Name___________________________ Date __________ Period____ Group____ Investigation 9.1: Variation in Size of Organisms (attach graph to the back) Purpose: _______________________________________________________________ ______________________________________________________________________ Procedure Part A – Line Graph: 1. Choose an object and measure its length in millimeters. How “typical” do you think this object is in terms of its length? Guess how many millimeters larger the longest object will be. Then guess how much smaller the smallest object will be. Record the object’s length and your two guesses in your data table. Partner 1 Partner 2 Guess Guess Actual (mm) (mm) (mm) Typical Object Smallest Object 2. Choose three team members to measure the Largest Object objects. The fourth member will record the data. Using a metric ruler, measure the length of the other 49 objects to the nearest millimeter. Record the measurements in your data table. Line Graph Data All Objects (record in order by whole mm) 3. Next, group the data into increments of 5 or 10 mm (eg. 0-10 mm, 11-20 mm, etc) and place tally marks on the data table below. This is called a frequency distribution. Frequency Distribution Data (Part B) All Objects (size by whole mm increments) mm mm mm mm mm mm mm mm mm mm mm Tally each object in the Appropriate column Totals Procedure Part B – Histogram 4. On graph paper, label the x axis Length of _______. The size of your largest object will determine the length of this axis (should start at 0). Divide the axis and label it with a convenient interval that fits your paper (10 mm, 20 mm, etc). 5. Label the y axis Number of _________. Divide the axis and label it with a convenient interval that fits your paper (0, 1, 2, 3, etc.) 6. Use the data from the frequency distribution table above to create a histogram. A histogram is simply a bar graph with the intervals on the horizontal axis and the frequency (number of individuals at each interval) on the vertical axis. 7. Draw a line of best fit through the bars of your histogram, like this: Discussion Questions: 1. Is there variation within your population? 2. How close were your guesses about the largest and smallest objects? a. Do you think that using a small sample of 50 is a good way to predict the characteristics of a large population? Explain. 3. Calculate the mean of your data. The mean is the sum of all measurements divided by the number of individuals you measured. 4. Find the median, which is the value for the middle sample, when the values (lengths) are arranged in order. 5. What is the mode, or high point, on the histogram? The mode is the value that occurs the most often and would be the highest bar on your histogram. 6. Look at the data and your histogram. What is the difference in length between the longest and shortest objects in your sample? 7. Given the overall size of the objects, do you think this difference is important? a. What might be the advantage or disadvantage of being smaller or larger than average? 8. Would you have noticed the differences if you had not measured the objects? 9. Do you think there would be any size difference if the objects were of different ages or from different places? 10. When do you think a histogram is better, or more accurate, way to present data than a line graph?