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Name Unit 4 Cell Division WHAT I KNOW How is a new cell made? Why don’t cells get very big? What is a mutation? What is cancer? Unit 4 Cell Division Content Expectations CELL GROWTH Explain cell division, growth, and development as a consequence of an increase in cell number, cell size, and/or cell products. (B2.1C) ASEXUAL SEXUAL Describe different reproductive strategies employed by various organisms and explain their advantages and disadvantages. (B3.5d) MITOSIS MEIOSIS Compare and contrast the processes of cell division (mitosis and meiosis), particularly as those processes relate to production of new cells and to passing on genetic information between generations. (B4.3A) MUTATION EFFECTS Show that when a mutation occur in sex cells, they can be passed on to offspring (inherited mutations), but if they occur in other cells, they can be passed on to descendant cell only (non-inherited mutations). (B4.2A, B4.3B, B4.3f) CANCER Explain that gene mutation in a cell can result in uncontrolled cell division called cancer. Also know that exposure of cells to certain chemicals and radiation increases mutations and thus increases the chance of cancer. (B4.4b) CELL SPECIALIZATION Describe how, through cell division, cells can become specialized for specific function. (B2.1d, B4.3g) 1 Unit 4 Big Idea Through cell division, mitosis explains while meiosis explains . Unit 4 Core Concepts The process of mitosis produces and these cells . Meiosis ensures genetic continuity, by producing , which passes on genes . CELL GROWTH Explain cell division, growth, and development as a consequence of an increase in cell number, cell size, and/or cell products. The larger a cell becomes, the more . In addition, a larger cell is less efficient in . In other words, it is beneficial for a cell . Food, oxygen, and water enter a cell through the . Waste products leave in the same way. The rate at which this exchange takes place depends on the of a cell. The rate at which food and oxygen are used up and waste products are produced depends on the cell’s . As the length of the sides of a cube increases, its volume increases than its surface area, decreasing the ratio of surface area to volume. Soon, we will complete a lab about cell size. You will cut different size cells and measure how far a substance can get into the cells in a certain amount of time? What do you think will happen? What will be the difference between the large and the small cells? 2 Before a cell grows too large, it in a process called . Before cell division, . It then divides into two “daughter” cells. Each daughter cell . Cell division cell volume. It also results in an I , for each daughter cell. ASEXUAL SEXUAL Describe different reproductive strategies employed by various organisms and explain their advantages and disadvantages. Asexual reproduction is reproduction . The offspring produced are, in most cases, . Asexual reproduction is a . Both prokaryotic and eukaryotic single-celled organisms and many multicellular organisms can reproduce asexually. In sexual reproduction, offspring are produced by the . These fuse into a single cell before the offspring can grow. The offspring produced . Most animals and plants, and many single-celled organisms, reproduce sexually. Comparing Sexual and Asexual Reproduction 3 MITOSIS MEIOSIS Compare and contrast the processes of cell division (mitosis and meiosis), particularly as those processes relate to production of new cells and to passing on genetic information between generations. The genetic information that is passed on from one generation of cells to the next is carried by . Every cell must copy its before cell division begins. Each daughter cell gets . Cells of every organism have a specific number of . The Prokaryotic Cell Cycle The prokaryotic is a regular pattern of growth, DNA replication, and cell division. Most prokaryotic cells begin to replicate, once they have grown to a certain size. When DNA replication is complete, the cells through a process known as . Binary fission is a form of . For example, bacteria reproduce by binary fission. The Eukaryotic Cell Cycle The eukaryotic cell cycle consists of four phases: G1, S, G2, and M. INTERPHASE is the . It is a period of growth that consists of the G1, S, and G2 phases. The M phase is the period of cell division. Think Intermission when you think of . If cell division is the show to watch, this is the time between each division. G1 PHASE: CELL GROWTH In the G1 phase, cells . S PHASE: DNA REPLICATION In the S (or synthesis) phase, . 4 G2 PHASE: PREPARING FOR CELL DIVISION In the G2 phase, many of the . M PHASE: CELL DIVISION In eukaryotes, cell division occurs in two stages: mitosis and cytokinesis. Mitosis is the . Cytokinesis is the . Mitosis Chromatid – Centromere – Centrioles – Spindle – PROPHASE (THINK PROLOGUE OF A STORY) During prophase, the first phase of mitosis, . The centrioles move to opposite sides of nucleus and . The spindle forms and DNA strands attach at a point called their . The and nuclear envelope breaks down. Spindle fibers – METAPHASE (MIDDLE) During metaphase, the second phase of mitosis, the . The spindle fibers . 5 ANAPHASE (APART) During anaphase, the third phase of mitosis, the . The chromosomes . TELOPHASE (TWO NUCLEI) During telophase, the fourth and final phase of mitosis, the chromosomes . A around each cluster of chromosomes. The spindle breaks apart, and . CYTOKINESIS (CELL SPLITTING) Cytokinesis is the . Cytokinesis in Animal Cells The cell membrane is drawn in until . Each part contains its own nucleus and organelles. Cytokinesis in Plant Cells In plants, the cell membrane is not flexible enough to draw inward because of the rigid cell wall. Instead, a cell plate forms between the divided nuclei that develops into cell membranes. A in between the two new membranes. Cell Cycle Review 6 What are chromosomes? A body cell , as shown in the figure. Four . These two sets of chromosomes are homologous, meaning that each of the four chromosomes from the male parent has a corresponding chromosome from the female parent. Chromosomes— . The genes are located in specific positions on chromosomes. Also, humans have 23 pairs of chromosomes while this organism has only 4 pairs. One of our 23 pairs are either XX (female) or XY (male) which defines our gender. This is a picture of the . You can clearly see the 23rd pair (XY) which indicate this human is genetically a male. Diploid Cells have of chromosomes. Haploid Cells have as many chromosomes. Meiosis is a process in through the separation of homologous chromosomes in a diploid cell. Meiosis usually involves two distinct divisions, called meiosis I and meiosis II. By the end of meiosis II, the diploid cell becomes four haploid cells. Meiosis I Just prior to meiosis I, the cell undergoes a round of . Each replicated chromosome consists of two identical chromatids joined at the center. Prophase I The cells begin to divide, and the , which contains four chromatids. As homologous chromosomes pair up and form tetrads, they undergo a process called crossing-over. First, the chromatids of the homologous . Then, the crossed sections of the . Crossing-over is important because it in the cell. 7 Metaphase I As prophase I ends, a spindle forms and attaches to each tetrad. During metaphase I of meiosis, . Anaphase I During anaphase I, spindle fibers pull each homologous chromosome pair . When anaphase I is complete, the separated chromosomes cluster at opposite ends of the cell. Telophase I During telophase I, around each cluster of chromosomes. Cytokinesis Cytokinesis follows telophase I, forming . Meiosis I Meiosis I results in . Because each pair of homologous chromosomes was separated, neither daughter cell has the two complete sets of chromosomes that it would have in a diploid cell. The two cells produced by meiosis I . Meiosis II The two cells produced by meiosis I now enter a second meiotic division. Unlike the first division, . Prophase II —each consisting of two chromatids— As the cells enter prophase II, their . The chromosomes do not pair to form tetrads, because the homologous pairs were already separated during meiosis I. 8 Metaphase II During metaphase of meiosis II, . Anaphase II As the cell enters anaphase, the paired chromatids . Telophase II and Cytokinesis In the example shown here, produced in meiosis II These four daughter cells now contain the (N)—half the chromosomes each. Gametes to Zygotes The haploid cells produced by meiosis II are . In male animals, these gametes are called sperm. In some plants, pollen grains contain haploid sperm cells. In female animals, generally only one of the cells produced by meiosis is involved in reproduction. The female gamete is called an egg in animals and an egg cell in some plants. Comparing Meiosis and Mitosis In mitosis, when the two sets of genetic material separate, each daughter cell receives one complete set of chromosomes. In meiosis, homologous chromosomes line up and then move to separate daughter cells. Mitosis does not normally change . This is not the case for meiosis, which . Mitosis results in the production of , whereas meiosis produces Mitosis is a form of . , whereas meiosis is an . 9 In mitosis, when the two sets of genetic material separate, . In meiosis, homologous chromosomes line up and then move to separate daughter cells. As a result, . The in meiosis result in a than could result from mitosis. Mitosis of the original cell. Meiosis . Changes in Chromosome Number A diploid cell that enters mitosis with will divide to produce , each of which also has . is a single cell division, resulting in the production of . requires , and, in most organisms, produces a total of . Chromosomal Disorders What happens if there are errors during meiosis? If occurs during meiosis, gametes with an may result, leading to a disorder of chromosome numbers. The parent cell has 8 chromosomes (paired in 4 sets). If nondisjunction hadn't occurred, the two daughter cells formed after Meiosis I would each have 4 chromosomes (2 pairs). There would be two red and two yellow. But, because nondisjunction occurred during Meiosis I, the daughter cells have an abnormal number of chromosomes. Therefore, as they split again in Meiosis II, the sex cells that will be used during sexual reproduction have an . If two copies of an autosomal (paired) chromosome fail to separate during meiosis, an individual may be born with . 10 , meaning “three bodies.” The most This condition is known as a common form of trisomy, involving three copies of chromosome 21, is , which is often characterized by mild to severe mental retardation and a high frequency of certain birth defects. Nondisjunction of the can lead to a disorder known as . A female with Turner’s syndrome usually inherits only . Women with Turner’s syndrome are sterile, which means that they are unable to reproduce. Their sex organs do not develop properly at puberty. Genetically, females lack a Y chromosome while males are characterized by the presence of a Y chromosome. In males, nondisjunction may cause from the inheritance of an , resulting , which interferes with meiosis and usually prevents these individuals from reproducing. There have been no reported instances of babies being born without an X chromosome, indicating that this chromosome contains genes that are vital for the survival and development of the embryo. MUTATION EFFECTS Explain why only mutations occurring in gametes (sex cells) can be passed on to offspring. Genetic disorders result from . The offspring's cells replicate the abnormal DNA during Mitosis and therefore the problem is replicated in all the cells of the offspring. Genetic disorders could also result from mutations that happen to an offspring's DNA (chromosomes) during the early stages of development. Those mutations/changes in DNA are also replicated in all the cells of the offspring. Genetic Disorders Sickle-shaped cells are more rigid than normal red blood cells, and they tend to get stuck in the capillaries. 11 CANCER Explain that gene mutation in a cell can result in uncontrolled cell division called cancer. Also know that exposure of cells to certain chemicals and radiation increases mutations and thus increases the chance of cancer. The can turned on and off. For example, when an injury such as a broken bone occurs, cells are stimulated to divide rapidly and start the healing process. The rate of cell division slows when the healing process nears completion. be are a family of proteins that regulate the timing of the cell cycle in eukaryotic cells. This graph shows how cyclin levels change throughout the cell cycle in fertilized clam eggs. Internal regulators are proteins that respond to events inside a cell. They allow the cell cycle to proceed only once certain processes have happened inside the cell. External regulators are proteins that respond to events outside the cell. They direct cells to speed up or slow down the cell cycle. Growth factors are external regulators that stimulate the growth and division of cells. They are important during embryonic development and wound healing. is a process of programmed cell death. Apoptosis plays a role in development by shaping the structure of tissues and organs in plants and animals. How do cancer cells differ from other cells? Cancer cells do not respond to the signals that regulate the growth of most cells. As a result, the cells is a disorder in which body cells lose the ability to control cell growth. Cancer cells divide uncontrollably to form a mass of cells called a . A is noncancerous. It does not spread to surrounding healthy tissue. A is cancerous. It invades and destroys surrounding healthy tissue and can spread to other parts of the body. The spread of cancer cells is called metastasis. Cancer cells absorb nutrients needed by other cells, block nerve connections, and prevent organs from functioning. Cancers are caused by division. Some sources of gene defects are in genes that regulate cell growth and . A damaged or defective p53 gene is common in cancer cells. It causes cells to lose the information needed to respond to . 12 CELL SPECIALIZATION Describe how, through cell division, cells can become specialized for specific function. All organisms start life as just one cell. Most multicellular organisms pass through an early stage of development called an embryo, which gradually develops into an adult organism. During development, an organism’s cells become more for particular functions. The process by which cells become specialized is known as . During , cells differentiate into many different types and become specialized to perform certain tasks. Differentiated cells carry out the jobs that multicellular organisms need to stay alive. Cell differentiation in mammals is controlled by a number of interacting factors in the embryo. generally reach a point at which their differentiation is complete and they can no longer become other types of cells. Regulating is especially important in shaping the way a multicellular organism develops. Each of the specialized cell types found in the adult originates from the same fertilized egg cell. As an embryo develops, different sets of genes are regulated by transcription factors and repressors. helps cells undergo differentiation, becoming specialized in structure and function. 13