Responding to Changes to Environment Flashcards
what is a stimulus?
a detectable change in the environment
what are taxes?
- simple response in which an organism will move its entire body towards a favourable stimulus (positive taxis) or away from an unfavourable stimulus (negative taxis)
what is kinesis?
- when an organism changes the speed of movement and the rate it changes direction
- in less favourable conditions = inc rate of change of direction
why may an organism move in a straight line when in favourable conditionss? what is this an example of?
- to inc chance of finding a new area with favourable conditions
- positive kinesis
what is IAA? what does it do?
- growth hormone (type of auxin)
- can control cell elongation
- made in tip of roots/shoots and diffuses to other cells
what is the effect of IAA on shoots?
promotes cell elongation/growth
what is the effect of IAA on roots?
inhibits cell elongation/growth
explain phototropism in shoots, including the role of IAA
- postively phototropic (grow towards light)
- need light for LDR
- shoot tip cells produce IAA, which diffuses to other cells
describe the effect unilateral light would have on a shoot
- if light shines in one direction, IAA diffuses to the shaded side of the shoot
- causes the cells on shaded side to elongate more so plant bends toward light source
explain phototropism in roots, including the role of IAA
- negatively phototropic (grows away from light)
- no photosynthesis occurs in roots so light not needed
- root cells elongate more on the light side (IAA inhibit growth) so root bends away from light
describe gravitropism in shoots, including the role of IAA
- negatively gravitropic (grows away from gravity)
- IAA diffuse from upper side to lower side
describe gravitropism in roots, including the role of IAA
- positively gravitropic (grows towards gravity)
- IAA diffuse from lower side to upper side
the cardiac muscle is myogenic. what does myogenic mean?
can contract without stimulus
where is the sinoatrial node (SAN) located?
right atrium
where is the atrioventricular node (AVN) located?
in between the left ventricle and right atrium
where is the Bundle of His located?
runs through the septum
where are Purkyne/Purkinje located?
in the walls of the ventricles
describe the sequence of events that controls heart rate
- SAN sends impulses which initate heartbeat, as it is the pacemaker
- impulses spread through the atria, causing it to contract
- impulse reaches AVN
- AVN delays the impulse to allow atria to finish contracting
- impulse spreads down Bundle of His, which splits into branches
- impulse spreads around Purkinje fibres in the ventricle walls, causing the apex + then walls of the ventricle to contract
what part of the brain contols heart rate via the autonomic nervous system?
medulla oblongata
what are the two parts of the nervous system? what effect do they have on heart rate?
- sympathetic (inc hr)
- parasymathetic (dec hr)
what effect can high blood pressure have on the heart?
can cause damage to the walls of the arteries
what effect can low blood pressure have on the heart?
- may be insufficient supply of oxygenated blood to respiring cells
- may be insufficient removal of waste, resulting in a buildup
what causes a decrease in blood pH? how can it return to normal?
- inc respiration = inc CO2/lactic acid produced = acidic
- inc HR allows CO2 to diffuse out into the alveoli more rapidly
what type of receptor detects changes in blood pH?
chemoreceptor
what type of receptor detects changes in blood pressure?
baroreceptor
where are chemoreceptors and baroreceptors found?
carotid arteries and aorta
describe what happens when blood pH or pressure decreases
- more electrical impulses sent to medulla oblongata
- more impulses sent to SAN by sympathetic nervous system
- heart rate increases
describe what happens when blood pH or pressure increases
- more electrical impulses sent to medulla oblongata
- more impulses sent to SAN by parasympathetic nervous system
- heart rate decreases
what kind of images are produced by rod cells? why?
- black and white
- unable to distinguish between different wavelengths of light (low visual acuity) as many rod cells connect to one sensory neurone
what level of light intensity can be detected by rod cells? why?
- low intensity
- very sensitive to light as many rod cells connect to one sensory neurone
what chemical must be broken down to create a generator potential in a rod cell?
rhodopsin
what kind of images are produced by cone cells? why?
- colour images can be perceived, depenending on the proportion of each cone cell stimulated
- there are 3 different types of iodopsin pigments that all absorb different wavelengths of light
why do cone cells have high visual acuity?
- no retinal convergence, only one cell connects to each bipolar cell
- can distinguish between different wavelengths of light
what is the peripheral nervous system (PNS) made up of?
receptors, sensiry neurones, motor neurones
what is the central nervous system (CNS) made up of?
coordination centres, e.g. brain and spine
what is the role of the pacinian corpuscle?
respond to pressure changes
describe the structure of a pacinian corpuscle
- consists of a single sensory neurone wrapped with layers of connective tissues separated by gel
- has special channel proteins in plasma membrane
- membranes surrounding the sensory neurones have stretch-mediated sodium ion channels
what happen when pressure is applied to pacinian corpuscle?
- neurone in plasma membrane deformed
- stretch-mediated Na+ channels widen so Na+ enter
- generator potential established
how is resting potential maintained in a pacinian corpuscle?
in resting state, Na+ channels too narrow for Na+ to diffuse into the sensory neurone
briefly state the function of a dendrite
carry action potentials to surrounding cells
briefly state the function of a cell body of a neurone
- contains organelles found in a typical animal cell
- proteins and neurotransmitters made here
briefly state the function of Schwann cells
wrap around the axon to form myelin sheath
briefly state the function of the myelin sheath
- lipid
- does not allow charged ions to pass through
what are the gaps between myelin sheath called?
nodes of Ranvier
what causes the difference in electrical charge between the inside and outside of a neurone when a resting potenial is established? what is the potential difference of the inside of the neuron at this point?
- more positive ions (Na+ and K+) outside compared to the inside of the neurone
- -70mv
outline how a resting potential is maintained
- Na+/K+ pumps in axon actively transports Na+ out of cell and K+ into cell
- K+ move out of axon through K+ channels along the conc gradient
- results in lesser conc of pos ions in axon so inside more neg than outside
- K+ ions pulled back into axon due to electrochemical gradient
- electrochemical gradients counteract so no net movement of K+, therefore pd of -70mv maintained
outline the process of an action potential being generated from resting potential
- stimulus arrives, causes Na+ channels to open so Na+ enter axon, causing neighbouring voltage gated (VG) channels to open, so even more Na+ diffuse in resulting in an inc of voltage
- at 40mv, Na+ VG close and K+ open, causing K+ to leave the axon, decreasing the overall charge
- K+ continue diffusing out, causing a temp overshoot of the gradient, resulting in the inside of the axon being more neg than usual (hyperpolarisation)
- all closable gates close, so resting potential is restored
what is the all or nothing principle?
- if the depolarisation does not exceed -55mv (threshold value) then no action potential will be produced
- any stimuli that triggers depolarisation to -55mv will always peak at the same maximum voltage
- larger stimuli do not inc the max voltage, instead inc the frequency of action potentials
why is the all or nothing principle important?
makes sure only respond to large enough stimuli, rather than every slight change
what is the refractory period?
- after an action potential has been generated, the membrane enters a refractory period
- can’t be stimulated as Na+ channels are recovering + can’t be opened
why is the refractory period important?
- ensures discrete impulses are produced - an action potential can’t be generated immediately after another so they are separate (no overlap)
- ensures action potential only travels forward in one direction - stops an action potential from spreading out in 2 directions which would prevent a response as threshold value not reached
- limits the number of impulse transmission - prevents over reaction to a stimulus so senses are not oversimulated
list 3 factors that affect the speed of an action potential
- myelination + saltatory conduction
- axon diamater
- temperature
how do myelination + saltatory conduction affect the speed of an action potential?
- action potential jumps from node to node (saltatory conduction)
- therefore travels along the axon faster as it doesn’t have to generate an action potential along the entire length, just the Nodes of Ranvier
how does axon diameter affect the speed of an action potential?
- wider diameter = inc speed of conductance
- wider diameter = less leakage of ions so action potential travels faster
how does temperature affect the speed of an action potential?
- higher temp = faster speed of conductance
- ions diffuse faster
- enzymes involved in respiration work faster so more ATP available for active transport in the Na+/K+ pump
outline the transmission of a synapse
- ap arrives at synaptic terminal. depolarisation of terminal leads to opening of Ca2+ channels so Ca2+ diffuse into synaptic knob
- vesicles containing neurotransmitter move towards + fuse with presynaptic membrane. neurotransmitter released to synaptic cleft
- neurotransmitter diffuses down conc gradient across synaptic cleft to post synaptic membrane + binds to complementary receptors on surface of post synaptic membrane
- Na+ ion channels on post synaptic membrane open + Na+ diffuse in. if enough neurotransmitter, enough Na+ diffuse in so above threshold + post synaptic neurone becomes depolarised
- neurotransmitter is degraded + released from receptor, Na+ channels close + post synaptic neurone re-establishes resting potential. neurotransmitter transported back to presynaptic neurone where it is recycled
what is the neurotransmitter in a cholinergic synapse?
acetylecholine (Ach)
what is acetylecholine broken down by? into what?
- acetylcholinesterase
- acetate + choline
what are the 2 types of summation?
- spatial
- temporal
why is summation necessary?
some action potentials do not result in sufficient concentrations of neurotransmitter being released to generate an action potential
what is spatial summation?
many different neurones collectively trigger a new action potential by combining the neurotransmitter they release to exceed the threshold value
what is temporal summation?
one neurone releases neurotransmitter repeatedly over a short period of time to add up enough to exceed the threshold value
what are inhibitory synapses? how do they work?
- cause chloride ions to move into post synaptic neurone + potassium ions to move out
- causes hyperpolarisation so action potential highly unlikely
why are inhibitory synapses useful?
prevents a response to every single stimulus
what are neuromuscular junctions?
- synapses that occur between a motor neurone and a muscle
- very similar to synaptic junctions
give 1 similarity between neuromuscular junctions and a cholinergic synapse
both unidirectional as neurotransmitter receptors only on post synaptic membrane
list 4 differences between a neuromuscular junction and a cholinergic synapse
- NJ = excitatory only, CS = excitatory or inhibitory
- NJ connects motor neurone to muscles, CS connects 2 neurones (could be sensory, relay or motor)
- NJ = end point for ap, CS = new ap generated in the next neurone
- in NJ, Ach binds to receptors on muscle fibre membranes, vs post synaptic membrane of a neurone in CS
put in order from largest to smallest: myofibril, muscle, sarcomere, muscle fibre
muscle, muscle fibre, myofibril, sarcomere
outline sliding filament theory
- ap arrives
- Ca2+ enter + cause tropomyosin to move from the actin + expose the binding sites for the myosin heads
- whilst ADP is attached to the myosin head, it can bind to binding site on actin to form crossbridge
- angle craeated in crossbridge created tension + as a result the actin filament is pulled + slides along the myosin
- this causes ADP molecules to be released
- an ATP molecule can then bind to the myosin head, causing it to change shape slightly so detaches from actin
- ATPase hydrolyses the ATP, releasing energy for the myosin head to return to original position
- continues if enough Ca2+ present
what is the function of phosphocreatine?
-acts as a reserve supply of phosphate so in anaerobic conditions, pi can bind with ADP to continue producing ATP
list 5 components of a myofibril
- A band
- I band
- H zone
- M line
- Z lines
what is the A band of a myofibril?
entire myosin length
what is the I band of a myofibril made of?
actin only
what is the H zone of a myofibril made of?
myosin only
what are the Z lines of a myofibril?
form boundaries
what is the M line of a myofibril?
middle line
what happens to the A band when the sarcomere contracts?
stays same width (myosin does not move)
what happens to the I band when the sarcomere contracts?
becomes shorter
what happens to the H Zone when the sarcomere contracts?
becomes shorter
what happens to the Z lines when the sarcomere contracts?
slide closer together but do not shorten
compare fast and slow twitch muscle fibres
- F = thicker, S = thinner
- F = more myosin filaments, S = large myoglobin store
- F = large glycogen store, S = rich blood supply
- F = in biceps, S = in calf muscles
- F = contract faster for shorter period, S = contract slower for longer
- F = more powerful, S = less powerful
- F = intense exercise, S - endurance
- F = anaerobic, S = aerobic
what is negative feedback?
when any deviation from the normal values are restored to their original level
outline the response when there is a rise in blood glucose levels
- detected by beta cells in the islets of langerhans
- beta cells release insulin
- liver cells become more permeable to glucose, enzymes are also activated to convert glucose to glycogen
- glucose is removed from blood + stored as glycogen in cells
- BG returns to normal levels
outline the response when there is a fall in blood glucose levels
- detected by alpha cells in the islets of langerhans
- alpha cells release glucagon
- adrenal gland releases adrenaline
- 2nd messenger model occurs to activate enzymes to hydrolyse glycogen
- glycogen is hydrolysed to glucose + so more glucose is released back into blood
- BG returns to normal levels
define glycogenesis
- glucose to glycogen
- happens when BG is higher than normal, usually occurs in the liver
define glycogenolysis
- glycogen to glucose
- happens when BG lower than normal, in liver
define gluconeogenesis
- non-carb stores (e.g. amino acids) to glucose
- in liver
- occurs if all glycogen hydrolysed but body still needs more glucose
outline how insulin decreases blood glucose
- attaches to receptors on surface of target cells which changes tertiary structure of the channel proteins resulting in more glucose being absorbed by facilitated diffusion
- more protein carriers are incorporated into cell membranes so that more glucose is absorbed from the blood into cells
- enzymes involved in the conversion of glucose to glycogen are activated -> results in glycogenesis in the liver
outline how glucagon increases blood glucose
- attaches to receptors on surface of target cells (liver cells)
- when glucagon binds it causes a protein to be activated into adenylate cyclase + to convert ATP into cAMP
- cAMP activates protein kinase that can hydrolyse glycogen into glucose
- enzymes involved in conversion of glycerol + amino acids into glucose are activated
in the second messenger model, what is the first messenger?
glucagon
in the second messenger model, what is the second messenger?
cAMP
outline the second messenger model
- glucagon binds to glucagon receptors
- once bound, it causes a change in shape to the enzyme adenyl cyclase, which activates it
- activated adenyl cyclase enzymes convert ATP to cAMP
- cAMP activates protein kinase, which in turn converts glycogen to glucose
describe the role of adrenaline in the second messenger model
if BG too low, adrenal glands will secrete adrenaline which will inc BG
outline how adrenaline increases blood glucose
- attaches to receptor on the surface of target cells
- this causes G protein to be activated which converts ATP to cAMP
- cAMP activates enzyme that can hydrolyse glycogen into glucose
what is type 1 diabetes? what could be the cause? how is it treated?
- body unable to produce insulin
- could be result of autoimmune disease where beta cells attacked
- treatment involves insulin injections
what is type 2 diabetes? what could be the cause? how is it treated?
- receptors on target cells lose responsiveness to insulin
- usually develops in adults due to obesity + poor diet
- controlled by regulating intake of carbs, inc exercise + sometimes insulin injections
