HOMEOSTASIS: RP8/plant hormones

• 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. Leave in warm place to germinate

  5. Water seeds 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 different light intensities
• Control variables


  • Volume of water
  • Type of seed
  • Number of seedlings
• Seedlings in full sunlight and partial light have similar height
• Seedlings in the dark have grown the longest
• Seedlings grow towards the light source

  Due to phototropism
• Auxin concentrates on side of seedling furthest from light


  Causes that side to grow faster
• Seedlings in the dark have small, yellow leaves
• Investigating effect of gravity on seedlings

  1. Place dish of seedlings on its side in the dark

  2. Shoots grow upwards against gravity

  3. Roots grow downwards towards gravity
• Auxin inhibits cell growth in roots

  • Gravity causes auxin to build up on lower side of root
  • Lower side grows more slowly than upper side
  • Makes root grow in direction of gravity
• You'll find plenty of questions on this required practical in the revision workbook