Download The rate of cell division in onion roots

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?