Step 4 - Planning the experiment

Designing the experiment
Listing what you need Describe how you will use them. Make a diagram if you want.

30 cress seeds cotton wool

3 dishes cling film



  1. Put a layer of about 2 cm depth of cotton wool in each dish.
  2. Add 5 cm3 water to each.
  3. Lay 10 cress seeds on top of each piece of cotton wool.
  4. Cover the dish with cling film. Leave dish A at 10 °C, dish B at 20 °C and dish C at 30 °C.
  5. Leave each for three days, then count how many seeds have sprouted in each dish

The pupils now plan the experimental procedure. It is very important to stress that only one of the variables can be changed during the experiment. As a result the variable being measured will, presumably, change. All other variables must be kept constant to ensure a fair test.

Step 3 - Asking a question

Step 5 - Carrying out the experiment