Cells

• Nucleoid region


  • Containing circular DNA chromosome
• Cell differentiation


  • Animal cells differentiate most of their cells in the embryonic stage of development
  • Plant cells can differentiate throughout their whole lives
• Cell cycle


  1. The cell begins to divide

  2. The DNA replicates to form two copies of each chromosome

  3. The nuclear membrane breaks down

  4. The chromosomes line up across the centre of the cell

  5. One set of chromosomes is pulled to each end of the cell and the nucleus divides

  6. The cytoplasm and cell membranes divide to form two identical cells
• Embryonic stem cells


  • The cells that make up the early embryo (2-3 days old)
  • Have the ability to differentiate into any type of specialised cells
• Adult stem cells


  • Stem cells found in the bodies of animals which are born, including children
  • Are limited as to which types of cells they can differentiate into depending on where they are found in the body
• Where adult stem cells can be found

  • Bone marrow
• Specialised animal cells


  • Sperm cell
  • Muscle cell
  • Nerve cell
• Specialised plant cells


  • Root hair cell
  • Phloem cell
  • Xylem cell
• Embryonic stem cells


  • The most useful as they can be used to differentiate into any type of cell
  • Can be created with cloning technique to make sure the cells have the patient's own DNA
• Light microscope

  • Smaller, used to see 2D specimens
  • Lower magnification and resolution
• Electron microscope


  • Larger, used to see 3D images of specimens
  • Higher magnification and resolution
  • More expensive
• Practical microscopy


  1. One drop of water onto microscope slide

  2. Epidermal tissue from onion onto slide

  3. 2 drops of iodine solution onto onion, place on cover slip

  4. Move lowest power lens, focus

  5. Move to higher power objective lens

  6. Focus

  7. Make a labelled drawing and annotate total magnification factor
• Diffusion


  Movement of particles from an area of higher concentration to an area of lower concentration
• Higher concentration of oxygen


  Oxygen will diffuse outside cell
• Lower concentration of oxygen

  Oxygen will diffuse inside cell
• Factors affecting rate of diffusion

  • Temperature - hotter = faster
  • Surface area - larger = faster
  • Concentration gradient - larger = faster
• Osmosis


  The net movement of particles from a dilute solution to a more concentrated solution across a partially permeable membrane
• Active transport


  Uses energy from respiration to move substances against the concentration gradient
• Required practical osmosis


  1. Cut three potato cylinders of same diameter and length

  2. Number the potato tubes

  3. Measure and record the length and mass of each tube

  4. Place 1st tube in water, 2nd tube in 0.5M sugar solution, 3rd tube in 0.25M sugar solution

  5. Leave overnight

  6. Dap dry, Re-measure and record the length and mass of each tube

  7. Calculate the % change in mass