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sunflower Scientists

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					Scientists cannot possibly count every organism in a population. One way to estimate the
size of a population is to collect data by taking random samples. In this activity you will look
at how data obtained by random sampling compares with data obtained by an actual count.
Sampling is used to track population growth in an ecosystem. It is one of many methods used
by scientists to collect data when studying ecosystems.

Procedure
1. Cut a sheet of paper into 20 slips each approximately 4 cm x 4 cm.
2. Number 10 of the slips from 1 to 10, respectively. Put the numbered slips in a small container.
3. Label the remaining 10 slips from A through J and put them in a second container.

4. The grid shown here represents a meadow
measuring 10 m on each side. Each grid




                                                                                                        # of sunflower
segment is 1 m x 1 m. Each black circle




                                                                                                        coordinates
represents one sunflower plant.




                                                                                                        plants
5. Randomly remove one slip from each




                                                                                                        grid
container. On the table to the right of the
grid write down the number-letter combination                                                      1
you drew and find the grid segment that
matches that combination. Count the number                                                         2
of sunflower plants in that grid segment.                                                          3
Record this number on the table beside the
grid.   Return each slip to the appropriate container.                                             4

                                                                                                   5
6. Repeat step 6 until you have data for 10 different grid segments. These 10 segments
represent a sample. Gathering data from a randomly selected sample of a larger area or             6
group is called sampling.
                                                                                                   7

7. Find the total number of sunflower plants for the 10-segment sample. This is an                 8
estimate, based on sampling, of the number of plants in the meadow. Divide this number
by 10 to determine the average number of sunflower plants per square meter in the                  9
sample. Record this number in the table below. Multiply the average number of sunflower            10
plants per square meter by 100 to find the total number of plants in the meadow. Record
this number in the table below.

  Method        Average # of plants per grid segment                     Total # of plants
  Sample
Actual Count


8. Count all the sunflower plants actually shown in the meadow. Record this number in the
above table. Divide this figure by 100 to calculate the average number of sunflower plants
per square meter. Record your data.
1.   Compare the actual count with the data you recorded for your random sampling estimate.




2. Why was the paper-slip method used to select grid segments?




3. What is the percentage error in your estimate? To calculate percentage error find the
   difference between the actual count and the estimated count. Divide this difference by
   the actual count and multiply by 100.




4. How could you change the procedure in this activity to reduce your percentage error?

				
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