THE CELL

The basic unit of plant structure is the cell. All plants from the most simple to the most complex are composed of one or more cells. In plants that are of agricultural importance the cells are highly organised structures and are termed eukaryotic because each contains a well-defined nucleus, as distinct from prokaryotic cells found in plants such as bacteria, blue-green algae and mycoplasmas, which do not contain nuclei.

Study of a rapidly dividing stem or root apex (meristem) of a plant reveals a mass of newly formed cells surrounded by a box-shaped structure, the cell wall, which differentiates plant cells from those found in the animal kingdom (Fig. 2.1).

The cell contents

Within the cell wall is found the living content of the cell, called protoplasm. Even under a light microscope the protoplasm can be seen to contain a number of structures. The development of electron microscopy has substantially increased the number that can now be identified. However, because of their complexity of both micro-structure and function, only the major components of the cell will be discussed.

The protoplasm is separated into two major parts, the nucleus and the cytoplasm. The nucleus is usually spherical in shape and contains DNA which carries genetic information; this DNA is usually contained within the chromosomes. In a growing plant, when new cells are formed, the chromosomes reproduce exact copies of themselves in a process called mitosis.