Investigation 7: Mitosis Lab #Money #LilWayne #WongIsALegend

Devansh Taori

Biology AP, Per. 2

Mr. Rodney Wong

Introduction

One of the major keys to life is replicating and passing on genetic material to the next generation. In eukaryotes, the process is extremely complex and involves three phases: interphase, mitosis, and cytokinesis. Interphase has the first growth stage (G1), synthesis (S, where the chromosomes are replicated), followed by the second growth stage (G2). In mitosis, the duplicated chromosomes separate into two nuclei. Finally, in cytokinesis, the cytoplasm divides and two daughter cells are formed.

Cell division involves many different proteins – in particular, CDKs (cyclin-dependent kinases). These CDKs turn off and on various processes in cell division, thus facilitating the overall cycle. The way CDKs do this is by partnering with proteins called cyclins (how aptly named!). One such complex is mitosis-promoting factor, and it contains cyclin A or B and cyclin-dependent kinase. CDK is activated when it is bound to cyclin, allowing the cell to proceed from G2 into mitosis. CDKs prevent cells from progressing through its cycle naturally. There are 3 checkpoints that a cell must pass through: the G1 checkpoint, G2 checkpoint, and the M-spindle checkpoint. These checkpoints all ensure that there is no damage to the DNA, that external growth factors exist, and that the mitotic spindles are properly attached to their kinetochores. In this way, these checkpoints prevent mutations that could derail the process.

Objective

The backstory for this experiment is that scientists reported that a fungal pathogen may negatively affect the growth of soybeans. Close relatives of the fungal pathogen are plant pathogens that grow in the soil. A protein (lectin) was found in the soil around the soybean roots , and it induces mitosis in some special tissues. This rapid cell divisions tends to weaken plant tissues. The objective of this experiment is to determine whether the fungal pathogen protein affects the number of cells undergoing mitosis in a different plant. This experiment models this using a root tip.

Materials

- untreated and lectin-exposed roots

- a magnification scope

Procedure

1. Observe the cells at high magnification (400–500 X). 

2. Look for well-stained, distinct cells. 

3. Within the field of view, count the cells in each phase. Repeat the counts in two other root tips. 

4. Collect the class data for each group, and calculate the mean and standard deviation for each group. Make a table in your notebook for the class data. 

5. Compare the number of cells from each group in interphase and in mitosis.

Hypothesis

I hypothesize that because the lectin-like protein induces mitosis in special tissues, the cells of the lectin-exposed roots will have a significantly higher chance of being in the process of mitosis, compared to cell of the untreated roots.

Data

Control Root Tip 1 –

Control Root Tip 2 –

Control Root Tip 3 –

Lectin-exposed Root Tip 1 –

Lectin-exposed Root Tip 2 –

Lectin-exposed Root Tip 3 –

Graphs –

Table of observed values –

Table of expected values –

Calculation of chi-square values –

Critical values of chi-square distribution –

The degree of freedom for this experiment is one, because it equals the number of treatment groups minus one multiplied by the number of phase groups minus one. In this case, there are two treatment groups and two control groups, therefore df = (2-1)(2-1) = 1.

Our total calculated for the chi-square is 5.23186, and thus, the null hypothesis is rejected, since it is greater than the critical value of 3.84. There is a statistically significant error.

Conclusion
Ultimately, my hypothesis was proven true, because the cells exposed to lectin had higher rates of mitosis compared to the control cells. Specifically, the number of cells exposed to lectin and undergoing mitosis was 62, whereas the number of control cells undergoing mitosis was 41. That increase of 21 shows that my hypothesis was true. 

After conducting chi-square evaluations though, I realized that there was a statistically significant error that had occurred, due to human error. My calculations demonstrated that the observed was significantly different from the expected, and thus, there is a big chance that my data wasn't 100% accurate. The probability of error was too large.

Ultimately, however, I learned at the end that the Wongster trolled our class – he, in fact, did not expose one group of cells to lectin. He simply labeled them as so. This raises the question then – why did my data show that lectin-exposed cells had higher rates of mitosis? This is because of perception bias – I must have counted the cells in such a way to confirm my hypothesis that the supposed "treated" cells had higher rates of mitosis. I unconsciously skewed my data in such a way to fit what I thought would be correct.

If I were to conduct this experiment again, I would – this time – actually expose a few root tips to lectin to see if there's any effect on mitosis.

I would like to thank Mr. Wong for letting us conduct this experiment. It was tons of fun!

Thank you, based Wong. 

#ILoveWong #MarryMe #GonnaMissYouOverBreak