Plant Cell Wall

A plant cell has a cell wall, a rigid structure located outside the plasma membrane that surrounds the cell. The cell wall helps support and protect the cell, maintains its shape, and prevents excessive expansion of the cell when water enters.

Plant cell walls can have up to three layers—the middle lamella, the primary cell wall, and the secondary cell wall.

Each layer contains polysaccharides such as pectin, hemicellulose, and cellulose, as well as structural proteins.

The outermost layer of the cell wall is shared between adjacent cells, which is why it is called the “middle” lamella. This layer is rich in pectin, which helps cells stick together and form plant tissues.

The primary cell wall forms between the middle lamella and the plasma membrane.

It is a thin, flexible layer that forms as the plant divides and grows.

The primary cell wall is a layer of cellulose microfibrils embedded in a gel-like matrix of pectin and hemicellulose.

After a plant cell matures and stops growing, it may build a secondary cell wall between the primary cell wall and the plasma membrane.

This layer is thick and rigid. It contains cellulose and hemicellulose, along with lignin, a strong polymer that hardens the wall.

Both wood and grasses build secondary cell walls that include lignin. But their cell wall compositions differ to suit their structural needs.

Wood, unlike grass, has thick secondary cell wall layers that give trees strength and rigidity.

Even within the same plant, different cell types build specialized secondary walls. For example, vessel elements and tracheids—cells that transport water—develop thickened walls that help them withstand the pressure exerted by water movement.

Plant cell walls are not impenetrable barriers. Small channels called plasmodesmata connect the cytoplasm of neighboring cells. These channels allow cells to exchange water, nutrients, and other vital molecules.