Topic six Flashcards
(97 cards)
1
Q
Stimulus
A
A detectable change in the internal / external environment of an organism that leads to a response.
2
Q
Taxes
A
-Movement of a motile organism in response to a stimulus
-A simple directional response, based on the direction of the stimulus
-Positive taxis is when the organism moves towards a favourable stimulus
-Negative taxis is when the organism moves away from an unfavourable stimulus
3
Q
Kineses
A
-Non-directional response
-The organism changes the speed of movement and the rate it changes direction in response to stimulus
-If the organism moves into unfavourable conditions, the rate of turning decreases, so the organism moves in long straight lines before turning
-Movement is random
4
Q
What is a tropism?
A
-When a plant responds to stimuli by growth
-Positive-when the plant grows towards the stimulus
-Negative-when the plant grows away from the stimulus
-Plants can respond to light, gravity and water
-Controlled by plant growth factors
5
Q
Indoleacetic acid (IAA)
A
-A type of auxin that can stimulate cell elongation in shoots, but inhibit cell growth in roots
-It is made in the tip and shoots, but can diffuse to other cells
6
Q
Positive phototropism in plants
A
-Shoot tip cell produces IAA, which causes elongation in the shoot and can diffuse to other cells
-If light is unilateral, the IAA will diffuse to the shaded side of the plant, increasing the concentration there
-IAA causes the cell elongation, so the shaded side grows more, causing the plant to bend towards the light
7
Q
Negative phototropism in plants
A
-Roots do not need light, growing away from the light is an advantage, as it allows the roots to grow deep into the soil, anchoring the plant
-IAA inhibits growth in roots, so the plant will elongate more on the lighter side to bend away from the light
8
Q
Negative gravitropism in plant shoots
A
-IAA diffuses from the upper side to the lower side of a shoot
-If the plant is vertical, this will cause it to elongate and grow upwards
-If the plant is on its side, the cells on the lower side will elongate, causes it to bend up which is negative gravitropism
9
Q
Positive gravitropism in plant roots
A
-IAA diffuses to the lower side of the root, so the upper side will elongate
-This causes the roots to bend downwards towards gravity, anchoring the plant
10
Q
Role of CNS
A
Processes information
11
Q
Role of sensory neurones
A
Carry electrical impulses from the peripheral sense organs to the CNS
12
Q
Role of motor neurones
A
Send electrical impulses from the CNS to effector organs
13
Q
Stimulus
A
Change in the internal or external environment
14
Q
Receptor
A
Detects a stimulus, receptor cells are specific to one type of stimulus
15
Q
Control centre
A
Also known as the coordinator, this is the CNS
16
Q
Effector
A
Produces a response
17
Q
Voluntary response
A
Involves the brain, for conscious thinking, and the spinal chord
18
Q
Involuntary response
A
Occurs without thinking and often involves the spinal chord
19
Q
Key features of sensory reception
A
-Stimuli are detected through receptor cells
-Each receptor cell responds to a single specific stimulus
-Receptors are found at the end of sensory neurones
-They act as transducers by converting a stimulus to an electrical signal (first by a generator potential, then an action potential in a sensory neurone
20
Q
Describe a simple reflex arc
A
Receptor detects stimulus
-> relay neuron in CNS -> coordinates response -> motor neuron -> response by effector
21
Q
Advatages of a simple reflex arc
A
-Rapid response to potentially dangerous stimuli as only three neurons are involved
-Instinctive
22
Q
Describe the structure of the pacinian corpuscle
A
-Single nerve fibre surrounded by layers of connective tissue that are separated by a viscous gel and contained by a capsule
-Stretch mediated Na+ channels on a plasma membrane
-Capillary runs along the base layer of the tissue
23
Q
Describe how the pacinian corpuscle works
A
-At rest, the stretch-mediated Na+ channels, located on the nerve ending membrane, are too narrow to allow Na+ through
-When pressure is applied to the skin, it deforms the layers of connective tissue on the pacinian corpuscle and sensory neurone membrane, opening the stretch mediated Na+ channels
-Na+ surrounding the neurone diffuses in and causes depolarisation, producing a generator potential
24
Q
Pigment in rod cells
A
-Rhodopsin
-There is only one type
-High sensitivity to light
25
Pigment in cone cells
-Iodopsin
-Three types, each sensitive to a different wavelength of light
-Low sensitivity to light
26
How is a generator potential produced by photoreceptors
The pigment breaks down and triggers a change in sodium permeability
27
Describe rod cells
-Used to see in low light intensities, as they are highly sensitive to light
-Multiple rod cells synapse with a singular sensory neurone, they use summation
-Low visual accuity-a bit blurry and not as clear in high light intensities
28
Describe cone cells
-Only responds to high light intensity, as they have a low sensitivity to light
-Each cone cell synapses with its own separate sensory neurone, there is no summation
-Good visual accuity-clear, detailed images
29
Describe the distribution of rod and cone cells
-Uneven distribution in the retina
-Light is focused on the fovea, which is the part of the retina directly opposite the lens, so the fovea receives the highest intensity of light
-Therefore, most cone cells are located near the fovea as they only respond to high light intensities
-Rods are further away from the fovea as they can still respond to low light intensities
30
Describe the electrical conduction system of the heart
-Electrical activity spreads from the sino-atrial node, causing the atria to contract
-The wave of excitation enters a second group of cells, which is the atrio-ventricular node
-There is a short delay for blood to flow into the ventricles
-The wave of excitation continues along the bundle of His, then branches further
-The wave passes to the base of the ventricle along purkyne tissues, which causes the ventricles to contract from the base upwards
31
Describe the autonomic nervous system
-Part of the motor nervous system that sends messages to organs to stimulate responses
-Autonomic nervous system has two branches, their actions often oppose each other
-Parasympathetic and sympathetic
32
How does the autonomic nervous system control heart rate
-Medulla oblongata controls the heart rate via the autonomic nervous system
-This is done through two parts
-There is a centre linked to the SAN that increases the heart rate via the sympathetic nervous system
-Another centre can decrease heart rate via the parasympathetic nervous system
33
The role of chemoreceptors in controlling heart rate
-Exercise causes the rate of respiration in the muscles to increases
-This increases CO2 levels in the blood, in turn decreasing the pH
-Chemoreceptors detect this change and send impulses to the medulla oblongata
-The medulla increases the frequency of impulses through the sympathetic nervous system to the SAN
-The SAN increases the heart rate
-This increases blood flow in the lungs to allow CO2 to be excreted, increasing the blood pH back to its set point
34
Describe the role of pressure receptors in decreasing heart rate
-Blood pressure is higher than normal
-Baroreceptors detect the change and send impulses to the medulla
-The medulla increases the frequency of impulses through the parasympathetic nerves to the SAN
-SAN decreases the heart rate, which decreases blood pressure
35
Describe the structure of a myelinated axon
-Cell body-contains the typical animal cell organelles, proteins and neurotransmitter chemicals are made here
-Dendrites carry the action potential to cells
-Axons-long, conductive fibre that carries a nervous impulse along the motor neurone
-Schwann cells-wrap around the axon to form the myelin sheath. It is a lipid so doesn't allow charged ions through, has gaps called nodes of ranvier
36
What is a resting potential
-When the neurone isn't conducting an electrical impulse, there is a difference between the electrical charge inside and outside of the neurone
-More positive ions, sodium and potassium, are outside the neurone than inside
-Therefore inside the neurone is comparatively more negative at -70mV
37
How is a resting potential established
-Maintained by a sodium-potassium pump, this involves active transport and the use of ATP
-The pump moves two K+ in, and three Na+ out
-This creates an electrochemical gradient where K+ diffuses out and Na+ diffuses in
-The membrane is more permeable to K+, so more are moved out to create the -70mV resting potential
38
Describe an action potential
-The arriving stimulus disturbs the resting membrane potential, causing voltage gated sodium channels to open
-Na+ diffuses into the axon, causing the membrane to depolarise
-The membrane potential reaches +40mV, the Na+ voltage gates channels close, and K+ gates open
-K+ diffuses out of the axon, causes the membrane to repolarise
-The membrane potential overshoots the membrane resting potential to roughly -70/-75mV
-Voltage gated potassium channels close
-Leak channels and Na/K channels restore the resting potential
39
Describe how an action potential passes along an unmyelinated axon
-Depolarisation occurs in the axon
-This sets up the electrical currents that occur ahead
-This triggers the opening of voltage-gated sodium channels in the region further along
-The region develops an action potential whilst the area behind repolarises
40
Describe how an action potential passes along a myelinated axon
-Saltatory conduction
-Myelin acts as an electrical insulator
-Action potential jumps between nodes of Ranvier, localised currents arise
-Conduction is faster than in myelinated axons
-Myelinated axons are only present in vertebrates
41
Explain the all-or-nothing principle
-Nothing-If the depolarisation doesn't exceed -55mV, then an action potential and impulse won't be produced
-All-any stimulus that does trigger depolarisation to -55mV will always peak at the same maximum voltage, bigger stimuli will only increase the frequency of action potentials
-This makes sure animals only respond to large enough stimuli, as responding to every slight change would be overwhelming
42
What is the refractory period?
After the action potential, the membrane enters a period where it cannot be stimulated, the sodium channels are recovering so cannot open
43
Why is the refractory period important?
-Ensures that discreet impulses are produced, an action potential cannot be generated immediately after another one to ensure they are separate from each other
-Ensures all action potentials travel in one direction, it stops them from spreading out in two directions which would prevent a response
-Limits the number of impulse transmission. This is important to prevent an over reaction to stimulus, which would overwhelm the senses
44
How does myelination affect the speed of conduction?
Impulses travel faster by jumping between nodes of Ranvier-saltatory conduction
45
How does axon diameter affect the speed of conduction?
Impulses travel faster in larger axons, as there is less resistance to ion flow
46
How does axon diameter affect the speed of conduction?
-Enzymes and ion diffusion are affected by temperature
-Decreased temperature can slow transmission in organisms that don't regulate their body temperature
47
Describe transmission across cholinergic synapse
-Depolarisation of presynaptic membrane/action potential
-Calcium channels open and calcium diffuses in
-Calcium ions cause vesicles to fuse with the presynaptic membrane and release acetylcholine
-Acetylcholine diffuses across the synaptic cleft and binds to receptor cells on the post synaptic membrane
-Sodium channels open, causing Na+ to diffuse in and cause depolarisation
48
What is summation?
-The rapid build-up of neurotransmitters in the synapse to help generate an action potential
-Needed as some action potentials don't result in sufficient neurotransmitter concentrations being released to generate an action potential
49
Spatial summation
Many neurones collectively trigger an action potential by combining the neurotransmitter they release to exceed the threshold value
50
Temporal summation
One neurone repeatedly releases neurotransmitter over a short period of time to exceed the threshold value
51
Describe an inhibitory synapse
-Causes chloride ions to move into the post synaptic neurone, and potassium to move out
-The combined effect of negative ions moving in and positive ions moving out makes the membrane potential -80mV (hyperpolarisation), so an action potential is unlikely
52
Describe a neuromuscular junction
-A synapse that occurs between a motor neurone and muscle, similar to a synaptic junction
-The action potential triggers muscle contraction
53
How is a cholinergic synapse and neuromuscular junction different?
-Cholinergic can be excitatory or inhibitory, neuromuscular is only excitatory
-Cholinergic is two neurones, neuromuscular is a motor neurone and muscle
-Cholinergic generates a new action potential in the next neurone, neuromuscular ends the action potential
54
Describe skeletal muscle
-Attached to the bone
-Its role is to move the skeleton
-It is under voluntary, conscious control
55
Describe a myofibril
-Made up of fused cells that share a nucleus and sarcoplasm
-They have a high number of mitochondria
-Made up of two key proteins-myosin and actin that form a sarcomere
56
Describe muscle fibres
-Made up of millions of myofibrils that collectively bring about force to cause movement
57
Describe sliding filament theory
-An action potential reaches the muscle and stimulates a response
-Ca2+ enter, causing tropomyosin to move and uncover binding sites
-Whilst ADP is attached to the myosin head, it can bind to the binding site on actin to create a cross-bridge
-Angles in the cross-bridge create tension, so the actin filament is pulled and slides along the myosin, ADP and Pi molecules are released
-An ATP can then bind to the myosin head, causing the shape to slightly change, so it detaches from actin
-In the sarcoplasm ATPase, which is activated by Ca2+, hydrolysed the ATP on the myosin head, providing enough energy for the myosin head to return to its original position
-The process repeats whilst Ca2+ levels are high, which is when the muscle is stimulated by the nervous system
58
Describe the importance of ATP and phosphocreatine in muscle contraction
-A high concentration of ATP is required for muscle contraction
-When this isn't available through aerobic respiration, anaerobic respiration occurs
-This is helped by phosphocreatine which is stored in muscles. It helps by providing phosphates to regenerate ATP from ADP
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A band
Total width of myosin
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H zone
Myosin only
61
I band
Actin only
62
M line
The middle point of the myosin
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Z line
Parameters of one sarcomere
64
What happens to bands/zones/lines during muscle contraction
-The H zone and I band shorten
-The A band is constant
-Z-lines move closer together
65
Describe slow-twitch muscle fibres
-In calf muscles
-Have a large store of myoglobin, a rich blood supply, and many mitochondria
-They contract slower and can respire aerobically for longer periods of time due to rich blood supply and myoglobin oxygen store
-For endurance work, such as marathons
66
Describe fast-twitch muscle fibres
-In biceps
-Thicker with more myosin filaments, they have a large store of glucose and phosphocreatine, with a high concentration of enzymes for anaerobic respiration
-Contract faster to provide a short and powerful contraction
-For intense exercise such as sprinting or weight lifting
67
Explain the importance of homeostasis
-Enzymes are sensitive to changes in temperature in temperature and pH, which are essential for chemical reactions in cells
-Blood glucose needs to be high enough to supply cells with respiratory substrate. Too high of a blood glucose lowers water potential.
-Changes in a cells water potential can cause it to shrink or swell, affecting its function. Solute concentration needs to be maintained
-The ability to maintain a stable internal environment means organisms can live in a wider range of external environments
68
Negative feedback
Self-regulatory mechanisms that return an internal environment to optimum when there is a fluctuation
69
Positive feedback
When a fluctuation triggers changes that result in an even greater deviation from the normal level
70
Outline the stages involved in negative feedback
Receptor detects deviation -> coordinator -> corrective mechanism by effector -> receptors detect that conditions have returned to normal
71
Glycogenesis
-Excess glucose is converted to glycogen
-Occurs when blood glucose levels are too high
-Happens in the liver
72
Glycogenolysis
-Glycogen is hydrolysed to glucose in the liver
-Occurs when blood glucose is too low
73
Glyconeogenesis
-Amino acids/non-carbohydrates are converted to glucose in the liver
-Occurs when all glycogen has been converted to glucose, but the body still needs more
74
Action of insulin
-Beta cells in the islets of Langerhans detect increase in blood glucose
-Insulin attaches to receptors on the surface of target cells, changing the tertiary structure of protein channels, so more glucose can be absorbed by facilitated diffusion
-More protein channels in the cell surface membrane, so more glucose is absorbed from the blood
-Activating enzymes that that stimulates glycogenesis in the liver
75
How does insulin add more channel proteins to the membrane
-Insulin receptors release intracellular chemical
-Stimulates vesicles with glucose channel proteins that fuse with the cell surface membrane
76
Describe glucagon action-second messenger model
-Alpha cells in the islets of Langerhans detect low blood glucose levels and secrete glucagon
-Attaches to receptors on the surface of liver cells
-Activates adenyl cyclase by a shape change
-Activated adenyl cyclase converts ATP to cyclic AMP-the second messenger
-cAMP activates protein kinase that hydrolyses glycogen to glucose
77
Describe how adrenaline increases blood glucose-the second messenger model of adrenaline and glucagon action
-Attaches to receptor proteins on target cell surface, activating a protein that converts ATP to cAMP
-cAMP activates the enzyme that hydrolyses glycogen to glucose
78
Describe type one diabetes
-Due to the body being unable to produce insulin
-Often begins in early childhood, and can be the result of an autoimmune disease where beta cells were destroyed
-Treatment involves insulin injections
79
Describe type two diabetes
-When receptors on target cells lose their responsiveness to insulin
-Usually develops in adults due to obesity and poor diet
-Controlled by regulating carbohydrate intake, increasing exercise and sometimes insulin injections
80
Describe the role of the glomerulus
Filters small solutes from the blood
81
Describe the role of the Proximal convoluted tubule
-Reabsorbs ions, water, and nutrients
-Removes toxins and adjusts filtrate pH
82
Describe the role of the distal tubule
Selectively secretes and absorbs different ions to maintain blood pH and electrolyte balance
83
Describe the role of the collecting duct
Reabsorbs solutes and water from the filtrate
84
Describe the role of the descending loop of Henle
Aquaporins allow water to pass from the filtrate into the interstitial fluid
85
Describe the role of the ascending loop of Henle
Reabsorbs Na+ and Cl- from the filtrate into the interstitial fluid
86
Describe how filtering and reabsorption occurs
-Ultrafiltration occurs due to high hydrostatic pressure-water and small molecules are forced out of the glomerulus capillaries into the renal capsule
-Selective reabsorption occurs in the proximated convoluted tubule
-The loop of Henle maintains a Na+ gradient so water can be reabsorbed by the blood
-Water moves out of the distal convoluted tubule and collecting duct to return back to the blood, the collecting duct then carries the urine to the ureter
87
Describe ultrafiltration
-Blood enters through the afferent arteriole, which splits into lots of capillaries that make up the glomerulus, causing a high hydrostatic pressure in the blood
-Water and small molecules, such as glucose and mineral ions, are forced out of the capillaries as the glomerulus filtrate
-Large proteins and blood cells are too large to fit through gaps in the capillary endothelium, so remain in the blood which leaves through the efferent arteriole
88
Describe selective reabsorption
-Concentration of Na+ in the PCT cells are low, as Na+ are actively transported into the blood in the capillaries
-Due to the concentration gradient, Na+ diffuse through a co-transporter with glucose
-Glucose can then diffuse from PCT epithelial cells to the blood stream, reabsorbing all the glucose
89
Describe how a sodium ion gradient is maintained in the loop of Henle
-Mitochondria in cells provide energy for the active transport of Na+ out of the ascending limb of the loop of Henle
-The accumulation of Na+ outside of the nephron in the medulla lowers the water potential
-So water diffuses out by osmosis into the interstitial space and then the blood capillaries
-At the base of the ascending limb some Na+ diffuse out, as there is now a very dilute solution as all water has moved out
90
Describe the reabsorption of water at the distulated convoluted tubule and the collecting duct
-Due to all the Na+ actively transported out of the loop of Henle, when the filtrate reaches the DCT it is dilute
-The filtrate moves into the DCT and collecting duct, this section of the medulla is highly concentrated
-So even more water diffuses out of the DCT and collecting duct
-What remains is transported to form urine
91
Why do desert animals have a longer loop of Henle?
-The longer the loop of Henle, the more Na+ are actively transported out, so an even more negative water potential is created.
-More water is being reabsorbed into the blood and very concentrated urine
92
Why is osmoregulation important?
-If the blood is hypertonic, too much water will leave the cells causing them to shrivel
-If the blood is hypotonic, too much water will move into cells causing them too burst
93
Describe the corrective mechanism for hypertonic blood (too low of a water potential)
-More water is reabsorbed by osmosis into the blood from the tubules of the nephrons
-This makes urine more concentrated as less water is lost in the urine
94
Describe the corrective mechanism for hypotonic blood (too high of a water potential)
-Less water is reabsorbed by osmosis into the blood from the tubules of the nephrons
-This makes urine more dilute and more water is lost in the urine
95
Describe the role of the hypothalamus and posterior pituitary gland
-Changes in blood water potential are detected by osmoreceptors
-It produces ADH in response, which moves to the posterior pituitary gland, from here it is released into the capillaries and into the blood
-ADH travels through the blood to the kidney
96
Describe the affects of ADH
-Causes an increase in the permeability of the walls of the collecting duct and distal convoluted tubule
-This means that more water leaves the nephron and is reabsorbed into the blood, so urine is more concentrated
97
Aquaporins
-Channel proteins that allow water to pass through
-With more aquaporins in the membrane, more water leaves the DCT and collecting duct to be reabsorbed into the blood
