What does it mean when a cell is permeable, does it have anything to do with what a cell is used for once its fully developed?
Yes, the types and amounts of substances allowed to pass through the cell membrane will depend largely on the purpose of that cell. Typically, permeability is discussed regarding a specific compound. A cell is made to be selectively permeable to given compounds; the cell membrane will be permeable to some substances but not others.
Could you give me a specific example?
Certainly! One example of a cell with specific permeability characteristics is the red blood cell. The red blood cell is permeable to small molecules such as oxygen and carbon dioxide, but it is not permeable to larger molecules like glucose. This is because the red blood cell's primary function is to transport oxygen and other gases, so it needs to be permeable to those molecules. On the other hand, if a cell's primary function is to store and regulate the levels of glucose in the body, it would need to be permeable to glucose and other similar-sized molecules.

Another example is the cell membrane of neurons, which is selective for positively charged ions such as sodium and potassium ions. This is because the flow of these ions plays an important role in transmitting nerve signals.