Biology » Introduction to Biology » Presenting Data

Pie Charts in Biology

Drawing Pie Charts in Biology

• You want to give a visual representation of percentages as a relative proportion of the total of a circle.
• They are a type of graph even though they do not have any axes.
• A pie chart is a circle divided into sectors (think of them as the slices of a cake).
• 100% represents the whole complete circle, 50% represents a half circle, 25% is a quarter circle, and so on.

Example:

• Count the number of each species and record it in a table.
• Work out the total number of species in the ecosystem.
• Calculate the percentage of each species.
• Use the following formula to work out the angle of each slice:

$$a = \cfrac{v × 360^{\circ}}{t}$$

Slice Angle

Insects17$$\cfrac{17 × 100}{50} = 34\%$$$$\cfrac{34 × 360}{100} = 122.4^\circ$$
Plants16$$\cfrac{16 × 100}{50} = 32\%$$$$\cfrac{32 × 360}{100} = 115.2^\circ$$
Birds9$$\cfrac{9 × 100}{50} = 18\%$$$$\cfrac{18 × 360}{100} = 65.0^\circ$$
Amphibians8$$\cfrac{8 × 100}{50} = 16\%$$$$\cfrac{16 × 360}{100} = 57.6^\circ$$
• Use a compass to draw the circle and a protractor to measure accurate angles for each slice.
• Start with the largest angle/percentage starting at 12 o’ clock and measure in a clockwise direction.
• Shade each slice and write the percentage on the slice and provide a key.