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E. organelles3

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cell wall AS level

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E. organelles3

  1. 1. Cell Wall These are found in plant cells only Cell walls provide mechanical support and protection
  2. 2. Because the wall prevents the cell from bursting this allows turgor pressure to give the plant support
  3. 3. The wall is made from cellulose and other polysaccharides Fungi and Prokaryotes have cell walls made of other substances
  4. 4. The cell wall is made in Golgi apparatus Golgi vesicles move to the cell plate (at the equator of a dividing cell) at the end of nuclear division Golgi vesicles containing Calcium pectate Forming cell plate with middle lamella being formed Note the vesicle membrane surrounds the new wall
  5. 5. The vesicles fuse to form the middle lamella This contains Calcium Pectate which holds the neighbouring cell walls together The membranes from the vesicles fuse to form the cell surface membrane
  6. 6. • The primary cell wall is made next • This is made of cellulose molecules that are bundled together to form microfibrils
  7. 7. The bundles are held by Hydrogen-bonds These are in turn bundles to form cellulose fibres Hemicellulose and pectins hold fibres together Cellulose has a high tensile strength
  8. 8. The primary cell wall laid down in different directions There are gaps in the wall called plasmodesmata through which cytoplasmic connections are made between cells The Secondary wall is only laid down once the cell has stopped growing
  9. 9. The cellulose fibres are laid in different directions which increases the strength They may have lignin or suberin added The cellulose cell wall is freely permeable. Water and ions move through the spaces between the cellulose fibres. This is called the apoplast

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