Answer 6 of the following. If you answer more only the 1st six will be graded (6 points each)
1. Give two differences between the insect compound eye and the human eye. One of these can be
optical in nature, but the other should describe a difference in the arrangements of nerve connections
that leads from the photo receptor to the CNS.
.a. Human: single eye lens that focuses image on many receptor cells in the retina. Individual light
receptor cells (rods and cones) make multiple connections with bipolar cells that also make
connections with other cell types which results in stimulation or inhibition. The bipolar cells also
make multiple connections with the ganglion cells that make up the optic nerve and conduct impulses
to the brain for further integration. Unlike the compound eye these connecting cells are located in
front of the receptor cells in the light path and considerable integration of the transduced signal occurs
in these retina connections.
b.compound eye: eye consists of many light detectors (ommatida) each with its own cornea and
focusing lens that focuses the light on a few receptor cells in that ommitida. The receptor nerve exitst
at the bottom of the ommitida and each sends its own signal to the brain where most all the
integration takes place.
2. The liver plays a prominent role in nutrition and digestion. In humans the circulation blood levels
of glucose are regulated at 100 mg/100 mls of blood. When you eat a meal containing lots of sugar
how does the body regulate the blood level when large amounts of glucose are absorbed from the
small intestine and what is the involvement of the liver?
a. The glucose that is absorbed from the small intestine enters the hepatic portal (venous) system
which empties directly into the liver. If the blood exiting the liver into the general circulation has
high levels of glucose, the release of insulin by the pancreas directs the liver to covert glucose to
glycogen. (First part sufficient for full credit). If insufficient glucose in the general circulation then
the pancreas secretes glucagon which causes the liver to break down glycogen into glucose.
3. The absorption of digested carbohydrates (glucose) and lipids (free fatty acids and glycerol) from
the small intestine differ in mechanism where by they cross the intestinal wall. They also follow
different routes before entering the general circulation at the right atrium. Describe these differences
and indicate the route each follows before entering the right atrium of the heart.
a. Carbohydrates are absorbed as glucose and are transported into the hepatic portal circulation which
enters the liver where it may or may not be converted to glycogen and stored. Lipids are absorbed as
free fatty acids and glycerol by intestinal epithelial cells, resynthesized into triglycerides, complexed
with cholesterol within the cell and then exocytosed into the lacteals (blind channel of the lymphatic
circulation). The lymph enters the blood circulation just upstream of the right atrium.
4. As you heard in class or read in your text, if a human is born without an immune system they are
unable to survive. Part of the bodys defense involves recognition of pathogenic antigens that enter
and a specific response to the pathogenic antigen by certain cells. One of the aspects of the specific
response is clonal selection. What is clonal selection and what cells of the immune system are
involved?
A. When one of the white blood cells (lymphocyte) recognizes a specific antigen (it only recognizes
one epitope), it is induced to divide repeatedly and differentiate into large number of identical
effector B or T cells and memory B or T cells.
The cells that undergo colonal selection are lymphocytes, both the B and T cells.
5. Why is the oxygen transport pigment, hemoglobin housed in red blood cells as opposed to
circulating free in solution? Give two reasons why it is contained in reb blood cells and not as a free
molecule in solution.
a. If free in solution it is small enough to pass through the glomerular filter in the kidney and thus
would be excreted, a waste of energy. It would also make a large contribution to the osmotic pressure
of the blood (Accept either one of these as a reason).
b. By housing hemoglobin in the red cells its gas binding properties (Oxygen and carbon dioxide) can
be modified relative to the plasma by modifying the cytoplasmic concentration of certain solutes. As
an example: RBCs have high concentrations of organophosphates which compete for the oxygen
binding site. Also carbon dioxide can be converted to bicarbonate and the free protons can bind to the
hemoglobin molecule preventing a drop in pH. This would not happen if in solution ( accept answer
indicating Hb properties can be modified in the cell environment to facilitate gas binding and
transport). If they give and example that can count too as the answer.
6. What is the difference between an endocrine and an exocrine organ. Give one example of an
endocrine organ, one example of an exocrine organ and an organ that has both endorcrine and
exocrine function.
A. An endocrine organ secretes a hormone (factor) directly into the blood and it is usually
targeted to a receptor on some organ or endocrine gland some distance away. An exocrine gland
secretes proteins or fluid into a system of collecting ducts and main duct empties into a lumen
(usually the digestive track).
A. Endocrine: adrenal gland, pituitary, thyroid gland etc.
B. Exocrine: Liver (bile), prostate
C. Organ with both endocrine and exocrine function: Pancreas, (endocrine, ,insulin) and
exocrine ( bicarbonate and enzymes).
7. In the vertebrate world of vision there are photoreceptor cells in the eye. What is a rod and
what is a cone? How does their function differ? What molecule do they both have that absorbs
the photons of light?
A. rod is a photoreceptor that contains rhodopsin and transduces light of any wave length. Cones
contain photoopsins and only transduce light energy of the wave length that their photopigment
absorbs. The opsin (protein portion of the photopigmetn) differs for the three color receptors and
for rhodopsin.
All use retinal a derivative of Vit A to absorb light. The light converts the retinal from its cis
form to its trans form (straight molecule). In its active form it is attached to the opsin protein
molecule.
8. Which is energetically more costly swimming or running? Give the main reason why you
say one of these modes of locomotion is more costly than the other.
Running because in terrestrial mammals they have to overcome the effects of gravity. Aquatic
organisms are often neutrally buoyant and only have to overcome the frictional drag of their
bodies in water. Thus they have streamlined bodies.
9. Describe the role that calcium plays in the binding of actin to myosin? Also indicate what
structure the calcium is released from within the muscle cell.
a. Calcium binds to troponin causing a conformational change that causes the tropomyosin to
shift and expose the myosin binding sites on the actin. The myosin head can then bind to the
actin and pull itself along.
Calcium is released from the sarcoplasmic reticulum (SR is ok for this answer).
10. Diagram an action potential and label the axes (abscissa as millivolts and ordinate as time).
Indicate below your diagram the relative concentrations of sodium and potassium (ie high or low
on the inside versus the outside) in the resting axon. Describe the ion movements (Na or K gates
opend or closed) across the cell membrane during the rising phase (depolarization) and
descending phase (repolarization) of the axon.
a. When the axon is depolarized to a level above the threshold potential then the sodium
channel gates open and allow sodium to flow into the cell depolarizing it. When depolarized,
the sodium gates close and, the potassium channel gates open allowing potassium to flow out of
the cell repolarizing it. The Na/K ATPas keeps the resting membrane potential negative by
pumping sodium out and potassium into the cell. They need to show that the resting potential is
negative and goes positive during the action potential. Also must mention sodium gates open
and close and when k gates open and close.