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Plant Cell Walls-An Overview

Plant cells exhibit typical eucaryotic cell structure. They possess plasma membranes, a variety of specialized membrane-bound organelles, well defined nuclei, and DNA in linear, paired chromosomes. Although similar to animal cells in many ways, plant cells are different in possessing a cell wall.

Cell walls are also found in bacteria and fungi but the components of these walls are different between the groups. Bacterial cell walls are made of peptidoglycan. Fungal cell walls contain chitin. Cellulose as a cell wall material, is unique to plants.

Now, roll over the nucleus of the plant cell in the diagram!

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A Tire and the Cell Wall-An Analogy

Cell walls act as rigid barriers around delicate plasma membranes, providing osmotic stability to cells. All cells contain solutes that attract water due to osmosis (the diffusion of water molecules). Plant cells exert control over solute concentrations and thereby influence osmotic pressures inside cells. Forces result that a plant uses in various ways for support, movement, and transport.

An analogy to help visualize the function of a cell wall can be found in tires. Tires contain tubes. Think of a tire tube as a membrane analogous to the plant cell plasma membrane. Air pressure within the tube is analogous to osmotic pressure. With increases in air pressure the tube can rupture. A tire (analagous to the cell wall) is an outer, rigid but flexible layer that allows air pressure in the tire to be inflated beyond limits of the tube alone. A durable, flexible structure results that can support the weight of an automobile..

Now, roll over the nucleus of the stable cell in the diagram!

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Some Comparisons of Cells

In this view of some plant tissues notice the variations in cell appearances. Start with the outermost layer of cells. This is the epidermis of most plant structures. Beneath the epidermal layer are several layers of cells with irregular thickened walls. A little deeper, you encounter two or three layers with thin cell walls. And finally, at lower right, cells are encountered with thick, uniform wall thickenings. All cells shown here possess primary cell walls. Cells just below the epidermis have irregularly thickened primary cell walls while those to the lower right have additional secondary cell walls.

Each cell type shown here is given a name and the function served by these cells varies. Cell walls play a key role in these functions so now we will learn about primary and secondary cell walls!

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