Mitosis: Cell Division

Transcription

1 Name Mitosis: Cell Division by Cindy Grigg

2 Answer the following questions BEFORE you read this book. It is okay if you do not know as much as you thought. Do the best you can! 1.How do children grow? Do their cells grow bigger? 2.What happens to cells when they grow old? 3.What are chromosomes? How many chromosomes do people have? Plants, animals, and all living things are made up of cells. Some living things are made of only one cell, like this amoeba. Others, like humans, are made of trillions of cells. 1 2 Mitosis: Cell Division

3 Cells cannot just happen - they come from other cells. Existing cells pass on their traits to new cells. They do this in a process called cell division. In cell division, a cell divides to form two new daughter cells, each of which contains the same genetic material as the original cell. This process lets living things replace old, worn-out cells. Each of your body cells (skin and muscle cells, for example) holds 46 chromosomes containing your genes. This is the diploid number of chromosomes. A diploid cell has two complete, matching sets of chromosomes. One set of 23 chromosomes came originally from your father while the other set came from your mother. These 46 chromosomes contain all the genetic information to make you who you are - they determine your eye color, hair color, and many other traits. 3 4 Mitosis: Cell Division

4 Skin cells only live about one month. Cells wear out, so they are constantly replacing themselves. You also grow new cells because your body is growing bigger. When you grow, new cells lengthen your bones. Growing new skin cells makes your skin bigger. Cell division also helps living things replace injured cells. Before one of your cells divides, the genetic material in the nucleus of the cell copies itself. Each daughter cell gets genetic material that is the same as the parent cell's genetic material. The dividing of the nuclear material is known as mitosis. In the last stage of cell division, the cytoplasm divides, creating two new cells. That stage is known as cytokinesis. After cytokinesis, there are two new and complete cells where there used to be one. 5 6 Mitosis: Cell Division

5 Cell division occurs in a predictable series of stages or phases. Before cell division starts, the cell is in interphase. Interphase is the main period in a cell's life cycle when it is not undergoing mitosis. As a cell prepares to divide, each chromosome in the nucleus replicates; it makes an exact copy of itself. The two copies are called sister chromatids. They stay attached to each other after replication. During prophase, the chromosomes condense and become visible. The chromosome copies are held together at their centers, called centromeres, so they look like an X. When looking at cells under a microscope, the chromosomes are not visible in this stage. Also in prophase, the spindle forms in the cytoplasm. The nuclear membrane starts to break down. 7 8 Mitosis: Cell Division

6 During metaphase, the two copies of each chromosome line up in the center of the cell, called the metaphase plate. The copies of the chromosomes are attached to protein fibers that form the spindle. The spindle fibers cause the sister chromatids to separate and go to different daughter cells when the cell divides. During anaphase, the copies separate into two groups. One complete set of chromosomes is pulled by the spindle fibers to one side of the cell. The other complete set is pulled to the other side of the cell. A new nuclear membrane forms around each set of daughter chromosomes Mitosis: Cell Division

7 The cytoplasm pinches in at the center of the cell. The division of the cytoplasm is called cytokinesis. Telophase is the final stage of cell division. Two groups of chromosomes are now located at opposite ends of the cell. Then nuclear membranes begin to form around each group. The chromosomes begin to uncoil and spread out. The spindle begins to break down. When cytokinesis is complete, two new daughter cells are formed. The daughter cells are identical to the parent cell. In plant cells, each daughter cell will construct a new cell wall around itself Mitosis: Cell Division

8 Glossary cell division-- the process by which a cell divides to form two daughter cells, each of which contains the same genetic material as the original cell chromosomes-- structures in the cell nucleus containing the genes cytokinesis-- the division of the cytoplasm; the last stage of cell division To help you remember a cell's life stages in order, you can remember this: I picked my apples today. The first letter of each word begins with the first letter of the stages. I stands for interphase, p stands for prophase, m stands for metaphase, a stands for anaphase, and t stands for telophase. Some people remember the stages by just the letters PMATI (with interphase at the end). This drawing shows cells in different stages. Can you tell which is which? diploid-- a cell having two complete, matching sets of chromosomes, one from each parent interphase-- the main period in a cell's life cycle when it is not undergoing mitosis; chromosomes replicate in interphase just before mitosis begins mitosis-- dividing of the nucleus, including genetic material, resulting in two new daughter cells, each of which has the same number of chromosomes as the original cell Mitosis: Cell Division

9 Answer the following questions AFTER you have completed this book. 5.Name the phases of mitosis and write a short description of what happens in each phase. 1.A diploid body cell (such as skin, muscle, etc.) contains how many chromosomes? 2.Circle the correct answer. The dividing of the nucleus and its genetic material is called: cytokinesis interphase mitosis telophase 3.What is the end result of mitosis? 4."Sister chromatids" are Mitosis: Cell Division

10 6.Imagine that you are a cell going through mitosis. Write a first-person account describing this process. Mitosis: Cell Division 17