Plants & Human Affairs (BIOL106) - Stephen G. Saupe, Ph.D.; Biology Department, College of St. Benedict/St. John's University, Collegeville, MN 56321; ssaupe@csbsju.edu; http://www.employees.csbsju.edu/ssaupe |
Pod Size in Rapid Cycling Brassica rapa (RCBr)
Learning Objectives: Upon completion of this lab you should be able to:
Introduction:
The purpose of this lab is two-fold.
First, this lab will provide the opportunity for you to study the growth
of a plant throughout its entire life
cycle. To learn more about the
history and biology of RCBr visit the visit the Wisconsin
Fast Plants^{�} web site. This site provides a wealth of
information, including the on-line
version of Dr. Williams article and slides/images
of the plants. The second major
purpose of this lab is to use Fast Plants^{�} as a model experimental
organism to study the physiological mechanisms
involved in fruit growth.
Exercise 1:
Structure (Morphology) of Rapid-Cycling Brassica
rapa Pods
Recall that the pod is a fruit which is derived from the
pistil of the flower. As a result, in many flowers we can still observed
the remnants of the pistil parts. The purpose of this exercise is to
familiarize you with the
structure of RCBr pods and to relate the pod structure to that of the pistil.
Method:
Table 1: Size and seed number of wild type RCBr pods |
||||
Pod length (mm) | Seed Number | Pod Length (mm) | Seed Number | |
Exercise 2. RCBr Pod Size
Analysis
If
you scan Table 1 it should be obvious that some pods are long while others are
short. Or in other words, pod length exhibits considerable variation.
After collecting such data, a scientist will
typically use descriptive statistics to help summarize and depict the central
tendencies in these data. A scientist will want to know the answers to
such questions as: How big is the average pod? What is the largest
pod? What is the smallest pod? How much variation exists in pod
size?
Method:
Complete Table 2. A spreadsheet program such as Excel can simplify these calculations.
Prepare a histogram of pod length. Label it "Figure 1 - Frequency Distribution of RCBr pods." To do so, first sort your data in size classes in Table 3. Then plot a histogram of these data.
Data & Analysis:
Table 2. RCBr Pod Statistics | |
Maximum pod length (mm) | |
minimum pod length (mm) | |
average pod length (mm) | |
standard deviation |
Table 3. Pod Frequency Distribution | |
Size Category (mm) | Number of individuals (observations) |
0 - 5 | |
5 - 10 | |
11 - 15 | |
16 - 20 | |
21 - 25 | |
26 - 30 | |
31 - 35 | |
36 - 40 | |
41- 45 | |
46 - 50 |
Exercise 3: What determines pod size
in RCBr?
Why are some pods longer than others?
Hypotheses: Make a list of several potential hypotheses to explain pod length variation in RCBr.
H_{0}
H_{1}
H_{2}
H_{3}
H_{etc.}
Experiment:
Consider the hypothesis - "Pod size is related to seed
number. Longer pods have more seeds." We can test this hypothesis
with the data we previously collected (Table 1). We will analyze these
data graphical. Make a graph plotting both variables. Label this
graph Figure 2 and give it a proper caption.
To determine the
relationship between the two variables we can draw the best fit line
(regression) and do a statistical test called a correlation. In class I
will show you how to use Excel to perform these tests. Record the
correlation coefficient (r^{2}).
Last updated: 07/30/2005 / � Copyright by SG Saupe