Name: ______________________________
The Effect of Natural Plant Toxin “Lectin” on the Cell Division in Root Tips
Scientists reported that a fungal pathogen, may negatively affect the growth of
soybeans (Glycine max). Soybean growth decreased during three years of high rainfall,
and the soybean roots were poorly developed. A fungus, R. anaerobis, is thought to be
a plant pathogen and was found in the soil growing around the roots of the soybeans.
A lectin-like protein was found in the soil around the soybean roots. This protein may
have been secreted by the fungus. Lectins induce mitosis in some root apical
meristem tissues. In many instances, rapid cell divisions weaken plant tissues.
You have been asked to investigate whether the fungal toxin lectin affects the number
of cells undergoing mitosis in a different plant, onions. You examine photographs of
root tip meristems (zone of division). One set of photographs is from roots that were
treated with lectin. The other set is from roots not treated (control group).
The "expected group" is the "control" group - no lectin
The "observed group" is the "experimental " group with lectin.
Count 50 cells from each group following a search pattern. In the data table below,
record the number of cells in interphase and the number in mitosis. (You do not need
to identify the different phases of mitosis.)
Calculation of chi-square
# observed (o)
# expected (e)
(o-e)
(o-e)2
(o-e)2/e
(with lectin)
(without lectin)
Interphase cells
Mitosis cells
Total cells
(must be the same
for both)
X2 = sum (o-e)2/e =
Calculating Chi-square:
 Use the control group (no lectin) for the expected values.
 Use the lectin -treated group for the observed values.
 Calculate the X2 for your data.
 Calculate the degrees of freedom. The degrees of freedom (df) equals the number of groups minus one. In this
case, there are two groups, interphase and mitosis; therefore, df = 2-1 = 1
 Find the chi-square critical (table) value for your degrees of freedom and row 0.05 from the table below.
Chi Square Table


The p value is 0.05 meaning that we are 95% confident that our data fits in this group.
The “critical value” is 3.84.


If the calculated chi-square value is greater than or equal to this critical value, then the two groups (lectin and
no lectin) are significantly different, and the null hypothesis is rejected.
If the calculated chi-square value is less than this critical value, then the two groups (lectin and no lectin) are
not significantly different, and the null hypothesis is not rejected.
Is the calculated chi-square greater or less than the table value? _____________________

Are the two groups significantly different or not significantly different? ____________________

1. Write the null hypothesis for this part of the investigation.
2. What does it mean if the null hypothesis is rejected in terms of this part of the investigation?
3. Write a short results section saying if the two groups significantly different or not, and which group had
more mitotic figures. (Be sure to specify calculated chi square value & p value. Based on values, is there
a significant difference between 2 groups? If yes, which one had more mitotic figures? Is null rejected or not rejected.)
4. Write a short conclusions section explaining what conclusions that can be made from this experiment.