B1 revision

• Microscopes

  • Light microscopes
  • Electron microscopes
• Light microscopes

  • Low resolution
  • Low magnification
  • Cheaper
  • Small and easy to use
  • Allow you to see the outlines of cells
• Electron microscopes

  • High resolution
  • High magnification
  • Expensive
  • Complex to use
  • Allow you to visualise finer details
• Magnification

  Object size / Image size
• Cells are measured in micrometres
• 1pm = 1 x 10^-6m
• To convert pm to mm, divide by 1,000
• Organelles

  Sub-cellular structures
• Eukaryotic cells

  Contain their genetic material (DNA) enclosed in a nucleus
• Plant cells

  • Have a cell wall
  • Have chloroplasts
  • Have a large central vacuole
• Animal cells

  • Do not have a cell wall
  • Do not have chloroplasts
  • Do not have a large central vacuole
• Prokaryotic cells

  Their genetic material (DNA) is not enclosed in a nucleus, rather it is in a loop called a plasmid
• Example of prokaryotic cells: bacteria cells
• Specialised cells

  Cells that have a specific function, e.g. sperm cells, muscle cells, nerve cells
• All specialised cells start off as stem cells
• Stem cells

  Can be found in animal embryos and plant meristems
• Some stem cells are made in your bone marrow and can only specialise into blood cells
• Embryo clones can be made of a person to harvest stem cells, which can then be used to treat conditions without the risk of body rejection
• Cloning can also be used to preserve species or produce crops with desired traits
• All human cells have 23 pairs of chromosomes, except gametes (eggs/sperm) which have 23 chromosomes
• Mitosis

  1. DNA is duplicated

  2. The two sets of chromosomes move to different sides

  3. The cell divides, producing two genetically identical diploid cells with new nuclei
• Chromosomes

  Lengths of tightly wound DNA that contain the genetic code
• Bacteria reproduces by binary fission
• Aseptic techniques for making bacterial cultures

  1. Sterilise air by moving lid towards flame

  2. Put drop of culture on agar and spread evenly

  3. Put drops of antibiotics on culture

  4. Place bits of tape to allow air for aerobic respiration

  5. Incubate at 25 degrees Celsius
• To measure size of culture areas with no bacteria, use the equation: πr^2
• What is resolution?

  Your ability to see between 2 points
• Diffusion

  The movement of particles from an area of high concentration to an area of low concentration down the concentration gradient
• Diffusion is passive as it requires no energy
• As the concentration gradient increases

  The rate of diffusion increases
• As temperatures increase In diffusion …

  Particles have more kinetic energy so the rate of diffusion increases
• Organisms in diffusion

  • Leaves (located in the stomata for diffusion of oxygen, water out and carbon dioxide in)
  • Lungs (located in the Alveoli for diffusion of oxygen and carbon dioxide)
• Osmosis

  The movement of water molecules across a semi-permeable membrane from a high to a low concentration
• Osmosis practical - Potatoes


  1. Weigh and measure potato pieces, record initial measurements

  2. Add potato pieces to test tubes with sugar solution, fill last tube with distilled water

  3. Leave potatoes for chosen time

  4. Remove potatoes, dry, measure new mass and length

  5. Record measurements and calculate change
• Active transport

  The movement of particles through a membrane via carrier proteins, requires energy, and can move against the concentration gradient
• give three examples of specialised cells?

  • root hair cells
  • palisade cells
  • stoma(guard cells)