Investigation 7 Part 2: Effects of Environment on Mitosis

Investigation 7 Part 2: Effects of Environment on Mitosis
Introduction:
We are now studying cell division and mitosis. After studying the different phases of a cell – mitosis and interphase, we are doing this lab to practice our identification of cells in mitosis or interphase. We are also testing to see whether a cell affected by the environment in various ways, has a different number of cells undergoing mitosis. To do this, we are treating an onion root tip to see whether it will change the cells.
We are also doing this to practice our chi-square calculations which will determine the degrees of freedom (df). This equals the number of treatment groups minus one, multiplied by the number of phase groups minus one. In this experiment since there are only two treatment groups (control and treated) and two phase groups (interphase and mitosis) the degrees of freedom is 1. (2 – 1) x (2 – 1) = 1.
I believe that the treated cells will have a higher number of cells undergoing mitosis because since they are being affected by the environment, they will need to replicate faster and more cells will be in mitosis rather than interphase.

Materials:
  1. Microscope with high magnification capabilities
  2. 6 prepared slides of onion root tip squashes (3 control and 3 treated)
  3. Camera / Phone
  4. Calculator

Procedures:
  1. Prepare chromosome squashes of onion root tips
  2. Place the slides of onion root tip from the control group underneath the microscope
  3. Focus the microscope and take pictures of each of the controlled onion root tips
  4. Repeat steps 2 and 3 except with the treated onion root tips
  5. Clean up work station
  6. Using the pictures, count the number of cells in interphase and mitosis from all 6 onion root tips
  7. Create a table of observed values and a table of expected values using the results from the pictures
  8. Calculate the Chi-Square values using the observed and expected values for the experiment

Picture:

Tables:
Table of Observed Values (o):
Interphase
Mitosis
Total
Control
264.5
12.9
277.4
Treated
256.7
13.5
270.2
Total
521.2
26.4
547.6

Table of Expected Values (e):
Interphase
Mitosis
Control
264
13.4
Treated
257.2
13

Calculation of Chi-Square Values:
Group
Observed (o)
Expected (e)
(o-e)
(o-e) ^2
(o-e) ^2/e
Control Interphase
264.5
264
0.5
0.25
0.000946
Control Mitosis
12.9
13.4
-0.5
0.25
0.018656
Treated Interphase
256.7
257.2
-0.5
0.25
0.000972
Treated Mitosis
13.5
13
0.5
0.25
0.01923
Total of (o-e) ^2/e = chi-square = 0.0398

Conclusion:
At the end of this experiment we saw that there was a very minor difference between the treated and controlled cells. This is because we were tricked by Mr. Wong who never treated the onion root tips with the substance described in the lab book. Although we were not able to prove our hypothesis we were still able to see the cells within the onion root tip. We counted the number of cells in interphase and mitosis which was exhausting because we had to count hundreds of cells since we could not magnify any further.
We were also able to conclude that our chi-square value was 0.0398 or 0.04 which means that the probability would be around 85-90%. This means that the null hypothesis is rejected and we believe in the alternative hypothesis – that a statistically significant difference does exists between the number of cells in mitosis or interphase within the parameters of controlled and treated onion root tips.

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