Section 6 Flashcards
A student investigated the effects of indoleacetic acid (IAA) on the growth of oat
seedlings (young plants).
The student:
* removed the shoot tip from each seedling and cut out a 10 mm length of
shoot
* placed 10 lengths of shoot into each of 5 Petri dishes
* added to each Petri dish an identical volume of 5% glucose solution
* added to each Petri dish 40 cm3 of a different concentration of IAA solution
* left the Petri dishes at 20 °C in the dark with their lids on for 5 days
* removed the shoots after 5 days and measured them
* determined the mean change in length of shoot at each concentration of
IAA.
Explain why the lids were kept on the Petri dishes
To prevent evaporation
Changes IAA concentration/ Changes water potential
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.
The fovea of the eye of an eagle has a high density of cones. An eagle
focuses the image of its prey onto the fovea.
Explain how the fovea enables an eagle to see its prey in detail.
high visual acuity
Each cone cell connected to its own bipolar cell
Sends seperate impulses to the brain
The retina of an owl has a high density of rod cells.
Explain how this enables an owl to hunt its prey at night.
High visual sensitivity
Many rod cells connected to same bipolar neurone
Spatial summation to overcome/reach threshold
Or
Enough neurotransmitter released to reach threshold
Explain how the resting potential of –70 mV is maintained in the sensory
neurone when no pressure is applied.
Membrane more permeable to K+ than Na+
Na+ actively transported out of the neuron membrane, K+ actively transported into the neuron membrane
Explain how applying pressure to the Pacinian corpuscle produces the
changes in membrane potential recorded by microelectrode P.
deforms membrane/lamella of pacinian corpuscle
Causes Na+ channels in membrane to open
Na+ moves into the neuron membrane
Increased pressure= increased Na+ channels open
The membrane potential at Q was the same whether medium or heavy
pressure was applied to the finger tip. Explain why.
Threshold has been reached
At or above threshold causes maximal response/all or nothing principle
Multiple sclerosis is a disease in which parts of the myelin sheaths
surrounding neurones are destroyed. Explain how this results in slower
responses to stimuli.
less saltatory conduction/ depolarisation can’t jump from node-node
Depolarisation occurs over whole length
Differences between slow and fast twitch muscle fibres
Slow twitch
Slower less powerful contractions over longer period of time
More myoglobin
More mitochondria
More blood vessels
More glycogen
Fast twitch
Rapid more powerful contractions over short duration
More phosphocreatine
More enzymes for anaerobic respiration
more and thicker myosin filament
High glycogen conc
Similarities between Neuromuscular junction and cholinergenic synapse
Neurotransmitter diffuses across synapse
Neurotransmitter broken down by same enzyme in synapse to prevent constant stimmulation of post synaptic membrane
Neurotransmitter bind to receptors on post synaptic membrane- cause influx of Na+
Use sodium/pottassium pump to repolarise
Differences between neuromuscular junction and cholinergenic synapse
Neuromuscular excitatory whereas C= excitatory or inhibitory
Neuromuscular= only motor neurones C= sensory,motor or relay neurones
N=stops action potential (end of neural pathway) C=new action potential may be created in post synaptic neurone
N=acetylcholine binds to receptors on muscle fibre membrane C=binds to receptors on post synaptic neurone
N= only links neurones to muscles C=links neurones to neurones/neurones to other effector muscles
Suggest a reason why there are many mitochondria in the sarcoplasm
requires more energy for contraction
most energy from krebs cycle and electron transfer chain in respiration
Both occur in mitochondria
Sprinters have high conc phosphocreatine in muscles
Suggest advantage
Supplies more phosphate groups to combine with more ADP to make more ATP for muscular contraction (regeneration ATP)
Anaerobic conditions- supply ATP from mitochondria decreases as supply of O2 doesnt meet demand of muscle cells
With increased conc phosphocreatine ATP can be supplied for longer
(c)
Another group of scientists suggested that a decrease in the force of
muscle contraction is caused by an increase in the concentration of
inorganic phosphate, Pi, in muscle tissues.
Their hypothesis is that an increase in the concentration of Pi prevents the
release of calcium ions within muscle tissues.
Explain how a decrease in the concentration of calcium ions within muscle
tissues could cause a decrease in the force of muscle contraction
No/less Tropomyosin moves to expose binding site/less tropomyosin changes shape to expose binding site
Fewer actin-myosin cross-bridges
Mysosin head does not move/does not pull actin filament
During vigorous exercise, the pH of skeletal muscle tissue falls. This fall in
pH leads to a reduction in the ability of calcium ions to stimulate muscle
contraction.
Suggest how.
Change in shape of Ca 2+ receptors
Less Ca2+ binds to tropomyosin
Less tropomyosin moves away
Les binding sites on actin exposed
Less cross-bridges form
Explain how a resting potential is maintained across the axon membrane in
a neurone.
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;
Accept ‘more’ for ‘higher concentration’.
Accept ‘sodium ions can’t diffuse in (due to
alternative explanation).
2.
3.
(Membrane) more permeable to potassium ions (leaving
than sodium ions entering)
OR
(Membrane) less permeable to sodium ions (entering
than potassium ions leaving);
Accept for ‘less permeable to sodium ions’ is
‘impermeable to sodium ions’ or ‘sodium
gates/channels are closed’ (alternative
explanation).
Sodium ions (actively) transported out and potassium ions in;
Q2.
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;
Using your knowledge of the kidney, explain why glucose is found in the
urine of a person with untreated diabetes.
High glucose CONCENTRATION in blood/filtrate
Less glucose reabsorbed in PROXIMAL CONVOLUTED TUBULE
cotransport/carrier proteins saturated/working at maximum rate
(d)
Explain how increasing a cell’s sensitivity to insulin will lower the blood
glucose concentration.
Increased insulin binds to receptors on cells
Stimulates uptake of glucose by channel/transport proteins
Activates enzymes which convert glucose to glycogen
Explain how inhibiting adenylate cyclase may help to lower the blood
glucose concentration.
Less ATP converted to Cyclic AMP
Less protein kinase activated
less glycogen converted to glucose/less glycogenolysis
Furosemide inhibits the absorption of sodium and chloride ions from the
filtrate produced in the nephrons.
Explain how furosemide causes an increase in the volume of urine
produced.
Decreases water potential of filtrate
Less water reabsorbed by osmosis
In collecting duct
Furosemide and CVT are drugs used to remove excess fluid from the body.
Scientists investigated the effect of these drugs on the volume of urine produced
by human volunteers.
All the volunteers were given the same food for 3 days.
Suggest and explain one reason why they were given the same food.
Affects the water potential of the blood
affects volume of urine
Describe the role of myosin in muscle contraction
Head of myosin binds to actin and pulls the actin filament
Detatches froms actin and moves further along actin filament
Uses ATP
Explain the importance of ATPase during muscle contraction.
Hydrolysis ATP->ADP and Pi
Yields energy
used to break/form actin-myosin cross bridge
The myosin-ATPase of type 1 muscle fibres has a faster rate of reaction than that in type 2 fibres. Use your knowledge of the mechanism of muscle contraction to explain how this will help type 1 muscle fibres to contract faster than type 2.
Overall rate limited by rate of ATP hydrolysis
ATPase hydrolyses ATP to ADP and Pi
Energy required to cock/move myosin head
The blood leaving an active muscle with a high percentage of type 1 muscle fibres contained a higher concentration of lactate than that leaving a muscle with a high percentage of type 2 muscle fibres. Explain why.
Lactate is a product of anaerobic respiration
Type 1= fewer mitochondria
type 1 has higher activity of glycolytic enzymes / has lower activity
of Krebs cycle enzymes
