Download Topic 8 Checkpoint Answers File

Checkpoint answers for topic 8
Q8.1 Draw up a table comparing the structure and location of motor, relay and sensory
neurones.
General
structure
Location of
cell body
relative to
CNS
Dendrites
Axons
Function
Motor
Relay
Sensory
Cells have cell body,
short dendrites and
long axon.
Cell body and
dendrites inside CNS,
axons outside CNS.
Cells have cell body,
short dendrites and
short or long axon.
Cell bodies inside
CNS.
Dendrites synapse
with other neurones in
CNS.
Axons synapse with
effector cells (muscles
and glands).
Conduct impulse to an
effector (muscle or
gland).
Dendrites synapse
with other neurones in
CNS.
Cells have cell body,
long dendrites and
short axon.
Cell body and
dendrites outside
CNS. Cell body is in
dorsal root ganglia at
entrance route to the
spinal cord.
Dendrites synapse
with sensory receptor
cells.
Axons synapse with
other neurones in
CNS.
Conduct impulse to
the CNS.
Axons synapse with
other neurones.
Connect sensory
neurones with
appropriate motor
neurone.
Q8.2 Produce a bullet-point summary of the membrane changes and ion movements that
cause an action potential. You should aim to have at least 10 bullet points.
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At resting potential Na+ and K+ voltage-dependent channels are closed.
There is no significant flow of ions across the membrane.
Some voltage-dependent Na+ channels open.
Na+ flow in.
Depolarisation: the potential difference across the membrane becomes +40 mV.
Voltage-dependent Na+ channels close.
Voltage-dependent K+ channels open.
K+ flow out.
The membrane is hyperpolarised.
Voltage-dependent K+ channels close.
K+ diffuse back into the axon, restoring the resting potential.
Q8.3 Construct a flowchart to show the sequence of events that occurs when a nerve
impulse crosses a synapse.
An impulse arrives at the presynaptic knob.
The membrane depolarises.
Calcium ion channels in the membrane open.
Calcium ions enter the presynaptic knob.
Vesicles holding neurotransmitter fuse with the membrane.
Neurotransmitter is released into the synaptic cleft.
Neurotransmitter diffuses across the synaptic cleft.
Neurotransmitter binds to receptors on the postsynaptic membrane.
Channels on the postsynaptic membrane open.
Ions enter the postsynaptic neurone.
The postsynaptic membrane is depolarised.
An action potential is triggered in the postsynaptic neurone.
Q8.4 Make a list of key words to distinguish the features of: a nervous and b hormonal
control. If you can compose a mnemonic to help you remember these, even better.
Nervous control
neurones
impulses
electrical (and chemical)
action potentials
synapses
rapid
short-term
specific
response local
muscle cell or gland
Hormonal control
blood
chemical
slow
long-term
widespread
target cells
Q8.5 Draw up a table that summarises the similarities and the differences between the
action of hormones in animals and growth substances in plants.
Similarities
Both hormones and plant growth
substances are chemical messengers.
Some hormones and some plant growth
substances bring about long-term
changes through control of growth and
development. (Other hormones and
plant growth substances bring about
rapid changes.)
Some hormones and some plant growth
substances affect gene expression,
Other hormones and plant growth
substances have direct effects, for
example on enzymes or membrane
properties.
Differences
Hormones are produced by endocrine
glands whereas plant growth
substances are produced by dividing
cells (meristems).
Hormones are transported in the blood
whereas plant growth substances move
from cell to cell or in vascular tissue.
Q8.6 Produce a series of statements that describe what happens in rod cells to enable
light to generate an action potential in a bipolar cell. Get a friend to order the statements
as a revision exercise.
In the dark
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Na+ flow into the outer segment through non-specific cation channels.
This slightly depolarises the rod cell to +40 mV.
The slight depolarisation triggers release of neurotransmitter (glutamate).
Neurotransmitter binds to the bipolar cell and stops it from firing.
In the light
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Light falls on rhodopsin.
Rhodopsin breaks down into retinal and opsin.
Opsin activates membrane-bound reactions which cause cation channels to
close.
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Na+ influx is reduced.
Na+ channels in the inner segment continue to pump out Na+.
The inside of the rod cell becomes more negative.
The rod cell becomes hyperpolarised.
Release of neurotransmitter stops.
Neurotransmitter no longer inhibits cation channels in bipolar cells.
Cation channels in bipolar cells open.
The bipolar cell depolarises and produces an action potential.
The impulse crosses the synapse to the optic nerve.
The impulse is carried to the brain.
Q8.5
Q8.7 Construct a spider diagram showing the ways in which drugs can affect synaptic
transmission. Include examples of the types of drugs that produce each effect.
Q8.8 List the key benefits and risks of using GMOs
Benefits
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Improved crop plants; this may include higher yields, higher vitamin content, plants
that can manufacture drugs, drought-resistant plants and trees from which paper
can be made without the need for chlorine to be used.
Crops that are unpalatable to insect herbivores reduce insecticide use.
Crops resistant to disease and pests would increase yield and help feed the world.
Crops modified to contain vitamins or other enhanced nutritional contents could
have health benefits.
Plants, animals and micro-organism modified to produce medicines could make
these drugs cheaper and more widely available.
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Organisms modified to give higher yields would reduce the cost of production and
may reduce the clearing of natural habitats to provide additional agricultural land
Risks
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Antibiotic resistance genes may be transferred to bacteria in the gut which could
build up resistance to certain antibiotics used in medical treatments.
There are health concerns related to the formation of harmful products in the GMO
by new genes, and the products are then eaten.
Transfer of genes to non-GM plants may create superweeds and adversely affect
food chains.
GM crops could crossbreed with organic crops; these are no longer organic
affecting the livelihood of the organic farmers.
Chemical use is increased in GM crops which are resistant to herbicide (weedkiller).
Insects exposed to high doses of an insecticide could allow ‘superbugs’ to develop,
requiring an increasing use of chemicals on crops
Large biotechnology companies patenting genes, techniques and organisms
developed could threaten the livelihood of small farmers particularly in less
developed countries.