Emma+Human+Life+Cycle+1

Human Life Cycle 16.1 p. 320 (1) How many chromosomes does a mother contribute to a new individual? A father? Both the egg and the sperm contribute 23 chromosomes. (2) Where does meiosis occur in males? in females? For males meiosis takes place in the testes while sperm is being produced and for females in the ovaries while eggs are being produced. (3) Compare and egg cell to a sperm cell. -Both an egg and sperm cell have 23 chromosomes (4) What is the difference between meiosis and mitosis. -Mitosis duplication division,cells create exact copies of themselves. Meiosis is reduction division, during meiosis the chromosome number is reduced from the normal 46 (diploid number) chromosomes to 23 chromosomes (haploid number). There are two divisions in meiosis called meiosis I and II

Development Chapter 17 17.1 (5) Describe in detail how fertilization occurs -Fertilization begins with the sperm swimming toward the egg by means of its flagellum tail. The sperm then penetrate the corona radiata, several sperm attempt to penetrate the zona pellucida but only one sperm enters the egg. It does so because after a sperm binds tightly to the zona pellucida the acrosome releases digestive enzymes that forge a pathway for the sperm through the zona pellucida. When a sperm binds to the egg, their plasma membranes fuse, and this sperm enter the egg. Next comes fusion of the sperm and egg nuclei. (6) What is polyspermy and how is prevented during fertilization? -Polyspermy is the entrance of one or more sperm into an egg and it is prevented because as soon as a sperm touches the egg the egg's plasma membrane depolarizes, which prevents the binding of any other sperm.

17.2 (7) Describe the processes involved in development. -cleavage- occurs immediately after fertilization as the zygote begins to divide into cells [2,4,8,16,32...] Cell division during cleavage s mitotic and each cell receives a full complement of chromosomes and genes. -Growth- During embroytic development, cell division is accompanied by an increase in size of the daughter cells. Morphogenesis-shaping of the embryo first evident when certain cells are seen to move,or migrate in relation to other cells. It is these movements that shape the embryo Differentiation- cells take on specific structure and funtion. Fist system to do this is the nervous system. (8) What are the extraembryonic membranes and what is their role? -1.Chorion- develops into the fetal half of the placenta, organ that provides the embryo/fetus with nourishment and oxygen and takes away its waste. -2. Allantois-accumulates the small amount of urine produced by the fetal kideys and later gives rise to the urinar bladder -3. Yolk Sac-first embryonic membrane to appear. It is the first site of blood cell formation. 4.-Amnion- contains the fluid to cushion and protect the embryo, which develops into a fetus. (9) What happens during pre-emrbyonic development? -Pre-embryotic development includes he zygote repeatedly dividing as it passes down the oviduct to the uterus. a morula is a compact ball of embroytic cells that becomes a blastocyst. The many cells of the blastocyst then organize themselves to form an inner cell mass surronded by an outer layer of cells. Inner cell mass will become the embryo and the outer layer will becomes the chorion. Each cell in the inner mass is capable genetically to become any type of tissue. Sometime during developement, the cells of the morula seperate or the unner cell mass splits abd two pre-embryos are present rather than one. This will result in twins, either fraternal or identical. (10) What happens during embryonic development? -The embryo plants itself in the wall of the uterus. The chorion then secretes enzymes to digest away some of the tissue and blood vessels of the endometrium of the uterus. Human Chorionic gonadotropin (HGC) is secreted which means 100% pregnant and there is no menstruation. Over the second week the inner cell mass becomes the embryonic disk and two more extraembryonic membranes form. Yolk sac is first site of blood cell formation, amniotic cavity surronds embryo/fetus. Amniotic Fluid acts as an insulator from heat, cold and shock.Three primary germ layers are formed (see below). the third week is characterized by the formation of the nervous system and the heart. Fourth and fifth weeks includes the embryo being connected t the chorion and the formation of the umbilical cord. Arms, legs, hands and feet become apparent and the head enlarges. It is even possible to make out developing eyes, ears and even nose. Sixth through eight weeks embryo changes into a more human-like form. Body is in proportion as the neck region develops. Nervous system is developed enough to have reflex actio. Embryo is about 1.5 in long even though all organ systems have been established. (11) What are the primary germ layers and what body structures come from each layer? -The primary germ layers are the ectoderm, mesoderm and endoderm. Ectoderm (outer layer) produces the epidermis of skin;epithelial lining of oral cavity and rectum;nervous system. Mesoderm (middle layer) skeleton;muscular system;dermis of skin;cardiovascular system;urinary system; reproductive system; outer layers of respiratory and digestive systems. Endoderm (inner layer) epithelial lining of digestive tract and respiratory tract; associated glands of these systems; epithelial lining of urinary bladder.