Everything Life Sciences Grade 10

FACT

The human body
cannot break down
the cellulose in cell
walls because we
do not produce the
enzyme cellulase.

Primary cell wall: is on the inside of the middle lamella and is mainly composed of cellulose.

Secondary cell wall: lies alongside the cell membrane. It is is made up of a thick and tough

layer of cellulose which is held together by a hard, waterproof substance called lignin. It is

only found in cells which provide mechanical support in plants.

Figure 3.10: Diagram of plant cell wall showing the structure of the outermost layer of the cell which

includes the cell wall and plasma membrane.(You will not be expected to draw this diagram in an

exam but it is important to know how the various components of the plant cell wall interact with one

another.)

Figure 3.11: Scanning electron microscope micrographs of diatoms showing the external appearances

of the cell wall. Scale bar: A, B, D:10 um, C20 um

Functions of the cell wall

• The main function of the wall is to protect the inner parts of the plant cell, it gives plant
  cells a more uniform and regular shape and provides support for the plant body.


• The cell wall is completely permeable to water and mineral salts which allows distri-
  bution of nutrients throughout the plant.


• The openings in the cell wall are called plasmodesmata which contain strands of cy-
  toplasm that connect adjacent cells. This allows cells to interact with one another,
  allowing molecules to travel between plant cells.

72 3.3. Cell structure and function