1 - cell biology

• Eukaryotic cells


  Larger and more complex
• Prokaryotic cells


  Smaller and single-celled
• Bacteria are prokaryotes
• 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 chemical reactions happen, contains enzymes
• Cell membrane


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


  Where most reactions for aerobic respiration take place, transfer energy the cell needs
• Ribosomes


  Where proteins are made in the cell
• Additional 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
• Structures in bacterial cells

  • Cell membrane
  • Cytoplasm
  • Cell wall
• Bacterial cells don't have chloroplasts or mitochondria
• Bacterial cells


  Have a single circular strand of DNA floating in the cytoplasm, may also have plasmids
• Light microscopes


  Use light and lenses to form an image and magnify
• Electron microscopes


  Use electrons instead of light, have higher magnification and resolution
• Electron microscopes let us see smaller things in more detail, like internal structures of mitochondria and chloroplasts, and even ribosomes and plasmids
• Magnification


  Calculated using the formula: image size / real size
• To prepare a slide, add a drop of water, place specimen tissue in, add stain, and cover with a coverslip
• Using a light microscope

  1. Clip slide onto stage

  2. Select low-power objective

  3. Use coarse adjustment to focus

  4. Refine focus with fine adjustment

  5. Swap to higher-power objective if needed
• Cells differentiate to become specialised for different functions
• Differentiation


  The process by which a cell changes to become specialized for its job
• Most differentiation occurs during development, and differentiated cells in mature animals mainly serve for repair and replacement
• Some cells are undifferentiated stem cells that retain the ability to differentiate
• Examples of specialised cells

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


  • Long tail and streamlined head to swim to egg, many mitochondria for energy, enzymes to digest egg cell membrane
• Nerve cells


  • Long to cover distance, branched connections to form a network, carry electrical signals
• Muscle cells


  • Long to contract, contain many mitochondria for energy
• Root hair cells


  • Grow long "hairs" to increase surface area for absorbing water and minerals
• Phloem and xylem cells


  • Form tubes to transport substances like food and water, are long and joined end-to-end
• Culture medium


  • Contains the carbohydrates, minerals, amino acids and vitamins microorganisms need to grow
• Growing bacteria on agar plates

  1. Agar jelly is poured into Petri dishes

  2. Inoculating loops or pipettes are used to transfer microorganisms to the agar

  3. Microorganisms multiply on the agar
• In the lab at school, cultures of microorganisms are not kept above 25°C because harmful pathogens are more likely to grow above this temperature
• In industrial conditions, cultures are incubated at higher temperatures so they can grow faster
• Investigating effect of antibiotics on bacterial growth

  1. Place paper discs soaked in antibiotics on agar plate with bacterial growth

  2. Antibiotic diffuses into agar, killing non-resistant bacteria and leaving clear inhibition zones

  3. Use a control disc with no antibiotic

  4. Leave plate for 48 hours at 25°C

  5. Larger inhibition zones indicate more effective antibiotics
• Avoiding contamination when culturing microorganisms

  • Petri dishes and culture medium must be sterilised before use
  • Inoculating loop must be sterilised before use
  • Petri dish lid should be taped on to prevent air contamination
  • Petri dish should be stored upside down to prevent condensation
• Inhibition zone


  The clear area around an antibiotic disc where bacteria have been killed
• Calculating size of inhibition zones

  1. Measure diameter of inhibition zone

  2. Calculate radius from diameter

  3. Use area of circle equation (πr²) to calculate area
• The larger the inhibition zone, the more effective the antibiotic is against the bacteria