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Unformatted text preview: Exam 2 Fall 2015
1. Different body cells can respond differently to the same peptide hormones because _____.
A) different target cells have different sets of genes
B) a target cell's response is determined by the components of its signal transduction
C) the circulatory system regulates responses to hormones by routing the hormones to
D) the hormone is chemically altered in different ways as it travels through the circulatory
It is the presence of receptors and signal transduction pathways that determines the
response to a chemical signal.
2. Analysis of a blood sample from a fasting individual who had not eaten for twenty-four
hours would be expected to reveal high levels of _____.
Glucagon stimulates the breakdown of glycogen to glucose in the liver when blood
glucose level is low. You could make the argument for Glucose in this question as
well, though it would presumably be metabolized since the individual is fasting. For the following two (2) questions A=True, B=False
3. Lipid-soluble signaling molecules, such as testosterone, cross the membranes of all cells
but affect only target cells because intracellular receptors are present only in target cells.
True, a hormone will only have an action in a cell if a receptor is present.
4. Conformational change in a signal-receptor complex that activates an enzyme is the first
step in the process of signal transduction. True, a signal binding to a receptor initiates
signal transduction. Exam 2 Fall 2015 5. Which of the following can act as a second messenger in a signal transduction cascade:
B) Cyclic AMP
D) All of the above
These can all be components of a signal transduction cascade. 6. Which of the following statements best summarizes the acid-growth hypothesis in an
actively growing shoot?
A) Auxin stimulates proton pumps in the plasma membrane and tonoplast.
B) Auxin-activated proton pumps lower the pH of the cell wall, which breaks bonds
and makes the walls more flexible.
C) Auxins and gibberellins together act as a lubricant to help stretch cellulose microfibrils.
D) Auxins activate aquaporins that increase turgor pressure in the cells.
The acid growth theory states that cell expansion occurs by breaking crosslinks
between cellulose microfibrils in the cell wall, and the breaking of crosslinks is a
result of acidification of the wall. 7. A population of plants experiences several years of severe drought. Much of the
population dies due to lack of water, but a few individuals survive. You set out to discover
the physiological basis for their adaptation to such an extreme environmental change. You
hypothesize that the survivors have the ability to synthesize higher levels of _____ than their
D) abscisic acid
Abscisic acid is produced under water stress, and induces stomata to close,
conserving water under drought conditions. Exam 2 Fall 2015 8. Although the membrane of a "resting" neuron is highly permeable to potassium ions, its
membrane potential does not exactly match the equilibrium potential for potassium
because the neuronal membrane is also _____.
A) slightly permeable to sodium ions
B) fully permeable to calcium ions
C) impermeable to sodium ions
D) highly permeable to chloride ions
The slight permeability of the membrane to sodium ions, allows for some leakage of
sodium into the cell, making the membrane potential more positive, keeping it away
from the Equillibrium potential for potassium. For the following three (3) questions A=True, B=False
9. For a neuron with an initial membrane potential at -70 mV, an increase in the movement
of potassium ions out of that neuron's cytoplasm would result in the hyperpolarization of
the neuron. True. Hyperpolarization is where the membrane potential becomes
more negative, and will occur if potassium moves out (efflux of positive charge).
10. A toxin that inhibits activity of voltage-gated sodium channels in axons would be
expected to prevent action potential generation. True . The action potential initiates by
the opening of voltage gated sodium channels when the membrane depolarizes to the
threshold membrane potential.
11. During the RELATIVE REFRACTORY PERIOD of a neuron, the permeability to Na+ is low
while that of K+ is high. True. The relative refractory period occurs during the
“overshoot” of the membrane potential, when the membrane hyperpolarizes due to
the open potassium channels. Exam 2 Fall 2015 Refer to the following graph of an action potential to answer the following 5 questions (1216). For the following five (5) questions Answer A, B, C, D, or E.
12. The labeled point on the graph where the membrane potential is closest to the
equilibrium potential for Potassium is D. The equilibrium potential for potassium is
more negative than the resting potential (for reasons explained earlier). The
membrane potential is closest to this point at D, when potassium channels are open
and the membrane is hyperpolarized.
13. The labeled point on the graph where the membrane's permeability to sodium ions is at
its maximum is B. Maximum sodium permeability will occur where the membrane
potential is closest to the equilibrium potential for sodium, or the point ox maximum
depolarization on the figure, which is B.
14. The minimum graded depolarization needed to operate the voltage-gated sodium and
potassium channels is indicated by the label A. This is describing the threshold
potential, the point where voltage gated channels open and the action potential is
15. The cell is not hyperpolarized; however, repolarization is in progress, as the sodium
channels are closing or closed, and many potassium channels have opened at label C. The
membrane is repolarizing where it is moving back to the resting potential following
depolarization. The only point on the graph where it is repolarizing but not yet Exam 2 Fall 2015
hyperpolarized is C.
16. The neuronal membrane is at its resting potential at label E. Resting potential is
where the membrane potential is most stable and occurs between action potentials. 17. The fastest possible conduction velocity of action potentials is observed in _____.
A) thin, non-myelinated neurons
B) thin, myelinated neurons
C) thick, non-myelinated neurons
D) thick, myelinated neurons
Myelination and increased diameter of neurons both speed up action potential
propagation. 18. Acetylcholine released into the junction between a motor neuron and a skeletal muscle
binds to a sodium channel and opens it. This is an example of _____.
A) a voltage-gated potassium channel
B) a ligand-gated sodium channel
C) a second-messenger-gated sodium channel
D) a chemical that inhibits action potentials
Ligand gated channels open in response to binding of chemical signals. 19. The following steps refer to various stages in transmission at a chemical synapse.
1. Neurotransmitter binds with receptors associated with the postsynaptic membrane.
2. Calcium ions rush into neuron's cytoplasm.
3. An action potential depolarizes the membrane of the presynaptic axon terminal.
4. The ligand-gated ion channels open.
5. The synaptic vesicles release neurotransmitter into the synaptic cleft.
Which sequence of events is correct?
A) 1 → 2 → 3 → 4 → 5
B) 2 → 3 → 5 → 4 → 1
C) 3 → 2 → 5 → 1 → 4
D) 4 → 3 → 1 → 2 → 5
This one is self-explanatory Exam 2 Fall 2015
Motor neurons release the neurotransmitter acetylcholine (ACh). Acetylcholinesterase
degrades ACh in the synapse. A neurophysiologist applies onchidal (a acetylcholinesterase
inhibitor) to a synapse.
For the following two (2) questions A=True, B=False
20. The result would be constant muscle stimulation. True, since there is no breakdown
of the neurotransmitter, action potentials will continue to be triggered.
21. There would be a decrease in the frequency of action potentials arising from synapses
to which onchidal is applied. False, for reasons described above. For the following question A=True, B=False
22. A given photon of light may trigger an action potential with thousands of times more
energy because the signal strength is amplified by the triggering several receptors at once.
False, amplification comes from signal transduction pathways, as a photon only binds
to one receptor. 23. The middle ear converts _____.
A) air pressure waves to fluid pressure waves
B) fluid pressure waves to air pressure waves
C) air pressure waves to nerve impulses
D) fluid pressure waves to nerve impulses
Review page 1108 of the text for an explanation. 24. All of the following could be associated with a nocturnal lifestyle EXCEPT:
A) Large eye with large pupil.
B) Long photoreceptors relative to what would be seen in diurnal species.
C) More cones than rods.
D) More rods than cones. Exam 2 Fall 2015
Nocturnal eyes have more rods than cones.
25. Rods exposed to light will _____.
A) depolarize due to the opening of sodium channels
B) hyperpolarize due to the closing of sodium channels
C) depolarize due to the opening of potassium channels
D) hyperpolarize due to the closing of potassium channel
In the dark, rod cells are depolarized, upon exposure to light, sodium channels close
leading to hyperpolarization. A seedling is placed on its side parallel to the ground, and left to sit for several hours,
eventually showing a gravitropic response.
34. Researchers tried to explain how vesicular transport occurs in cells by attempting to
assemble the transport components. They set up microtubular tracks along which vesicles
could be transported, and they added vesicles and ATP (because they knew the transport
process requires energy). Yet, when they put everything together, there was no movement
or transport of vesicles. What were they missing?
A) an axon
B) contractile microfilaments
C) endoplasmic reticulum
D) motor proteins
Without motor proteins there will be no movement along the microtubules.
35. Which of the following is not one of the three main types of fibers that make up the
C) Intermediate filaments
D) Actin filaments
Kinesins are motor protons, and not structural fibers.
For the following five (5) questions A=True, B=False
36. The cytoskeleton of eukaryotes is a static structure most resembling scaffolding used
at construction sites. False, The cytoskeleton of a cell is dynamic, changing shape in
some cells and involved with cellular and organellar motion.
37. Although microtubules are common within a cell, actin filaments are rarely found Exam 2 Fall 2015
outside of the nucleus. False, actin filaments are not localized to the nucleus.
38. Movement of cilia and flagella is the result of motor proteins causing microtubules to
move relative to each other. True, motor proteins causing microtubules to slide over
one another drives motion.
39. Chemicals that block the assembly of the cytoskeleton would have an effect on a cell's
response to external stimuli. True, the ability to transport vesicles, move organelles in
response to stimuli rely on the cytoskeleton.
40. When an action potential from a motor neuron arrives at the neuromuscular junction
(NMJ), a series of events occurs that leads to muscle contraction. Which of the following events
will occur last (that is, after all of the others)?
A) acetylcholine (ACh) release from the presynaptic terminal
B) conformational change in troponin
C) depolarization of the muscle cell
D) release of Ca2+ from the sarcoplasmic reticulum
41. A skeletal muscle deprived of adequate ATP supplies will _____.
A) immediately relax
B) enter a state where actin and myosin are unable to separate
C) fire many more action potentials than usual and enter a state of "rigor"
D) sequester all free calcium ions into the sarcoplasmic reticulum ...
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