EXERCISE 2-MITOSIS cells. This is a topics laboratory because the main goal is to observe and identify the stages of e to support current literature regarding the timing of the cell cycle The purpose of this laboratory is to reinforce your pvortiese lf this laboratory is to reinforce your understanding of the process of cellular reproduction in toi This laboratory also includes a short obsérvational experiment that enables you to collect The specific laboratory objectives are: I. To identify the stages of mitosis in plant cells. 2. To identify the stages of mitosis in animal cells. 3. To determine the longest stage of the plant cell life cycle. ty to reproduce is one of the fundamental properties of life. It is the mechanism by which cells Chromosomes are the carriers of and organisms, pass their genetic information to the next generation. the ch chromosomes are replicated and segregated into daughter cells. The two mechanism goal are mitosis and meiosis. In mitosis, the cell is dividing to make more cells. In genetic information. Therefore, in order to understand heredity, it is important to understand the tha t accomplish this this diploid and cells. In this Both cells are the chromosome number remains the same. In meiosis, the cell is dividing to produce sex n both processes is the division of the cytoplasm, known as cytokinesis. Cell division in one on for cell division (S phase), and a second growth phase in preparation for cell division (G2 process, one cell typically produces two daughter cells that are identical to the original. process, one cell typically produces four haploid daughter cells that ean later combine with er sex cells to produce a genetically different diploid offspring. Simultaneous with the division of the part of the cell cycle and takes up about 10% of the life of cells. The remaining portion of the cell cycle is uring this phase, the cell goes through normal growth and metabolism (G1 phase), DNA ratory, you will observe interphase and mitosis in the cells of the onion root tip and phase). In this laborat the whitefish blastula. The focus of our lab today is mitosis. During Gl of interphase, a cell will decide if the conditions are right to divide, this point in the cell life cycle is known as the restriction point. If a cell decides to divide, it will move into S phase where it replicates its DNA. The two identical copies of DNA, called sister chromatids, are held together at the chromosome’s centromere. After a second growth phase (G2), the cell enters mitosis. In prophase, the chromosomes condense and become visible under the light mi croscope. The nuclear membrane begins to break down, but the chromosomes still appear to be held in a circular structure. In metaphase, the spindle fibers from each pole of the cell have attached to each chromosome at the centromere and aligned all the chromosomes at the center of the cell. At this point, one of the differences between plants and animals is clear. The plant chromosomes are large and a clear center cannot be found, but the nuclear membrane is gone and the chromosomes are at the center of the Iwith arms hanging out in both directions (Fig 1A). The animal chromosomes are small and they form a dark line at the center of the cell. Also, in animal cells, the spindle fibers that align the chromosomes ible (Fig 1B). In anaphase, the spindle fibers shorten the chromosome centromere divides and sister chromatid is pulled to the opposite side of the cell. In telophase, the two sets of chromosomes are visi (once you separate sister chromatids, they are each considered a single chromosome) are at opposite ends of the cell. They are de-condensing and the nuclear membrane is reforming around them. Additionally at this stage, cytokinesis can be observed. In the plant cell, a new cell wall forms between the two cells In the animal cell, the cytoplasm pinches of forming a cleavage furrow that will eventually separate the two cells. At this point, two identical cells are formed and each can start GI and the entire cell life cycle again. 2-1 he process of miosis is fundamentally the same in all cukaryotic cells, although some differenceve wll exist. Today we will focus on some of the differences seen when comparing plants use the onion root tip as a model for plant mitosis and the whitefish blastula as a model for animal mitosis. Both of these cell types are highly proliferative and you should be able to identify all the stages of mitosis in each. The per se, but rather in the shape of the cell, the size of the chromosomes, the process of spindle formation differences you will observe between plants and animals do not involve mitosis I on the next page shows a representative stage of mitosis for the root tip (IA) and the whitefish blastula (IB), Take a few moments to look at the labeled structures note the differences between the two organisms and Interphase Nucleus Spindle Fibers Cell Wall Cell membrane (A) Onion Root Tip (B) Whitefish Blastula Figure 1. Representative stages of mitosis in plant (A) and animal (B) cells The Procedure A. Mitosis in Onion Root Tip 1. Examine a prepared slide of the onion root tip. This is a thin, longitudinal section of the root tip. Identify the various stages of mitosis in these cells. 2. In the space provided in your post lab assignment, make drawings of all the stages of mitosis that can be identified in the onion root tip sections. Use the onion root tip slide to perform a short observational experiment on the time a dividing cell type spends in each phase of the cell cycle. Each prepared root tip is a snapshot in time. By counting cells in each phase you can determine the percentage of cells in each phase at one given time. This number is directly proportional to the amount of time the cell spends in each phase. Use the space provided in the post lab as a guide for the completion of this experiment. 3. B. Mitosis in Animal Cells 1. Examine slides of mitosis in whitefish blastula under low and high power. Identify the various stages of mitosis in these cells and note the differences that exist between mitosis in plant and animal cells (they may not all be observable from these slides but you should know them from your coursework). 2. In the space provided in your post lab assignment, make drawings of the various stages of mitosis showing as much detail as possible. Investigation into the timing of the plant cell cycle 5. Based upon the information provided in the introduction, write a hypothesis for this observational experiment. (1) 2-3 prediction should contain specific information about the model organism and how you will know if your hypothesis is correct. (2) 6. Based upon your hypothesis, write a prediction for this observational experiment. Remember that the 7. In order to determine the time cells spend in each stage of mitosis, we take a snapshot in time and count how many are in each stage. The percentage of cells in each stage will tell you how long each stage is relative to the others. Using the prepared slide of the onion root, count 100 cells As you are counting, you should count cells in one field (le. Don’t skip around to find cells in a particular stagex (1) Percentage of cells in stage Number of cells in stage Stage S9 2.5 Interphase Prophase Metaphase Anaphase Telophase 100 Total 8. Based upon the data collected, what conclusion can be made regarding the longest phase of the cell life cycle? (1) esis Be sure to state your answer in terms of your hypothesis and the data collected. (1) 10. In the table (on the next page): Make drawings of Interphase AND the 4 stages of Mitosis in onion root and in White fish blastula. Draw the entire cell, not just the chromosomes. Use the prepared slides for your drawings, not a textbook figure. (2.5) a. b. Indicate important features that define the stage (even if you did not observe the differences). (2) 2-4