1. Introduction to Graphing

2. The Island of Krakatau
In 1883 the island of Krakatau experienced a violent volcanic eruption.
The island was destroyed!
All life was killed.

3. What Has Happened Since 1883?
This table shows the data that was collected over the 100 years following the eruption.
Each row shows a year and the number of species of birds that were observed on the island.
Year (x)
# Species (y)
1883
1908 13
1920 28
1950 34
1985 38

4. What Else Can We Do With the Data Table?
Scientists look for trends in data & then attempt to explain those trends.
Scientists use GRAPHS to make it easier to see trends in data.
Year (x)
# Species (y)
1883
1908 13
1920 28
1950 34
1985 38

5. I.D. Parts of a Graph Graph Title:
The title of the graph should tell the reader what data is being represented.
Always read the title of a graph BEFORE looking at any other data!

6. I.D. Parts of a Graph Y-axis:
The vertical axis along the left is called the Y-axis. Number of species is represented along this axis.
The lower value on the Y-axis is O and the highest value is 40.

7. I.D. Parts of a Graph X-axis:
The horizontal axis along the bottom is called the X-axis.
Years are represented along this axis.

8. I.D. Parts of a Graph Origin:
The point where the X and Y axis meet is called the ORIGIN.
It is the smallest value a point can have on the graph for both axes.

9. More on the X and Y Axes
The X and Y axes identify your experimental variables.
Independent Variable (I.V.)
Goes on the X-axis (horizontal)
Dependent Variable (D.V.)
Goes on the Y-axis (vertical)

10. Data Table Review Independent Variable:
The I.V. if found in the left column of your data chart.
This information is placed on the x-axis.
Year (x)
# Species (y)
1883
1908 13
1920 28
1950 34
1985 38

11. Data Table Review Dependent Variable:
The D.V. if found in the right column of your data chart.
This information is placed on the y-axis.
Year (x)
# Species (y)
1883
1908 13
1920 28
1950 34
1985 38

12. Graph this Data
We are going to graph this data in your notes together.
This graph is going to be a line plot of the data set.
Each point will represent one row of the table.
We will start with row 1.
Year (x)
# Species (y)
1883
1908 13
1920 28
1950 34
1985 38

14. Row Two of the Data Table
Year (x)
# Species (y)
1883
1908 13
1920 28
1950 34
1985 38

16. Row Three of the Data Table
Year (x)
# Species (y)
1883
1908 13
1920 28
1950 34
1985 38

18. Row Four of the Data Table
Year (x)
# Species (y)
1883
1908 13
1920 28
1950 34
1985 38

20. Row Five of the Data Table
Year (x)
# Species (y)
1883
1908 13
1920 28
1950 34
1985 38

22. Double-Check Your Work!

23. Which statement below BEST summarizes the trend shown by the graph?
Why Connect the Dots?
The connecting lines allow you to visualize the trends in the data.
A. Land birds have been unsuccessful at colonizing the Krakatau islands since the 1883 eruption.
B. Colonization by land birds has steadily increased the number of species since the 1883 eruption.
C. Land birds colonized the islands immediately after the eruption, but the number of species has steadily decreased over the past century.
Which statement below BEST summarizes the trend shown by the graph?

24. Good Graphing Checklist
Does your graph have a title?
Have you placed the independent variable on the x-axis and the dependent variable on the y-axis?
Have you labeled the axes correctly and specified the units of measurement?
Is your data plotted correctly and clearly?

25. Graphing Practice Make a line graph of the data below:
Refer back to your Good Graphing Checklist.
pH of Water
Number of Tadpoles
8.0 45
7.5 65
7.0 70
6.5 80
6.0 40
5.5 20

26. Graph Title? Independent Variable? Dependent Variable?
Effect of pH on Tadpole Populations
Graph Title? 80 70 60 50 40 30 20 10
Dependent Variable?
Numbers of Tadpoles (y-axis)
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
8.5
Independent Variable?
pH of Water (x-axis)

27. Data
Analysis

28. What is the independent variable?

29. What is the dependent variable?

30. What is the optimum pH for tadpole development?

31. Between what two pH readings is there the greatest change in tadpole number?

32. How many tadpoles would you expect to find in water with a pH reading of 5.0?

33. Practice
Interpreting
Data…

34. Identify the Graph that Matches the Story…
I had just left home when I realized I had forgotten my books so I went back to pick them up.

35. Identify the Graph that Matches the Story…
I started out calmly, but sped up when I realized I was going to be late.

36. Identify the Graph that Matches the Story…
Things went fine until I had a flat tire.