Plasma membrane

Plasma membrane

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Plasma membrane surrounding organelles

What is and functions

Simply put, we can define the plasma membrane as a cell envelope. This wrapper will be responsible for the shape of the cell and the substances entering and leaving it.

Composition and other characteristics

Its chemical composition is lipoprotein (fat + protein), however, it is not homogeneous.

There are two types of substances that cross the plasma membrane: water-soluble and liposoluble.

Water-soluble substances reach inside cells only after passing through the pores contained in the carrier proteins. However, this transport will only occur if these substances are smaller than the pore size of this protein.

In the case of fat soluble substances, they cross the plasma membrane much more easily, since most of the plasma membrane is formed by lipid. Here, substances need not be small, necessarily, to get inside the cell.

This process of substance entry and exit through the plasma membrane is known as passive transport (diffusion and osmosis) and active transport (endocytosis, phagocytosis, exocytosis).


- Water-soluble substances that cross the plasma membrane are: water (H2O), oxygen (O2), carbon dioxide (CO2), urea, vitamin C, glucose, salicylic acid, lactic acid, small proteins (smaller than the pore size of the carrier proteins), amino acids and minerals.