Study sets, textbooks, questions
Upgrade to remove ads
Synapses, skeletal muscles, inheritance, succession
Terms in this set (36)
Explain the role of the Na+ and K+ channels in producing the membrane resting potential.
Sodium ions pumped out (to create diffusion gradient);
sodium gates open
Acetylcholine increases the permeability of the postsynaptic membrane to Na+ ions. Explain how acetylcholine released from neurone A generates an action potential in neurone C.
ACh combines with receptor (on neurone C / on postsynaptic membrane);
causes influx of Na+ ions;
down gradient / diffuse;
less negative/more positive inside/ 'depolarisation' occurs;
reference to above threshold (to generate action potential)
Neurone B releases a substance called GABA as its neurotransmitter. GABA increases the permeability of the postsynaptic membrane to Cl- ions. Suggest how impulses in neurone B would reduce the chances of an action potential in neurone C
(Cl- entry to neurone C) makes potential more negative inside/hyperpolarises;
requires more stimulation (from A) / ACh / Na+/ more impulses
The rate of oxygen consumption of a neurone increases when it conducts a high frequency of impulses. Explain why.
Oxygen used in respiration; [Reject: Anaerobic reference]
Valid reference to ATP/energy; [Reject: Production of energy]
(For) sodium-potassium pump/ active transport of ions/ uptake/ synthesis
of transmitter/ vesicle movement;
(Higher rate of impulses means) more high / amount of sodium ion entry/
potassium ion loss / transmitter uptake / release / vesicle movement
Explain how synapses ensure that a nerve impulse is transmitted in only one direction.
Transmitter substance/ neurotransmitter only produced in pre-synaptic
Receptor proteins for neurotransmitter only in post-synaptic membrane;
Enzymes in post-synaptic neurone hydrolyse neurotransmitter
Describe the events that take place in a neurone which produce an action potential.
Stimulus to threshold / critical firing level;
2 Sodium channels/gates open;
3 Sodium ions enter;
4 Down electrical/chemical gradient;
5 Positive feedback;
7 Inside becomes positive / membrane potential reverses;
8 Potassium channels/gates open;
9 Potassium ions leave;
10 Down electrical/chemical gradient
[Note: only credit if not awarded earlier in point 4]
12 Sodium channels/gates close;
13 Undershoot / hyperpolarisation;
14 Sodium-potassium pump restores resting potential; max 6
Describe how transmission occurs across a synapse.
Presynaptic membrane depolarises;
2 Calcium channels/gates open;
3 Calcium ions enter;
4 Vesicles move to/fuse with presynaptic membrane;
5 Release of transmitter / exocytosis;
6 Diffusion across gap/cleft;
7 Binds to receptors in postsynaptic membrane;
[Reject: references to active site]
8 Sodium channels open / sodium ions enter;
Explain what is meant by the tertiary structure of a protein and describe the importance of this in transmission across a synapse.
1 Polypeptide (chain) folds;
2 Named bond; [Reject: peptide bond]
3 Between R groups;
4 Receptors/binding sites are proteins;
5 Reference to neurotransmitter shape;
6 Acetylcholinesterase/breakdown enzyme, is protein;
7 Carrier/channel protein;
8 Protein has a shape;
9 Idea of complementary/fit/bind/attach to; [Note: in correct context] max 5
[Ignore: 'lock and key']
Explain how the release of acetylcholine at an excitatory synapse reduces the membrane potential of the postsynaptic membrane.
Binds to receptor/proteins; and opens Na+ channels;
Na+ enter and make membrane potential less negative/depolarised
When the postsynaptic membrane is stimulated by acetylcholine, an action potential is less likely if GABA is released at the same time. Explain why.
GABA opens K+ and Cl- channels;
K+ passes out and Cl- passes in;
Membrane potential more negative/hyperpolarised;
Requires increased stimulation/must open more Na+ channels/allow
more Na+ to enter;
To reach threshold; max 4
Name the transmitter released from the postganglionic motor neurones of the sympathetic division of the autonomic nervous system.
Describe how the resting potential is established in an axon by the movement of ions across the membrane
active transport / pump of Na+ out of axon;
diffusion of K+ out of axon / little diffusion of Na+ into the axon;
Sodium and potassium ions can only cross the axon membrane through proteins. Explain why.
can not pass through phospholipid bilayer;
because water soluble / not lipid soluble / charged / hydrophilic / hydrated
What is meant by the 'all or nothing' nature of a nerve impulse?
All action potentials are the same size;
threshold value for action potential to occur
Neurones can respond to both strong and weak stimuli. Describe how a neurone conveys information about the strength of a stimulus.
frequency of action potentials
Describe what is meant by temporal summation at a synapse.
several (sub-threshold) impulses add to produce an action potential
Describe the sequence of events which leads to the transmission of an impulse at a cholinergic synapse.
calcium ions move into synaptic knobs / presynaptic membrane;
causing synaptic vesicles to move;
towards presynaptic membrane;
where they release acetylcholine into gap;
transmitter/acetylcholine diffuses across gap;
binds onto receptor / protein molecules;
on postsynaptic membrane;
causing depolarisation / opening of sodium gates / action potential in
postsynaptic cell membrane; max 6
Describe how a resting potential is maintained in an axon.
active transport/pumping of sodium (ions across membrane);
out of neurone/higher concentration outside;
differential permeability to K+ and Na+;
What is meant by the refractory period?
no (new) action potential/nerve impulse be produced in this time;
Describe the role of calcium ions and ATP in the contraction of myofibril
Calcium ions diffuse into myofibrils from sarcoplasmic reticulum
Calcium ions cause movement of tropomyosin on actin
This movement causes exposure of the binding sites in the actin
Myosin heads attach to binding sites on actin
Hydrolysis of ATP causes myosin heads to bend
Attachment of a new ATP molecule to each myosin head causes myosin heads to detach
What is the role of ATP in myofibril contraction?
Allows binding of myosin to actin
Provides energy to move myosin head
Use your knowledge of succession to explain the increase in biomass in the first 20 years
Change in abiotic conditions / less hostile / more habitats / niches;
Increase in number / amount / diversity of species / plants
Explain how the change in species composition occurs in a succession.
species present change the habitat/named change; other species able to colonise;
new species better competitors;
Succession occurs in natural ecosystems. Describe and explain how succession occurs.
1. (Colonisation by) pioneer (species);
2. Change in environment/example of change caused by organisms present;
3. Enables other species to colonise/survive;
4. Change in diversity/biodiversity;
5. Stability increases/less hostile environment;
Changes in ecosystems can lead to speciation. In Southern California 10 000 years ago a number of interconnecting lakes contained a single species of pupfish.
Increasing temperatures caused evaporation and the formation of separate, smaller lakes and streams. This led to the formation of a number of different species of pupfish. Explain how these different species evolved
2. Separate gene pools/no interbreeding (between populations);
3. Variation due to mutation;
4. Different environmental/abiotic/biotic conditions/selection pressures;
5. Selection for different/advantageous, features/characteristics /mutation//allele;
6. Differential reproductive success/(selected) organisms survive and reproduce;
7. Leads to change in allele frequency; 8. Occurs over a long period of time;
In this question must refer to allele where appropriate, not gene.
Explain how succession led to formation of a forest
a) pioneers/suitable example colonise land; example of change in environment;
enables change in species;
conditions change further/example to favour trees
What is meant by a community?
a) populations of different species; living in the same environment/habitat;
Explain what limits the size of populations in a climax community
1. named nutrient availability;
2. numbers of producers providing energy (for a food chain);
3. light intensity affecting the rate of photosynthesis;
4. disease killing (weaker) members of species;
5. space for nest building / niches;
6. reproductive rate balancing death rate;
7. competition for a named limited resource;
8. (intra and interspecific) competition explained;
9. predation described;
What is meant by succession?
change in community over time;
either due to change environmental/abiotic factors / change is due to species present;
Describe those features of a succession that would bring about an increase in the index of diversity
Initial environment hostile / few organisms adapted;
These organisms change the environment / suitable example; More niches / more habitats;
Allowing other organisms to become established;
What is meant by a climax community?
stable community/no further succession/final community;
Explain what is meant by codominant alleles
Both alleles are expressed
Male cats with a tortoiseshell phenotype do not usually occur. Explain why
Y chromosome does not carry allele
Explain why the scientists used the same restriction endonuclease enzymes on each DNA sample
Cut (DNA) at same (base) sequence / (recognition) sequence;
(So) get (fragments with gene) R / required gene.
In fruit flies, the genes for body colour and wing length are linked. Explain what this means.
Genes / loci) on same chromosome
In birds, males are XX and females are XY.
Use this information to explain why recessive, sex-linked characteristics are more common in female birds than in male birds.
Recessive) allele is always expressed in females / females have one
(recessive) allele / males need two recessive alleles / males need to be homozygous recessive / males could have dominant and recessive alleles / be heterozygous / carriers;
Sets found in the same folder
Topic 1 - Biological molecules
Topic 2 - cells, transport, immune system
Topic 3 - genetic information, variation and relat…
PCR, epigenetics, mutations
Other sets by this creator
Microbiomes, evolution and health