Cell Wall

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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: Gram-negative are not stained by the Gram method. They have two membranes, as shown in the diagram. The inner membrane is the real plasma membrane. The outer membrane has proteins containing large channels which allow large molecules through. Between these membranes lies the cell wall and a periplasmic space, usually filled with proteins secreted by the bacterium. Gram-positive bacteria are simpler, having only a plasma membrane and a cell wall.
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 Animal cells, unlike those of bacteria and plants, do not have a cell wall.
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