The answer to this question is phase. These three properties, amplitude, frequency and phase are basic properties of waves. Frequency refers to the number of cycles per second, amplitude refers to the strength, and phase is the position of the wave on the time axis.
-Surface area to volume ratio. (surface area / volume)
-Nucleo-cytoplasmic ratio.
-Fragility of cell membrane.
-Mechanical structures necessary to hold the cell together (and the contents of the cell in place)
Facilitated diffusion is the diffusion of solutes through transport proteins in the plasma membrane. Facilitated diffusion is a type of passive transport. Even though facilitated diffusion involves transport proteins, it is still passive transport because the solute is moving down the concentration gradient.
Provided that there's no diagram, most molecules have particular areas on the molecules, called the "active area" that act as a lock to a particular substrate's molecular structure, providing the key.
An enzyme's active area is only able to be "unlocked" by a certain substrate's "key".
