(Print )NAME _________________________________________
TA ___________________________
2nd Midterm Exam,
July 31, 2000
1. Write your name at the top of every page. Points will be deducted from your total score if you do not.
2. Read every question first. Then start by answering those you know best. Be sure to read each
question carefully.
3. Keep your answers brief and to the point.
4. If you don't understand the question, raise your hand and a TA will come to you to try to answer it. If you still don't understand the Q., write down what you think the Q. is, and answer that.
5. Do NOT write answers on the back of your test pages. Use only the front of the page for real answers. The back of the page can be used for scribbles or notes.
(18 pts) 1. Compare and contrast the types of cellular movements during gastrulation in the frog and the sea urchin embryos. (Be sure to include the site of gastrulation initiation and the presumptive germ layer involved.)
Discuss 3 points of comparison:
a) In the frog, the site of gastrulation initiation is in the P. endoderm, just beneath the grey crescent/chordamesoderm region, and begins with cells sinking inward due to the bottleneck shape. In the sea urchin, gastrulation begins with the flattening of the vegetal plate cells and ingression of the primary mesenchyme cells from the plate which is a mixture of p. endoderm and primary mesenchyme cells, into the blastocoel.
b) In both animals invagination of endoderm cells, and both endoderm and notochord in the frog form the archenteron
c) In the frog, the notochord is formed by convergent
extension of the chordamesoderm, which is broad on the outside and
funnels down a long narrow rod inside along the dorsal midline. The
sea urchin does not have a notochord, but uses convergent extension
of endoderm cells to elongate the archenteron
2. (16 pts) Give two examples of genes involved in forming the
anterior-posterior axis of the Drosophila embryo. (a) bicoid (b)
nanos
Where is the site of transcription of these genes (in which cell(s)) ? in the nurse cells during oogenesis
1) Where are the two mRNAs translated (in what part of the embryo - be specific)
bicoid is translated in the anterior end and nanos is translated in the posterior end of the Drosophila fertilized egg/embryo
2) Do these genes/mRNAs exemplify regulative or mosaic development? mosaic
Explain the reasoning behind your answer.
The bicoid and nanos mRNAs are synthesized during oogenesis and
stored in the growing oocyte. They are therefore, cytoplasmic
determinants which are present at the time of fertilization, meaning
that the ant-post axis is already determined at the time of
fertilization and development of the embryo.
3. ( 19 pts ) a) How does determination differ from
differentiation
1) determination precedes differentiation
2) determination does not produce any outward visible morphological changes indicated a commitment or change in determination
3) differentiated cells do show both morphological
c) Are determined cells differentiated? Not necessarily.
Are differentiated cells determined? YES
1) Describe an experiment that would prove that a particular group of cells was determined:
- Describe the experiment and the results: explant a group of cells into TC or to another location on the same or different embryo. Observe the development of the cells. If the cells differentiate according to their fate, they were determined at the time of transplant. H the cells differentiate according to their new surroundings, they were not determined at the time of explant.
Describe the control(s): explant earlier (before determination) the cells will differentiate according to -----explant a tissue known to be setermined--observe it differentiate according to its fate.
- State the conclusion: If the cells differentiate
according to their fate, then they were determined at the time
of explant.. Explant later, or do not explant at all, one can see
what the cells normally differentiate into.
4. (18 pts). In the development of the vertebrate eye, which
tissues/structures induce which other tissues to become what?
- Briefly describe an experiment that demonstrates the need for induction for one of your
examples above. EX. Remove optic vesicle from one side of
embryo, no lens will form. Other side of embryo serves as unoperated
control and forms normal lens. OR Insert piece of cellophane between
two tissues and show that induction does not occur, etc.
5. ( 24 pts) (a) Compare and contrast the mechanism(s! for
blocking polyspermy during fertilization of a sea urchin egg, for the
FAST BLOCK vs. the SLOW BLOCK. Keep your answer brief.
1) FAST BLOCK = electrical barrier, preventing fusion of sperm p.m. and egg p.m.; Slow Block is mechanical block to polyspermy, i.e. the fertilization membrane., which hardens and is impervious to further sperm.
2) FAST BLOCK lasts one min and then fades; Slow Block is permanent
3) Fast Block uses Na++ ions from sea water to depolarize the egg's resting membrane potential; Slow block uses internal (SER) stores of Ca++ to promote fusion of the egg p.m! and the cortical granule p.m. and release of the cort. Granule contents into the perivitelline space whene in conjunction with the vitelline layer, the fertilization membrane is formed
(b)Describe an experiment that demonstrates the mechanism for blocking polyspermy for I of these blocks.
The experiment and the results: Ex. FB: If fertilize egg in Na-free sea water, there will be no Na to rush into egg, and egg membrane resting potential will remain at-70 or -80 mv, and polyspermy will occur. Or SB: Inject EGTA into egg, add sperm in sea water, fertilization will occur, but no fertilization membrane will be formed due to the absorption of all the released internal CA binding to the EGTA>, and thus no fusion of egg p.m. with cort. Granule p.m. etc.
The control(s):
The conclusion:
|
hornworm |
rat |
|
|
name of excretory organ |
Malphigian tubules |
Kidney |
|
liquid this organ removes waste from |
hemolymph |
Blood/plasma |
|
form of nitrogenous waste produced |
Uric acid |
urea |
_______sea squirt_(tunicates)_______ why?-- we are both members of phylum Chordata
(This was the question I posed to you in class during the
animal diversity lecture)
(3 pts) 8. In the animal diversity lab you used Invertebrate
Ringer's solution (saline solution) to submerge your animals. In
words (not a number) what is osmolarity of this solution --defend
your answer.
Osmolarity of this solution must be the same as osmolarity of
the tissue (it is isotonic)-- otherwise the tissue would become
disfigured due to loss (if Ringers hypertonic) or gain (if ringers
hypotonic) of water by the cells of the animal.
(4 pts) 9. In the lab, I have a normal cell in normal
interstitial fluid with a resting membrane potential of
(-) 88 mV. I place an electrode into the cell and change the membrane potential to (-100 mV).
Will potassium ions move? if so in which direction ? defend your answer.
Potassium would move INTO the cell. The Ek is -88mV (at -88 mV
the electrical and chemical gradients are balanced and there is no
net movement of potassium). However, at -100mV (the artificial
condition) the electrical gradient is now "stronger" than the
chemical gradient and the (-) environment inside the cell will
attract K ions into the cell (K will move against its gradient).
(8 pts) 10. What is the driving force (and how is it generated)
for movement of
a) glucose across Bowman's Capsule?
Driving force:Hydrostatic pressure (blood pressure)--
generated by: the beating heart and blood volume in vessels
b) glucose across the lumenal membrane of the PCT?
Driving force: Na gradient from lumen to cell interior (used by Na-Glucose transporter)
Generated by: the Na/K ATPase pump on basal membrane
c) water out of the descending Loop of Henle
Driving force: osmotic gradient (high Na, Cl, urea) in extracellular fluid surrounding loop
Generated by: Na/K pump on ascending limb of Loop
( 2 pts.)11. In this phylum, the blastopore becomes the mouth & members have a coelem. ___Mollusca or Arthropoda or _Annelids (basically anything from the animal diversity lab.__________