Biology 449 - Animal Physiology

Spring 2006

Midterm 1 - Key

Answers in italics

Fill in your scantron form as follows.  This is worth 1 point:

· Write and bubble in your name in the upper left (last name first).

· Follow any additional instructions provided in class.

· Sign your form in the upper right.

Multiple choice:   As always, choose the best answer for each multiple-choice question.  Answer on your scantron form.  Each question is worth 3 points.

1. Claude Bernard was a nineteenth century Frenchman who

a. discovered the first hormone.

b. realized the importance of regulation in physiological systems.

c. identified the cause of diabetes.

d. conditioned dogs to salivate when they heard a bell.

e. designed the Statue of Liberty.

2. Which of the following statements about living organisms is not true?

a. They are open systems.

b. They are at complete equilibrium with the environment.

c. For a regulated variable, if the rate of influx decreases, the rate of efflux must be indecreased to maintain the regulated state.

d. Regulation of a variable requires the use of energy.

e. An organism may regulate some variables but not others.

3. As part of the thermoregulatory process in humans, the release of sweat is an effector system intended to

a. reduce heat gain.

b. increase heat gain.

c. reduce heat loss.

d. increase heat loss.

e. generate a funky aroma.

4. Positive feedback

a. is a process that regulates a variable at a constant value.

b. is useful for anticipating a change in a regulated variable.

c. results in a rapid increase or decrease in a variable.

d. is another term for behavioral regulation.

e. is the mechanism that drives conformation.

5. Which of the following does not directly help ions cross a cell membrane?

a. Channel proteins

b. Uniport carrier proteins

c. Symport carrier proteins

d. G-proteins

e. All of the above help ions cross a cell membrane.

6. In secondary active transport

a. only one membrane protein is involved.

b. an antiport mechanism is never involved.

c. no ATP is involved.

d. no substances move against their concentration gradient.

e. at least one substance moves down its concentration gradient.

7. The spinal cord of vertebrates

a. is responsible for the regulation of body temperature.

b. is responsible for the regulation of breathing.

c. is part of the central nervous system.

d. Two of the above.

e. None of the above.

8. Which of the following conditions must be met for a potential to be generated across a membrane?

a. There must be a concentration difference of one or more ions across the membrane.

b. The membrane must be permeable to at least one ion.

c. The membrane must be permeable to no more than one ion.

d. a and b.

e. a and c.

9. If we say a cell shows a graded potential, this means that

a. the cell has depolarized above threshold.

b. the cell has depolarized above zero volts.

c. the cell has depolarized by an amount proportional to the strength of the stimulus acting on the cell.

d. the cell has depolarized by a stereotypical amount.

e. the cell has hyperpolarized.

10. The propagation of action potentials along a myelinated axon occurs more quickly than in a non-myelinated axon because.

a. myelin acts as an electrical insulator for the axon.

b. myelin increases the diameter of the axon.

c. action potentials cannot occur in the myelinated portion of the axon.

d. action potentials have a greater magnitude at nodes of Ranvier than on an unmyelinated axon.

e. sodium channels open more quickly at the nodes of Ranvier than on an unmyelinated axon.

11. Which of the following is associated with adrenergic receptors?

a. Acetylcholine

b. Epinephrine

c. Dopamine

d. GABA

e. Glutamate

12. An example of a pair of sensory receptors that respond to the same type of stimulus but show a different dynamic range is

a. Ruffini's capsule and a Pacinian corpuscle.

b. a salt and a sour taste receptor.

c. a hair cell in an otolith organ and a hair cell in the cochlea.

d. the stereocilia and kinocilium of a hair cell.

e. a rod and a cone photoreceptor.

13. Lateral inhibition helps increase perception of relatively faint stimuli by

a. increasing action potential frequency in the afferent neuron from the stimulated receptor.

b. increasing the size of the receptive field of the stimulated receptor.

c. decreasing action potential frequency in the afferent neurons from the receptors surrounding the stimulated one.

d. decreasing the size of the receptive field of the receptors surrounding the stimulated receptor.

e. Two of the above.

14. The number of different types of receptors in the olfactory system of mammals is

a. about five.

b. about a dozen.

c. about a hundred.

d. about a thousand.

e. millions.

15. The sensory system responsible for detecting rotational movements in vertebrates is

a. the baroreceptors.

b. the nociceptors.

c. the otolith organs.

d. the proprioceptors.

e. the semicircular canals.

16. One of the main reasons that prolonged exposure to moderately loud noises can cause hearing loss is that

a. the eardrum may become thickened.

b. the ossicles may shatter.

c. the oval or round windows may be punctured, causing a loss of endolymph.

d. the stereocilia of the hair cells may be torn from the tectorial membrane.

e. the afferent neurons may become permanently adapted to strong stimulation.

17. To be classified as a hormone, a substance must

a. be a chemical messenger.

b. activate an intracellular receptor.

c. be made of amino acids.

d. be secreted by a gland.

e. be carried in the bloodstream.

This question should have been phrased differently.  The intended answer was “e”, but “a” was also accepted.

18. Which of following represents a correct hormonal cascade?

a. Follicle-stimulating hormone ® gonadotropin releasing hormone ® sex hormones

b. Thyroid stimulating hormone ® thyrotropin releasing hormone ® thyroid hormone

c. Corticotropin releasing hormone ® adrenocorticotropic hormone ® cortisol

d. Prolactin ® growth hormone ® IGF-I

e. None of the above is correct.

19. One major way in which thyroid hormones help to increase body temperature is by promoting

a. shivering.

b. increased cutaneous vasoconstriction.

c. increased hunger.

d. increased Na⁺/K⁺ ATPase activity.

e. increased protein repair.

20. Toy poodles (you know, the little ones) represent a mutant offshoot of Standard poodles (the big ones).  Interestingly, the Toys have the same levels of growth hormone in their bloodstreams as the Standards.  This observation suggests

a. that Toys are smaller because they are hyporesponsive to growth hormone.

b. that Toys are smaller because they secrete less growth hormone releasing hormone than Standards.

c. that Toys are smaller because they secrete more growth hormone inhibiting hormone than Standards.

d. that Toys are smaller because they sleep less than Standards.

e. that Toys are smaller because Standards’ owners overfeed them.

Short answer:  Write a concise answer to each of the following questions.  Your answers should fit in the spaces provided.  Diagrams must be accompanied by written explanations.  Each question is worth 8 points.

21. Consider a system with a potassium phosphate [KH₂PO₄] solution on one side of a membrane and a calcium phosphate [Ca(H₂PO₄)₂] solution on the other.  The first solution yields 0.5M K⁺ and 0.5M H₂PO₄^-, while the second yields 0.25M Ca²⁺ and 0.5M H₂PO₄^-.

a. Give the Fick equation, and indicate what each variable stands for.

J = DA DC/Dx, where

J = net diffusion flux or rate
A = area for diffusion
DC = difference in concentration
Dx = distance of diffusion – thickness
D = permeability constant – varies with temp., substance, membrane 

b. Provide a qualitative description of what the equilibrium state would be if the membrane were permeable to only the calcium ions and nothing else.

If ionic charge effects were not present, Ca²⁺ would move down its concentration gradient until it reached equal concentration on both sides of the membrane.  However, because it is an ion, as soon as Ca²⁺ starts diffusing across the membrane a charge will begin to build up across the membrane that opposes further movement of the ions.  When the positive charge on the KH₂PO₄ side counters the concentration gradient of the Ca²⁺ ions, the system will have reached electrochemical or Donnan equilibrium.

c. If instead the membrane were permeable to only water and nothing else, in which direction (if either) would water move, and why?

The total solute concentration on the KH₂PO₄ side is 0.5M + 0.5M = 1.0Osm, while on the Ca(H₂PO₄)₂] side it is 0.25M + 0.5M = 0.75Osm.  Water will move from the second, hyposmotic side to the first, hyperosmotic side.

22. Answer the following questions about action potentials:

a. Describe the changes in the permeability of an axon to sodium and potassium ions during an action potential, and what effects the changing permeabilities have on overall membrane potential.  You do not need to describe the specific activities of the various gates in the channel proteins.

Once threshold voltage is reached, voltage-gated sodium channels quickly open, increasing P_Na and causing rapid depolarization of the axon membrane.  The sodium channels then begin closing, and at about the same the slower potassium channels are opening.  The drop in P_Na back to resting values and the increase in P_K cause the membrane to rapidly repolarize and then hyperpolarize.  As the potassium channels then close, P_K returns to resting levels and the membrane returns to resting potential.

b. What would be the likely effect on the pattern or shape of an action potential if voltage-gated potassium channels did not function?  Explain your answer.

If the voltage-gated potassium channels did not function, there would be no efflux of potassium to rapidly repolarize and then hyperpolarize the membrane.  However, because membrane permeabilities will be back at their normal resting values after the voltage-gated sodium channels close, the membrane will still return to its normal resting potential.  This return will be slower than normal, though, and there will be no hyperpolarization.

23. Describe the process of synaptic transmission for a chemical synapse with ionotropic receptors, up to the point when the receptor is activated.

In his type of synapse, the pre- and post-synaptic neurons are separated by a small space, the synaptic cleft.  When an action potential arrives at the axon terminal of the pre-synaptic neuron, the depolarization triggers the opening of voltage-gated calcium channels, allowing Ca²⁺ to enter the terminal.  These Ca²⁺ ions trigger the release of neurotransmitter-containing synaptic vesicles from the cytoskeleton.  The vesicles then migrate to the synaptic membrane where they fuse with docking proteins and release their contents into the synaptic cleft.  The released neurotransmitter molecules diffuse across the cleft to the post-synaptic neuron and activate the ligand-gated channels (i.e. the ionotropic receptors).

24. The following questions relate to post-synaptic potentials:

a. Provide a complete definition or explanation for an “excitatory post-synaptic potential.” (By complete I mean don’t define just the “excitatory” part.)  Then explain how this differs from an inhibitory post-synaptic potential.

An excitatory post-synaptic potential is a short-lived  positive change (a depolarization) in the membrane of the post-synaptic neuron, triggered by the neurotransmitter released when a single action potential arrives at a pre-synaptic neuron.  In an inhibitory p.s.p., the change is negative (re- or hyperpolarization) instead.

b. Indicate for each of the following whether the effect would be excitatory or inhibitory:

Opening Na⁺ channels – Excitatory                   Opening K⁺ channels – Inhibitory

A Ca²⁺ influx into the cell– Excitatory              A Cl^- efflux from the cell – Excitatory

25. Describe the process by which a vertebrate photoreceptor transduces light.  Be sure your explanation specifies how membrane potential changes in the light and dark.

The light-sensitive components of the photoreceptors are located in the lamellae.  Specifically, the molecule retinal is changed from the cis- to the trans- conformation when struck by a photon.  In the dark, the cis-retinal is bound to an opsin, forming rhodopsin.  In this form, the opsin is inactive.  Also in dark, ligand-gated sodium channels are activated (opened) by cGMP, allowing Na⁺ influx and depolarizing the cell.  When struck by photons in the light, the now trans-retinal dissociates from the opsin, activating this molecule.  Activated opsin activates the G-protein transducin, which in turn activates the enzyme phosphodiesterase (PDE).  PDE converts cGMP to 5’-GMP, reducing cGMP levels so that the sodium channels are no longer kept open.  The result is a drop, or re-/hyperpolarization of the cell membrane.  Thus in the dark the photoreceptor releases more neurotransmitter and in the light it releases less.