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a-level bio > Topic 6 > Flashcards

Topic 6 Flashcards

1
Q

Define stimulus

A

A detactable change in the environment

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2
Q

Define receptors

A

Cells that can detect changes in the environment

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3
Q

How do organisms increase their chances of survival?

A

By responding to stimuli via different response mechanisms

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4
Q

Define tropism

A

When a plant responds to stimuli via growth

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5
Q

Positive tropisms are growing towards or away from a stimulus?

A

Towards

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6
Q

What are tropisms controlled by?

A

Growth factors
eg Indoleacetic acid (IAA)

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7
Q

What is IAA

A

A type of auxin and can control cell elongation in shoots and inhibit cell elongation in roots

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8
Q

Where is IAA made in plants?

A

The tip of the roots and shoots but can diffuse to other cells

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9
Q

Why does positive phototropism benefit plants?

A

Light is needed for the light dependent reaction in plants

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10
Q

How does positive phototropism work in plant shoots?

A

The shoot tip produces IAA causing cell elongation
The IAA diffuses to other cells
If there is unilateral light, the IAA will diffuse to the shaded side of the shoot resulting in higher concentrations of IAA there
The cells on the shaded side elongate more and leads to the plant bending towards the light source

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11
Q

Why is negative phototropism beneficial in roots?

A

Roots do not photosynthesise and do not need light, but need to anchor the plant deep into the soil

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12
Q

How does IAA cause negative phototropism in the roots?

A

A high concentration of IAA inhibits cell elongation, causing root cells to elongate more on the lighter side
This makes the root bend away from the light

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13
Q

How does IAA cause negative gravitropism in shoots?

A

IAA diffuses from the upper side to the lower side of a shoot
If a plant is already vertical, this causes plant cells to elongate and the plant grows upwards
If a plant is on its side, it will cause the shoot to bend upwards

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14
Q

How does IAA cause positive gravitropism in the roots??

A

IAA moves to the lower side of roots so that the upper side elongates and the root bends down towards gravity to anchor the plant

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15
Q

Define a reflex

A

A rapid, automatic response to protect you from danger

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16
Q

Reflex arc’s 3 neurones?

A

Sensory neurones
Relay neurones
Motor neurones

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17
Q

Why does the simple reflex protect us well?

A

It is fast due to only having 2 synapses total

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18
Q

Reasons for Taxes and Kinesis responses

A

They keep mobile organisms within a favourable environment (correct amounts of light, moisture etc)

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19
Q

Taxes response

A

An organism moving its entire body towards a favourable stimulus (+ve) or away from an unfavourable stimulus (-ve)

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20
Q

Kinesis response

A

When an organism changes the speed of movement and the rate it changes direction
This allows it to return to favourable conditions fairly quickly
After a while, an organism may decrease rate of turning to move in a straight line to increase chances of finding a new location with favourable conditions

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21
Q

Each receptor responds only to ________ stimuli

A

specific

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22
Q

What generally happens when a receptor is stimulated

A

A generator potential is established which can cause a response

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23
Q

3 receptors

A

Pacinian corpuscle
Rods
Cones

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24
Q

What does the pacinian corpuscle detect?

A

Changes in pressure

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25
Q

Where to find pacinian corpuscles

A

Deep in skin, mainly in fingers and feet

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26
Q

Structure of the pacinian corpuscle?

A

Neurone ending of a sensory neurone surrounded by connective tissue with gel in between each layer

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27
Q

How is a generator potential established in pacinian corpuscles?

A

The membranes in the PC have stretch mediated sodium ion channels
These open and allow Na+ to enter the sensory neurone only when they are deformed/stretched
With pressure, the neurone plasma membrane is stretched and widens the Na+ channels so that Na+ diffuses in, leading to a generator potential being established

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28
Q

Where are the photoreceptors located?

A

both rods and cones are in the retina

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29
Q

How do rod cells process images

A

Black and white

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30
Q

How do rod cells create a generator potential for a black and white image?

A

A pigment of rod cells called rhodopsin must be broken down by light energy

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31
Q

Why do rod cells detect very low intensity light?

A

Many rod cells connect to one sensory neurone -> retinal convergence

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32
Q

Why do rod cells have low visual acuity?

A

Many rod cells connect to one sensory neurone so the brain cannot distinguish between the seperate sources of light that stimulated it

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33
Q

How do cones process images in colour

A

There are 3 types of cone cells with different types of Iodopsin pigment (R,G,B) which all absorb different wavelengths of light

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34
Q

Why can cone cells only generate action potentials with high light intensities?

A

Iodopsin is only broken down (generating an AP) if there is a high enough light intensity
Each cone cell also connects to its own bipolar cell

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35
Q

Why can’t colour be seen in the dark

A

Cones only respond to high light intensity

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36
Q

Why do cone cells have a high visual acuity

A

Each cone cell is connected to one bipolar cell so the brain can distinguish between the seperate sources of light detected due to separate impulses

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37
Q

Distribution of rods and cones in the eye

A

Most cone cells are located near the fovea (which recieves the highest light intensities)
Rod cells are locared further away

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38
Q

What does myogenic mean in regards to cardiac muscle?

A

It contracts of its own accord

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39
Q

If the cardiac muscle is myogenic, what do depolarisation waves do?

A

Control the rate of contraction

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40
Q

Where is the sino atrial node located (SAN)

A

Right atrium (pacemaker)

41
Q

Where is the atrioventricular node located? (AVN)

A

Near the border of the right and left ventricle within the atria

42
Q

Where is the bundle of His located?

A

It runs through the septum

43
Q

Where are the Purkyne fibres

A

In the walls of the ventricles

44
Q

How is the contraction of the heart controlled?

A

SAN releases a wave of depolarisation across the atria causing it to contract
AVN releases another wave of depolarisation when the first reaches it
A non conductive layer between the atria and ventricles prevents the wave of depolarisation reaching the ventricles
AVN causes delay.
Instead, the bundle of His conducts the wave of depolarisation down the septum + the Purkyne fibres
Then, after a short delay the ventricular walls contract
Then, the cells repolarise and the cardiac muscle relaxes

45
Q

Where in the brain controls the heart rate and via what nervous system?

A

Medulla oblongata via the autonomic nervous system

46
Q

Heart rate changes in response to what 2 things, detected by what?

A

changes in pH and blood pressure detected by chemoreceptors and pressure receptors in the aorta and carotid artery

47
Q

Heart rate response to low blood pH

A

chemoreceptors detect low pH due to high respiratory rate causing production of CO2 or lactic acid which must be removed from the blood rapidly to prevent enzymes from denaturing
Increasing heart rate by sending more impulses via the sympathetic nervous system to SAN allows CO2 to diffuse out into the alveoli more rapidly

48
Q

Heart rate response to any change in blood pressure and why it’s necessary

A

If too high, BP can cause damage to artery walls
More impulses via parasympathetic nervous system to decrease the heart rate
If the blood pressure is too low, there could be an insufficient supply of oxygenated blood to respiring cells or waste removal.
More impulses via sympathetic nervous system increases the heart rate

49
Q

Myelinated neurone structure

A

Cell body of the neurone contains organelles of a typical animal cell, and makes proteins and neurotransmitter chemicals
Dendrites carry action potentials to surrounding cells
The axon is a conductive long fibre that carries the nervous impulse along the motor neurone
Schwann cells wrap around the axon to form the myelin sheath which is a lipid, so it is insulated, not allowing charged ions to pass through it
Gaps in the myelin sheath are nodes of Ranvier

50
Q

What is resting potential

A

The difference between electrical charge inside and outside of the neurone when a neurone is not conducting an impulse

51
Q

Why is the resting potential -70mV?

A

There are more positive ions (Na+ and K+) outside compared to inside, therefore the inside of the neurone is comparatively more negative

52
Q

How is resting potential maintained

A

Sodium potassium pump (using active transport and ATP) moves in 2 K+ ions and 3 Na+ ions out
This creates an electrochemical gradient causing K+ to diffuse out and Na+ to diffuse in
The membrane is more permeable to K+ resulting in -70mV

53
Q

What is an action potential

A

When the neurones voltage increases beyond a set point from the resting potential generating a nervous impulse due to depolarisation

54
Q

What causes depolarisation

A

The neurone membrane becomes more permeable to Na+ and then more positive

55
Q

What happens to an action potential after it is generated (myelinated and non myelinated axons)

A

it moves along the axon at each node of ranvier in a myelinated axon or slowly in an unmyelinated one as it occurs at every point along the axon

56
Q

What is the all or nothing principle

A

If the depolarisation does not exceed -55mV an AP and impulse are not produced
And if a stimulus does trigger depolarisation to -55mV, it will always peak at the same maximum voltage, but bigger stimuli increaase the frequency of APs

57
Q

Why is the All or nothing principle necessary?

A

Makes sure only large enough stimuli are responded to instead of every slight change in the environment

58
Q

What is the refractory period?

A

The amount of time that a membrane can’t be stimulated for because sodium channels are recovering and can’t be opened

59
Q

3 reasons for the importance of the refractory period

A

Ensures that discrete impulses are produced
Ensures that APs travel in one direction instead of spreading out in 2 directions which would prevent a response
It also limits the number of impulses transmitted preventing over reaction to a stimulus

60
Q

Factors affecting speed of conductance

A

Myelniation and saltatory conduction
Axon diameter
Temperature

61
Q

How does myelination increase speed of conduction

A

AP jumps from node to node (saltatory conduction) so AP travels along the axon faster due to the generation of less APs

62
Q

How does axon diameter increase speed of conductance

A

Wider diameter means less ion resistance so APs travel faster

63
Q

How does temperature increase speed of conductance

A

Ions diffuse faster due to having more kinetic energy
The enzymes involved in respiration work faster so there is more ATP for active transport in the NA+/K+ pump

64
Q

What is a synapse and what happens at one

A

The gaps between the end of fthe axon of one neuron and the dendrite of another one.
The AP is transmitted as neurotransmitters that diffuse across the synapse

65
Q

How does transmission across a choligernic synapse occur

A

An AP arrives at a synaptic knob, depolarising it, opening Ca2+ channels and Ca2+ diffuses into synaptic knobs
Vesicles containing acetylcholine neurotransmitter move towards and fuse with the presynaptic membrane releaasing it into the synaptic cleft
Acetylcholine diffuses down the concentration gradient across the synaptic cleft to the post synaptic membrans where the acetylcholine binds by complementarity of shape to receptors on the surface of the post synaptic membrane
Na+ ion channels on the post synaptic membrane open and Na+ diffuses in; if there is enough neurotransmitter then enough Na+ diffuses in above the threshold and post synaptic neuron becomes depolarised
The neurotransmitter is degraded and released from the receptor, the Na+ channels close and the post synaptic neuron can reestablish resting potential, and the neurotransmitter is transported back into the presynaptic neurone to be reused

66
Q

How is transmission across a synapse unidirectional?

A

Neurotransmitters are only in the presynaptic neurone and the diffusion gradient is from the pre to post synaptic neurone
Receptors are only on post synaptic membrane

67
Q

What is summation in synapses

A

Rapid build up of neurotransmitters in the synapse to help generate an action potential by either spatial or temporal summation

68
Q

Spatial summation?

A

Many neurones collectively trigger a new AP by combining the neurotransmitter they release to exceed the threshold value

69
Q

Temporal summation?

A

One neurone releases neurotransmitter repeatedly over a short period of time to add up to enough to exceed the threshold value

70
Q

What does an inhibitory synapse do?

A

They cause Cl- ions to move into the post synaptic neurone and K+ ions move out
This makes the membrane potential decrease to -80mV, hyperpolarisation and is therefore an action potential is highly unlikely

71
Q

Differences in neuromuscular junction and cholinergic synapse

A

Both are unidirection due to the neurotransmitter receptors only being on the posti synaptic membrane

NJ are only excitatory. CS are excitatory or inhibitory.
NJ connect motor neurones to muscles. CS connect 2 neurones.
NJ is the end point for action potential. CS is not, as a new AP is produced in the next neurone.
NJ acetylcholine binds to receptors on muscle fibre membranes, CS acetylcholine binds to receptors on post synaptic membrane of a neurone

72
Q

What do muscles do?

A

Act as antagonistic pairs against an incompressible skeleton

73
Q

What are myofibrils made up of?

A

Fused cells that share nuclei and sarcoplasm and there is a high number of mitochondria

74
Q

What are muscle fibres made up of?

A

Millions of myofibrils which collecively bring about the force to cause movement

75
Q

What proteins are myofibrils made up of?

A

Myosin and actin, and they form a sarcomere

76
Q

Describe the structure of a sarcomere

A

Myosin is a thick myofilament and appears as a dark band (called the A band)
Actin is a thin myofilament and appears as a light band (called the I band)
Sarcomeres are joined together lengthways at the Z-line.
Right in the middle of the sarcomere is a region called the M-line.
The H-zone refers to the portion of the A-band which only contains myosin filaments (and not the portions where actin overlaps with myosin).

77
Q

What is the sliding filament theory

A

An AP reaches a muscle stimulating a response
Ca2+ enters so tropomyosin moves to expose actin’s binding sites
While ADP is attached to the myosin head, the myosin heads to the actin to form a cross-bridge
The angle created in this cross bridge creates tension and the actin filament is pulled and slides along the myosin, releasing ADP molecules (powerstroke)
ATP then binds to the myosin head, causing it to change shape slightly, so the myosin head detaches from the actin
ATPase from the sarcoplasm is activated by the Ca2+ ions to hydrolyse the ATP on the myosin head into ADP and releases enough energy to return the myosin head to its normal position
The process all repeats while the Ca2+ conc remains high

78
Q

What 2 molecules are important to muscle contraction and why?

A

ATP for moving the myosin head back to its original position and Phosphocreatine, which is stored in muscles, provides the phosphate to regenerate ATP from ADP

79
Q

Slow twitch fibres vs fast twitch fibres, comparing their structure, location and properties

A

ST
large myoglobin store
rich blood supply
many mitochondria
FT
thicker myosin
large glycogen store
phosphocreatine store

ST in calf muscles and FT in biceps

ST
contracts slower
can respire anaerobically for longer due to supplies
for endurance
FT
contracts faster
short but powerful contractions
for intense exercise eg sprinting

80
Q

What is homeostasis in mammals?

A

physiological control systems that maintain the internal environment within restricted limits

81
Q

Why maintain a stable core temperature and stable blood pH

A

Enzymes could denature at extreme values of either

82
Q

What is osmoregulation

A

Controlling water potential of blood

83
Q

Why is hypertonic blood a problem

A

Too low water potential of blood
Too much water will leave cells -> into the blood by osmosis so cells will shrivel

84
Q

Why is hypotonic blood a problem?

A

Too much water will move in to the cells from the blood via osmosis which can make the cells burst

85
Q

Causes of hypertonic blood

A

Too much sweating
Not drinking enough water
Lots o ions in diet

86
Q

Causes of hypotonic blood

A

Drank too much water
Not enough salt in diet

87
Q

Corrective mechanism for hypertonic blood

A

More water reabsprbed by osmosis into the blood from nephron tubules so urine is more concentrated and less water is lost through it

88
Q

Corrective mechanism for hypotonic blood

A

Less water reabsorbed by osmosis into the blood from nephron tubules, so urine is more dilute and more water is lost through it

89
Q

Where does osmoregulation occur

A

Nephrons in the kidneys

90
Q

Steps of filtration and reabsorption

A
  1. Ultrafiltration
  2. Selective reabsorption
  3. The loop of Henle maintains a Na+ gradient so water can be reabsorbed into the blood
  4. water moves out of the distal convoluted tubule and collecting duct to return back to the blood
  5. The collecting duct carries the remaining liquid (urine) to the ureter
    (This is the summary…)
91
Q

Role of the hypothalamus and posterior pituitary gland in osmoregulation

A

Changes in water potential of the blood are detected by osmoreceptors in it

If WP of blood is too low, water leaves the osmoreceptors via osmosis and they shrivel, stimulating the hypothalamus to produce more ADH

If WP of blood is too high, water enters the osmoreceptors via osmosis, stimulating the hypothalamus to produce less ADH

The hypothalamus produces ADH to move into the posterior pituitary and is released from here into the blood

92
Q

What does ADH do?

A

Increase permeability in the walls of the collecting duct and distal convoluted tubule to water
This causes more water to leave the nephron and be reabsorbed into the blood so urine is more concentrated

93
Q

Ultrafiltration steps

A

Blood enters through the afferent arteriole and splits into lots of capillaries making up the glomerulus, causing a high hydrostatic pressure in the blood
Water and small molecules such as glucose and mineral ions are forced out ofo the capillaries and for the glomerulus filtrate
Large proteins and blood cells are too big to fit through the gaps in the basement membrane and capillary endothelium so remain in the blood, which leaves by the efferent arteriole

94
Q

Selective reabsorption of glucose and water occurs where? How is it adapted?

A

In the proximal convoluted tubule with microvilli for SA and lots of mitochondria for active transport’s energy

95
Q

Selective reabsorption steps

A

The conc of Na+ in the PCT cell decreased as the Na+ are actively transported out of the PCT cells into capillaries
Due to the conc gradient, Na+ diffuses down the gradient from the lumen of the PCT into the cells lining the PCT. This is an example of co-transport.
The glucose from co-transport can diffuse into the blood stream from the PCT cell which is how all glucose is reabsorbed

96
Q

Maintaining of Na+ gradient steps

A

Mitochondria in the walls of the cells provide energy to AT Na+ out of the ascending limb of the loop of Henle
The accumulation of Na+ outside the nephron in the medulla lowers water potential
Water diffuses out by osmosis into the interstitial space and then the blood capillaries (water is reabsorbed in to the blood)
At the base of the ascending limb some Na+ are transported out by diffusion as there is now a very concentrated solution due to all the water that has moved out

97
Q

Selective reabsorption steps of water at DCT

A

Due to all the Na+ ions being AT out of the loop of Henle, when the filtrate reaches the DCT it is very dilute
The filtrate moves into the DCT and collecting Duct, and this section of the medulla is very concentrated
Therefore even more water diffuses out of the DCT and collecting duct
What remains is transported to form urine

98
Q

The longer the loop of Henle…

A

The more Na+ is actively transported out, so an even more negative WP is created
More water gets reabsorbed into the blood + very concentrated urine forms

99
Q

Positive feedback mechanism?

A

A causes more B
B also causes more A

a-level bio (9 decks)

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