1. Patterns in Nature Topic 8: Surface Area
Part of the Patterns in Nature Module
Biology in Focus, Preliminary Course

2. DOT Point
Explain how the surface area to volume ratio affects the rate of movement of substances into and out of cells.
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3. What is surface area?
The surface area of an object is that part of the object exposed to its surroundings. If the object is a cube (eg die):
The area of one side is calculated as the length multiplied by the width (l x w), and is measured in cm.
For example, in a cube that is 2cm in width and 2cm in height, each side will have an area of 2cm x 2cm
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4. What is surface area?
The surface area of the whole cube is calculated by taking into account that there are six sides to a cube (think of a die): 6 x (l x w) In a 2cm cube it would be: 6 x (2x2)cm² = 24cm²
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5. What is volume?
The volume of an object is the amount of space that it occupies. To calculate the volume of a cube, the length, width and height must all be multiplied together: l x w x h (measured in cm³) In a 2cm cube, this would be: 2cm x 2cm x 2cm = 8cm³
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6. What is surface area to volume ratio?
Example: 2cm cube Surface area: 6x (2x2)cm² = 24cm² Volume: 2cm x 2cm x 2cm = 8cm³ Surface area:volume 𝑆𝐴 𝑉 24𝑐𝑚² 8𝑐𝑚³ = 3 1 Therefore the ratio would be 3:1
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7. Why do biologists care?
Substances that enter cells must travel from the outside environment across the surface of the cell and then diffuse inwards until they reach the centre of the cell. If a cell has a large volume, the organelles in the centre are farther from the outside. If a cell is flatter and smaller the organelles in the centre are closer to the outer surface.
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8. Why do biologists care?
If a cell has a larger surface to volume ratio, this increases the efficiency of substances diffusing into or out of the cell. Flatter objects have a greater surface area to volume ratio.
biologyjunction.com

9. Activity Students to complete:
-Chapter 2 Membranes, chemicals and movement in and out of cells (found on teacher resource CD)