Trait Frequency Curves

Problem: What kind of frequency curve does the size of leaves occur on?

Research: All organisms on Earth have outstanding structural, behavioral, and physiological adaptations that have allowed them to be "fittest" and survive the struggle for existence. Their genes have been successfully passed on. Regardless of the traits that are observed, they tend to follow a common frequency curve. The shape of that curve will be experimentally determined in this lab.


Materials: cm ruler, lab partner, campus tree, and a pencil.


1) Please cooperate with the people at your table so that there are 4 people per group. Each individual takes their own data, but the the 100 measurements from the group will be analyzed.
2) As a group, choose an individual tree where the leaves are low enough to measure easily.
3) Each member of the group should measure the length of the blade for 25 leaves (do not remove leaves from tree). Please measure mature leaves and not the tiny ones at the end of the branches. Measure from where the blade starts on the petiole (stem) to the tip of the leaf to the nearst .1 cm. Try not to measure the same leaf twice.
4) Record each measurement in the data table.
5) Go to data analysis and follow the instructions given.

Data Table:

Leaves 1-5 Leaves 6-10 Leaves 11-15 Leaves 16-20 Leaves 21-25








Data Analysis:

1) Use the 4 people at your table so you have 100 leaves measured.
2) What is the shortest leaf size?_____ Round this down to the nearest whole number. A______
3) What is the longest leaf size? _____ Round this up to the nearest whole number. B_____
4) Subtract the shortest from the longest to get the difference (B - A)?_____
5) To determine your 7 equal ranges, divide the difference by 7 (round to the nearest .1 cm). C_____
7) Place the 7 equal ranges in the "Group Frequency Table for 100 Leaf Sizes"
8) Please enter the frequency of the ranges for your 100 leaf sizes (count the number of leaves in each range).

Group Frequency Table for 100 Leaf Sizes
range from short
to long -->
range 1
A to (A+C)
range 2 range 3 range 4 range 5 range 6 range 7
(B-C) to B
range cm              
Trait Frequency Histogram
Leaf Size Ranges (cm)

1) What shape does your histogram of leaves look like? Explain.


2) What other traits of leaves might be plotted on a histogram (give at least 2)?

3) What traits in a human population might be plotted on a histogram (give at least 2)?

4) Why must there be variation in traits for evolution to occur in a population?