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Biology- Topic 6 > 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

What is a stimulus?

A

Detectable change in the environment
- detected by cells called receptors.

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2
Q

What are the two main structures of the nervous system?

A
  • Central nervous system (CNS) = brain and spinal cord;
  • Peripheral nervous system = receptors, sensory and motor neurones.
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3
Q

What is a 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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4
Q

What is the importance of simple reflexes?

A
  • rapid - short pathway: only 3 neurones + few synapses
  • autonomic - unconscious
  • protect from harmful stimuli
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5
Q

What is 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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6
Q

What is phototropism?

A

Response of plants to light.

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7
Q

What is gravitropism?

A

Response of plants to gravity.

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8
Q

What is hydrotropism?

A

Response of plants to water.

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9
Q

What is indoleacetic acid (IAA)?

A

Type of auxin (plant hormone) that controls cell elongation in shoots and inhibits growth of cells in roots.
- made in tips of roots/shoots
- can diffuse into other cells

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10
Q

How does phototropism occur in shoots?

A

Shoot tip produces IAA which diffuses to other cells; IAA accumulates on shaded side of shoot, stimulating cell elongation and causing the plant to bend towards light.
- ( positive phototropism)

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11
Q

How does phototropism occur in roots?

A

Root tip produces IAA; IAA concentration increases on lower (darker) side, inhibiting cell elongation, causing root to bend away from light. (negative)

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12
Q

How does gravitropism occur in shoots?

A

Shoot tip produces IAA which diffuses from upper side to lower side in response to gravity, stimulating cell elongation and causing the plant to grow upwards.
- negative gravitropism

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13
Q

How does gravitropism occur in roots?

A

Root tip produces IAA; IAA accumulates on lower side in response to gravity, inhibiting cell elongation and causing the root to bend downwards.
- positive gravitropism

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14
Q

What is taxis?

A

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

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15
Q

What is kinesis?

A

When an organism changes its speed of movement and rate of change of direction in response to a stimulus.

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16
Q

What are receptors?

A

Cells that respond to specific stimuli; stimulation leads to establishment of a generator potential, causing a response.

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17
Q

What is a Pacinian corpuscle?

A

Receptor that responds to pressure changes, occurring deep in skin mainly in fingers and feet.
- sensory neurone wrapped with layers of tissue

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18
Q

How does a Pacinian corpuscle detect pressure?

A

When pressure is applied, stretch-mediated sodium ion channels are deformed, allowing sodium ions to diffuse into the sensory neurone, increasing membrane potential and establishing a generator potential.

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19
Q

What are rod cells?

A

Photoreceptor cells concentrated at the periphery of the retina, containing rhodopsin pigment
- do not detect colour
- connected in groups to one bipolar cell

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20
Q

What are cone cells?

A
  • concentrated on the fovea, fewer at periphery of retina
  • 3 types containing different iodopsin pigments
  • detect coloured light
  • one cone connects to one neurone
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21
Q

How do rods and cones differ in sensitivity to light?

A

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

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22
Q

How do rods and cones differ in visual acuity?

A

Cones provide higher visual acuity; rods have lower visual acuity.

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23
Q

What is visual acuity?

A

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

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24
Q

How do rods and cones differ in colour vision?

A

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

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25
Q

Why do 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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26
Q

Why do cones have low sensitivity to light?

A

One cone connects to one neurone
- no retinal convergence
- requiring higher light intensity to reach threshold potential.

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27
Q

Why do rods have low visual acuity?

A

Rods are 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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28
Q

Why do cones have high visual acuity?

A

One cone connects to one neurone, allowing the brain to receive distinct impulses from adjacent cones.
- can distinguish between seperate sources of light

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29
Q

Why do rods have monochromatic vision?

A

Rods contain one type of pigment (rhodopsin).

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30
Q

Why do cones provide 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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31
Q

myogenic

A

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

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32
Q

What is the sinoatrial node?

A

Located in the right atrium, known as the pacemaker - releases a wave of depolarisation across the atria, causing muscle contraction.

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33
Q

What is the atrioventricular node?

A
  • Located near the border of the right/left ventricle within the atria
  • releases another wave of depolarisation after a short delay when it detects the first wave from the SAN.
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34
Q

What is the Bundle of His?

A

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

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35
Q

What are Purkyne fibres?

A
  • in the walls of the ventricles
  • they spread the wave of depolarisation from the AVN across the bottom of the heart
  • the muscular walls of ventricles contract from bottom up
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36
Q

What is the role of non-conductive tissue in the heart?

A

Located between the atria and ventricles, it prevents the wave of depolarisation from travelling down to the ventricles, causing a slight delay in contraction so that ventricles fill before contraction

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37
Q

Why is there a 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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38
Q

What is the role of the medulla oblongata?

A

Controls heart rate via the autonomic nervous system, using sympathetic and parasympathetic systems to control SAN rhythm.

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39
Q

What are chemoreceptors?

A

Located in the carotid artery and aorta, they respond to pH / CO2 concentration changes.

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40
Q

What are baroreceptors?

A

Located in the carotid artery and aorta, they respond to pressure changes.

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41
Q

What is the 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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42
Q

What is the response to low blood pressure?

A

Baroreceptor detects low blood pressure, sends impulse to medulla, which sends more impulses to SAN along sympathetic neurones ( releasing adrenaline), increasing heart rate.

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43
Q

What is the 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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44
Q

What is the 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
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45
Q

What is 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 is -70mV.
46
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
47
Q

What is action potential?

A

When the neurone’s voltage increases beyond the -55mV threshold, generating a nervous impulse due to increased membrane permeability to Na+.

48
Q

action potential stimulus

A

Voltage-gated Na+ channels open, making the membrane more permeable to Na+, which diffuses into the neurone, increasing the voltage.

49
Q

What happens during depolarisation in action potential?

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

50
Q

What happens during repolarisation in action potential?

A

Na+ channels close, K+ voltage-gated channels open, allowing K+ to diffuse out of the neuron down conc-gradient , causing the voltage to rapidly decrease.

51
Q

What happens during hyperpolarisation in action potential?

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
52
Q

What is the all or nothing principle?

A

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

53
Q

What is the importance of the all or nothing principle?

A

Ensures animals only respond to large enough stimuli, preventing overwhelming responses to every small change in the environment.

54
Q

What is the refractory period?

A

After an action potential has been generated, the membrane cannot be stimulated as Na+ channels are recovering and cant be opened

55
Q

What is the importance of the 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
56
Q

What factors affect the speed of conductance?

A

Myelination, axon diameter, and temperature.

57
Q

How does myelination affect 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

58
Q

How does axon diameter affect speed?

A

Increased diameter reduces ion leakage, increasing speed of conductance.

59
Q

How does temperature affect 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
60
Q

What is 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
61
Q

What is a synapse?

A

Gaps between the end of the axon of one neurone and the dendrite of another, where impulses are transmitted as neurotransmitters.

62
Q

What is the 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
63
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
64
Q

What is a 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

65
Q

What is 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
66
Q

What is spatial summation?

A

Many different neurones collectively trigger a new action potential by combining neurotransmitters to exceed the threshold value.

67
Q

What is temporal summation?

A

When one neurone releases neurotransmitters repeatedly over a short period of time to exceed the threshold value.

68
Q

What are inhibitory synapses?

A

Causes chloride ions (Cl-) to move into the post-synaptic neurone and K+ to move out, making the membrane hyperpolarised and less likely to propagate an action potential.

69
Q

What is a neuromuscular junction?

A

A synapse that occurs between a motor neurone and a muscle, similar to a synaptic junction.

70
Q

What is a myofibril?

A

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

71
Q

What is the 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
72
Q

What is the 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
73
Q

What is the 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
74
Q

What is the 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
75
Q

What is phosphocreatine?

A

A chemical stored in muscles that can rapidly regenerate ATP from ADP by providing a Pi group for continued muscle contraction.

76
Q

What are 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
77
Q

What are 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
78
Q

What is homeostasis?

A

Maintenance of a constant internal environment via physiological control systems.

79
Q

What is myoglobin?

A

A protein that contains many mitochondria for high rates of aerobic respiration to release ATP.

80
Q

What is the role of capillaries in muscle tissue?

A

They supply high concentrations of glucose and O2 and prevent the build-up of lactic acid.

81
Q

What are fast-twitch muscle fibers specialized for?

A

Producing rapid, intense contractions of short duration.

82
Q

What is the process of glycogen hydrolysis?

A

Glycogen is hydrolyzed to glucose, which then undergoes glycolysis.

83
Q

What does negative feedback involve?

A

Restorative systems are put in place to return deviations from normal values back to original levels.

84
Q

What are the Islets of Langerhans?

A

Regions in the pancreas that detect changes in blood glucose levels
- contain endocrine cells (alpha and beta) which release hormones to restore blood glucose levels

85
Q

What do alpha cells in the Islets of Langerhans do?

A

Release glucagon when blood glucose concentration is too low.

86
Q

What do beta cells in the Islets of Langerhans do?

A

Release insulin when blood glucose concentration is too high.

87
Q

What factors affect blood glucose concentration?

A

Eating carbohydrates increases glucose in the blood; exercise increases respiration using glucose.

88
Q

What is the 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
89
Q

What is the 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
90
Q

What is the role of adrenaline in blood glucose regulation?

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
91
Q

What is 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
92
Q

What is glycogenolysis?

A

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

93
Q

What is glycogenesis?

A

Conversion of glucose to glycogen when blood glucose is higher than normal, caused by insulin.

94
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
95
Q

What is the process of the second messenger model?

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)
96
Q

What is diabetes?

A

A disease when blood glucose concentration cannot be controlled naturally.

97
Q

What is Type 1 diabetes?

A

An autoimmune disease where the body cannot produce insulin, starting in childhood.

98
Q

What is Type 2 diabetes?

A

Occurs when target cell receptors lose responsiveness to insulin, usually due to obesity and poor diet.

99
Q

What is osmoregulation?

A

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

100
Q

What is the nephron?

A

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

101
Q

How is glomerular filtrate formed?

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
102
Q

Reabsorbtion 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
103
Q

What is the 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
104
Q

How is water reabsorbed by the DCT and 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
105
Q

What is the role of the 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
106
Q

What is anti-diuretic hormone (ADH)?

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.
107
Q

What is the role of the pituitary gland in osmoregulation?

A
  • ADH moves to the pituitary gland from the hypothalamus - releases ADH into capillaries
  • travels through blood -> kidney
108
Q

compare the NMJ with a cholinergic synapse

A

BOTH= unidirectional
NMJ= excitatory CS= excitatory or inhibitory
NMJ= connects motor neurones- muscles CS= connects 2 neurones
NMJ= end point for action potential CS= new action potential generated in next neurone
NMJ= ach binds to receptors on muscle fibre CS= ach binds to recpetors on post-synaptic membrane

109
Q

what is 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

110
Q

pacinian corpsule structure

A

Biology- Topic 6 (1 decks)

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