Adhesion of cells to form tissuesSpec B2.1.17
In short
Cell-adhesion molecules (CAMs) are proteins in the plasma membrane that bind cells to each other so that they form tissues. Different forms of CAM are used for different types of cell–cell junction, for example junctions that seal cells together or junctions that anchor them firmly. CAMs on adjacent cells bind to each other, holding the tissue together.
In multicellular organisms, cells must stick together to form tissues. Cell-adhesion molecules (CAMs) are membrane proteins, usually glycoproteins, that project from the cell surface and bind to CAMs on neighbouring cells.
There are different forms of CAM for different types of cell–cell junction. Some junctions seal adjacent cells tightly so that fluid cannot leak between them, as in the epithelium lining the gut. Others anchor cells firmly so a tissue can withstand stretching, as in skin and heart muscle.
You need the term cell-adhesion molecules (CAMs) and the idea that different CAMs form different junctions. Names and details of individual CAMs and junctions are not required.
Quick check
Which part of a phospholipid is hydrophobic?
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The two hydrocarbon (fatty acid) tails.
Name the channel protein that lets water cross membranes rapidly.
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Aquaporin.
What does a pump protein use to move particles against a concentration gradient?
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Energy from ATP.
On which side of the plasma membrane are the carbohydrate chains of glycoproteins?
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The extracellular side.
HL only How many Na⁺ and K⁺ ions does the sodium–potassium pump move in one cycle?
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Three Na⁺ out and two K⁺ in.
Written and checked against the IB Biology HL specification · Updated October 2026