Cell Biology

Preparing a slide to view onion cells

  • Add a drop of water to the middle of a clean slide
  • Cut up an onion and separate it out into layers. Use tweezers to peel off some epidermal tissue
  • Using the tweezers, place the epidermal tissue into the water on the slide
  • Add a drop of iodine solution, the Iodine solution is a stain, Stains are used to highlight objects in a cell by adding color to them
  • Place a cover slip on top. To do this, stand the coverslip upright on the slide, next to the water droplet. Then carefully tilt and lower it so it covers the specimen. Try not to get any air bubbles - it will obstruct your view.
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Mitosis

  • Cells grow bigger and increase in their mass
  • DNA replicates to form two copies of each chromosome
  • Increased numbers of mitochondria & ribosomes etc.
  • Chromosomes separate and one set is pulled to each end of the cell
  • Nucleus forms around each set of chromosomes
  • The cytoplasm and cell membranes divide
  • Two identical daughter cells are formed
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Binary Fission

  • The circular DNA and plasmids replicate
  • The cell gets bigger and the circular DNA strands move to opposite 'poles' (ends) of the cell
  • The cytoplasm begins to divide and the new cell walls begin to form
  • The cytoplasm divides and two daughter cells are produced. Each daughter cell has one copy of the circular DNA but can have a variable number of copies of plasmids
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