Plant Cell Walls - 7  
311 Syllabus

The Cell Wall "Glues" Cells together.

The Cell Wall provides Structural Support

Turgor Pressure is partly responsible for the shape of plants. A limp balloon supports nothing. An inflated balloon supports something. A lot of inflated balloons can support a lot.

The Pattern and Amount of Cellulose Deposition determines the Degree of Structural Support

These Cells have relatively thin Cell Walls and they would not provide much Structural Support.	This cell has an extremely thick Cell Wall which would provide a lot of Structural Support.

Xylem Water Translocation requires Cells that do not Collapse under Negative Pressure. A weak straw collapses when you try to suck up the dense ice cream at the bottom of a real milk shake. However, a steel straw would never collapse under this tension.

Cross section of the Xylem. Note the relatively thick walled cells in the center of the photo. These are the water-conducting cells that must resist collapse. The red color indicates the presence of Lignin.	Longitudinal Section of Xylem Vessels. The Secondary Cell Walls are very strong and are almost impossible to collapse.

Presence of Lignin has a great effect on structural properties. Lignin makes cell walls rigid and strong.

Water Permeability is determined by the Cell Wall.

Water(solvent) and dissolved chemicals (solute) can move in the Apoplast of MOST cell walls.

The wall Provides a Diffusion Barrier for the movement of Macromolecules. Large molecules like Proteins do not move freely in the Apoplast.

Pectins = 80-90% Water. They allow the diffusion of Solutes like Sugar or other low molecular weight chemicals that dissolve in water.

Lignin & Suberin are waterproof. They block Apoplastic water/solute movement.

The Cell Wall can be used as a Carbon Reserve (Few Seeds)

These cells are part of   Palm Endosperm. The thick Cell Walls can be used as a carbon source during seed germination. The image on the right has been modified to show the extent of the Cell Walls. The dark areas are the Protoplasts of the cells in both photos.