Lab 6 - Paul Gonzales BIO 206L Lab 6 1) After the addition...

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Paul Gonzales BIO 206L Lab 6 1) After the addition of sperm it took about 3-5 minutes for the fertilization membrane to form. It took about an hour after fertilization for cleavage to occur. 2) First the sea urchin egg and sperm meet and form a zygote, and a wave of calcium ions sweeps through the cytosome, starting at the initial point of sperm egg fusion. Following the path of the calcium wave, the fertilization envelope follows, and protects the fertilized egg from the outside environment and protects the cell from addition sperm. The rise in cytosolic calcium triggers an elevation of the fertilization envelope, through the process of exocytosis. Exocytosis releases hydrolytic enzymes in vesicles and action of the released hydrolases causes a swelling of the membrane surrounding the cell, which in turn elevates the fertilization envelope. Within an hour, cleavage occurs and complete division of the cytoplasm follows. After 6 hours of cleavage, a blastula is formed. Then the cells are arranged to form a bastocoel, which includes an inner layer surrounding a hollow space. Gastrulation occurs after 1 day following the initial fertilization, in which cells leave the outer surface of the blastula and move into the blastocoel (called ingression) and invagination in which movements occur at the vegetal pole. Together in gastrulation the “gut”, the anus, the mouth, the muscles, and skeleton are formed. Sperm cells are about 2.5 micrometers in length under a 40X objective lens, while egg cells are about 7.5 micrometers under the 40X objective. In comparison fertilized embryonic cells are much smaller because cleavage has occurred and are therefore much smaller than the original gamete cells. Matter or volume may be conserved in this cell but the cleavage process decreases the amount of cytoplasm. 3) In the early blastula stage volume constraints force the formation of the blastocoel.
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Lab 6 - Paul Gonzales BIO 206L Lab 6 1) After the addition...

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