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The rate of cell division in onion roots New cells are “born” or produced by cell division – this happens when a cell divides in two. Each new cell is called a “daughter cell”. Each daughter cell has to have a copy of the DNA from the mother cell, so preparing to divide means the mother cell has to copy its DNA. Cells divide for various reasons: 1. growth of organism 2. healing or repair of tissues 3. to increase the efficiency of cells grown too large 4. reproduction in single-celled living things The onion root tip is a zone of active cell division, also known as a meristem. In plant meristems, cells divide and then elongate to make the roots grow. Get to know the different stages in a cell’s life cycle. What are the major events in each stage? Stage of Cell Cycle Interphase Prophase Major events Sketch or image of cell Metaphase Anaphase Telophase Identify cells in each of the stages of mitosis in the figure below. Questions to investigate: Use a microscope and prepared slide of onion root tip to find and compare the number of cells in each stage of the cell cycle in different regions of an onion root including the tip and a couple of places behind the root tip. find how the proportion of cells dividing changes as you go toward the root tip. find in what stage of the cell cycle cells spend most of their time. Procedure: 1. Examine a slide of an onion root tip. Locate the root cap and root tip – these are the newest or youngest cells. The area behind it is where newly divided cells are getting longer. It is called the zone of elongation. 2. Focus on an area of the root where there are lots of cells visible. Switch to medium or high power. Identify cells in each stage of the cell cycle. Check with your teacher or another student. 3. Under medium or high power, count the total number of cells and the number of cells in each stage of the cell cycle at the root tip. Results: Table 1. The number of cells in each stage of the cell cycle in the root Number of cells by stage Total cells in view Interphase Prophase Metaphase Anaphase Telophase 100% Discussion: 1. What does the cell do during interphase in order to prepare to divide? 2. Why do cells divide? 3. How does the cell prepare for division? 4. Determine the stage that cells spend the most time in. How can you tell? 5. Which area of the root had the highest percentage of dividing cells (or the most intense cell division)? How do you know?