15 Jun If the posterior region of an early limb bud in a chicken embryo
Question
1. Apoptosis
a. involves the self-destruction of cells
b. is a developmental abnormality with no known genetic basis
c. is a normal part of development
d. Both a & c are true
2. If the posterior region of an early limb bud in a chicken embryo (containing the ZPA)
is excised and transplanted onto the anterior region of a limb bud in a second embryo,
what would you predict would be the phenotype of the limb in the second embryo
when it has developed?
a. it will have a normal limb
b. it will have a limb with twinned digits organized as mirror images of each other
c. it will have a limb with two ventral surfaces (equivalent to two “palm” surfaces)
d. it will have a limb with two dorsal surfaces (equivalent to two “back of hand”
surfaces)
3. For a neuron at its resting potential, the forces acting on potassium (K+) ions are
a. a concentration gradient pulling K+ inward & an electrical potential pulling K+
outward
b. a concentration gradient pulling K+ outward & an electrical potential pulling K+
outward
c. a concentration gradient pulling K+ outward & an electrical potential pulling K+
inward
d. none, since no ions can move in or out of a neuron when it is at its resting
potential
4. During the first part of an action potential
a. increasing numbers of Na+ channels open & the membrane potential eventually
matches the Nernst potential for Na+
b. increasing numbers of Na+ channels open & the membrane potential moves
toward the Nernst potential for Na+ but doesn’t reach it because Na+ channels start
to shut down and K+ channels start to open
c. increasing numbers of K+ channels open & the membrane potential eventually
matches the Nernst potential for K+
d. increasing numbers of K+ channels open & the membrane potential moves toward
the Nernst potential for K+ but doesn’t reach it because K+ start to shut down and
Na+ channels start to open
5. When Na+ channels open in a neuron during an action potential
a. Na+ ions pour into the cell, but the relative Na+ concentrations inside & outside
the cell are essentially unchanged
b. Na+ ions pour into the cell, reversing the relative ion concentrations so that the
Na+ concentration becomes higher inside the cell than outside the cell, causing
depolarization
c. the net charge throughout the cytoplasm inside the neuron shifts from negative to
positive
d. both A & C are true
6. Which of the following developmental processes occur in animal embryos, but not in
plants?
a. cell proliferation
b. cell differentiation
c. cell migration
d. expression of homeotic genes that regulate the identity of a body part
7. At some synapses, neurotransmitters hyperpolarize (rather than depolarize) the
postsynaptic neuron, moving it farther away from the threshold for generating an
action potential. Which of the following neurotransmitter effects would hyperpolarize
a postsynaptic neuron at resting potential?
a. Opening K+ channels in the cell membrane
b. Closing K+ channels in the cell membrane
c. Opening Na+ channels
d. Both a & b
8. Homeotic fruitfly mutants
a. result from particular Hox gene mutations being expressed in the segments
exhibiting mutant phenotypes
b. have normally developed body parts in abnormal locations
c. have abnormally developed body parts in normal locations
d. Both A & B are true
9. You are working in a clinic in Brazil when someone brings in a young woman who
has been having convulsions. They bring a sample of a plant she has been taking as
herbal medicine. You immediately recognize it as a plant you know inhibits the
sodium-potassium pump in neurons. You quickly take her blood and send it to the
lab. They send you back an analysis which allows you to compare her values to
normal values:
Ion
Pion
Inside cell
Blood (normal) Blood (your patient)
K+
1
140
5.5
10
Na+
0.02
15
150
150
Cl-
0.01
9
125
125
You calculate the resting potential of your patient using the Goldman
equation:
THERE SHOULD BE A LOG BEFORE THE PARENTHESES, BUT
IT’S TOO TRICKY TO FIX THIS RIGHT NOW AND YOU DON’T
NEED TO MEMORIZE THIS EQUATION ANYHOW…
" P [K + ] + P [Na + ] + P [Cl − ] %
out
Cl
in
Emembrane = 62mV $ K + out Na
‘
+
−
P
[K
+
P
[Na
+
P
[Cl
# K
in
Na
in
Cl
out &
" 1*10mM + 0.02 *150mM + 0.01* 9mM %
= 62mV $
‘ = −64mV
# 1*140mM + 0.02 *15mM + 0.01*125 &
a. (2 pts) Why does the term for chloride ion have the concentration inside in
the numerator whereas the terms for potassium and sodium have the
concentration inside in the denominator?
b. (1 pts) What part of the Goldman equation is modified by particular types
of ion channels opening & closing?
c.
(2 pts) If the resting potential of a healthy person is -75 mV, why does
your patient’s value make sense based on her blood results?
d. Draw a line across the graph of a normal action potential, below, that
indicates your patient’s resting potential. Based on this result, why does it
make sense that your
patient is having
convulsions?
11.
Ion
Concentra
tion inside
cell
+
K
150 mM
Na+ 15 mM
Cl9 mM
Othe 140 mM
r
anio
ns
Concentra
tion
outside
5.5 mM
150 mM
125 mM
40 mM
a. Using the tabled numbers above, draw a cell (a circle will do!) and label the
ion concentrations inside and outside the cell.
b. Use the Nernst equation to calculate the membrane potential for K+, Na+ and
Cl-ions, individually, in a warm-blooded vertebrate (assume a temperature of
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