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:

\(a = \cfrac{v × 360^{\circ}}{t}\)

Species

No. of Types

%

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.

pie-chart

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