Surface Area of Leaves and Cells

Year Nine
A description how a leaf and a cell are adapted to ensure that they have a large surface area in relation to their volume and explanation of why they need a large surface area, using diagrams to help.


In order to function efficiently, both a leaf and a cell require a large surface area in relation to their internal volume.


Why cells need surface area


In order for a cell to take in water and nutrients, the substances must defuse through the cell’s membranes. In order to take in a sufficient amount of nutrients, the cell membrane must be made as large as possible. In particular: the surface area must be large enough for the cell’s internal volume. A cell with a large surface area and a small internal volume will be able to take in nutrients more efficiently than one with a small surface area and a large internal volume (1).


How cells ensure a large surface area


A common way in which cells increase their surface area is division: when a cell splits itself in half, the cell’s internal volume remains the same, but the surface area is doubled. The cell can therefore take in nutrients twice as efficiently as before (2).


The surface area of a cell can also be increased by changing the cell’s shape. Having a smooth, spheroid outer layer does not allow for a particularly large surface area. However, if the membrane contains small infoldings, or small bumps/spikes, the surface area is considerably increased (3).


Why leaves need surface area


Whereas cells derive energy through diffusion of nutrients, leaves are fed by beams of sunlight. The more light a leaf absorbs, the more it can photosynthesise and therefore the more food is produced for the plant to which the leaf is attached. A larger plant will thus need larger leaves in order to maintain a sufficient supply of food (4).


How leaves ensure a large surface area


The surface area of a leaf is helped by its shape. Leaves are normally wide, flat and long. This increases the amount of material exposed to direct sunlight, while minimalising the leaf’s internal volume (5). Like cells, leaves are often quite rough, because having multiple points which are concave or convex again increases the area. The final method to increase the input of light from leaves is to simply have more of them (6). This is especially useful for plants which grow in confined spaces, and thus lack sufficient room for large leaves, or whose stems are not strong enough to support them.


Originally written October 2011 by Robin Taylor. Scored at A