Embryology Biology 441 Spring 2007 Albert Harris and Andrius Masedunskas
Review Questions for First ExamApproximately how many differentiated cell types do human and other mammal bodies contain? What are ten specific examples of differentiated cell types? What are some kinds of animals that have many fewer differentiated cell types? Name the three primary germ layers? Do they have anything to do with germs in the sense of infectious diseases? Hint: no, they don't. What are several major organs that develop primarily from each of these primary germ layers? What is gastrulation? What is neurulation? Neurulation subdivides which of the three primary germ layers into what three sub-divisions? What do the brain and spinal cord develop from? What is the epidermis? It is the outer layer of what part of the body? What embryological process controls where hairs, feathers and scales will form?
Describe and draw sequential stages of the process of gastrulation as it occurs in sea urchins? Compare this with the geometry of gastrulation in the embryos of frogs and salamanders. Draw stages of gastrulation in a frog embryo. What is the approximate diameter of a sea urchin egg? What is the diameter of a human egg? (about the same: 100 micrometers) What is a pluteus larva? What part of a birds egg corresponds to the oocyte (hint: the yolk), and materials are secreted around this in the oviduct of the bird, before laying. Describe gastrulation in birds: in what ways does it differ from gastrulation in amphibians (=frogs and salamanders) and in sea urchins. Describe and draw the paths of movement of mesoderm cells in frog gastrulation, and in the gastrulation of birds. What about the paths of movement of future endoderm cells? Gastrulation in mammals is more like that in birds, or more like that in frogs? (hint: birds).
What is the defining difference between holoblastic cleavage versus meroblastic cleavage? The eggs of sea urchins, frogs, salamanders and humans undergo which of these forms of cleavage? Do the eggs of birds and teleost fish undergo meroblastic cleavage, or holoblastic cleavage? How are these differences in cleavage correlated with the amount and distribution of yolk in the cytoplasm of egg cells in different kinds of animals? Describe this yolk distribution.
What is polyspermy? Why do mechanisms evolve to prevent polyspermy? Thought question: If you had chemicals or some other treatment that could activate the mechanisms for preventing polyspermy, then how could you use them as a new method of contraception? Conversely, could contraception also result from drugs that prevent the normal mechanisms that block polyspermy? What is the acrosome? Where is it located? What does it contain? How are these contents released? When are these contents released, and for what purpose? Might it be possible to achieve contraception by preventing these contents from being released, or from serving their function? What are cortical granules? Where are they located, and in what particular kind of cell? When and for what purpose are the contents of cortical granules secreted into the space surrounding the oocyte? What is the "fast block" to polyspermy? What are some examples of the slow block to polyspermy? What is the fertilization membrane? When, where, and why is it formed? In an unfertilized oocyte, what electrical voltage difference exists across the plasma membrane? This voltage is caused by differences in the concentration of what ions? How does this voltage change as a result of fertilization? What change in permeability causes this voltage change? Compare this change with the mechanism of propagation of nerve impulses along axons. Thought question: in the sense that the fast block is comparable to a nerve impulse (action potential), then what is comparable to a nerve cell's secretion of vesicles of acetyl choline, or other neurotransmitter substances? During normal fertilization of an egg cell, what are three examples of fusion between plasma membranes and other membranes?
What is the definition of the animal pole of en embryo? What is the definition of the vegetal pole? Which end of egg cells almost always has a higher concentration of yolk in the cytoplasm, and is therefore heavier? What are polar bodies? Polar bodies are formed by what special kind of divisions, that starts with a M. Why do oocytes form polar bodies, but developing sperm cells do not form anything comparable. What are 3 or 4 other important differences between the development of sperm cells as compared with the development of egg cells (=oocytes). All sperm are haploid at fertilization, but human oocytes are still diploid at fertilization: true or false? What logical reason can you suggest for this difference? Are some kinds of animals pentaploid for a while after fertilization? Had their embryos formed any polar bodies, yet, at the time they were fertilized? When do human embryos form their second polar body, relative to the time of fertilization? Echinoderms and Cniderians (Hydra, corals, jelly-fish, etc.) are unusual in the animal kingdom in that their egg cells form both polar bodies before their eggs are fertilized. How does that differ from the situation in humans?
What are ameloblasts? What do they secrete? What is the stomodeum? What is Rathke's pocket? Odontoblasts form what part of what organs? Describe the embryonic formation of teeth. Draw a cross section of a neurulating embryo at the time of separation of the neural crest, and label the different parts, and what future parts of the body each will develop into. What important discovery was made by Koller and Fisher? What did the results of this experiment imply about the mutations that caused the loss of teeth during the evolution of modern birds? What possible misinterpretation might have occurred in the Koller and Fisher experiment? If there were some major difference between the enamel of teeth in mammals, as compared with the teeth of reptiles and ancient birds, then how might this difference be used to prove whether Koller and Fisher interpreted their results correctly? (Hint: What if the enamel of the teeth that grew in their experiments turned out to resemble mammal enamel?)
What is the germinative layer of the skin? What does the process of cornification mean? Make a rough sketch of a cross section of an individual hair. What are dermal papillae? How are they related to the location where hair and feathers form? Draw a cross section of an eye during its process of formation, including the lens and the cornea. What is the lateral line system? What kinds of animals have lateral lines?
What are the olfactory placodes? Where do they form? From which subdivision of which primary germ layer do all placodes develop. How does the lens of the eye develop, and from what? How is the development of the inner ear similar to the development of the lens and the nose? The nostrils develop from what? Why could an animal not breathe through its nostrils when they are first forming? The nerve fibers that sense smell and sound "grow" (actually meaning something like "crawl") to the brain from the sensory organ: how is that different from other sensory nerves? Besides sound, what other variables does the inner ear serve to detect? Describe the "hair cells" (= neuromast cells) of the inner ear (and also of the lateral line system)?
What are the major subdivisions of the mesoderm? Describe the notochord? Describe its cellular and molecular structure, and its physical properties? Draw a sketch of a notochord. Where is the notochord located? (below what? between what? The cells of the primitive node become the notochord! Can you visualize why? Hint: it's because they are the last mesodermal cells to move into the interior in animals like birds, reptiles and mammals, which have the primitive streak pattern of gastrulation. What are somites? Where do somites form? Describe the process of separation of somites from each other? What are the dermatome, myotome and scerotome? What parts of the adult body develop from each of these? Draw the geometrical shape of a somite in the process of subdivision into these three parts. What is the dermis? How is it related to the epidermis? What (and where) is the intermediate mesoderm? What parts of the body does the intermediate mesoderm develop into? What and where is the lateral plate mesoderm? What does lateral plate mesoderm develop into. Where does the coelom form? From what tissue does the heart form? What are some examples in which type I collagen becomes arranged into many layers, with the fibers of each layer oriented perpendicular to the layers directly above, and directly below, it?
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