AP Biology · Exam guide
AP Biology Graphing Question Explained: How to Construct a Graph and Interpret the Data
The second long question on the AP Biology exam is worth 9 points, and it adds a graph to the task of the first long question: you are given data and asked to draw the graph yourself. Careful graphing earns reliable points, because each feature is checked separately. The data below are made up for practice.
What the graph is scored on
| Feature | What graders check |
|---|---|
| Axes | The independent variable on the x-axis and the dependent variable on the y-axis, each labeled with the variable and its units. |
| Scale | Even intervals that use most of the grid, starting from a sensible value. |
| Plotting | Every point or bar drawn at the correct value. |
| Type | A line for data that change continuously, such as time or temperature, and bars for separate categories. |
| Error bars | Bars of plus and minus two standard errors, when the question gives you the error values. |
A made-up data set
| Light color | Mean height after 14 days (cm) | Two standard errors (cm) |
|---|---|---|
| Red | 13.0 | 1.4 |
| Blue | 8.0 | 1.4 |
How to draw it, step by step
- Light color is a category, so use a bar graph with one bar for red and one for blue.
- Put "Light color" under the x-axis, and "Mean seedling height after 14 days (cm)" along the y-axis.
- Choose a scale of 0 to 16 cm in steps of 2, so the tallest bar and its error bar fit comfortably.
- Draw the red bar to 13.0 and the blue bar to 8.0.
- Add an error bar on each bar: red from 11.6 to 14.4, and blue from 6.6 to 9.4.
When to use a line instead
If the question gave seedling height measured at 2, 4, 6 and 8 days, time would be the independent variable, and you would draw a line graph with time on the x-axis. Connect the points only if the variable changes continuously.
Answering the questions after the graph
It repeats what the graph shows and does not connect it to the question.
It uses the means and the error bars to draw a conclusion.
Common mistakes
- Putting the dependent variable on the x-axis.
- Leaving off units, or forgetting to label an axis.
- Choosing a scale that squeezes all the data into a small corner of the grid.
- Connecting bars or categories with a line.
- Forgetting the error bars, or drawing them at the wrong size.
Frequently asked questions
How many points is the graphing question worth?
Nine points. It is the second of the two long questions.
Do I need a ruler?
A straightedge helps keep the axes neat, and the grid on the page is there to be used.
What if I do not know whether to draw bars or a line?
Ask whether the values on the x-axis are separate groups (bars) or points along a continuous scale (a line).
Do I have to start the y-axis at zero?
Not always, but starting at zero is the safest choice for bars, because the bar's height should match its value.
Where can I find the official scoring rules?
Exam formats change a little from year to year, so check the current course and exam description on the College Board site before test day.
Keep practicing
Every unit in the AP Biology course ends with a quiz of 15 multiple-choice questions and 5 short free-response questions, with a writing space that scores against the four-point rubric and a model 4 out of 4 response to compare against. These free lessons also build the skills the free-response section tests:
See the AP Biology course Free lessons and lesson list
Other free-response guides:
- AP Biology FRQ Guide: The Six Free-Response Questions and the 4-Point Rubric
- AP Biology Long Free-Response Question Explained: Interpreting and Evaluating Experimental Results
- AP Biology Short Free-Response Questions Explained: The Four Types and the 4-Point Rubric
AP is a registered trademark of the College Board, which is not affiliated with and does not endorse this site. This guide is our own explanation of the question types and scoring. For the official scoring guidelines, see the College Board.