6 Organisms respond to changes in their internal and external environments Flashcards
Describe the effect of IAA on root and shoot growth. [6]
- IAA synthesised in shoots tips.
- IAA diffuses into cell elongation growing region.
- Light causes movement of IAA from light side to shaded side.
- Proportionally more IAA on shaded side.
- Causes directional growth as there is** greater cell elongation on shaded** side.
- Shaded side elongates faster and causes shoot to bend towards the light.
- IAA synthesised in root tips.
- IAA diffuses into growing (cell elongating) region.
- IAA moves towards underside/shaded side.
- Inhibits cell elongation.
- Uneven growth (more elongation on side with less IAA).
- Causes directional growth away from light and downwards towards gravity.
Describe what is meant by the term taxis
*(Whole organism) moves towards or away from directional stimulus
Describe what is meant by the term kinesis
- (Whole organism) movement is random/non-directional response
Compare & Contrast taxis and tropism [2]
- Both are directional responses to stimuli
- Taxis involves the movement of the entire organism whereas tropism is the movement of part of an organism
Explain the advantages of simple reflex arcs [3]
- Rapid;
- Protect against damage to body tissues;
- Do not have to be learnt;
- Help escape from predators;
- Enable homeostatic control;
As a neurone transmits an impulse, its rate of oxygen consumption increases.
Explain why.
[2]
- ATP required for active transport;
- Na+ (actively) moved out only at nodes in myelinated / Na+ (actively) moved out along whole length of axon in non-myelinated;
Describe how a resting potential is maintained in a neurone. [4]
- active transport/pumping of sodium (ions across membrane);
- out of neurone/higher concentration outside;
- differential permeability to K+ and Na+;
- Membrane more permeable to K+ ions;
The potential across the membrane is reversed when an action potential is produced.
Describe how.
[2]
- Sodium ion gates / channel (proteins) open;
- Na+ (rapidly) diffuse in;
REJECT INFLUX
SYNAPSE:
Describe the sequence of events leading to the release of acetylcholine and its binding to the postsynaptic membrane. [5]
- Depolarisation of presynaptic membrane;
- Ca2+ channels open and calcium ions enter synaptic knob (by facilitated diffusion);
- (Calcium ions cause) synaptic vesicles move AND fuse with presynaptic membrane and release acetylcholine / neurotransmitter;
- Acetylcholine/neurotransmitter diffuses across (synaptic cleft);
- (Acetylcholine attaches) binds to receptors on the postsynaptic membrane;
- Sodium ions enter (postsynaptic neurone) leading to depolarisation;
When a nerve impulse arrives at a s[3]ynapse, it causes the release of neurotransmitter from vesicles in the presynaptic knob.
Describe how.
[3]
- (Nerve impulse/depolarisation of membrane) causes Ca2+ channel (proteins) to open;
- Ca2+ enter by (facilitated) diffusion;
- Causes (synaptic) vesicles to fuse with (presynaptic) membrane;
Give two reasons why transmission across a cholinergic synapse is unidirectional. [2]
- (Only) the presynaptic neurone/knob/membrane releases/has neurotransmitter/acetylcholine;
2.(Only) the postsynaptic neurone/membrane has receptors OR No receptors in the presynaptic neurone/membrane;
The binding of GABA to receptors on postsynaptic membranes causes negatively charged chloride ions to enter postsynaptic neurones.
Explain how this will inhibit transmission of nerve impulses by postsynaptic neurones. [3]
- (Inside of postsynaptic) neurone becomes more negative/hyperpolarised;
- More sodium ions required (to reach threshold) OR Not enough sodium ions enter (to reach threshold);
- For depolarisation/action potential;
Describe how the speed of the conduction could be increased in a neurone. [2]
- Axon is myelinated which provides (electrical) insulation;
- So shows saltatory conduction/ Action potentials jump from node of Ranvier to node of Ranvier;
OR - Axon has a larger diameter;
- So less resistance to flow of ions; / more surface area for more channel proteins which meeans faster rate of diffusion of ions.
Myelination affects the rate of conduction of a nerve impulse. Explain how. [3]
- Myelination provides (electrical) insulation;
- Action potentials jumps from node of Ranvier to node of Ranvier / depolarisation only at node of Ranvier;
- Fewer jumps / depolarisations to travel length of axon;
Describe how the inhibition of acetylcholinesterase affects the action of synapses. [2]
- Acetylcholine not broken down / stays bound to receptor;
- Na+ ions (continue to) enter / (continued) depolarisation / Na+ channels (kept) open / action potentials;
Describe what is meant by the term refractory period [2]
- (Refractory period) limits number of impulses per second/frequency of nerve impulses;
- Maximum frequency of impulse transmission
- Period of time between threshold and resting membrane potential.
- When maximum frequency reached/exceeded, no further increase in information/ all (higher) stimuli seem the same;
What is meant by the All or Nothing rule.
- Action potential ALWAYS occurs if THRESHOLD is reached.
- No action potential if stimulus is SUB THRESHOLD
- Size of stimulus (above threshold) does not increase the membrane potential above +40mV.
Explain how pressure on the Pacinian corpuscle produces the changes in membrane potential recorded by microelectrode A. [6]
- (Pressure) deforms lamellae.
- Opens stretch-mediated Na+ (sodium ion) channel proteins;
- Na+ diffuse into neurone / across membrane;
- Causing depolarisation;
- Increased pressure opens more channels / greater sodium entry;
- Size of generator potential determines frequency of action potentials
The rate of ATP consumption of a de-myelinated neurone is greater than that of a myelinated neurone when conducting impulses at the same frequency.
Explain why.
[3]
- Greater entry of sodium ions / greater exit of K+
- in de-myelinated neurone;
- Ref. to active transport / ref. to ion pumps;
Explain how the fovea increases the detail of an image [3]
- High (visual) acuity
- Each / every single cone is connected to a single bipolar/neurone
- Each cone sends separate impulse / action potential to the brain
Explain how the connection of several rods to a single bipolar cell (Retinal convergence) influences visual acuity [2]
- (Spatial) Summation means cannot distinguish between stimuli from different rod cells linked to same bipolar cell;
- Decreased acuity;
Explain how the connection of several rods to a single bipolar cell (Retinal convergence) influences sensitivity [2]
- (Summation of) sub-threshold stimuli produces threshold stimulation;
- Increases sensitivity;
People with red-green colour blindness are unable to distinguish between red and green, and also between other colours
Explain why. [3]
- Green sensitive pigment/cones non-functional
OR
Cones that detect green light non-functional; - Three different types of pigment/cone;
- Other/different colours (‘seen’) due to stimulation of more than one cone/pigment;
Exercise causes an increase in heart rate.
Describe the role of receptors and of the nervous system in this process.
[4]
- Chemoreceptors detect rise in CO2 / H+ / acidity / carbonic acid /fall in pH
OR
Baro / pressure receptors detect rise in blood pressure; - Send more frequent actionn potentials / impulses to cardiac centre/medulla;
- More impulses to SAN;
- By sympathetic (nervous system for chemoreceptors / CO2)
OR
By parasympathetic (nervous system for baro / pressure receptors / blood pressure);
Explain how nervous control in a human can cause increased cardiac output during exercise. [5]
- Coordination via medulla (of brain) / cardiac centre;
- (Increased) impulses along sympathetic nerve;
- To S.A. node;
- Release of noradrenalin;
- More impulses sent from S.A.N (across atria);
- Increased heart rate / increased stroke volume;
Explain why increased cardiac output is an advantage during exercise. [5]
- Higher cardiac output - Increases O2 supply (to muscles);
- Increases glucose supply (to muscles);
- More ATP produced by oxidative phosphorylation / more energy release / more aerobic respiration / actively respiring muscles
- Increases CO2 removal (from muscles) / lactate removal;
- Increases heat removal (from muscles) / for cooling;
- Delays the formation of lactate
Describe how the Pacinian corpuscle propagates an action potential. [4]
- (Pressure causes) membrane/lamellae to become deformed/stretched;
- Stretcg=h mediated Sodium ion channels in membrane open and sodium ions (f) diffuse / move in;
- Depolarisation leading to generator potential;
- Greater pressure more channels open/sodium ions enter (greater generator potential);
Describe what is meant by the term threshold [2]
- When threshold has been reached;
- (Threshold or above) causes maximal response / all or nothing principle;
How do you calculate Cardiac output?
Cardiac Output = Heart Rate X Stroke Volume
units = dm3 min-1
Contrast Cholinergic & NMJ synapses. [2]
NMJ:
* ACh is always excitatory
* Post synaptic membrane (sarcolemma) highly folded to increase surface area for more ACh protein receptors
* Neurone to effector (not neurone to neurone)
Describe the banding pattern in striated muscle [3]
- Lightest band is I band, Actin only
- Darkest band is overlapping region, Actin and Myosin
- Medium shading is H zone/band is Myosin only.
Describe the sliding filament theory [4]
- Attachment / cross bridges between actin and myosin heads;
- ‘Power stroke’ / movement of myosin heads / pulling of actin (over myosin);
- Detachment of myosin heads (requires ATP binding);
- (Energy from ATP) Myosin heads move back/to original position / ‘recovery stroke’;
Describe the function of calcium ions in muscle contraction [4]
- Ca2+ Binding/changing shape/removing tropomyosin;
- Exposes actin binding sites;
- Myosin head attaches/cross-bridge formation;
- Activates ATP hydrolase;
Nerve impulses arriving at the presynaptic membrane at the neuromuscular junction
result in shortening of sarcomeres. Describe how [6]
- Entry of calcium ions (presynaptic membrane);
- Vesicles fuse with membrane / exocytosis /release Ach (Acetylcholine);
- Neurotransmitter diffuses;
- Binds to receptors, postsynaptic / membrane / muscle membrane;
- Depolarisation / sodium ions enter;
- Release of calcium ions (from sarcoplasmic reticulum);
- Removes tropomyosin / bind to troponin;
- Exposing binding sites on the actin;
- Actinomyosin cross bridge formation / myosin binds;
- Myosin head moves / pulls the actin along;
- Rachet mechanism / description /detach and reattach;
- ATP hydrolase activated;
Explain the importance of ATP hydrolase during muscle contraction. [2]
- Hydrolysis of ATP releasing energy;
- used to form / break actinomyosin cross-bridges;
State 3 uses of ATP in muscle contraction [3]
- Breaks Actinomyosin cross bridges
- Hydrolysis to release energy for power/recovery stroke
- Active reuptake / removal / transport of Ca”+ from sarcoplasm into sarcoplasmic reticulum.
Muscle contraction requires ATP. What are the advantages of using aerobic rather than anaerobic respiration to provide ATP in a long-distance race? [4]
- Aerobic respiration releases more energy /produces more ATP;
- Little/no lactate produced / does not accumulate;
- Avoids cramp / muscle fatigue;
- CO2 easily removed from the body / CO2 removed by breathing;
A muscle fibre contracts when it is stimulated by a motor neurone. Describe how transmission occurs across the synapse between a motor neurone and a muscle fibre.
[6]
- Ca2+ channels / gates open;
- Ca2+ ions enter (pre-synaptic neurone);
- Vesicles move towards / fuse with presynaptic membrane;
- Release / exocytosis of transmitter substance / of acetylcholine;
- Diffusion (of transmitter) across gap / cleft;
- (Transmitter) binds to receptors in postsynaptic membrane;
- Na+ channels open / Na+ ions enter (postsynaptic side);
After death, cross bridges between actin and myosin remain firmly bound resulting in rigor mortis. Explain what causes the cross bridges to remain firmly bound. [3]
- respiration stops;
- no ATP produced;
- ATP required for separation of actin and myosin/cross bridges;
Describe the role of calcium ions in the contraction of a sarcomere. [4]
- interact with/move/touch tropomyosin; (allow troponin as alternative)
- to reveal binding sites on actin; (not active sites)
- allowing myosin (heads) to bind/touch actin / actinomyosin formed;
- activate ATP hydrolase / energy released from ATP;
Describe slow twitch muscle fibres [2]
- have lots of mitochondria/ (slow fibres) respire aerobically;
- More myoglobin
- Less / no glycogen stores
Describe fast twitch muscle fibres [5]
- used for rapid/brief/powerful/strong contractions;
- Phosphocreatine used up rapidly during contraction/to make ATP;
- Anaerobic respiration involved;
- ATP used to reform phosphocreatine;
- Lots of phosphocreatine in fast twitch fibres;
- No myoglobin
Describe the role of phosphocreatine [2]
- Provides (energy and) phosphate / phosphorylates;
- To make ATP from ADP & Pi;
Explain how insulin reduces the blood glucose concentration. [3]
- (More) insulin binds to receptors of target cells (All body cells);
- (Stimulates) uptake of glucose by GLUT channel/transport proteins;
- Activates (liver & muscle) enzymes which convert glucose to glycogen;
Explain the action of Glucagon [3]
- Attaches to receptors on target cells and activates/stimulates enzymes;
- Glycogen to glucose / glycogenolysis;
- Gluconeogenesis;
Describe how a change in blood pH or blood pressure can cause a change in heart rate. [6]
- (Carbon dioxide) detected by chemoreceptors / (pressure) detected by baroreceptors;
- Medulla/cardiac centre involved;
- More impulses to SAN/along sympathetic nerve;
- (Decrease) pH detected by chemoreceptors in carotid artery /aorta;
- Sends (more) impulses to medulla (oblongata);
- More Nerve impulses sent by sympathetic nervous system to SAN;
Less CO2 in the blood leads to a reduction in heart rate.
Describe how.
[5]
- (less CO2 in blood) Detected by chemoreceptors;
- (Chemoreceptors) located in aorta / carotid artery;
- Fewer impulses to cardiac centre / medulla (oblongata);
- (More) impulses along parasympathetic nerve OR less impulses along sympathetic nerve;
- (To) SAN;
Describe the secondary messenger model [3]
- Adenylate cyclase activated / cAMP produced / second messenger produced;
- Activates protein kinase enzyme(s) (in cell);
- (So) glycogenolysis/ gluconeogenesis occurs / glycogenesis inhibited;
Describe the role of glycogen formation and its role in lowering blood glucose levels. [4]
- Glucose concentration in cell/liver falls;
- Below that in blood (plasma)/ higher in blood;
- Creates/maintains glucose concentration/diffusion gradient;
- Glucose enters cell/leaves blood by facilitated diffusion/via carrier(protein)/channel (protein);
Describe how ultrafiltration occurs in a glomerulus. [4]
- High (higher than normal) blood/hydrostatic pressure;
- Two named small substances pass out eg water, glucose, ions, urea;
- (Through small) gaps/pores/fenestrations in (capillary) endothelium;
- (And) through (capillary) basement membrane;
Describe and explain how three features of the cells in the proximal convoluted tubule allow the rapid reabsorption of glucose into the blood. [6 ]
- Microvilli provide a large surface area OR Folded (cell-surface) membrane provides a large surface area;
- Many channel/carrier proteins for facilitated diffusion;
- Many carrier proteins for active transport;
- Many channel/carrier proteins for co-transport;
- Many mitochondria produce ATP OR Many mitochondria for active transport/co-transport;
- Many ribosomes to produce carrier/channel proteins;
Explain why a thicker medulla leads to more concentrated urine. [3]
- Thicker medulla means a longer loop of Henle;
- (The longer the loop of Henle means) increase in sodium ion concentration (in medulla) so sodium ion gradient maintained for longer (in medulla);
- (Therefore) water potential gradient maintained (for longer), so more water (re)absorbed (from loop and collecting duct) by osmosis;
Describe the action of ADH in the kidney [6]
- ADH bind to (target cell) membrane receptor proteins on cells lining DCT and CD
- Permeability of membrane/cells (to water) is increased;
- More water absorbed from/leaves distal convoluted tubule/collecting duct;
- by osmosis;
- Smaller volume of urine produced;
- Urine becomes more concentrated;
Explain why glucose is found in the urine of a person with untreated diabetes. [3]
- High concentration of glucose in blood/filtrate;
- Not all the glucose is (re)absorbed at the proximal convoluted tubule;
- Carrier/co-transport proteins are working at maximum rate OR Carrier/co-transport proteins/ are saturated;
Define homeostasis
The maintainance of a constant internal environment, within restricted limits / set point.
Define a negative feedback loop
Any change / deviation away from a set point leads to a response that returns back to the the set point.
Define positive feedback.
Any deviation away from the set point, leads to even further deviation from the set point.
More leads to even more.
Less leads to even less.
What is a stimuls?
A detectable change to the internal or external environment
What is a response?
A change that occurs by the action of an effector (Muscle or gland)
Define Cardiac output
= Stroke Volume X Heart Rate
SV= Volume of blood exiting the Left ventricle
CO= Volume of blood circulated around the body per minute
Calculate the speed of nerve impulse transmission, when:
- The length of one nerve pathway involved is 175 cm.
- A reaction time took 136 ms
Answer Units are m per second
12.9 m per second
In response to touch, nerve impulses can be transmitted at speeds of 76.2 m s–1
Suggest THREE reasons why in reality this could be slower. [3]
- Synaptic transmission OR Transmission at neuromuscular junction;
- Time for muscle contraction;
- Time taken for (stretch-mediated) sodium ion channels to open (in the Pacinian corpuscle);
- Time taken for coordination/comprehension (by the brain);
Explain how a resting potential is maintained across the axon membrane in a neurone. [3]
- Higher concentration of potassium ions inside and higher concentration of sodium ions outside (the neurone) OR potassium ions diffuse out OR sodium ions diffuse in;
- (Membrane) more permeable to potassium ions (leaving than sodium ions entering) OR (Membrane) less permeable to sodium ions (entering than potassium ions leaving);
- 3 Sodium ions (actively) transported out and 2 potassium ions in;
A scientist investigated the effect of inhibitors on neurones. She added a respiratory inhibitor to a neurone. The resting potential of the neurone changed from –70 mV to 0 mV.
Explain why. [3]
- No/less ATP produced;
- No/less active transport OR Sodium/potassium pump inhibited;
Accept Na+ not/fewer moved out and K+ not/fewer moved in.
- Electrochemical gradient not maintained OR (Facilitated) diffusion of ions causes change to 0 mV OR (Results in) same concentration of (sodium and potassium) ions (either side of membrane) OR No net movement of (sodium and potassium) ions;
Accept reaches electrical equilibrium/balance.
Damage to the myelin sheath of neurones can cause muscular paralysis.
Explain how. [3]
1. (Refers to) saltatory conduction OR (Nerve) impulses/depolarisation/ions pass to other neurones
OR Depolarisation occurs along whole length (of axon);
Accept suitable description that refers to (transmission) from node to node (of Ranvier).
Accept action potential for depolarisation.
1 and 2. Accept action potentials for impulses.
2. (Nerve) impulses slowed/stopped;
3. (Refers to) neuromuscular junction OR (Refers to) sarcolemma;
Suggest two advantages of simple reflexes.
- Rapid;
- Protect against damage to body tissues;
- Do not have to be learnt;
- Help escape from predators;
- Enable homeostatic control.
In the nerve pathway in the diagram, synapses ensure that nerve impulses only travel towards the muscle fibre.
Explain how. [2]
- Neurotransmitter only made in / stored in / released from pre-synaptic neurone;
- (Neuro)receptors only on the post-synaptic membrane;
Cannabinoid receptors are found in the pre-synaptic membrane of neuromuscular junctions. When a cannabinoid binds to its receptor, it closes calcium ion channels.
Suggest how cannabinoids could prevent muscle contraction. [4]
- Prevents f.diffusion of calcium ions (into pre-synaptic membrane);
- (Synaptic) vesicles don’t fuse with membrane / vesicles don’t release neurotransmitter; Accept vesicles don’t release acetylcholine
- Neurotransmitter does not diffuse across synapse / does not bind to receptors (on post-synaptic membrane); Accept: sarcolemma / muscle membrane for post-synaptic membrane
- No action potential / depolarisation (of post-synaptic membrane) / sodium (ion) channels do not open / prevents f.diffusion of sodium ions.
