Why do smaller cells grow more effectively than larger cells?
In order for a cell to be able to grow, nutrients are required from the environment to provide raw materials for this life process. Cells rely on the cell membrane to transport materials into the cell and once inside, these materials normally are distributed by diffusion--a slow process where molecules spread from high to low concentrations and cyclosis--the normal streaming of the cytoplasm.
The ratio of the cell's surface area to its volume is important to note in order for the cell to sustain life. For example, in a smaller cell, its surface area which is its cell membrane, is in contact with the environment and in relation to its volume inside, is large enough to transport necessary substances inside and allow them to be distributed in a timely manner for the cell to be able to grow and remain alive. However, if a cell gets too large, the cell membrane's surface area would not be to supply enough necessary materials in a short enough time, to its increasing volume.
The surface to volume ratio becomes a limiting factor which restricts how large a cell can actually grow. Adaptations to increase surface to volume ratio are cells that have projections increasing the surface area in contact with the surrounding environment, or cells with numerous folds to increase the surface area.