Paper 1 Required Practicals

Cards (23)

  • Optical microscope
    Used to look at cells on a prepared microscope slide
  • Optical microscope
    • Has a stage to place the microscope slide
    • Has a light source (lamp or mirror) to illuminate the slide
    • Has objective lenses with different magnifications (4x, 10x, 40x)
    • Has an eyepiece lens with 10x magnification
    • Has coarse and fine focusing dials
  • Using an optical microscope to view a prepared slide
    1. Place slide on stage and secure with clips
    2. Select lowest power (4x) objective lens
    3. Slowly turn coarse focus dial to lower lens until it almost touches slide
    4. Look through eyepiece and turn coarse focus dial to bring cells into focus
    5. Use fine focus dial to sharpen focus
    6. Calculate total magnification by multiplying eyepiece (10x) and objective (4x, 10x, 40x) magnifications
  • What you might see under an optical microscope
    • Animal cells: nucleus, cytoplasm, cell membrane, possible mitochondria
    • Plant cells: cell wall, cytoplasm, nucleus, possible vacuole and chloroplasts
  • An optical microscope can only show limited detail, cannot see organelles like ribosomes
  • Drawing of cells should include a magnification scale
  • More questions on this required practical can be found in the revision workbook
  • Osmosis
    Diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane
  • Plant cells placed in water
    Water moves into the cell by osmosis, causing the cell to expand
  • Plant cells placed in concentrated solution
    Water moves out of the plant cell by osmosis, causing the cell to shrink
  • Investigating the effect of osmosis on plant tissue
    1. Peel potato
    2. Use cork board to produce cylinders
    3. Trim cylinders to same length
    4. Measure length and mass of cylinders
    5. Place cylinders in test tubes with different solutions
    6. Leave overnight
    7. Remove cylinders, gently roll on paper towel
    8. Measure length and mass of cylinders again
  • Distilled water
    Contains no dissolved substances that could affect the weight of osmosis
  • Percentage change
    Calculated as: (change in value / original value) x 100
  • Concentration of sugar solution
    Affects percentage change in mass or length of potato cylinder
  • Graph of percentage change vs sugar solution concentration shows water moving in/out of cell by osmosis
  • Carrying out chemical tests for carbohydrates, proteins and lipids
    1. Grind food sample with distilled water using mortar and pestle to make a paste
    2. Transfer paste to beaker and add more distilled water
    3. Stir to dissolve chemicals
    4. Filter solution to remove suspended food particles
  • Carbohydrates
    Include starch and sugars such as glucose
  • Test for starch
    1. Place 2cm3 of food solution in test tube
    2. Add a few drops of iodine solution
    3. Blue-black colour indicates presence of starch
    4. Orange colour indicates no starch
  • Test for sugars (e.g. glucose)
    1. Place 2cm3 of food solution in test tube
    2. Add 10 drops of Benedict's solution
    3. Heat test tube in hot water bath for 5 minutes
    4. Green colour = small amount of sugar
    5. Yellow colour = more sugar
    6. Brick red colour = a lot of sugar
  • Reducing sugars
    • Sugars that the Benedict's test works for (e.g. glucose)
    • Non-reducing sugars (e.g. sucrose) do not work with Benedict's test
  • Test for proteins
    1. Place 2cm3 of food solution in test tube
    2. Add 2cm3 of Biuret solution
    3. Purple/lilac colour indicates presence of protein
  • Test for lipids/fats
    1. Grind food with distilled water using mortar and pestle (do not filter)
    2. Transfer 2cm3 of solution to test tube
    3. Add a few drops of distilled water and ethanol
    4. Shake gently
    5. White cloudy emulsion indicates presence of lipids
  • Ethanol is highly flammable, so no naked flames should be present