NH+Development+HW

=Human Life Cycle 16.1 p. 320= //During the production of sex cells, meiosis, the diploid number of chromosomes (46) is reduced by half (to 23), the haploid number. Both the mother and father contribute 23 chromosomes.//
 * (1) How many chromosomes does a mother contribute to a new individual? A father?**

//Meiosis occurs in the testes in males and the ovaries in females.//
 * (2) Where does meiosis occur in males? in females?**

(**3) Compare and egg cell to a sperm cell.** //Both have 23 chromosomes. The sperm is much smaller, its sole purpose is to carry chromosomes to an egg. The egg is bigger. It contains the other half of the chromosomes as well as the cytoplasm for the zygote after fertilization.//

//Mitosis is the process of cell replication, so the chromosome number stays the same form one "generation" to the next. Meiosis, on the other hand, is the process of producing sex cells which only have half of the chromosomes as the parent cell.//
 * (4) What is the difference between meiosis and mitosis.**

=Development Chapter 17=

17.1
//The sperm gets through the corona radiata//. //Digestive enzymes are released from the acrosome (where the chromosomes are stored). these enzymes eat away at the zona pellucida// (//an extracellular matrix that surrounds the plasma membrane of the egg). The sperm then binds to the plasma membrane. Then, the sperm nucleus and the egg nucleus fuse, forming one nucleus with all 46 chromosomes. As soon as one sperm cell attaches, the plamsa membrane depolarizes, preventing any other sperm from fertilizing it. Cortical granules then release enzymes that cause the zona pillucida to become impenetrable.//
 * (5) Describe in detail how fertilization occurs.**

//Polyspermy is the entrance of more than one sperm. The process of how this is prevented is described in the previous question.//
 * (6) What is polyspermy and how is prevented during fertilization?**

17.2
//The first step is cleavage, when the zygote immediately starts dividing through mitosis. The cell does not grow though. Growth is the next stage in which the daughter cells start to increase in size. The next stage is morphogenesis. This is when the embryo starts to take shape and you can see for the first time that cells are interacting with each other. Differentiation is when the cells begin to take on specific structure and function.//
 * (7) Describe the processes involved in development.**

//The chorion provides the embryo/fetus with nourishment and oxygen and takes away waste. The allantois accumulates the urine made by the kidneys. It also bring blood to and from the fetus. The yolk sac is where the first blood cells are formed. The amnion contains fluid to cushion and protect the fetus as it grows.//
 * (8) What are the extraembryonic membranes and what is their role?**

//Pre-embryonic development is just the first week of development. Immediately after fertilization, the zygote begins to divide but not grow. This dense ball of embryonic cells is a morula which becomes a blastocyst. The cells of the blasocyst arrange themselves so that there is an inner cell mass surrounded by a layer of cells. The layer of cells will become the chorion.//
 * (9) What happens during pre-emrbyonic development?**

//Goes from the second week to the end of the second month of development. During the second week, the embryo begins to implant itself in the uterus, and the inner cell mass becomes the embryonic disk via gastrulation. At this stage, the embryonic disk has primary germ layers that become the different systems in the body. During the third week, the nervous system and the heart begin to develop. In the fourth and fifth weeks, the umbilical chord is developed. Limb buds begin to appear, the head enlarges and the sense organs develop more. In the sixth through eighth week, a neck region develops, the nervous system has developed enough to have reflex actions,//
 * (10) What happens during embryonic development?**

//The primary germ layers are part of the embryonic disk. They are what become the different systems in the body. The ectoderm becomes the skin, lining of the oral cavity and rectum. It also becomes the nervous system. The mesoderm becomes the skeleton, muscular system, dermis of skin, cardiovascular system, urinary system, reproductive system, and outer layers of respiratory and digestive systems. The endoderm becomes the epithelial lining of the digestive, respiratory and urinary bladder.//
 * (11) What are the primary germ layers and what body structures come from each layer?**