Name_______________________________________
Biology—Mr. Nelson
Variation in a Population
Evolution is a concept that some find hard to understand because we can’t observe it happening
in macroscopic organisms. You probably realize that in every population there is variation.
Certain types of variations can be selected for and reproduce at a higher rate. Those that aren’t
selected do not reproduce as often. This activity will show you some variation in a population.
Procedure;
1. Students are studying the variation in kidney bean length in plants that are growing
naturally in a field.
2. In year one of your study, students measured the length of 50 randomly selected kidney
beans to the nearest millimeter.
3. They recorded their data for each bean in a box in Table 1 below.
4. This data was then graphed. You have a copy of this graphed data.
Table 1. Kidney Bean Length. Year 1 of Study
Size in millimeters
Total # of bean in class
9 mm
10 mm
11 mm
12 mm
13 mm
14 mm
15 mm
16 mm
17 mm
18 mm
0
2
11
15
28
35
35
19
5
0
Analysis Questions
1. Which size had the most number of beans?
2. Which size had the least number of beans?
3. What was the average length of the beans?
4. How is the length of a kidney bean trait determined? Explain.
5. After a kidney bean fully develops in a pod, can an individual bean change its length?
Explain.
6. You do an extensive study of kidney bean germination. Suppose your study shows that
kidney beans need to get at least 5 cm deep in the soil in order to avoid drying out and
failing to germinate. Your study also indicates that larger beans (15mm and larger) on
average cannot get deep enough down into the soil compared with the smaller beans
(less than 15 mm). Your data represents kidney bean length during year 1. You go back
to this field in year 10 and measure another 50 kidney beans. Explain how a graph of
your data in year 10 would compare to the year 1 graph? Why does it look like this?
7. Using a colored pen or pencil on the graph, add a new graph line that would represent
what the graph would look like in year 10 of your study.
8. Imagine you are a kidney bean farmer. You are starting your fields from scratch and
each year you will hand plant your seeds. What if your customers only liked to eat larger
size kidney beans (they taste better). Every year, you sell most of your kidney bean crop
to your customers but you use some beans to plant for the following year’s crop. Is it a
good or bad idea to use the left over beans, that your customers don’t buy, as the stock
for the following year’s crop? Explain your answer