Limits to Cell Size

Why does a cell divide when it reaches a certain size?

To optimize the rate at which substances enter, pass and leave the cell.

What dictates this optimisation?

The surface area: volume

What substances need to enter the cell?

Oxygen, Nutrients, Water, Energy.

What substances need to leave the cell?

Carbon dioxide, Waste products, Energy lost.

What is the function of the cell membrane?

Acts as the surface area for the exchange of heat and materials, determining the rate at which materials enter or leave the cell.

What are the functions of the cytoplasm and cell interior?

Act as the volume of the cell, facilitate transport of materials and metabolic processes, determining the rate at which materials are used or produced

How does surface area affect substance transport in a cell?

More surface area allows substances like nutrients to diffuse in more rapidly, but also increases the rate at which substances are lost.

The larger the cell

The larger its volume

What happens to the rate of metabolism as the volume of the cell increases?

Metabolism becomes slower and requires more effort and energy for all actions and processes.

What doesn’t surface area and volume do?

Increase proportionally

Large volume

More effort and energy is required for all metabolic processes

Small volume

Substances are used and processed quickly

Large surface area

The cell may lose heat too rapidly and requires a high metabolism to compensate.

Small surface area

Required substances ad heat can’t pass through the cell membrane quick enough

	1cm side length	2cm side length	3cm side length	4cm side length
Surface area
Volume
SA:V ratio

	1cm side length	2cm side length	3cm side length	4cm side length
Surface area	(1x1) x 6 = 6 cm^2	(2x2) x 6 = 24 cm^2	(3x3) x 6 = 54 cm^2	(4x4) x 6 = 96 cm^2
Volume	(1x1x1) = 1 cm^3	(2x2x2) = 8 cm^3	(3x3x3) = 27 cm^3	(4x4x4) = 64 cm^2
SA:V ratio	6:1 = 6	24:8 =  3	54:27 = 2	96:64 = 1.5

What does the SA:V ratio indicate?

The relationship between the surface area and volume of a cell; it decreases as the size of a cube increases.

What does this mean in relation to cells?

The bigger a cell grows the less SA they have for material exchange

What does this mean a single cell is limited in?

It’s growth

What is a solution to a low SA:V ratio in cells?

The cell must divide or organisms become multicellular.