Bio RP

• Preparing a slide of onion cells

  1. Use a dropping pipette to put one drop of water onto a microscope slide

  2. Separate one of the thin layers of the onion

  3. Peel off a thin layer of epidermal tissue from the inner surface

  4. Use forceps to put this thin layer on to the drop of water

  5. Make sure that the layer of onion cells is flat on the slide

  6. Put two drops of iodine solution onto the onion tissue

  7. Carefully lower a coverslip onto the slide

  8. Use a piece of filter paper to soak up any liquid from around the edge of the coverslip
• Focusing the microscope


  1. Turn the nosepiece to the lowest power objective lens

  2. Looking from the side, turn the coarse adjustment knob so that the end of the objective lens is almost touching the slide

  3. Looking through the eyepiece, turn the coarse adjustment knob to increase the distance between the objective lens and the slide until the cells come into focus

  4. Rotate the nosepiece to use a higher power objective lens

  5. Slightly rotate the fine adjustment knob to bring the cells into a clear focus

  6. Use the low-power objective (×40 magnification) to look at the cells

  7. Switch to a higher power (×100 or ×400 magnification)
• Equipment provided


  • a small piece of onion
  • a knife or scalpel
  • a white tile
  • forceps
  • a microscope slide
  • a coverslip
  • a microscope
  • iodine solution in a dropping bottle
• Investigating the effect of antiseptics on the growth of bacteria

  1. Prepare a lawn plate of bacteria

  2. Test the effectiveness of three different antiseptics
• Care must be taken when handling microorganisms such as bacteria
• Aseptic techniques


  Techniques used during the experiment to avoid contamination
• Contamination can be where microorganisms from the surroundings get into your experiment and spoil your results or your experiment get into the surroundings and cause a potential health hazard
• Clear zone

  The diameter of the area around the disc where there is no bacteria growing
• The larger the clear zone, the more effective the antiseptic
• Setting up the working area

  1. Spray the bench with disinfectant spray

  2. Wipe with paper towels

  3. Place Bunsen burner on heatproof mat

  4. Light Bunsen on yellow flame

  5. Wash hands with antibacterial hand wash
• Preparing the agar plate


  1. Mark the plate with wax pencil

  2. Divide plate into 3 sections

  3. Number the sections 1, 2, 3

  4. Place a dot in the middle of each section

  5. Write initials, date, bacteria name around the edge
• Inoculating the agar plate

  1. Turn Bunsen flame to blue

  2. Flame the neck of the bacteria culture bottle

  3. Collect 1ml of bacterial culture with pipette

  4. Flame the neck of the bottle again and replace lid

  5. Lift plate lid at an angle

  6. Pipette bacteria onto plate

  7. Replace plate lid

  8. Place pipette in discard beaker

  9. Turn Bunsen to yellow
• Spreading the bacteria


  1. Dip glass spreader in ethanol

  2. Flame the spreader

  3. Allow spreader to cool

  4. Lift plate lid at angle

  5. Spread bacteria around plate with spreader

  6. Place spreader in discard beaker
• Applying the antiseptics

  1. Place different antiseptics onto 3 filter paper discs

  2. Lift plate lid at angle

  3. Place each disc onto a dot on the plate

  4. Note which antiseptic is in each section

  5. Secure plate lid with tape
• Incubating and measuring


  1. Incubate plate at 25°C for 48 hours

  2. Measure diameter of clear zone around each disc

  3. Calculate mean diameter
• Record results in a table
• Osmosis


  The movement of water through a selectively permeable membrane from an area of high concentration of water to an area of lower concentration of water
• Plant tissues


  • Can be used to investigate osmosis
• Investigating osmosis in potato tissue

  1. Cut potato into equal sized cylinders

  2. Leave potato cylinders overnight in sugar solution and distilled water

  3. Measure changes in length and mass
• Amylase


  Enzyme that controls the breakdown of starch in our digestive system
• Simulating digestion


  1. Use solutions of starch and amylase in test tubes

  2. Find the optimum conditions required
• Iodine solution


  Used to determine the presence or absence of starch
• Measuring the time for amylase to break down starch at different temperatures

  1. Place one drop of iodine solution into each depression on the spotting tile

  2. Set up water baths for different temperatures

  3. Measure out 5 cm3 of starch solution into 4 test tubes

  4. Place one test tube of starch solution into each water bath

  5. Measure out 1 cm3 of amylase solution into 4 different test tubes

  6. Place one test tube of amylase solution into each water bath

  7. Wait until contents reach required temperature

  8. Pour amylase into starch solution and mix

  9. Remove one drop of mixed solution and place on first depression of spotting tile (time zero)

  10. Remove one drop every minute and place on next depression

  11. Continue until iodine solution no longer turns black

  12. Record temperature and time taken for starch breakdown
• Repeat the process for the other temperatures
• Testing for sugars


  1. Grind up food sample

  2. Transfer ground food to beaker and add distilled water

  3. Stir to dissolve food content

  4. Filter to obtain clear solution

  5. Half fill test tube with solution

  6. Add 3 drops of Benedict's solution to test tube and shake
• Benedict's solution


  Used to test for the presence of carbohydrates
• Iodine solution


  Used to test for the presence of carbohydrates
• Testing for lipids


  1. Grind up food sample

  2. Transfer ground food to beaker and add distilled water

  3. Stir to dissolve food content

  4. Filter to obtain clear solution

  5. Half fill test tube with solution

  6. Add 3 drops of Sudan III stain to test tube and shake
• Sudan III stain


  Used to test for the presence of lipids (fats)
• Sudan III contains ethanol, which is highly flammable. Keep the solution away from naked flames.
• Wear safety goggles.
• Photosynthesis


  The process where plants use carbon dioxide and water to produce glucose and oxygen
• Factors affecting photosynthesis rate

  • Light intensity
  • Light wavelength
• Pondweed


  An aquatic plant that produces visible bubbles of oxygen gas into the surrounding water when they photosynthesise
• Investigating the effect of light intensity on photosynthesis in pondweed

  1. Set up test tube rack with pondweed at 10 cm from light source

  2. Fill boiling tube with sodium hydrogen carbonate solution

  3. Place pondweed in boiling tube

  4. Leave for 5 minutes

  5. Start stopwatch and count bubbles for 1 minute

  6. Repeat bubble count twice more

  7. Move test tube rack to 20 cm, 30 cm, 40 cm from light source and repeat steps
• The closer the light source, the greater the light intensity
• The number of bubbles produced can be used as a measure of the rate of photosynthesis
• Investigating whether practice reduces human reaction times
• Messages travel very quickly around your body through the nervous system so you can respond to changes in the environment
• Reaction time


  The time it takes for you to respond to a change in the environment