Cell Wall
Structure
The cell wall of most plants is mainly cellulose which is a polysaccharide made from beta-glucose.
Beta-glucose bonds result in long, straight unbranched chains which are very rigid.

The molecules lie side by side forming microfibrils that are strengthened by hydrogen bonds.
The cellulose microfibrils are embedded in a framework of other substances, mainly the complex molecules hemicelluloses and pectins.
This image shows the cellulose microfibrils in the cell wall of a green alga
Function
The cell wall is needed to resist the force exerted by water that has entered the cell by osmosis. This means the cell is turgid and supports the stem and leaves.
The cell wall also allows water and solutes to pass into the cell.
It is important that the cell wall allows the cell to grow.
How structure helps function
Cellulose fibrils means that it is very strong and stable, which is ideal for a structural material such as a cell wall.
The microfibrils determine the shape of each cell wall, which makes it flexible enough to allow the cell to grow.
It is freely permeable so water and solutes are able to pass in and out of the cell.