Practical activity - Effects of light or gravity on seedling growth


Investigate the effects of light or gravity on the growth of newly germinated seedlings.

Germination is the beginning of plant growth, and the plant will continue to grow if the correct conditions are available.

Mustard or cress seeds are a good choice for this investigation because they grow fast and their roots and stems are clearly visible.


The independent variables for this investigation are to place plants in light and dark conditions. Other suitable independent variables are: different colours of light, intensity of light, or the direction light comes from.

The dependent variable is the mean height of seedlings.

Control variables are the number of seeds on each dish, how much they are spread out, the volume of water the seedlings are given, the temperature they are kept at.


  1. Put cotton wool into three petri dishes, and add the same volume of water to each dish.
  2. Add ten seeds to each dish and place them in a warm place where they won’t be disturbed.
  3. Allow the seeds to germinate, and add more water if the cotton wool dries out.
  4. Once the seeds have germinated, ensure the petri dishes each contain the same number of seeds, and remove any extra seeds if necessary.
  5. One petri dish will sit in full light on a windowsill, the second will be in a dark cupboard, and the final dish will be placed in partial light.
  6. Every day for one week, measure the height of each seedling and record the results in a table. You must record the height of the individual seedlings on each day.
  7. Calculate the mean of the seedlings each day, and compare the mean heights in the three different locations.