The plant cell wall is a strong, non-living layer outside the cell surface membrane. It is made mainly of cellulose.Structure
Cellulose is a polysaccharide made of long, straight chains of β-glucose joined by 1,4 glycosidic bonds. Neighbouring chains lie side by side and are held together by many hydrogen bonds, forming bundles called microfibrils. Microfibrils are very strong in tension.The microfibrils are laid down in layers, often at different angles to each other, and are embedded in a matrix of other polysaccharides, including hemicelluloses and pectins. This structure resembles reinforced concrete, and makes the wall strong in all directions.Between the walls of neighbouring cells is the middle lamella, a layer rich in calcium pectate, which glues cells together.In some cells, such as xylem vessels and sclerenchyma fibres, a thick secondary wall is laid down inside the first (primary) wall and impregnated with lignin, which makes it waterproof and even stronger.
Functions
• Mechanical strength and support for the cell and the whole plant.
• Preventing bursting: when water enters by osmosis, the cell swells and pushes against the wall. The wall resists, so the cell becomes turgid instead of bursting, which also supports non-woody plants.
• The arrangement of microfibrils controls the direction in which a cell can grow.
• The wall is freely permeable, so water and dissolved substances can pass through it and move along it (the apoplast pathway).
Cellulose is a polysaccharide made of long, straight chains of β-glucose joined by 1,4 glycosidic bonds. Neighbouring chains lie side by side and are held together by many hydrogen bonds, forming bundles called microfibrils. Microfibrils are very strong in tension.The microfibrils are laid down in layers, often at different angles to each other, and are embedded in a matrix of other polysaccharides, including hemicelluloses and pectins. This structure resembles reinforced concrete, and makes the wall strong in all directions.Between the walls of neighbouring cells is the middle lamella, a layer rich in calcium pectate, which glues cells together.In some cells, such as xylem vessels and sclerenchyma fibres, a thick secondary wall is laid down inside the first (primary) wall and impregnated with lignin, which makes it waterproof and even stronger.
Functions• Mechanical strength and support for the cell and the whole plant.
• Preventing bursting: when water enters by osmosis, the cell swells and pushes against the wall. The wall resists, so the cell becomes turgid instead of bursting, which also supports non-woody plants.
• The arrangement of microfibrils controls the direction in which a cell can grow.
• The wall is freely permeable, so water and dissolved substances can pass through it and move along it (the apoplast pathway).