The Cell Membrane (SQA National 5 Biology): Revision Note

Cell membrane structure & function

• Cell membranes are the thin boundaries that:

  • surround cells, separating the cell contents from the external environment

  • separate compartments within cells from the surrounding cytoplasm, e.g. nucleus, mitochondria and chloroplasts

• Cell membrane structure includes:

  • phospholipids

  • proteins

• Cell membranes are selectively permeable, meaning that they allow the passage of some substances and not others

  • Small molecules, such as water, carbon dioxide and oxygen, can pass freely across the cell membrane

  • Larger molecules, such as glucose and proteins, as well as charged particles, including sodium and chloride ions (Na⁺, Cl^-), require specialised transport proteins to move across membranes