Biology Foundations and Lab Skills Teaching Resources · High school biology; AP extensions where noted.
A useful graph makes the measured variables, units, and comparison clear. Choose the graph from the question and type of data, rather than making every biology dataset a line graph.
Learning goals and materials
Students will select an appropriate graph, label axes, plot values accurately, and write an evidence-based interpretation. Prerequisites: variables, units, and numerical scales. Materials: graph paper and pencil, or accessible spreadsheet software. The data below are simulated for teaching.
Choose a graph
- Line graph: useful for changes through ordered time points; connected segments suggest change between successive measurements.
- Bar chart: compare distinct categories. Keep gaps between categories and normally start the value axis at zero so bar lengths are meaningful.
- Scatterplot: examine paired numerical measurements, such as leaf length and width. Usually do not connect each point to the next; the order of independent cases is arbitrary.
In a simple experiment, the deliberately varied factor commonly goes on the horizontal axis. In an observational study, a horizontal-axis variable is not necessarily a manipulated cause. A key identifies multiple series; a caption explains the data and context. They serve different purposes.
Practice 1: change over time
| Time (days) | Seedling height (cm) |
|---|---|
| 0 | 0 |
| 2 | 4 |
| 4 | 7 |
| 6 | 9 |
| 8 | 10 |
Plot time against height, label units, and state which two-day interval shows the greatest increase. Treat this as a constructed record of one seedling, not evidence from replicated treatment groups.
Practice 2: compare categories
| Condition | Germinated seeds | Seeds observed |
|---|---|---|
| A | 8 | 20 |
| B | 14 | 20 |
| C | 11 | 20 |
Make a bar chart of germination percentage for each condition. Explain what the categories do and do not tell you: these labels give no details about treatment, replication, or assignment, so do not infer a specific biological cause.
Practice 3: paired measurements
| Leaf length (cm) | Leaf width (cm) |
|---|---|
| 3 | 1.5 |
| 4 | 2.0 |
| 5 | 2.1 |
| 6 | 3.0 |
| 7 | 3.2 |
| 8 | 4.0 |
Create a scatterplot and describe the relationship. Do not claim that changing length causes width to change.
Feedback and checks
- Practice 1: the largest increase is 4 cm from day 0 to day 2; the mean increase over that interval is 2 cm per day.
- Practice 2: A = 40%, B = 70%, and C = 55%. B exceeds A by 30 percentage points. That is not the same as a 30% relative increase.
- Practice 3: a positive association appears, with some variation in the increments. The points alone do not establish causation.
Check titles, axis labels, units, evenly spaced scale intervals, plotting, and claims supported by data. A nonzero origin on a scatterplot can be useful if clearly labeled; a rule that every graph must begin at zero is too broad. For AP extension, compare raw observations with summaries and explain any uncertainty bars used.
Legacy worksheet note
The previous Word download includes a medical diagnosis exercise with problematic units and claims. The revised practice above replaces that activity. Use these original nonmedical data for graphing; they are not an answer key to the legacy file.