Plant responses

• Independent variable


  Light intensity
• Dependent variable


  Height of seedlings
• Investigating effect of light intensity on seedling height

  1. Place cotton wool in 3 petri dishes

  2. Soak with equal volumes of water

  3. Place 10 mustard seeds in each dish

  4. Allow seeds to germinate

  5. Water seedlings daily with same volume

  6. Ensure same number of seedlings in each dish

  7. Measure height of each seedling daily for 5+ days

  8. Record results in table

  9. Calculate mean seedling height per day

  10. Draw diagrams to show effect of light intensity
• Seedlings in full sunlight vs partial light

  • Height similar, seedlings grow towards light source due to phototropism
• Seedlings in darkness


  • Grow the tallest, leaves small and yellow as they cannot photosynthesize
• Investigating effect of gravity on seedlings

  1. Place dish of seedlings on its side in dark

  2. Shoots grow upwards against gravity

  3. Roots grow downwards towards gravity

  4. Auxin inhibits cell growth, builds up on lower root side causing slower growth
• Auxin concentrates on side of seedling furthest from light, causing faster growth on that side leading to phototropism
• Seeds usually germinate underground and grow rapidly to reach light