| The delicate membrane of early life had to be surrounded by a strong wall, to stop the membrane breaking. Life was now packaged into little boxes called cells. Some cells today still have a cell wall. | ||
| Bacteria
Bacteria have cell walls made of peptidoglycan, a large polymer of amino acids and sugar molecules. They can be divided into two groups:
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| Plant
Plant cells are surrounded by a rigid wall made of chains of glucose molecules (making cellulose) and chains of other sugar molecules (making polysaccharides), together with glycoproteins.
Animal
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