Biology 441 Spring 2011, First Exam Key

Each question was worth 5 points total.

1. Gastrulation of what kind of animals occurs by involution?

    4 points for either "amphibians" or "frogs and salamanders"
    2 points off if ONLY frogs or ONLY salamanders
    1 point for the picture of an embryo undergoing involution
    should show a spherical embryo with the blastopore as a curved slit, viewed either head-on or from the side

2. If Driesch had done his experiment with embryos having mosaic development...
    Different parts of the animals' bodies would have developed from the separated cells - 3 points
    He wouldn't have discovered embryonic regulation - 1 point
    He wouldn't have hypothesized that development is controlled by an "Entelechy" - 1 point

3. By what method do researchers call development of sheep-goat chimeras?
    3 points off for saying they are impossible
    Get developing pre-blastocyst stage embryos from a pregnant goat and a pregnant sheep - 1 point
    Use enzymes to digest off the jelly coats - 2 points
    Place the 2 embryos in contact. Let the cells of the two embryos adhere and intermingle - 1 point
    Put the fused embryos into the uterus of either a sheep or a goat (although the uterus of a cow might work) - 1 point

4. The fast block to polyspermy is analogous to nerve impulse in what ways?
    2 points - depolarization of an electrical voltage difference between the inside and outside of the plasma membrane
    1 point - this depolarization is propagated, by opening of sodium channels
    1 point - increase of calcium ion concentration in the cytoplasm
    1 point - secretion of vesicles (cortical granules of oocyte, and synaptic vesicles in nerves

5. Somite cells rearrange to form what three structures? What differentiated cell types develop from each of these three?
    1 point each for the structures, and 1 each for at least 2 of the three cell types; i.e. 5 points for a fully correct answer
    sclerotome 1 point - skeleton, cartilage, or bone - 1 point
    myotome 1 point - muscle (skeletal muscle or voluntary muscle are both OK; also fibroblasts)
    dermatome - skin

6. What are the three primary germ layers? - 1 point for each. List tissues and organs that develop from each of these - full credit of 2 points for any two, i.e. 5 points total for the question
    ectoderm - 1 point; brain, spinal cord, nerves, outer layer of skin
    mesoderm - 1 point; muscle, bone, kidney, heart
    endoderm - 1 point; digestive tract, lungs, liver, pancreas

7. Name the process by which the cells of embryos are subdivided into these 3 germ layers
    5 points for the word "gastrulation"
    2 points for "invagination", "ingression", "involution"

8. Neurulation subdivides what into what three subdivisions?
    Ectoderm is divided into neural tube, neural crest, somatic ectoderm
    1 point off if only two are named correctly; 4 points off if only one is named correctly

9. Where are deep cells relative to the "enveloping" layer?
    Deep cells are under and surrounded by the enveloping layer - 5 points

10. Scientists use the word "chemotaxis to refer to several fundamentally different combinations of cell behavior .. describe as many as you can
    2 points: turning of crawling cells toward whichever side of a crawling or swimming cell detects a higher concentration of the "attractant" substance
    2 points: continuing to crawl or swim in the same direction as long as the attractant concentration increases, and turning (randomly) when the attractant concentration becomes lower
    1 point: slowing down or stopping where the attractant concentration becomes very large

11. Draw diagrams of major stages of embryonic development of sea urchins.
    5 points for a series like the top row in THIS FIGURE

12. [this question was asked incorrectly and was not graded]

13. Invent several ways in which cells could respond to substratum adhesiveness that would probably be regarded as haptotaxis...

    1 point - turning of crawling cells toward whichever side of a crawling or swimming cell adheres more to some surface, or to other cells
    1 point - continuing to crawl or swim in the same direction as long as adhesion to surfaces or to other cells increases, and turning (randomly) when this adhesion to other things becomes lower
    1 point - slowing down or stopping where the adhesion to surfaces or other cells is strong
    1 point - a tug of war between opposite sides of each cell, each pulling in a different direction
    1 point - passive pulling by the formation of adhesions to surfaces, collagen or other cells

14. How could you cause formation of a zebra fish that is homozygous for all its thousands of genes?
    X-ray the sperm (or badly damage their DNA in any other way), which you then use to fertilize oocytes;
    prevent the first mitotic division (by heat shock, or high pressure, or any other way you can)
    3 points off for failing to mention either sperm inactivation or blockage of the first mitotic division

15. Is gastrulation of human embryos similar to gastrulation in sea urchins, fish or bird embryos?
    bird embryos - 5 points

16. What are plutei? Why did their discoverers regard them as adults of species unrelated to sea urchins?
    3 points - larval sea urchins (or larval echinoderms...)
    2 points - because they were found in plankton nets, and free in the water, or because plutei just don't look at all like urchins

17. In human development, when are the two polar bodies formed, relative to fertilization?
    the first polar body is formed before fertilization (= at ovulation) - 2 points
    the second polar body is formed an hour or so after fertilization - 3 points

18. What is the defining property of the animal pole of an oocyte?
    It is where the polar bodies are formed - 5 points

19. Embryos of what kind of animals form their blastopore at the vegetal pole?
    sea urchins - 5 points; full credit also for "echinoderms"

20. Invent ways for quantitating chemotaxis, perhaps using Abercrombie's experiments on quantitation of contact inhibition as a model

    Good answers to this question included measures of speed of cell movement along a chemotactic gradient; comparison of numbers of cells accumulating vs. randomly arranged in different regions along a gradient, or when the presence of an attractant was compared to a control with no attractant; demonstration of a threshold of concentration at which chemotaxis occurred.

    Full credit was given for three distinctly different types of quantitation.
    Partial credit was given for two or more methods that were essentially variations on the same principle.

    Some students misinterpreted the question and described Abercrombie's experiments on contact inhibition. If the descriptions were accurate and complete, 2 points partial credit was given (i.e. 3 points were deducted for answering the wrong question).

    Grade distribution:

    90 and above A
    85-89 B+
    82-84 B
    73-81 C
    63-72 D
    62 and below F