Unit 6 - Organisms respond to changes in their internal and external environments Flashcards
1
Q
Homeostasis defintion
A
maintaining a constant internal environment within restricted limits in organisms
2
Q
What happens when there is an increase in body temperature?
A
- receptors (skin, hypothalamus) detect change
- hypothalamus
- sweat glands, vasodilation, hairs lie flat
3
Q
What happens when there is a decrease in body temperature?
A
- receptors (skin, hypothalamus) detect change
- hypothalamus
- vasoconstriction, shivering, hairs erect
4
Q
Vasodilation
A
arterioles dilate so blood in capillaries flows near surface of skin
5
Q
Vasoconstriction
A
arterioles constrict so blood in capillaries flows further from the surface of the skin
6
Q
Glycogenesis
A
glucose to glycogen
7
Q
Glycogenolysis
A
liver breaks down glycogen to glucose
8
Q
Gluconeogenesis
A
production of glucose from other sources e.g. glycerol, pyruvate and amino acids
9
Q
What are the specialised cells in the pancreas called?
A
islets of langerhans
10
Q
alpha cells
A
make and secrete glucagon when there is a low blood glucose conc
11
Q
beta cells
A
make and secrete insulin when there is a high blood glucose conc
12
Q
What does insulin stimulate?
A
- glycogenesis
- increased absorption rate (activates carrier proteins)
- increased respiratory rate
- fat
13
Q
What does glucagon stimulate?
A
- gluconeogenesis
- glycogenolysis
14
Q
What is the cause of Type I diabetes?
A
pancreas does not make enough insulin
15
Q
What is the effect of Type I diabetes?
A
uncontrolled blood glucose concentration, kidneys excrete glucose in urine
16
Q
What are symptoms of Type I diabetes?
A
thirsty, frequent urination, lack energy, tired, loss of weight
17
Q
What is the treatment for Type I diabetes?
A
insulin injections, transplants, adult stem cells and genetic engineering
18
Q
What is the cause of Type II diabetes?
A
insulin is made but less and cells stop responding to the insulin as receptors are less sensitive/ responsive
19
Q
What are risk factors of Type II diabetes?
A
people over the age of 40, obesity, lack of exercise, genetics
20
Q
What are the symptoms of Type II diabetes?
A
thirsty, lack energy, tired, loss of weight
21
Q
What is the treatment for Type II diabetes?
A
balanced diet, lose weight, regular exercise, drugs to help insulin work
22
Q
What is an auto-immune disease?
A
lymphocytes produce antibodies which destroy their own body cells
23
Q
What happens during ultrafiltration?
A
left ventricle contracts and creates high hydrostatic pressure which forces urea, water, glucose and amino acids out of the glomerulus into the renal capsule
24
Q
What do substances have to go through when filtered out of glomerulus?
A
- pores in capillary endothelium
- basement membrane
- podocytes
25
What happens in the proximal convoluted tubule?
selective reabsorption of all glucose, all amino acids, some water
26
What happens in the loop of Henle?
- in the ascending limb, Na+ are actively transported into the medulla
- this lowers the water potential of the medulla
- water is reabsorbed by osmosis out of the descending limb into the medulla
27
What are adaptations of the proximal convoluted tubule?
- folds in membrane create high surface area
- lots of mitochondria to release ATP to release energy for active transport
- lots of carrier and channel proteins for the facilitated diffusion of glucose
28
What happens when there is a low blood water potential?
- osmoreceptors detect change
- posterior pituitary gland releases more ADH
- ADH stimulate aquaporins to be inserted into membrane of collecting duct making it more permeable to water so more water is reabsorbed by osmosis
- small volume of concentrated urine
29
What happens when there is a high blood water potential?
- osmoreceptors detect change
- posterior pituitary gland releases less ADH
- distal convoluted tubule and collecting duct membrane is less permeable to water so less water is reabsorbed by osmosis
- large volume of dilute urine
30
Describe the second messenger model of glucagon action
- glucagon binds to receptor on cell surface membrane of liver cell
- stimulates adrenal cyclase to convert ATP into cAMP (second messenger)
- activates protein kinase which stimulate the conversion of glycogen into glucose (glycogenolysis)
31
What does insulin do?
- stimulate more channel proteins to be inserted into cell membrane so more glucose is absorbed by facilitated diffusion
32
Name all the key parts of a motor neurone
dendrites, cell body, nucleus, cytoplasm, axon, myelin sheath, schwann cell, schwann cell nucleus, nodes of ranvier
33
Explain how a resting potential is maintained across the axon membrane in a neurone
- higher concentration of K+ inside and high concentration of Na+ outside
- membrane more permeable to K+ leaving than Na+ entering
- Na+ actively transported out and K+ in
34
Describe the process of an action potential
- resting membrane potential at start
- stimulus causes Na+ channels to open
- Na+ diffuses into cell down electrochemical gradient, depolarising cell membrane
- Na+ channels close and K+ channels open at highest voltage
- K+ diffuses out of neuron through K+ channels down electrochemical gradient
- K+ channels remain open, additional K+ leave cell leading to hyperpolarisation
- voltage gated K+ channels close
- Na+/K+ pump returns neurone to resting potential
35
What is the all or nothing principle?
any stimulus that causes the membrane to reach threshold potential will generate an action potential. all action potentials have the same magnitude
36
What is the difference as a result of a weak or a strong stimulus?
a bigger stimulus will cause more frequent action potentials
37
Why does the refractory period occur?
Na+ channels closed during repolarisation. K+ channels closed during hyperpolarisation. Channels can't be forced to open.
38
Explain the importance of the refractory period
- ensures unidirectional action potentials
- ensures discrete action potentials
- limits frequency of action potentials
39
Name factors which affect the speed of conduction
- myelination
- temperature
- axon diameter
40
How does axon diameter affect the speed of conduction?
greater diameter means faster speed of conduction because there is less resistance to the flow of ions
41
How does temperature affect the speed of conduction?
higher temperature means faster speed of conduction because rate of diffusion is faster however when temperature is too high the Na+ and K+ protein channels denature
42
Explain why myelinated axons conduct action potentials faster than unmyelinated axons
- myelination provides insulation
- saltatory conduction
- in non-myelinated axon, depolarisation occurs along whole length of axon
43
What is saltatory conduction?
in a myelinated neurone, depolarisation only happens at the node of ranviers. action potential 'jumps' from node to node
44
What is the wave of depolarisation?
depolarisation spreads forward in one direction as Na+ diffuses causing channels in the next region of the neurone to open
45
What is a stimulus?
change in the internal/ external environment that leads to a response
46
What are the two types of behaviour in response to a stimulus?
taxis and kinesis
47
What is taxis?
a simple response whose direction is determined by the direction of a stimulus
48
What is kinesis?
random movement in response to a stimulus
49
What might organisms do to show taxis?
move towards or away a stimulus
50
What might organisms do to show kinesis?
change speed at which they move and rate they change direction
51
What is a tropism?
growth of a plant in response to a directional stimulus
52
How do plants respond to external stimuli?
- growth factors IAA
- small quantities
- affect growth
- made by cells not organs
- affect the tissue that releases them
53
Explain phototropism in shoots
- cells in the tip of the shoot produce IAA and it diffuses into the shoot
- IAA transported equally at first down the shoot
- light causes IAA to move to the shaded side of the shoot
- greater concentration of IAA builds up on the shaded side
- IAA causes cell elongation on the shaded side
- shaded side elongates faster than the light side hence the shoot tip bends towards the light
54
What is the effect of IAA in roots?
inhibits cell elongation
55
Explain gravitropism in roots
- cells in the tip of the root produce IAA and transport it down the root
- initially it is transported equally to both sides
- gravity influences the movement from the upper side to the lower side
- greater concentration of IAA builds up on the lower side
- IAA inhibits the elongation of root cells so with a greater concentration on the lower side they elongate less
- greater elongation on upper side so roots bends downwards due to gravity
56
What is the acid growth hypothesis?
active transport of H+ from the cytoplasm into the cell wall causes the cell wall to become more plastic and elongate by expansion
57
Describe the sequence of events involved in transmission across a cholinergic synapse.
Depolarisation of presynaptic membrane
Calcium channels open and calcium ions enter
(Calcium ions cause) synaptic vesicles move to/fuse with
presynaptic membrane and release
acetylcholine/neurotransmitter
Acetylcholine/neurotransmitter diffuses across (synaptic cleft)
(Acetylcholine attaches) to receptors on the postsynaptic membrane
58
What are the two types of synapse?
excitatory and inhibitory
59
Describe the sequence of events involved in transmission across an inhibitory synapse after the neurotransmitter is released
- neurotransmitters bind to complementary receptors on postsynaptic membrane causing Cl- channels to open and chloride ions diffuse in
- membrane potential becomes more negative
- less likely to generate an action potential because more Na+ needed to reach the threshold and depolarise the membrane
60
Why are synapses unidirectional?
- vesicles with neurotransmitter is only in presynaptic neurone
- receptors are only on postsynaptic membrane
61
What is temporal summation?
need multiple action potentials along the same presynaptic bulb to reach the threshold
62
What is spatial summation?
action potentials arrive along multiple neurones at the same time to reach the threshold
63
What is the sarcoplasm?
muscle cells cytoplasm
64
What is the sarcoplasmic reticulum?
a network of internal membranes that runs through the sarcoplasm. it stores and releases calcium ions that are needed for muscle contraction
65
What is the sarcolemma?
the cell membrane of muscle fibre cells
66
What are transverse (T) tubules?
bits of the sarcolemma that folds inwards across the muscle fibre and stick into the sarcoplasm. help spread the action potentials throughout the sarcoplasm so they reach all parts of the muscle fibre
67
What is a myofibril?
a long, cylindrical organelle within a muscle cells that's highly specialised for contraction
68
What is the sarcomere?
a short repeating unit that's part of a myofibril made up of overlapping myosin and actin filaments
69
What are the parts of a pacinian corpuscle?
capsule, lamella of connective tissue, stretch-mediated Na+ channels, sensory neurone ending
70
What do pacinian corpuscles respond to?
mechanical stimuli e.g. pressure and high frequency vibration
71
Resting state of pacinian corpuscles
Na+ channels are too narrow to allow for the diffusion of Na+ ions. membrane is polarised
72
What happens when pacinian corpuscles detect pressure?
- pressure deforms and stretches the membrane
- widens the stretch-mediated Na+ channels
- sensory neurone ending more permeable so Na+ diffuse in down electrochemical gradient
- neurone ending is depolarised which triggers an action potential
73
What are the two photoreceptors in the eye?
rods and cones
74
What is the blindspot?
the point in the eye where there are no receptors
75
What type of images do rod cells allow for?
black and white, low resolution
76
What happens when light hits a rod cell?
rhodopsin is broken down, the rod cells causes the bipolar neurone to depolarise, action potential is generated
77
Why can the brain not distinguish between seperate sources of light in low light intensities?
convergence of 3 rod cones to a single bipolar cell
78
What do rod cells give?
low visual acuity
79
What type of images do cone cells allow for?
colour, high resolution
80
Why can the brain distinguish between seperate sources of light in high light intensities?
each cone cell is connected to a separate bipolar cell so generates separate action potentials
81
What is found in a cone cell?
3 different types of iodopsin pigment (R, G and B) – different wavelengths
82
Where are cone cells mainly found?
fovea
83
Which filament is found in the I band?
actin
84
Which filaments are found in the A band?
actin and myosin
85
Which filament is found in the H band?
myosin
86
What happens in the sliding filament theory?
- I band gets shorter
- H zones get shorter
- Z lines get closer together
- A bands stay the same length
87
Explain how a muscle contraction occurs
- action potential moves down the T-tubules to the sarcoplasmic reticulum where voltage gated Ca2+ channels open
- Ca2+ diffuse down electrochemical gradient towards actin
- Ca2+ bind to protein (troponin) which causes tropomyosin to move and expose the actin-myosin binding site
- myosin head binds to actin-myosin binding site on the actin and forms an actinomyosin bridge
- Ca2+ activates ATP hydrolase which hydrolyses ATP into ADP+Pi
- the energy released from ATP causes the myosin head to bend which pulls the actin filament along
- another ATP molecule provides the energy to break the actinomyosin bridge so the myosin head detaches from the actin
- myosin head returns to its starting position and reattaches to a different binding site
- a new actinomyosin bridge is formed and the cycle is repeated
88
What is the phosphocreatine pathway?
ATP is made from phosphorylating ADP using a phosphate group taken from PCr
89
What are the two types of muscle fibres?
slow twitch and fast twitch
90
What do slow twitch muscle fibres do?
work for sustained lengths of time without getting tired
91
What do fast twitch muscle fibres do?
short bursts - anaerobic
92
How many mitochondria are there in slow and fast twitch muscle fibres?
slow twitch - many
fast twitch - few
93
How many capillaries are there in slow and fast twitch muscle fibres?
slow twitch - many
fast switch - few
94
What is the speed of contraction in slow and fast twitch muscle fibres?
slow twitch - slow
fast twitch - fast
95
Which muscle fibre has a PCr store?
fast twitch
96
What is the force of contraction in slow and fast twitch muscle fibres?
slow twitch - low
fast twitch - high
97
What is the activity type for slow twitch muscle fibres?
posture, long distance running
98
What is the activity type for fast twitch muscle fibres?
sprint, blinking
99
Which muscle fibre is resistance to fatigue?
slow twitch
100
Why can heart muscle cells be described as myogenic?
they will contract without any external stimulus
101
How is the cardiac cycle controlled?
- SAN (sinoatrial node) initiates heartbeat
- SAN sends wave of electrical activity causing atrial contraction
- AVN (atrioventricular node) delays electrical activity
- atria empty before ventricles contract
- AVN sends wave of electrical activity down bundle of His/ purkyne fibres
- causing ventricles to contract/ ventricular systole
102
What does the sympathetic nervous system do?
stimulates and speeds up activities
103
What does the parasympathetic nervous system do?
slows down activities and controls normal resting conditions
104
What do chemoreceptors do?
detect changes in the chemical concentrations of blood
105
Where are chemoreceptors found?
carotid sinus and aortic arch
106
What is the name of the sympathetic motor neurone that causes heart rate to increase?
accelerator nerve
107
What is the name of the parasympathetic motor neurone that causes heart rate to decrease?
vagus nerve
108
What is the detection and response to a decrease in blood pH levels?
- An increase in carbon dioxide leads to an increase in the concentration of H+ ions in the blood and a fall in the blood pH (acidity increases)
- Chemoreceptors in the carotid sinus and aortic arch detect the increase in H+ ions and sends
action potentials along a sensory neurone to the medulla oblongata
- increased frequency of action potentials are sent on the accelerator nerve from the CNS to the SAN
- pH of blood rises and the chemoreceptors reduce the frequency of action potentials to the medulla oblongata
- the medulla oblongata reduces the frequency to the SAN which reduces the heart rate
109
What do baroreceptors do?
detect change in blood pressure
110
Where are baroreceptors found?
carotid sinus
111
What happens when the baroreceptors detect a high blood pressure?
- action potential to the medulla oblongata
- action potential via the parasympathetic neurones which secrete acetylcholine
- ACh binds to receptors on the SAN
- heart rate slows down
- reduced blood pressure
112
What happens when the baroreceptors detect a low blood pressure?
- action potential to the medulla oblongata
- action potential via the sympathetic neurones which secrete noradrenaline
- noradrenaline binds to receptors on the SAN
- heart rate increases
- increased blood pressure
