert the change in some form of energy by the stimulus into a form( nerve impulse) that can be understood by the body.

Question 11

What are Pacinian Corpuscles?

Answer 11

A mechanoreceptor found on the skin.

Stimulus —-> Mechanical Pressure

Question 12

What are Baroreceptors?

Answer 12

Mechanoreceptors located in the Carotid sinus and aortic arch.
Stimulus —-> Detect changes in blood pressure stimulates by stretching.

Question 13

What is Chemo receptors?

Answer 13

Detect changes in chemical concentrations

In carotid sinus, They detect a change in the partial pressure of O2 and CO2.

Question 14

How can chemo receptors detect a change in pH?

Answer 14

As the partial pressure of CO2 increases the pH of blood plasma decreases (more acidic)
H2O + CO2 —-> H2CO3 (Carbonic acid)
H2CO3 —-> H+ + HCO3-
Hydrogen ion concentrations increases so acidity decreases.

Question 15

What is bleaching?

Answer 15

Rhodopsis —-Light energy —> Retinal + Opsin

Retinal - causes polarisation to be changed (generator potential = depolarised)
Rhodopsin can be regenerated using ATP + Darkness

Question 16

Define Resting Potential

Answer 16

The difference in charge maintained across the membrane of the axon of a neurone when not stimulated.
At rest the outside of the membrane is more positive than inside.
-70mv charge.

Question 17

How is Resting Potential achieved?

Answer 17

The sodium potassium pump pumps out 3Na+ and brings in 2K+ ions across the axon membrane. This creates a membrane potential. Furthermore the membrane is more selectively permeable to K+ ions than Na+ ions so K+ ions diffuse out of the cell. This creates a larger positive potential out of the cell than inside.

Question 18

Define Depolarisation

Answer 18

Temporary reversal of electrical charges on the cell surface membrane of a neurone that takes place when a nerve impulse is transmitted.

Question 19

What causes the depolarisation of the membrane?

Answer 19

Stimulus affects the Na+ ion channels
so they open
causing them to depolarise

Question 20

What are the steps in the depolarisation of a membrane?

Answer 20

1) Stimulus causes more Na+ channels to open
2) Na+ diffuse into the cell down a concentration gradient.
3) This changes the voltage causing the membrane to become more selectively permeable to Na+ ions and therefore more voltage gated Na+ channels to open which allows more Na+ to diffuse in.
4) Positive feedback loop when more and more Na+ ion channels open.
5) Once charges flip (+40 mv) then Na+ ion channels close and repolarisation begins.

Question 21

Define Action Potential

Answer 21

A change that occurs in the electrical charge across the membrane of an axon when it is stimulated and a nerve impulse passes.

Question 22

Define Hyperpolarisation

Answer 22

Is a change in the cells membrane potential that makes it more negatively charged than it already is. (opposite to depolarisation)

Question 23

Define Repolarisation

Answer 23

Return to the resting potential in the axon of a neurone after an action potential.

Question 24

What is the Refractory Period?

Answer 24

The area/period of time where hyperpolarisation takes place and the membranes charge is brought back to rest.
Absolute R.P —> No action potential ever
Relative R.P —> Need a stimulus > normal threshold.

Question 25

What are the stages in an action potential?

Answer 25

1) Initial depolarisation of membrane triggered by stimulus (cause generator potential) 2) Many generator potentials lead to overall depolarisation. 3) If generator potential reaches threshold then an action potential is generated. 4) positive feedback loop of Na+ channels opening 5) once action potential at +40 mv is established then repolarisation occurs but overshoots rest. 6) Hyperpolarisation brings charge back to rest.

Question 26

What are the stages/steps or repolarisation?

Answer 26

1) once an action potential of +40 mv is established, after a delay Na+ ion channels close and more K+ channels open. 2) K+ ions diffuse out of the cell down concentration gradient so positive charge gets re-established outside of cell. 3) Charge is overshot however so charge is more positive outside of cell than at resting potential. The ions are in the wrong places and therefore must be re established via the sodium potassium pump.

Question 27

How does hyperpolarisation restore the membranes charge to resting potential?

Answer 27

Since resting potential is overshot, and the ions are in the wrong places, the sodium potassium pump has to re-distribute Na+ and K+ ions back to their preferred environment and re-establish the -70 mv resting potential.

Question 28

What is an impulse and how do they work?

Answer 28

A wave of depolarisation. | In an impulse local currents are set up which causes depolarisation to occur along an axon membrane.

Question 29

Define Saltatory conduction

Answer 29

The Propagation of action potentials along myelinated axons from one node of ranvier to the next node. Depolarisation leaps from region (node to node) since myelin acts as an electrical insulator. This speeds up an impulse.

Question 30

Where do action potentials occur in a neurone?

Answer 30

Along the axon membrane in unmyelinated axons. | At the nodes of ranvier in myelinated axons.

Question 31

What is the central nervouse system made up of?

Answer 31

Brain and spinal chord

Question 32

What is the peripheral nervous system made up of?

Answer 32

Pairs of nerves that originate from either the brain or spinal chord.

Question 33

What are sensory neurones?

Answer 33

Neurones which carry electrical impulses from receptors towards the central nervous system.

Question 34

What are motor neurones?

Answer 34

Neurones which carry electrical impulses away from the central nervous system and towards the effectors.

Question 35

What is the voluntary nervous system.

Answer 35

Nerves/neurones which carry nerve impulses to body muscles and is under voluntary (conscious) control.

Question 36

What is the Autonomic nervous system?

Answer 36

Nerves/neurones which carry nerve impulses to glands, smooth muscle, cardiac muscle and is not under voluntary control (subconscious)

Question 37

What is the sympathetic nervous system?

Answer 37

This stimulates effectors and so speeds up any activity. Acts as an emergency controller. It helps us cope with stressful situations by heightening our awareness and preparing us for activity. "Fight or flight response"

Question 38

What is the parasympathetic nervous system?

Answer 38

Inhibits effectors and so slows down any activity. | It controls activities under normal resting conditions.

Question 39

What is a reflex action?

Answer 39

An Involuntary response to a stimulus that bypasses the brain.

Question 40

What is a reflex arc?

Answer 40

The pathway of neurones involved in a reflex

Question 41

What are the 3 neurones involved in a reflex arc?

Answer 41

Sensory neurone Relay neurone (intermediate) Motor neurone

Question 42

Why are reflex actions important?

Answer 42

- Protect us from danger - Fast due to short neurone pathway - Required no thinking.

Question 43

What is the process of a reflex arc?

Answer 43

1) Arrival of stimulus at receptor 2) Activation of sensory neurone starting an impulse 3) Relay neurone allows CNS to process information 4) Activation of motor neurone 5) Effector cells contract initiating a response

Question 44

What is a synapse?

Answer 44

The junction between 2 neurones where neurotransmitters diffuse to pass on an impulse.

Question 45

Give some examples of neurotransmitters

Answer 45

- Acetylcholine - Dopamine - Serotonin - Noradrenaline

Question 46

How is an impulse transmitted across a synapse?

Answer 46

1) Impulse arrives at synaptic knob/bulb 2) Causes membrane potential to change which opens Ca^2+ voltage gated channels 3) Ca^2+ diffuse rapidly into synaptic bulb 4) Ca^2+ cause vesicles containing neurotransmitters to move towards and fuse with presynaptic membrane. 5) Neurotransmitter is exocytosed from vesicles and diffuse across synaptic cleft. 6) Neurotransmitter binds to binding site of protein receptors (Na+ ion channels) causing them to open. 7) Na+ diffuse into post synaptic neurone and begin depolarisation causing and E.P.S.P or an I.P.S.P

Question 47

What do E.P.S.P and I.P.S.P stand for?

Answer 47

E.P.S.P - excitatory post synaptic potential | I.P.S.P - Inhibitory post synaptic potential

Question 48

What does E.P.S.P mean will happen?

Answer 48

Action potentials could form (if depolarisation exceeds threshold) and therefore an impulse can be passed on through the post synaptic neurone.

Question 49

What does I.P.S.P mean will happen?

Answer 49

No action potential will happen due to hyperpolarisation and therefore will result in no impulse being passed on.

Question 50

Why does the synaptic bulb contain loads of mitochondria and SER?

Answer 50

Mitochondria - Active processes in action potentials and transmission of an impulse across a synapse. SER - Synthesises lipids for phospholipid membrane of vesicles

Question 51

Why is a synapse uni-directional?

Answer 51

Impulses can only go in one direction due to no protein receptors being present in the pre synaptic membrane. Neurotransmitters must be actively transported back out of the synaptic cleft and then repackaged in vesicles.

Question 52

What is summation?

Answer 52

The rapid build up of neurotransmitters in the synaptic cleft - Temporal summation - Spartial summation Happens due to low frequency action potentials often leading to the release of an insufficient concentration of neurotransmitters to trigger a new action potential in the post synaptic neurone.

Question 53

What is spartial summation?

Answer 53

Where 2 or more pre synaptic neurones release neurotransmitters into the synaptic cleft so the concentration is above threshold and an action potential can be triggered. One neurone may not release enough neurotransmitters to get the concentration above threshold.

Question 54

What is temporal summation? (low frequency v high frequency action potential)

Answer 54

Low - Lead to neurotransmitters being broken down rapidly and therefore the concentration is below threshold and no action potential is triggered. High - Lead to high release of neurotransmitters in a short amount of time so the concentration is above threshold and an action potential can be triggered.

Question 55

How does Axon diameter affect conduction velocity?

Answer 55

- Increasing diameter increases nerve conduction velocity. Therefore a large axon means a larger membrane and therefore more ion channels for a greater influx of diffusion. - Increasing myelination (more myelin) means more ion channels are concentrated at the nodes of ranvier and therefore increasing conduction velocity.

Question 56

How does temperature affect conduction velocity?

Answer 56

- As temperature increases the amplitude and duration of action potentials decreases. - As temperature decreases the resting potential is reduced (depolarisation) and this leads to the formation of an action potential.

Question 57

What do Chemoreceptors measure?

Answer 57

A change in the chemical concentrations or partial pressures of 02 and CO2 in the body.

Question 58

What do Baroreceptors measure?

Answer 58

A change in the blood pressure of the body.

Question 59

What and where are the SAN and AVN nodes in the body?

Answer 59

SAN (Sinoatrial Node) - Right atrium of the heart. | AVN (Atrioventricular Node) - Between the ventricles and the atria in the centre.

Question 60

What do the SAN and AVN nodes do?

Answer 60

SAN - Controls the pace/rate of heart contractions (controls heart rate) AVN -Sends an impulse down a bundle of His to cause Ventricular Contraction. - Has a delay to enable the atria to empty before allowing the ventricles to contract.

Question 61

Define Myogenic.

Answer 61

Refers to cardiac muscle: | Innate/natural rhythm of contraction so heart muscle will contract without external impulses.

Question 62

How do SAN and AVN nodes work?

Answer 62

1) SAN initiates a heartbeat/ starts a heart rate. 2) SAN sends an electrical impulse across atria causing atrial contraction. 3) AVN delays electrical impulses allowing the atria to empty before the ventricles contract. 4) AVN sends an impulse down the bundle of His to the purkyne firbres causing the ventricles to contract from base up.

Question 63

What does the Autonomic nervous system control?

Answer 63

Involuntary (subconscious) activities of the internal muscles

Question 64

What do the sympathetic and parasympathetic nervous systems do?

Answer 64

Sympathetic - Speeds up activity by stimulating effectors | Parasympathetic - Slows down activity by inhibiting effectors.

Question 65

What is the Medulla Oblongata?

Answer 65

Region of the brain which controls the heart rate by sending impulses to the SAN node via the sympathetic or parasympathetic nervous system.

Question 66

What prevents the impulse from the SAN node from crossing into the ventricles? (Just cross into atria)

Answer 66

A layer of non-conductive tissue | Atrioventricular septum

Question 67

What do the 2 centres in the Medulla Oblongata do?

Answer 67

One centre is linked to the SAN node via the sympathetic nervous system ---> Increases the heart rate, and the other centre is linked to the SAN node via the parasympathetic nervous system ---> Decreases the heart rate.

Question 68

How do Chemoreceptors cause a change in heart rate?

Answer 68

- Blood has higher than normal CO2 concentration so the pH is lower. - Chemoreceptors detect the change in blood pH and therefore send nerve impulses to the Medulla Oblongata. - This sends impulses via the Sympathetic nervous system to the SAN node to increase the heart rate. - Increase in heart rate means that more CO2 is removed from the body via the lungs and the CO2 concentration returns to normal. - These chemoreceptors detect this change and the process repeats to reduce the heart rate by sending a message from the Medulla Oblongata to the SAN node via the parasympathetic nervous system.

Question 69

How do Baroreceptors cause a change in blood pressure?

Answer 69

- Baroreceptors detect blood pressure changes and therefore send more impulses to the Medulla Oblongata. - This sends impulses via the Sympathetic (to increase heart rate and therefore blood pressure) and parasympathetic ( to decrease heart rate and therefore blood pressure) Nervous system to the SAN node. - SAN node controls the heart rate to increase it and therefore blood pressure or decrease the heart rate and therefore blood pressure

Question 70

What is Auxin?

Answer 70

A plant growth hormone that stimulates cell elongation in shoots and inhibits cell elongation in the roots.

Question 71

Give an example of an Auxin and what does it do?

Answer 71

Indole Acetic Acid (IAA): - Apical dominance - Cell elongation in shoots - Inhibits cell elongation in roots

Question 72

Define Apical Dominance

Answer 72

Inhibits lateral growth | Enabling plants to control how they grow.

Question 73

Define Tropism.

Answer 73

The direction of growth is in response to the direction of a stimulus

Question 74

Define Meristem

Answer 74

A region of plant tissue found at the growing tips of shoots and roots - consisting of actively dividing cells (via mitosis) forming new tissues.

Question 75

What affect does Auxin have on shoots and roots?

Answer 75

Shoots - Stimulates cell elongation. | Roots - Inhibits cell elongation.

Question 76

How does auxin cause shoots to bend towards the light?

Answer 76

- Auxins (IAA) produced in tip move laterally to the darker side of the shoots. - Increased [Auxin] concentration so auxin diffuses down the darker side of the shoot. - More auxin molecules bind to the receptor sites of cells on the darker side of the the shoot in the zone for elongation. - Cell walls of shaded side remain flexible for longer. - Cell walls on shaded side elongate more than the light side causing shoot to curve and grow in direction of light.