The plasma membrane separates the inside of the cell from its outside environment.
Both prokaryotic and eukaryotic cells have a plasma membrane, a double layer of phospholipids, with proteins and cholesterol that separates the cell interior from the outside environment and it controls what can enter and exit the cell. Unlike the cell wall, it is not rigid and is flexible. Organelles within the cell are also surrounded by a cell membrane to contain their contents and prevent exposure to conditions in and outside of the cell. For example, the nucleus and endoplasmic reticulum are membrane-bound organelles.
MCAT Official Prep (AAMC)
• Prokaryotic and eukaryotic cells both have a plasma membrane, which acts as a barrier between the cell’s interior and it’s exterior environment.
plasma membrane: the semipermeable barrier that surrounds the cytoplasm (inside contents) of a cell
prokaryotic: a unicellular organism that lacks a membrane-bound nucleus, mitochondria
eukaryotic: organisms whose cells have a nucleus and organelles enclosed within membranes
phospholipids: a major component of cell membranes consisting of two hydrophobic fatty acid tails and a hydrophilic head consisting of a phosphate group
organelle: a small specialised structure in the cell
nucleus: centre of the cell containing chromosomes
endoplasmic reticulum: a folded organelle covered in ribosomes used for protein synthesis