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A-level Biology > organisms respond to changes in their internal and external environments > Flashcards

organisms respond to changes in their internal and external environments Flashcards

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1
Q

Stimulus

A

Detectable change in the environment
detected by cells called receptors

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2
Q

Nervous system structure

A

Central nervous system = brain and spinal cord
peripheral nervous system = receptors, sensory and motor neurones

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2
Q

Simple reflex arc

A

Stimulus (touching hot object) -> receptor
-> sensory neurone
-> coordinator (CNS / relay neurone
-> motor neurone
-> effector (muscle)
-> response (contraction

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3
Q

Importance of simple reflexes

A

Rapid - short pathway
only three neurones & few synapses
autonomic
conscious thought not involved - spinal cord coordination
protect from harmful stimuli
e.g., burning

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3
Q

Tropism

A

Response of plants to stimuli via growth
can be positive (growing towards stimulus) or negative (growing away from stimulus) controlled by specific growth factors (IAA)

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4
Q

Indoleacetic acid

A

Type of auxin (plant hormone) controls cell elongation in shoots inhibits growth of cells in roots made in tips of roots / shoots can diffuse to other cells

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4
Q

Specific tropisms

A

Response to light-phototropism
response to gravity-gravitropism
response to water-hydrotropism

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5
Q

Phototropism in roots

A

Root tip produces IAA
IAA concentration increases on lower (darker) side
IAA inhibits cell elongation root cells grow on lighter side root bends away from light negative phototropism

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6
Q

Phototropism in shoots

A

Shoot tip produces IAA diffuses to other cells
IAA accumulates on shaded side of shoot
IAA stimulates cell elongation so plant bends towards light positive phototropism

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7
Q

Gravitropism in shoots

A

Shoot tip produces IAA
IAA diffuses from upper side to lower side of shoot in response to gravity
IAA stimulates cell elongation so plant grows upwards
negative gravitropism

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8
Q

Gravitropism in roots

A

Root tip produces IAA
IAA accumulates on lower side of root in response to gravity IAA inhibits cell elongation root bends down towards gravity and anchors plant positive gravitropism

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9
Q

Kinesis

A

When an organism changes its speed of movement and rate of change of direction in response to a stimulus
if an organism moves to a region of unfavourable stimuli it will increase rate of turning to return to origin
if surrounded by negative stimuli, rate of turning decreases - move in straight line

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9
Q

Receptors

A

Responds to specific stimuli stimulation of receptor leads to establishment of a generator potential - causing a response
pacinian corpuscle
rods
cones

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10
Q

Taxis

A

Directional response by simple mobile organisms
move towards favourable stimuli (positive taxis) or away from unfavourable stimuli (negative taxis)

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11
Q

Pacinian corpuscle

A

Receptor responds to pressure changes
occur deep in skin mainly in fingers and feet
sensory neurone wrapped with layers of tissue

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11
Q

How pacinian corpuscle detects pressure

A

When pressure is applied,
stretch-mediated sodium ion channels are deformed sodium ions diffuse into sensory neurone
influx increases membrane potential - establishment of generator potential

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12
Q

Rod cells

A

Concentrated at periphery of retina
contains rhodopsin pigment connected in groups to one bipolar cell (retinal convergence)
do not detect colour

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13
Q

Cone cells

A

Concentrated on the fovea fewer at periphery of retina 3 types of cones containing different iodopsin pigments one cone connects to one neurone
detect coloured light

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14
Q

Rods and cones: describe
differences in visual acuity

A

Cones give higher visual acuity
rods have a lower visual acuity

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15
Q

Visual acuity

A

Ability to distinguish between separate sources of light
a higher visual acuity means more detailed, focused vision

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15
Q

Rods and cones: describe differences in colour vision

A

Rods allow monochromatic vision (black and white)
cones allow colour vision

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15
Q

Rods and cones: describe differences in sensitivity to light

A

Rods are more sensitive to light
cones are less sensitive to light

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16
Q

Why cones have low sensitivity to light

A

One cone joins to one neurone no retinal convergence / spatial summation
higher light intensity required to reach threshold potential

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16
Q

Why rods have high sensitivity to light

A

Rods are connected in groups to one bipolar cell
retinal convergence
spatial summation
stimulation of each individual- cell alone is sub-threshold but because rods are connected in groups more likely threshold potential is reached

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16
Q

Why rods have low visual acuity

A

Rods connected in groups to one bipolar cell
retinal convergence
spatial summation
many neurones only generate 1 impulse / action potential -> cannot distinguish between separate sources of light

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17
Q

Why cones have high visual acuity

A

One cone joins to one neurone 2 adjacent cones are stimulated, brain receives 2 impulses
can distinguish between separate sources of light

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18
Q

Why rods have monochromatic vision

A

One type of rod cell
one pigment (rhodopsin)

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19
Q

Why cones give colour vision

A

3 types of cone cells with
different optical pigments
which absorb different wavelengths of light red-sensitive, green-sensitive and blue-sensitive cones stimulation of different proportions of cones gives greater range of colour perception

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20
Q

Myogenic

A

When a muscle (cardiac muscle) can contract and relax without receiving signals from nerves

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21
Q

Sinoatrial node

A

Located in right atrium and is known as the pacemaker releases wave of depolarisation across the atria, causing muscles to contract

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22
Q

Atrioventricular node

A

Located near the border of the right / left ventricle within atria releases another wave of depolarisation after a short delay when it detects the first wave from the SAN

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23
Q

Bundle of His

A

Runs through septum
can conduct and pass the wave of depolarisation down the septum and Purkyne fibres in walls of ventricles

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24
Q

Purkyne fibres

A

In walls of ventricles
spread wave of depolarisation from AVN across bottom of the heart
the muscular walls of ventricles contract from the bottom up

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25
Q

Role of non- conductive tissue

A

Located between atria and ventricles
prevents wave of depolarisation travelling down to ventricles causes slight delay in ventricles contracting so that ventricles fill before contraction

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26
Q

Importance of short delay between SAN and AVN waves of depolarisation

A

Ensures enough time for atria to pump all blood into ventricles
ventricle becomes full

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27
Q

Role of the medulla oblongata

A

Controls heart rate via the
autonomic nervous system uses sympathetic and parasympathetic nervous system to control SAN rhythm

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28
Q

Chemoreceptors

A

Located in carotid artery and aorta
responds to pH / CO2 conc. changes

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29
Q

Baroreceptors

A

Located in carotid artery and aorta
responds to pressure changes

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30
Q

Response to high blood pressure

A

Baroreceptor detects high blood pressure
impulse sent to medulla
more impulses sent to SAN along parasympathetic neurones (releasing noradrenaline)
heart rate slowed

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31
Q

Response to low blood pressure

A

Baroreceptor detects low blood pressure
impulse sent to medulla
more impulses sent to SAN along sympathetic neurones (releasing adrenaline)
heart rate increases

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32
Q

Response to high blood pH

A

Chemoreceptor detects low CO2 conc / high pH
impulse sent to medulla
more impulses sent to SAN along parasympathetic neurones (releasing noradrenaline)
heart rate slowed so less CO2 removed and pH lowers

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33
Q

Response to low blood pH

A

Chemoreceptor detects low CO2 conc / high pH
impulse sent to medulla
more impulses sent to SAN along sympathetic neurones (releasing adrenaline)
heart rate increases to deliver blood to heart to remove CO2

33
Q

Resting potential

A

The difference between electrical charge inside and outside the axon when a neuron is not conducting an impulse more positive ions (Na+/K+) outside axon compared to inside
inside the axon -70mV

34
Q

How is resting potential established

A

Sodium potassium pump actively transports 3 Na+ out of the axon, 2 K+ into the axon membrane more permeable to K+ (more channels and always open)
K+ diffuses out down conc. gradient - facilitated diffusion
membrane less permeable to Na+ (closed Na+ channels) higher conc. Na+ outside

35
Q

Action potential

A

When the neurone’s voltage increases beyond the -55mV threshold
nervous impulse generated generated due to membrane becoming more permeable to Na+

36
Q

Action potential: stimulus

A

Voltage-gated Na+ channels open - membrane more permeable to Na+
Na+ diffuse (facilitated) into neurone down conc. gradient
voltage across membrane increases

36
Q

Action potential: depolarisation

A

When a threshold potential is reached, an action potential is generated
more voltage-gated Na+ channels open
Na+ move by facilitated diffusion down conc. gradient into axon
potential inside becomes more positive

37
Q

Action potential: repolarisation

A

Na+ channels close, membrane less permeable it Na+
K+ voltage-gated channels open, membrane more permeable to K+
K+ diffuse out neuron down conc. gradient
voltage rapidly decreases

38
Q

All or nothing principle

A

If depolarisation does not exceed -55 mV threshold, action potential is not produced
any stimulus that does trigger depolarisation to -55mV will always peak at the same maximum voltage

38
Q

Action potential: hyperpolarisation

A

K+ channels slow to close -> overshoot in voltage
too many K+ diffuse out of neurone
potential difference decrease to
-80mV sodium-potassium pump returns neurone to resting potential

38
Q

Importance of all or nothing principle

A

Makes sure animals only respond to large enough stimuli rather than responding to every small change in environment (overwhelming)

39
Q

Refractory period

A

After an action potential has been generated, the membrane enters a period where it cannot be stimulated
because Na+ channels are recovering and cannot be opened

40
Q

Importance of refractory period

A

Ensures discrete impulses produced - action potentials separate and cannot be generated immediately unidirectional - cannot generate action potential in refractory region
limits number of impulse transmissions - prevent overwhelming

41
Q

Factors affecting speed of conductance

A

Myelination (increases speed) axon diameter (increases speed)
temperature (increases speed)

42
Q

How myelination affects speed

A

With myelination - depolarisation occurs at Nodes of Ranvier only -> saltatory conduction
impulse jumps from node-node in non-myelinated neurones, depolarisation occurs along full length of axon - slower

43
Q

How axon diameter affects speed

A

Increases speed of conductance
less leakage of ions

44
Q

How temperature affects speed

A

Increases speed of conductance
increases rate of movement of ions as more kinetic energy (active transport/diffusion)
higher rate of respiration as enzyme activity faster so ATP is produced faster - active transport faster

45
Q

Saltatory conduction

A

Gaps between myelin sheath are nodes of Ranvier
action potential can “jump” from node to node via saltatory conduction - action potential travels faster as depolarisation across whole length of axon not required

46
Q

Synapse

A

Gaps between end of axon of one neurone and dendrite of another
impulses are transmitted as neurotransmitters

47
Q

Role of calcium ions in synaptic transmission

A

Depolarisation of the pre- synaptic knob opens voltage gated Ca2+ channels and Ca2+ diffuses into synaptic knob.
stimulates vesicles containing neurotransmitter to fuse with membrane and release neurotransmitter into the synaptic cleft via exocytosis

48
Q

Why are synapses unidirectional

A

Receptors only present on the post-synaptic membrane
enzymes in synaptic cleft break down excess-unbound neurotransmitter - concentration gradient established from pre-post synaptic neurone neurotransmitter only released from the pre-synaptic neurone

49
Q

Cholinergic synapse

A

The neurotransmitter is
acetylcholine
enzyme breaking down acetylcholine = acetylcholine- esterase
breaks down acetylcholine to acetate and choline to be recycled in the pre-synaptic neurone

50
Q

Summation

A

Rapid build-up of neurotransmitters in the synapse to help generate an action potential by 2 methods:
spatial or temporal
required because some action potentials do not result in sufficient concentrations of neurotransmitters released to generate a new action potential

51
Q

Spatial summation

A

Many different neurones collectively trigger a new action potential by combining the neurotransmitter they release to exceed the threshold value
e.g., retinal convergence for rod cells

52
Q

Temporal summation

A

When one neurone releases neurotransmitters repeatedly over a short period of time to exceed the threshold value
e.g., 1 cone cell signalling 1 image to the brain

53
Q

Neuromuscular junction

A

Synapse that occurs between a motor neurone and a muscle similar to synaptic junction

54
Q

Inhibitory synapses

A

Causes chloride ions (Cl-) to move into post-synaptic neurone and K+ to move out
makes membrane hyperpolarise (more negative) so less likely an action potential will be propagated

55
Q

Compare the neuromuscular junction (NMJ) with a cholinergic synapse

A

both: unidirectional- neurotransmitters receptors only on post-synaptic membrane

NMJ-only excitatory
cholinergic synapse- excitatory OR inhibitory

NMJ-connects motor neurons-muscles
cholinergic synapse- connect two neurones(relay, motor, sensory)

NMJ-end point for action potential cholinergic synapse-new action potential generated in next neuron

NMJ-ach binds to receptor on muscle fibre
cholinergic synapse-ach binds to receptor on post-synaptic membrane

56
Q

Role of Ca2+ in sliding filament theory

A

Ca2+ enter from sarcoplasmic reticulum and causes tropomyosin to change shape
myosin heads attach to exposed binding sites on actin forming actin-myosin cross bridge activates ATPase on myosin
ATP hydrolysed so energy for myosin heads to be recocked

56
Q

Myofibril

A

Made up of fused cells that share nuclei/cytoplasm (sarcoplasm) and many mitochondria
millions of muscle fibres make myofibrils - bringing about movement

57
Q

Role of tropomyosin in sliding filament theory

A

Tropomyosin covers binding site on actin filament
Ca2+ bind to tropomyosin on actin so it changes shape exposes binding site
allows myosin to bind to actin, forming cross bridge

58
Q

Role of ATP in myofibril contraction

A

Hydrolysis of ATP -> ADP + Pi releases energy
movement of myosin heads pulls actin - power stroke
ATP binds to myosin head causing it to detach, breaking cross bridge
myosin heads recocked
active transport of Ca2+ back to sarcoplasmic reticulum

59
Q

Role of myosin in myofibril contraction

A

Myosin heads (with ADP attached) attach to binding sites on actin.
form actin-myosin cross bridge power stroke - myosin heads move pulling actin
requires ATP to release energy ATP binds to myosin head to break cross bridge so myosin heads can move further along actin

60
Q

Phosphocreatine

A

A chemical which is stored in muscles
when ATP concentration is low, this can rapidly regenerate ATP from ADP by providing a Pi group.
for continued muscle contraction

61
Q

Slow-twitch muscle fibres

A

Specialised for slow, sustained contractions (endurance)
lots of myoglobin
many mitochondria - high rate aerobic respiration to release ATP
many capillaries - supply high concentrations of glucose/O2 & prevent build-up of lactic acid e.g. thighs / calf

62
Q

Fast-twitch muscle fibres

A

Specialised in producing rapid, intense contractions of short duration
glycogen -> hydrolysed to glucose -> glycolysis
higher concentration of enzymes involved in anaerobic respiration - fast glycolysis phosphocreatine store
e.g., eyelids/biceps

63
Q

Homeostasis

A

Maintenance of constant internal environment via physiological control systems
control temperature, blood pH, blood glucose concentration and water potential within limits

64
Q

Negative feedback

A

When there is a deviation from normal values and restorative systems are put in place to return this back to the original level
involves the nervous system and hormones

65
Q

Islets of Langerhans

A

Region in the pancreas containing cells involved in detecting changes in blood glucose levels
contains endocrine cells (alpha cells and beta cells) which release hormones to restore blood glucose levels

66
Q

Alpha cells

A

Located in the islets of Langerhans
release glucagon
when detect blood glucose concentration is too low

66
Q

Beta cells

A

Located in the islets of Langerhans
release insulin
when detect blood glucose concentration is too high

67
Q

Factors affecting blood glucose concentration

A

Eating food containing carbohydrates -> glucose absorbed from the intestine to the blood
exercise -> increases rate of respiration, using glucose

68
Q

Action of insulin

A

Binds to specific receptors on membranes of liver cells
increases permeability of cell membrane (GLUT-4 channels fuse with membrane)
glucose can enter from blood by facilitated diffusion
activation of enzymes in liver for glycogenesis
rate of respiration increases

69
Q

Action of glucagon

A

Binds to specific receptors on membranes of liver cells activates enzymes for glycogenolysis
activates enzymes for
gluconeogenesis
rate of respiration decreases blood glucose concentration increases

70
Q

Gluconeogenesis

A

Creating glucose from non- carbohydrate stores in liver e.g. amino acids -> glucose
occurs when all glycogen has been hydrolysed and body requires more glucose
initiate by glucagon when blood glucose concentrations are low

71
Q

Role of adrenaline

A

Secreted by adrenal glands above the kidney when glucose concentration is too low (exercising)
activates secretion of glucagon glycogenolysis and gluconeogenesis
works via secondary messenger model

72
Q

Glycogenolysis

A

Hydrolysis of glycogen back into glucose
occurs due to the action of glucagon to increase blood glucose concentration

73
Q

Glycogenesis

A

Process of glucose being converted to glycogen when blood glucose is higher than normal
caused by insulin to lower blood glucose concentration

74
Q

What is a second messenger model

A

Stimulation of a molecule
(usually an enzyme) which can then stimulate more molecules to bring about desired response adrenaline and glucagon demonstrate this because they cause glycogenolysis to occur inside the cell when binding to receptors on the outside

75
Q

Second messenger model process

A

Adrenaline/glucagon bind to specific complementary receptors on the cell membrane activate adenylate cyclase converts ATP to cyclic AMP (secondary messenger)
cAMP activates protein kinase A (enzyme)
protein kinase A activates a cascade to break down glycogen to glucose (glycogenolysis)

76
Q

Diabetes

A

A disease when blood glucose concentration cannot be controlled naturally

77
Q

Type 1 diabetes

A

Due to body being unable to produce insulin
starts in childhood autoimmune disease where beta cells attacked
treated using insulin injections

78
Q

Type 2 diabetes

A

Due to receptors in target cells losing responsiveness to insulin usually develops due to obesity and poor diet
treated by controlling diet and increasing exercise with insulin injections

79
Q

Osmoregulation

A

Process of controlling the water potential of the blood controlled by hormones e.g., antidiuretic hormone (affects distal convoluted tubule and collecting duct)

80
Q

Nephron

A

The structure in the kidney where blood is filtered, and useful substances are reabsorbed into the blood

81
Q

nephron structure

A
  1. glomerulus- filters small solutes from the blood
  2. proximal convoluted tubule- reabsorbs ions, water and nutrients removes toxins and adjust filtrate PH
  3. defending loop of Henle- aquaporins allow water to pass from the filtrate into the interstitial
  4. ascending loop of henel- reabsorbs Na+ and Cl- from the filtrate into the interstitial fluid
  5. distal convoluted tubule- selectively secretes and absorbs different ions to maintain blood pH and electrolyte balance
  6. collecting duct- reabsorbs solutes and water from filtrate
82
Q

Formation of glomerular filtrate

A

Diameter of efferent arteriole is smaller than afferent arteriole build-up of hydrostatic pressure water/glucose / ions squeezed out capillary into Bowman’s capsule through pores in capillary endothelium, basement membrane and podocytes
large proteins too large to pass

83
Q

Reabsorption of glucose by PCT

A

Co-transport mechanism
walls made of microvilli epithelial cells to provide large surface area for diffusion of glucose into cells from PCT sodium actively transported out cells into intercellular space to create a concentration gradient glucose can diffuse into the blood again

84
Q

Role of hypothalamus in
osmoregulation

A

Contains osmoreceptors which detect changes in water potential
produces ADH
when blood has low water potential, osmoreceptors shrink and stimulate more ADH to be made so more released from the pituitary gland

84
Q

Counter current multiplier mechanism

A

Describes how to maintain a gradient of Na+ in medulla by the loop of Henle.
Na+ actively transported out ascending limb to medulla to lower water potential
water moves out descending limb + DCT + collecting duct by osmosis due to this water potential gradient

85
Q

Reabsorbtion of water by DCT / collecting duct

A

Water moves out of DCT and collecting duct by osmosis down a water potential gradient controlled by ADH which changes the permeability of membranes to water

86
Q

Anti-diuretic hormone

A

Produced by hypothalamus, released by pituitary gland affects permeability of walls of collecting duct & DCT to water
more ADH means more aquaporins fuse with walls so more water is reabsorbed back to blood- urine more concentrated.

87
Q

Role of pituitary gland in osmoregulation

A

ADH moves to the pituitary gland from the hypothalamus releases ADH into capillaries travels through blood -> kidney

A-level Biology (8 decks)

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