Biology 441, Spring 2014


Sample Examination Questions: NOT yet the complete list; more will be added.

For every letter of the alphabet, you should be able to tell what symmetries it has (if it has any),
and draw whatever planes of symmetry it has, or what axes of two fold reflection symmetry, or what combination of symmetry it has.

You ought to be able t do the same for any character that can be typed on the typewriter.

For example * has 6 intersecting planes of reflection symmetry, of two kinds.

And & has no symmetry, but what about %, $ and # ?

You ought to be able to compose a sonnet that contains only words that start with a letter that has a single plane of reflection symmetry. Not really; but notice that rhyme schemes themselves consist of displacement symmetries of pronunciation.

What is Curie's Principle?

You should be sure to know what subdivision of which germ layer each of the following develops from. For example Lens develops from somatic ectoderm, more specifically from a placode.

  • Pigmented retina
  • Sensory retina
  • Olfactory nerves
  • Semi-circular canals
  • Cochleabr>
  • Otoliths
  • Brain
  • Spinal cord
  • Skeletal muscles
  • Epidermis
  • Hair
  • Feathers
  • (Reptile) scales
  • Heart
  • Adult kidney
  • Motor nerves
  • Sensory nerves
  • Schwann cells
  • Postganglionic autonomic nerves
  • Facial skeleton
  • Skeleton in the rest of the body
  • Pituitary gland
  • Salivary glands
  • Thyroid gland
  • Lungs
  • Liver
  • Pancreas
  • Intestine
  • Stomach
  • Capillaries, veins, arteries

    click here for the answers to many of these


    What symmetries do each of the following have? And for each one, name something else, NOT on the list, that also has that same symmetry or combination of symmetries.

  • A centipede
  • A four bladed propeller
  • A plaid piece of cloth
  • The color pattern of a Copperhead snake
  • A snail shell
  • A frog egg before it is fertilized
  • A human embryo before it has formed its inner cell mass
  • A human embryo after it has formed its inner cell mass, but before a primitive streak has developed
  • A human embryo that is developing into identical twins
    (Don't forget that there are three very different ways in which identical human twins develop) WE WILL COVER THIS LATER

  • A gastrulating or a neurulating embryo
  • Teeth in a mammal's mouth (difficult, but you can figure it out)
  • The individual vertebrae of your backbone

  • An individual Dictyostelium slug
  • An aggregating mass of Dictyostelium amoebae
  • A Dictyostelium fruiting body
  • Many Dictyostelium fruiting bodies, of different sizes, as compared with each other
  • The mechanism that controls the relative dimensions of fruiting divisions dilation symmetry

  • Mushrooms axial symmetry, dilation symmetry
  • The letter A
  • The letter N
  • The letter H
  • The symbol %
  • The symbol *
  • A zig-zag line
  • A pluteus larva
  • A starfish
  • Volcanos
  • Microscope lenses
  • (Old fashioned) balances for weighing things

  • Wheatstone bridge electrical circuits for measuring small differences in electrical resistances
    And why do they have this symmetry?
    (Don't worry if you haven't had physics, or have forgotten about Wheatstone bridges; but it's no accident they are symmetrical, and I hope you will think about it.)

  • Cumulus clouds in the sky
  • The graphs of any equation in which x only occurs as x squared, x to the fourth, or x to other even powers?
  • The graphs of any equation in which x only occurs as x cubed, x to the fifth power, and simply as x?
  • The graphs of any equation in which both x and y only appear squared, or to the fourth power.
  • The graph of x times y is equal to a constant?

    In general, how are the symmetries of x and y in an equation related to the symmetry of the graph of an equation? Relate this to Weyl's definition of symmetry.

    The mathematician Weyl invented the best definition of symmetry, that implies methods or criteria for inventing new kinds of symmetry. Put his definition in your own words. Or in Richard Feynman's words "A thing is symmetrical IF, there is something you can do to it (rotation, reflection, magnification, displacement by a certain distance, etc) After which it looks the same as it did before"

    Argue pro or con: Driesch discovered that whatever mechanisms control pluteus formation, these mechanisms have dilation symmetry.

    Argue pro or con: Embryonic development depends on many mechanisms that reduce/increase symmetry.

    Argue pro or con: Any completely deterministic system keeps whatever symmetry it started with. It can only become less symmetrical by means of some external signal, or by becoming sensitive to random fluctuations, like Brownian movement.

  • What are the 3 primary germ layers?

    List tissues and organs that develop from each of these three.

    Name and describe the process by which the cells of embryos are subdivided into these 3 germ layers.
    gastrulation, neurulation, somite formation

    Contrast this process in embryos of *sea urchins, *frogs & salamanders, *teleost fish, *birds & reptiles, and *mammals. You should be able to make sketches of sequential stages of development in each of these.

    Is there any relation between especially large and yolky eggs and the geometry of gastrulation? (Yes) Can you describe the sorts of differences that occur, in embryos with very large amounts of yolk, as compared with those having less yolk.

    Is mammal gastrulation more like gastrulation in echinoderm embryos, or frog embryos, or bird embryos?

    And why?)

    Neurulation subdivides what into what three subdivisions?

    Name these 3 subdivisions; what parts of the body, and what cell types develop from each?

    What are primordial germ cells?

    What specific cell types develop from them?

    What happens if all of an embryo's primordial germ cells are surgically transplanted to another animal?

    What is abnormal about the "donor" animal, from which the primordial germ cells are removed?

    What will be unusual about offspring of the animal to which the primordial germ cells are transplanted?

    From which germ layer do primordial germ cells develop? (Trick question!)

    In what sense do embryologists use the word "germ"? Not disease causing micro-organisms!

    Grafted Hensen's nodes from chick embryos can induce second neural tubes and whole second embryos, not only in early bird embryos, but also in mammal embryos (which I guess become chimeric for their notochord): what do you think this means, in terms of mechanisms and similarity of signaling mechanisms in different kinds of animals?

    There must have been a gradual evolutionary transition from embryos with blastopores to embryos with primitive streaks. Suggest what changes in the movements of future mesoderm and endoderm cells would have produced this transition.

    Pairs of somites develop along both sides of what mesodermal organ? And also along the sides of what ectodermal organ?
    notochord, neural tube

    Somite cells all disperse, and later in development you can only see remnants of where they had been: Can you suggest functional or mechanical reasons why the vertebrate body is segmented by transient rather than permanent blocks of cells?

    What groups of animals have very regulative development? mammals, echinoderms, amphibia

    What groups of animals have very mosaic development?

    nematodes, flies

    In what sequence do somites become separated from each other? First on one side, then on the other? First near the front, then one pair after another toward the rear? First at the rear and gradually toward the anterior? First in the middle, and then sequentially toward both ends? Or what?

    If you had a drug or treatment that could cause more somites to form on one side of the body than on the other side, then what anatomical abnormalities this would be expected to produce?

    Contrast the timing and geometric patterns of early cell divisions in embryos of mammals as compared with embryos of birds, amphibians, and teleost fish.

    What is the connection between the blastopore and the archenteron?
    The blastopore is the entrance to the archenteron.


    What is meant by symmetry "breaking"? Does anything actually have to break? Can something break, in symmetry breaking? What kind of symmetry does a frog egg have before it is fertilized? How much of this symmetry remains after the grey crescent is formed? Does this remaining symmetry remain in the adult frog or salamander? What symmetry does an adult starfish have? What symmetry does a pluteus larva have? What about the symmetry of an unfertilized echinoderm egg? ...Of an unfertilized human egg cell? Turing's "reaction diffusion system" of hypothetical chemical reactions would serve to break what kind of symmetry? Describe & name the kind of symmetry or combination of symmetries of any letter of the alphabet, or other geometric pattern (for example, Z has two-fold rotational symmetry, A has one plane of reflection symmetry, * has six planes of reflection symmetry), and also the symmetries of embryos at different stages of development.



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