The cell wall of a plant cell is mainly made up of:

The cell wall is a rigid, non-living outer layer found outside the cell membrane in plant cells, fungi, bacteria and some protists. Animal cells do not have a cell wall.

In plants, the cell wall is made mainly of cellulose, a complex carbohydrate (a polysaccharide) made of long chains of glucose units. Cellulose is the most abundant organic compound on Earth. The cellulose fibres are embedded in a matrix of other substances, such as hemicellulose and pectin. In older woody cells, a tough substance called lignin is deposited, making the wall very hard.

The plant cell wall has three main parts:

• The middle lamella, made mainly of calcium pectate, which cements neighbouring cells together.
• The primary wall, thin and flexible, formed while the cell is growing.
• The secondary wall, thicker and stronger, formed inside the primary wall in some mature cells.
• Neighbouring plant cells are connected through tiny channels in their walls called plasmodesmata.

The cell wall gives the plant cell its shape, provides mechanical strength and support, and protects it against injury and infection. It also prevents the cell from bursting when it takes in a lot of water, because the wall resists the pressure; this is called turgor pressure, and it keeps soft plant parts firm. The cell wall was first seen by Robert Hooke in 1665, when he looked at thin slices of cork under his microscope and named the empty compartments "cells".

Humans cannot digest cellulose, but it acts as dietary fibre (roughage). Cattle and termites digest it with the help of microbes.

Why not the other options?

• ✗Chitin forms the cell walls of fungi and the outer skeletons of insects.
• ✗Peptidoglycan (murein) forms the cell walls of bacteria.
• ✗Starch is a storage carbohydrate, not a structural part of the wall.