Topic 1 - Cell Biology

• All living things are made of cells
• Cells


  Can be either prokaryotic or eukaryotic
• Eukaryotic cells


  • Complex
  • Include all animal and plant cells
• Prokaryotic cells


  • Smaller
  • Simpler
  • e.g. bacteria
• Eukaryotes


  Organisms that are made up of eukaryotic cells
• Prokaryote


  A prokaryotic cell (a single-celled organism)
• Subcellular structures


  The different parts of a cell
• Subcellular structures in animal cells

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


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


  Gel-like substance where most of the chemical reactions happen
• Enzymes


  Control the chemical reactions in the cytoplasm
• Cell membrane


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


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


  Transfers energy that the cell needs to work
• Ribosomes


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

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


  Made of cellulose, supports and strengthens the cell
• Permanent vacuole


  Contains cell sap, a weak solution of sugar and salts
• Chloroplasts


  Where photosynthesis occurs, making food for the plant
• Chlorophyll


  Green substance in chloroplasts that absorbs the light needed for photosynthesis
• The cells of algae (e.g. seaweed) also have a rigid cell wall and chloroplasts
• Microscopes


  Let us see things that we can't see with the naked eye
• Microscopy techniques

  Developed over the years as technology and knowledge have improved
• Light microscopes

  • Use light and lenses to form an image of a specimen and magnify it (make it look bigger)
  • Let us see individual cells and large subcellular structures, like nuclei
• Electron microscopes

  • Use electrons instead of light to form an image
  • Have a much higher magnification than light microscopes
  • Have a higher resolution (ability to distinguish between two points, so a higher resolution gives a sharper image)
• Electron microscopes


  • Let us see much smaller things in more detail, like the internal structure of mitochondria and chloroplasts
  • Let us see tinier things like ribosomes and plasmids
• Magnification

  The ratio of the image size to the real size of an object
• You can calculate the magnification of an image using the formula: magnification = image size / real size
• Image size and real size should have the same units, and if they don't, you'll need to convert them first
• You can rearrange the magnification formula to find the image size or the real size of an object
• Preparing a slide to view onion cells

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

  2. Cut up an onion and separate it out into layers, use tweezers to peel off some epidermal tissue from the bottom of one of the layers

  3. Place the epidermal tissue into the water on the slide

  4. Add a drop of iodine solution

  5. Place a cover slip on top
• Slide


  A strip of clear glass or plastic onto which the specimen is mounted
• Cover slip


  A square of thin, transparent plastic or glass placed on top of the specimen
• Stain


  Used to highlight objects in a cell by adding colour to them
• Try not to get any air bubbles under the cover slip as they'll obstruct your view of the specimen
• Use a Light Microscope to Look at Your Slide

  1. Clip the slide you've prepared 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 of what's on the slide

  6. If you need to see the slide with greater magnification, swap to a higher-powered objective lens and refocus
• Light Microscope


  • Eyepiece
  • Coarse adjustment knob
  • Fine adjustment knob
  • High and low power objective lenses
  • Stage
  • Light
• Drawing under the microscope

  • Use a pencil with a sharp point
  • Drawing takes up at least half the space
  • Drawing has clear, unbroken lines
  • No colouring or shading
  • Subcellular structures drawn in proportion (if drawing cells)
  • Include title and magnification
• Drawing under the microscope

  • Use a pencil with a sharp point
  • Drawing takes up at least half the space
  • Drawing has clear, unbroken lines
  • No colouring or shading
  • Subcellular structures drawn in proportion (if drawing cells)
  • Include title and magnification
• Drawing steps


  1. Draw what you see under the microscope

  2. Make sure drawing takes up at least half the space

  3. Drawing should not include any colouring or shading

  4. If drawing cells, subcellular structures should be drawn in proportion

  5. Include title of what was observed and magnification