Chapter 15 Control & Coordination Essay QS Flashcards
Describe the roles of the endocrine & nervous systems in control & coordination in mammals. (9)
Endocrine:
- hormones
- chemical messengers
- released into blood
- target, organs / cells
- ref. receptors on cell membranes
- example of named hormone & effect
Nervous:
- impulses / action potentials
- along neurones
- synapse (with target)
- ref. receptor / effector or sensory / motor, neurones
Differences - endocrine:
- slow effect
- long lasting effect
- widespread effect
- AVP; e.g. extra detail of synapse
Compare the endocrine & nervous systems in control & co-ordination in mammals. (8)
Differences (nervous followed by endocrine system):
- Communication - action potential / impulse AND hormone
- Nature of Communication - electrical AND chemical
- Mode of Transmission - neurone AND blood
- Response Destination - muscle / gland AND target, organs / cells
- Transmission Speed - fast(er) AND slow(er)
- Duration - short-lived / temporary AND can be long-lasting
- Receptor Location - on cell surface membrane AND either on csm or within cell
Similarities:
- Both involve cell signalling.
- Both involve signal molecule binding to receptor.
- Both involve chemicals.
Describe the structures & function of a sensory neurone & of a motor neurone. (8)
Sensory neurones:
- a single long dendron
- a shorter / similar length axon
- cell body towards the centre of the cell
- cell body found in the dorsal root ganglion
- transmit impulses from a receptor to the CNS / brain & spinal cord
Motor neurones:
- dendrites attached to cell body
- nucleus in cell body
- many mitochondria
- much rough endoplasmic reticulum (in cell body)
- long axon
- synaptic knobs / terminal branches / axon terminals
- Schwann cells / myelin sheath / myelinated
- nodes of Ranvier
- cell body in CNS
- transmit impulses from CNS / brain & spinal cord, to effector
Describe how a resting potential is maintained in an axon. (9)
- axon phospholipid bilayer impermeable to K+ / Na+
- transmembrane sodium-potassium pump
- pump proteins use energy from hydrolysis of ATP to move ions against concentration gradient
- 3 Na+ (pumped) out / 2 K+ (pumped) in
- K+ diffuse out / Na+ diffuse in
- through, protein channels / transport proteins
- more K+ channels open than Na+ channels
- therefore, membrane more permeable to K+ or more K+ leave than Na+ enters (axon)
- inside relatively more negative than outside
- -65 mV; (A: -70 mV)
- electrochemical gradient
- Closure of voltage-gated channel proteins stops Na+ & K+ diffusing through axon membrane
Explain how an action potential is transmitted along a sensory neurone. (8)
- Na+ channels open (A: sodium channels)
- Na+ enters, cell / axon (R: enter membrane)
- inside becomes, less negative / positive / +40 mV or membrane depolarised
- Na+ channels close
- K+ channels open
- K+ move out (of cell)
- inside becomes negative or membrane repolarised
- local circuits / description
- (myelin sheath / Schwann cells) insulate axon / does not allow movement of ions
- action potential / depolarisation, only at nodes (of Ranvier) / gaps
- saltatory conduction / AW
- one-way transmission
- AVP; e.g. hyperpolarisation / refractory period
Describe how the structure of neurones speeds up the transmission of action potential. (6)
- myelin sheath / schwann cell
- insulates, axon / dendron
- impermeable to Na+ / K+
- depolarisation only at nodes of Ranvier
- ref. local circuits
- action potentials “jump” from node to node
- saltatory conduction
- speed increased by 50 times / 0.5 ms^-1 to 100 ms^-1
- axons with large diameter / giant axon
- reduce resistance
- elongated, axon / dendron / neurone
Explain how a cholinergic synapse functions. [9]
- depolarisation / action potential
- of pre-synaptic membrane / synaptic knob
- opening (voltage-gated) calcium ion channels (in pre-synaptic membrane)
- calcium ions enter presynaptic neurone
- vesicles containing acetylcholine fuse with PRE-SYNAPTIC MEMBRANE
- (ACh) released / secreted / exocytosis
- ACh DIFFUSES across SYNAPTIC CLEFT
- binds to receptors on post synaptic membrane (R protein channel)
- (ligand-gated) Na+ channels open AND Na+ enters post-synaptic neurone
- depolarises / action potential
- ACETYLCHOLINESTERASE breaks down ACh / recycles ACh
Outline the role of a chemoreceptor cell in the human taste bud in detecting stimuli and in stimulating the transmission of nerve impulses in sensory neurones. [7]
- chemicals act as a stimulus
- each chemoreceptor is covered with receptor proteins. Different receptor proteins detect different chemicals (ref. to specificity)
- Na+ ions diffuse into cell
- via microvilli
- membrane depolarised
- receptor potential
- stimulates opening of calcium (ion) channels
- calcium ions enter cell
- causes movement of vesicles containing neurotransmitter
- neurotransmitter released by exocytosis / described
- neurotransmitter stimulates, action potential / impulses, in sensory neurone
- ref. to (chemoreceptors are) transducers / description
- AVP - e.g. threshold / all-or-nothing law / papilla
Describe the ultrastructure of a striated muscle fibre. [8]
- fibres are multinucleate
- cell surface membrane is sarcolemma
- sarcoplasm has many mitochondria
- sarcoplasmic reticulum membranes have protein pumps
- transverse system tubules / T-system
- ref. to myofibrils
- thick filament / myosin, attached to M line
- thin filament / actin, attached to Z line
- interdigitation of filaments causes striated appearance
- description of, A / H / I, bands
- sarcomere is the distance between M lines
- myosin is a fibrous protein with globular protein head
- actin is a chain of globular protein molecules
- tropomyosin / troponin, attached to actin
Describe the roles of the neuromuscular junction, transverse system tubules (T-tubules) & the sarcoplasmic reticulum in stimulating contraction in striated muscle. [7]
- action potential / depolarisation / impulse, at pre-synaptic membrane
- (voltage-gated) calcium ion channels open / calcium ions enter (cell / cytoplasm / (motor) neurone / pre-synaptic knob)
- vesicles fuse with pre-synaptic membrane
- acetylcholine / ACh, released, by exocytosis / into synaptic cleft
- (ACh) binds to receptors on sarcolemma
- sodium ion channels open / sodium ions enter (muscle cell / sarcoplasm)
- depolarisation of, (muscle) cell surface membrane / sarcolemma
- (depolarisation) spreads / transmitted, to / down, T-tubules
- depolarisation of (adjacent) sarcoplasmic reticulum (membrane)
- (voltage-gated) calcium ion channels open
- calcium ions, diffuse out of SR
- calcium ions diffuse into sarcoplasm
- calcium ions, start contraction / bind to troponin
Describe the response of the Venus fly trap to touch. [8]
- mechanical energy converted to electrical
- ref. to sensory hair cell (is receptor / detects touch)
- cell membrane depolarises
- (if at least) 2 hairs touched (within 35 seconds)
- action potential occurs
- action potential / depolarisation, spreads over leaf
- ref. to hinge / midrib cells
- H+, pumped out of cells / pumped into cell walls
- cell wall, loosens / cross-links broken
- calcium pectate dissolves (in middle lamella))
- Ca2+ enter cells
- Water, enters / follows, by osmosis
- cells, expand / become turgid
- change from convex to concave
- trap shuts, quickly / in <1s / in 0.3s
- AVP; acid growth hypothesis / expansins / elastic tension
Explain how auxin causes plant cells to elongate. [7]
- acid-growth (hypothesis)
- auxin stimulates proton pumps
- (in) cell surface membrane
- protons / H+, pumped into cell wall
- using energy / by active transport
- pH of cell wall decreases / cell wall becomes (more) acidic
- expansins activated
- bonds between cellulose microfibrils broken
- idea that cell wall, ‘loosens’ / becomes more elastic / able to stretch
- (more) water enters cell / turgor pressure increases
- cell expands
Explain the role of gibberellins in the germination of wheat / barley. [9]
- seed absorbs water
- by osmosis
- gibberellin produced by embryo plant
- passes to aleurone layer
- switches on / activation, transcription enzyme genes
- stimulates synthesis / release of amylase
- amylase diffuses / moves into endosperm
- breaks down / hydrolyses starch to maltose
- maltose to glucose
- glucose diffuses / moves into embryo plant
- provides source of energy for growth of embryo plant
