biology required practicles

• GCSE biology required practicals for AQA

  • Microscopy
  • Osmosis
  • Enzymes
  • Food tests
  • Photosynthesis
  • Reaction times
  • Quadrats
  • Microbiology
  • Germination
  • Decay
• Tips for answering practical questions

  • Identify the independent variable (the thing you change)
  • Identify the dependent variable (the thing that changes as a result)
  • Identify the control variables (things you keep the same)
  • Describe the equipment used for measurements
  • Discuss safety precautions like using goggles, gloves, etc.
  • Discuss ways to improve accuracy and reduce errors (e.g. taking repeat measurements, using proper techniques)
  • Use bullet point format to clearly communicate key points
• Microscopy

  1. Prepare a thin layer of onion skin

  2. Place on microscope slide and add iodine stain

  3. Place cover slip

  4. Start with lowest magnification and focus

  5. Increase magnification and refocus if needed

  6. Measure cell size using graticule
• Osmosis

  1. Cut equal-sized cylinders from vegetable

  2. Place in test tubes with different sugar solution concentrations

  3. After set time, remove, dab dry, and reweigh

  4. Calculate percentage change in mass

  5. Plot against solution concentration to find concentration with no osmosis
• Enzymes

  1. Measure out enzyme and substrate solutions

  2. Mix together and start timer

  3. Every 10 seconds, test for presence of substrate using iodine

  4. Record time for complete reaction

  5. Repeat with different temperatures or pH values

  6. Plot time against temperature/pH and identify optimum
• Food tests

  1. Grind solid food and mix with water

  2. Test for starch using iodine

  3. Test for glucose/simple sugars using Benedict's solution

  4. Test for proteins using biuret reagent

  5. Test for lipids by adding ethanol and water
• Photosynthesis

  1. Set up pondweed in inverted test tube or cylinder

  2. Measure distance from light source

  3. Count bubbles or measure oxygen volume in set time

  4. Repeat at different distances

  5. Plot against distance and observe inverse square relationship
• Reaction times

  1. Hold ruler between partner's fingers

  2. Drop without warning and have them catch

  3. Calculate reaction time using distance and acceleration formula

  4. Repeat and calculate mean
• Quadrats

  1. Use random number generator to choose quadrat positions

  2. Count organism in each quadrat

  3. Calculate mean density and multiply by total area
• Microbiology

  1. Spot different bacterial cultures on agar and observe growth

  2. Or spread culture to make lawn and add antibiotic discs

  3. Use aseptic techniques to avoid contamination
• Germination

  1. Place seeds on damp cotton wool in Petri dish

  2. Observe root growth (geotropism) and shoot growth (phototropism)
• Decay

  1. Measure milk/cream volume and add sodium carbonate and phenolphthalein

  2. Add lipase enzyme and measure time for decolourisation

  3. Repeat at different temperatures and plot against time