FACT
DNA (the hereditary
information of cells)
is passed from
’parent’ cells to
’daughter’ cells
during cell division.
You will learn more
about this in the
following chapter:
Cell division.Cells are the smallest form of life; the functional and structural units of all living things. Your
body contains several billion cells, organised into over 200 major types, with hundreds of
cell-specific functions.
Some functions performed by cells are so vital to the existence of life that all cells perform
them (e.g. cellular respiration). Others are highly specialised (e.g. photosynthesis).
Figure 3.9 shows a two-dimensional drawing of an animal cell. The diagram shows the
structures visible within a cell at high magnification. The structures form theultrastructure
of the cell.
Figure 3.9: Diagram of the cell ultrastructure of an animal cell.We will now look at some of the basic cell structures and organelles in animal and plant
cells.
Cell wall DUMMY
The cell wall is a rigid non-living layer that is found outside the cell membrane and surrounds
the cell. Plants, bacteria and fungi all have cell walls. In plants, the wall is comprised of
cellulose. It consists of three layers that help support the plant. These layers include the
middle lamella, the primary cell wall and the secondary cell wall.
Middle lamella: separates one cell from another. It is a thin membranous layer on the outside
of the cell and is made of a sticky substance called pectin.
Chapter 3. The basic units of life 71