Cell Biology

• Organisms


  Can be Prokaryotes or Eukaryotes
• All living things are made of cells
• Cells


  Can be either prokaryotic or eukaryotic
• Eukaryotic cells


  • Cells that are complex and include all animal and plant cells
• Prokaryotic cells


  • Cells that are smaller and simpler, e.g. bacterial cells
• Eukaryotes are organisms that are made up of eukaryotic cells
• A prokaryote is a prokaryotic cell (it's a single-celled organism)
• Subcellular structures in animal cells

  • Nucleus
  • Mitochondria
  • Cytoplasm
  • Cell membrane
  • Ribosomes
• Nucleus


  • Contains genetic material that controls the activities of the cell
• Mitochondria


  • Where most of the reactions for aerobic respiration take place
• Cytoplasm


  • Gel-like substance where most of the chemical reactions happen, containing enzymes that control these chemical reactions
• Cell membrane


  • Holds the cell together and controls what goes in and out
• Ribosomes


  • Where proteins are made in the cell
• Additional subcellular structures in plant cells

  • Rigid cell wall
  • Chloroplasts
  • Permanent vacuole
• Rigid cell wall


  • Made of cellulose, supports and strengthens the cell
• Chloroplasts


  • Where photosynthesis occurs, containing chlorophyll that absorbs light needed for photosynthesis
• Permanent vacuole


  • Contains cell sap, a weak solution of sugar and salts
• Bacterial cells are much smaller and simpler than eukaryotic cells
• Bacterial cells


  • Don't have a 'true' nucleus, instead have a single circular strand of DNA floating freely in the cytoplasm
  • May also contain one or more small rings of DNA called plasmids
  • Don't have chloroplasts or mitochondria
• Microscopy


  The study of cells and other small structures using microscopes
• Light microscopes


  • Use light and lenses to form an image of a specimen and magnify it, allowing us to see individual cells and large subcellular structures
• Electron microscopes


  • Use electrons instead of light to form an image, have a much higher magnification and resolution than light microscopes, allowing us to see much smaller things in more detail
• Magnification


  The ratio of the image size to the real size of an object
• Preparing a slide for a light microscope

  1. Add a drop of water to the middle of a clean slide

  2. Cut up an onion and separate it into layers, use tweezers to peel off some epidermal tissue and place it in the water

  3. Add a drop of iodine solution (a stain)

  4. Place a cover slip on top, trying to avoid air bubbles
• Main parts of a light microscope


  • Objective lens
  • Coarse adjustment knob
  • Fine adjustment knob
  • Stage
  • Eyepiece
• Using a light microscope to view a slide

  1. Clip the slide onto the stage

  2. Select the lowest powered objective lens

  3. Use the coarse adjustment knob to move the stage up to just below the objective lens

  4. Look down the eyepiece and use the coarse adjustment knob to move the stage downwards until the image is roughly in focus

  5. Adjust the focus with the fine adjustment knob until you get a clear image

  6. Swap to a higher-powered objective lens and refocus if you need greater magnification
• Drawing observations from a microscope

  1. Draw what you see using a sharp pencil, taking up at least half the space available with clear, unbroken lines

  2. Do not include any colouring or shading

  3. Draw subcellular structures in proportion

  4. Include a title and the magnification used

  5. Label the important features using straight, uncrossed lines
• You can work out the real size of a cell by counting the number of cells in 1 mm of the sample, and use this to calculate the magnification of your drawing
• Cell differentiation

  The process by which a cell changes to become specialised for its job
• Undifferentiated cell


  A cell that has not yet become specialised
• Cell differentiation


  1. Cells develop different subcellular structures

  2. Cells turn into different types of cells
• Differentiation allows cells to carry out specific functions
• Differentiation in most animal cells

  • Ability to differentiate is lost at an early stage, after they become specialised
  • Many plant cells don't ever lose this ability
• Cells that differentiate in mature animals are mainly used for repairing and replacing cells, such as skin or blood cells
• Stem cells


  Undifferentiated cells
• Specialised cells


  • Sperm cells
  • Nerve cells
  • Muscle cells
  • Root hair cells
  • Phloem and xylem cells
• Sperm cells


  • Long tail and streamlined head to help swim to egg
  • Many mitochondria to provide energy
  • Enzymes in head to digest egg cell membrane
• Nerve cells


  • Long to cover more distance
  • Branched connections at ends to connect to other nerve cells
• Muscle cells


  • Long to have space to contract
  • Lots of mitochondria to generate energy for contraction
• Root hair cells


  • Grow into long "hairs" that stick out into the soil
  • Gives plant large surface area for absorbing water and minerals