The ultrastructure of plant cells

• Plant cells


  • Unlike animal cells, they are rigid structures
  • Have a cell wall surrounding the cell-surface membrane
• Cell wall


  • Made of cellulose, a complex carbohydrate
  • Freely permeable so substances can pass into and out of the cell
  • Gives the plant cell its shape
  • Contents of the cell press against the cell wall making it rigid
  • Supports the individual cell and the plant as a whole
  • Acts as a defence mechanism, protecting the contents of the cell against invading pathogens
• All plant cells have cellulose cell walls
• Vacuoles


  Membrane lined sacs in the cytoplasm containing cell sap
• Vacuoles in plant cells

  • Large permanent vacuoles
  • Important in the maintenance of turgor
  • Contents of the cell push against the cell wall
  • Maintain a rigid framework for the cell
• Tonoplast


  The membrane of a vacuole in a plant cell
• Selectively permeable


  Some small molecules can pass through it but others cannot
• Vacuoles in animal cells

  Small and transient (not permanent)
• Chloroplasts


  Organelles responsible for photosynthesis in plant cells
• Chloroplasts


  • Found in the cells in the green parts of plants such as the leaves and the stems but not in the roots
  • Have a double membrane structure, similar to mitochondria
  • Fluid enclosed in the chloroplast is called the stroma
  • Have an internal network of membranes, which form flattened sacs called thylakoids
  • Several thylakoids stacked together are called a granum (plural grana)
  • The grana are joined by membranes called lamellae
  • The grana contain the chlorophyll pigments, where light-dependent reactions occur during photosynthesis
  • Starch produced by photosynthesis is present as starch grains
  • Contain DNA and ribosomes, so able to make their own proteins
• The internal membranes provide the large surface area needed for the enzymes, proteins and pigment molecules necessary in the process of photosynthesis