Cell structure and diversity

• Plant cell components = cell wall and protoplast
• Cell wall structure - cellulose

  • most abundant organic molecules
  • glucose polymer
  • highly ordered
  • long ribbon like structures
• Cellulose forms microfibrils which is important for primary and secondary cell wall - Phase 1.
• Phase 2 = Matrix 


  The matrix involves hemicellulose and pectin
• Hemicellulose is a group of heterogenous that is cross linked with cellulose from microfibrils that contribute to the structure of cellulose.
• Pectin is gel-like polysaccharides that fill the spaces between cellulose microfibres and provides primary flexibility and retains water. They are also negatively charged and branched
• Protein extensin has a rough amino acid sequence and the extensibility can be controlled by extensin cross linking of pectin and cellulose
• Cross linking pectin and cellulose will:

  • dehydrate cell wall
  • reduces extensibility
  • increases strength
• Exocytosis transports material out of the cell or delivers it out the cell surface or releases extracellular matrix proteins.
• Synthesis of the primary cell wall

  the cellulose-producing rosettes move parallel to the cortical microtubules.
• Regulating cell is called cell morphology
• Cell morphology is the orientation of cellulose microfibrils influences cell morphology.

  1. They are randomly oriented, where they expand in all directions
  2. They have right angles to the long-axis of the cell
• The cell wall provides structural support by the protoplast pushing against the cell wall and so the cells become more rigid. Water loss reduces the protoplast volume, which wilting occurs.
• The cell wall prevents excessive water uptake as when water enters the cell wall by osmosis, the protoplast pushes and expands against the cell wall. The pressure from this limits the amount of water taken up.
• Vacuole structure

  It is an organelle surrounded by a single membrane. They are highly selective and controls what comes in and out of the vacuole
• Vacuoles regulate the shape by the high concentrations of solutes inside.
• Not all plants have a secondary cell wall. This is produced after the cell growth as stopped. They are thicker and stronger than the primary cell wall and provides more structural support.
• The secondary cell wall is made up of multiple layered cellulose microfibrils. Microfibrils in each layer have different orientations and strengthens the wall.
• Chemical characteristics of secondary cell wall

  • More cellulose
  • Less pectin
  • Lignin
• Lignin is the second most important organic macromolecule and a complex polymer. It adds strength and rigidity to the secondary cell wall and acts to exclude water.
• The plasmodesmata, the intercellular connects and enables cell to cell communication. it is continuous and is small enough to prevent organelle movements. They also allow the free exchange of small molecules.