Lucy+Development+homework

(1) How many chromosomes does a mother contribute to a new individual? A father? (2) Where does meiosis occur in males? in females? (3) Compare and egg cell to a sperm cell. (4) What is the difference between meiosis and mitosis.
 * A mother contributes 23.
 * A father contributes 23 also.
 * meiosis occurs in the testes of males
 * Meiosis occurs in the ovaries of females
 * The sperm cell is smaller compared to the egg. The sperm is specialized to carry only chromosomes as it swims to the egg. The egg is specialized to await the arrival of a sperm and to provide the new individual with cytoplasm in addition to chromosomes.
 * Mitosis is when a cell divided. Each cell in the body has 46 chromosomes and when is divided, the new cells also have 46 chromosome. Mitosis is duplication division. the cell copies itself during mitosis. Mitosis takes place during growth and repair of tissues.
 * Meiosis is reduction division. It takes place only in the testes of males during the production of sperm and in the ovaries of females during the production of eggs. The chromosome number is reduced from the normal 46 down to 23 chromosomes. Meiosis requires 2 successive divisions, meiosis I and meiosis II.

Development Chapter 17 17.1 (5) Describe in detail how fertilization occurs (6) What is polyspermy and how is prevented during fertilization? 17.2 (7) Describe the processes involved in development. (8) What are the extraembryonic membranes and what is their role? (9) What happens during pre-emrbyonic development? (10) What happens during embryonic development? (11) What are the primary germ layers and what body structures come from each layer?
 * The tail of the sperm allows it to swim towards the egg. The middle of the sperm has energy-producing mitochondria, an the hear of the sperm has a nucleus capped by a membrane-bound acrosome. The nucleus of the sperm fuses with the nucleus of the egg. Then the plasma membrane of the egg is surrounded by an extracellular matrix. The zona pellucida is surrounded by a few layers of adhering follicular cells. These cells nourished the egg when it was in a follicle of the ovary. Then several sperm penetrate the corona radiata. Only one sperm will enter the egg. After the sperm head binds tightly with the zoa pellucida, the acrosome releases digestive enzymes that forge a pathway for the sperm through the zona pellucia. When a sperm and egg attach, the plasma membranes fuse and the sperm enters the egg
 * .As soon as a sperm touches an egg, the egg's plasma membrane depolarized and this prevents the binding of any other sperm. Then the cortical vesicles release enzymes that cause the zona pellicuda to become an impenetrable fertilization membrane. Now sperm cannot bind to the zona pellucida either.
 * Cleavage: after fertilization, the zygote begins to divide so that there are first 2, then 4, 8, 16 and 32 cells. The increase in size doesn't accompany these divisions. Cell division during cleavage is mitotic and each cell receives a full complement of chromosomes and genes.
 * Growth: During embryonic development, cell division is accompanied by an increase in size of the daughter cells.
 * Morphogenesis: The shaping of he embryo and is first evident when certain cells are seen to move, or migrate in relation to other cells. The embryo begins to assume various shapes.
 * Differentiation: WHen cells take on a specific structure and function. The first system to become visibly differentiated is the nervous system.
 * They are not apart of the embryo and fetus. They are outside of the embryo. In shelled animals, the chorion lies next to the shell and carries on gas exchange. Their function is different in humans because humans develop inside the uterus. The chorion devlops into the fetal half of the placenta, the organ that provided the embryo/fetus with the nourishment and oxygen and takes away its waste. Allantosis, extends away from the embryo. It accumulates the small amount of urine produced by the fetal kidneys and later gives rise to the urinary bladder. The yolk sac is the first embryonic membrane to appear. in shelled animals, the yolk sac contains yolk, which is the food for the developing embryo. In humans, the function is taken over by the placenta. The yolk sac contains little yolk. The yolk sac contain plentiful blood vessels. Amnion enlarges as the embryo and then the fetus enlarges. It contains fluid to cushion and protect the embryo, which develops into a fetus.
 * The zygote divided repeatedly as it passed down the oviduct to the uterus. A morula is a compact ball of embryonic cells that become a blastocyst. The many cells of the blastocyst arrange themselves so the there is an inner cell mass surrounded by the embryo. The layer of the cells will become the chorion. Each cell within the inner cell mass has the genetic capability of becoming any type of tissue.
 * It begins the 2nd week and last until the end of the 2nd month of development. The embryo begins to process of implanting itself in the wall of the uterus. During implantation, the chorion secretes enzymes to digest away some of the tissue and blood vessels of the endometrium of the uterus. They also begin to secrete HCG. HCG acts like luteinizing hormone in that it serves to maintain the corpus luteum past the time it normally disintegrates. The corpus luteum secretes progesterone, the endometrium is maintained, and the expected menstruation does not occur. The embryo is now the size of a period. As the weeks progresses, the inner cell mass becomes the embryonic disk and 2 more extraembryonic membranes form. The yolk sac is the first site of blood cell formation. The amniotic cavity surrounds the embryo as it develops. In humans, amniotic fluids act as an insulator against cold an heat and also absorbs shock, such as that caused by the mother exercising.
 * Ectoderm - Skin, lining of oral cavity, rectum, nervous system
 * mesoderm- Skeleton, muscular system, Dermis of skin, cardiovascular system, urinary system, reproducing system, outer layers of the respiratory and digestive system.
 * endoderm- lining of digestive tract an respiratory tract, lining of the urinary bladder.