How surface area to volume ratio limits cell size?
Cell is the basic structural and functional unit of life. It means that cell controls all functions including all metabolic reactions (activities). The number of reactions increases as the volume of metabolic area increases. All the materials necessary for metabolism enter the cell through cell membrane by diffusion and osmosis.
The larger the volume of the cell, larger the amount of materials that can enter into the cell. Each unit of volume requires a specific amount of surface area to supply its metabolism with raw materials. The amount of surface area available to each unit of volume varies with the size of cell. As cell grows its surface area to volume ratio decreases. At some point in its growth its surface area to volume ratio becomes so small that supply of raw materials decreases to a very large extent. At this point the cell cannot get larger. When a cell has much greater volume than surface area, then diffusion process is defficult in this case. And thus diffusion process is unsufficient for providing required amount of materials to the cell. The cell become unable to function properly and effectively in larger cells as compared to smaller cells and places a limit on cell size.