Effect of light/gravity on plant growth (required practical): Homeostasis and response: Biology: GCSE (9:1)

• Germination


  The process where plants grow from seeds into a newly germinated seedling

  
• Mustard or cress seeds


  Quick growing plant species that are ideal for an investigation into plant growth

  
• Cotton wool

  A suitable growth medium that retains water well and does not contain minerals or nutrients that may affect experimental validity

  
• Petri dish


  A glass or plastic dish that would be a suitable container to hold cotton wool and germinating seeds

  
• Mean average

  The total sum of the data values divided by the number of times the data was recorded

  
• Number of seedlings

  The same number of seedlings should be grown in each different experimental condition to make the investigation fair

  
• Dependent variable


  The variable that is measured in this experiment such as the height of the seedlings or direction of plant growth

  
• Independent variable


  The variable that is changed such as angle of petri dish, removal of shoot tip or light intensity

  
• Control variables

  The variables that are kept the same such as volume of water, type of seed, frequency of water application and spacing of seedlings

  
• Clinostat

  A device which rotates to negate the effect of gravitropism in plants

  
• Effect of plant shoot tip removal

  No auxins are present in the plant shoot, so the stem does not grow longer

  
• Effect of no light on a plant shoot

  Equal concentrations of auxins causes the stem to grow evenly and longer on both sides, negative gravitropism still occurs

  
• Effect of light on one side of a plant shoot

  Auxins will have a greater concentration on the shaded side, causing the cells on the dark side of the stem to grow longer

  
• Expected results for seedlings in the dark

  Seedlings grown in dark conditions will grow the longest as germination normally takes place underground, where plants grow rapidly to reach the light

  
• Expected results for seedlings in partial light

  Seedlings will be a similar height to those kept in full light, but will bend and will have grown towards the light source due to phototropism

  
• Expected results for seedlings in full light

  Seedlings will be a similar height to those kept in partial light, but will be shorter than those in the dark as plants do not need full sunlight to grow efficiently

  
• Expected results regarding leaf quality

  The leaves of seedlings in the dark will be small and yellow as photosynthesis cannot take place to make products required for energy or growth

  
• Wavelength of light

  Seedling growth could also be measured under different light wavelengths using colour filters such as red, green or blue