ONION ROOT TIP ASSIGNMENT
INSTRUCTION SHEET
http://www.biology.arizona.edu/
1.
On the screen entitled “Problem sets and Tutorials scroll down to the link
(underlined) entitled “Online Onion Root Tips: Phases of the Cell Cycle”
Point and click.
2.
You will now view a screen entitled: Online Onion Root Tips. Read the passages and
answer the questions under INTRODUCTION on your lab sheet.
3.
When you have completed the questions, click on NEXT.
4.
Scroll down to the bottom of the page and click on NEXT.
5.
Read the Assignment. Then write a PURPOSE for the lab on your lab sheet.
6.
In the space provided on your lab sheet, draw a table like the one found on this
screen. Use a ruler and give the table a title.
7.
Click on NEXT.
8.
On this screen, you must use your knowledge to determine at what stage each cell is
at. You can use your notes and page 18 in you textbook to help you.
9.
To identify the particular stage the cell is at, click on the name of the stage:
INTERPHASE, PROPHASE, METAPHASE, ANAPHASE, TELOPHASE.
If you chose the correct stage, the cell will appear in the table, below the proper
stage.
10.
If you chose the incorrect stage, you will be given an explanation on why you were
wrong. Choosing the correct stage can be difficult and you will probably make some
mistakes. In science, mistakes are great learning experiences.
*** For two of your mistakes, write down on your lab sheet in the Observations
section:
• the stage you chose
• the explanation why it was incorrect
• what the stage should have been
11.
Continue until you have identified each cell (total of 36 cells).
12.
All the cells you identified are shown in the table. Count the number of cells in each
phase and record this number in your table.
13.
Calculate the percentage (%) of cells in each phase and include this in your table.
Include your calculations under the section Calculations. For example, the
percentage of cells in prophase is:
% cells in prophase =
14.
number of cells in prophase
× 100%
total number of cells
Using this data you will construct a cell cycle clock. Assume that it takes a cell 12
hours to complete a full cycle through interphase and into mitosis before it divides
into two daughter cells. Calculate the number of hours spent in each phase by
multiplying the percentage (%) of cells in each phase by 12 h.
For example if 20% of the cells are in prophase then the time spent in prophase is:
Time spent in prophase = 12h × 20%
= 12h × 0.20
= 2.4h
15.
Show all your calculations and use the numbers you get to make a clock under the
section Analysis. Be sure to identify the sections of the clock that correspond to the
appropriate stage.
16.
Answer the questions in the section Questions and complete the lab report.
17.
When you have completed this task, take a look at an animation of the different
stages of the cell cycle. Click on CELL BIOLOGY.
18.
Click on the link The Cell Cycle and Mitosis
19.
Click on Mitosis.
20.
Scroll to the bottom of the page and click on Mitosis Animation. You can look at the
different stages one frame at a time. What do you notice about the names of the
different stages? Are they the same as the ones you have? If not, why might they be
different?
ONION ROOT TIP ASSIGNMENT
Date: ______________
Name: __________________
Purpose
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Introduction
(a) Why are the root cells of a plant good for studying the different stages of mitosis?
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(b) Describe what was done to the onion root so you could view them on the computer
screen:
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(c) In the picture of the onion root tip, do all the cells appear the same? Why or why not?
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(d) Take a look at the animation. Can you see the different stages? Indicate the stage at
which the following events occur:
_____________ the chromosomes line up in the middle of the cell
_____________ the DNA changes from loosely packed chromatin to tightly packed
chromosomes.
_____________ the cell membrane pinches inwards to make two cells.
_____________ the chromosomes break apart into chromatids, and then the
chromatids move apart.
_____________ the cell does its regular work and also makes a copy of its DNA.
Observations
Table 1. ___________________
Errors
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Calculations
Analysis
The Cell Cycle Clock
Questions
1.
If a cell has 10 chromosomes before it divides, how many will each cell have after
cell division occurs? _____________
2.
Why should each cell have this number?
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3.
Why might someone be interested in the cell division rate of a plant?
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4.
If you did a similar experiment but looked at nerve and skin cells. Observing that
99.9% of the brain cells were in interphase but only 90% of the skin cells were. Can
you explain why based on how often these two types of cells divide?
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5.
Why are onion root tip cells good to use for an assignment such as this?
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