Bio Paper 1 RP

• 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. Using the tweezers, place the epidermal tissue into the water on the slide

  4. Add a drop of iodine solution

  5. Place a cover slip on top
• Using a light microscope to look at a prepared 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 eyepieces 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. If needed, swap to a higher-powered objective lens and refocus
• Drawing observations from a microscope

  • Draw what you see using a pencil with a sharp point
  • Make sure the drawing takes up at least half the available space and is drawn with clear, unbroken lines
  • Do not include any colouring or shading
  • Draw subcellular structures in proportion
  • Include a title and the magnification used
• You can work out the real size of a cell by counting the number of cells in 1 mm of the sample
• A light microscope is better than a naked eye for observing microorganisms
• Culturing microorganisms


  • Bacteria and some other microorganisms are grown in a "culture medium" which contains the carbohydrates, minerals, proteins and vitamins they need to grow
  • Bacteria grown on agar plates will form visible colonies on the surface of the jelly or will spread out to give an even covering
  • In the lab or 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 the effect of antibiotics on bacterial growth

  1. Place paper discs soaked in different antibiotics (or different concentrations) on an agar plate with an even covering of bacteria

  2. The antibiotic should diffuse into the agar jelly. Antibiotic-resistant bacteria will continue to grow around the paper discs, but non-resistant strains will die, leaving a clear area called an inhibition zone

  3. Use a control disc soaked in sterile water

  4. Leave the plate for 48 hours at 25°C
• Aseptic Techniques: Avoiding contamination when culturing microorganisms

  • The Petri dishes and culture medium must be sterilised before use
  • The inoculating loop used to transfer bacteria should be sterilised by passing it through a hot flame
  • The lid of the Petri dish should be lightly sealed to stop microorganisms from the air getting in
  • The Petri dish should be stored upside down to stop condensation falling onto the agar surface
• Calculating the size of inhibition zones

  1. Measure the diameter of the inhibition zone

  2. Divide the diameter by 2 to get the radius

  3. Plug the radius into the equation: Area = π x r²
• Culturing microorganisms RP The larger the inhibition zone, the more effective the antibiotic is against the bacteria
• Osmosis


  The passive movement of water particles from an area of higher water concentration to an area of lower water concentration
• Osmosis RP Observing how sugar solutions affect plant tissue

  1. Cut potato into identical cylinders and place them in beakers with different sugar solution concentrations (including pure water)

  2. Measure the mass of the cylinders before and after leaving them in the solutions for 24 hours

  3. Calculate the percentage change in mass to compare the effect of sugar concentration
• Dependent variable Osmosis RP


  • Chip mass
• Independent variable Osmosis RP


  • Concentration of the sugar solution
• CV all other variables (volume of solution, temperature, time, type of sugar used, etc.) must be kept the same
• Errors may arise when carrying out the method (e.g. if some potato cylinders were not fully dried, the excess water would give a higher mass)
• You could also carry out this experiment using different salt solutions and see what effect they have on potato chip mass
• Investigating the effect of pH on the rate of enzyme activity

  1. Add amylase solution and buffer solution to a boiling tube

  2. Add starch solution to the boiling tube

  3. Take samples every 30 seconds and test with iodine solution

  4. Repeat with buffer solutions of different pH values
• Amylase


  Enzyme that catalyses the breakdown of starch to maltose