Can you expose the hidden plants in your soil?
Biologists of all kinds use assays to determine how to design their experiments. An assay is an investigative process that reveals which variables can be measured in a study system. In this activity, you’ll determine how many seeds are buried in different depths of your soil by germinating the seeds, and you’ll explore the variables that impact seed germination.
- The Experiment Station
- 4 Pots
- 10 Lettuce seeds
- Potting mix
- Hand trowel
- 150 mL Irrigation syringe
- Grow light or a very sunny windowsill
- Felt tipped permanent marker
- Notebook and pencil
- Soil thermometer
1. Prepare pots
Take 4 pots and fill halfway with potting mix. Label each of 3 pots with these depths: 6 cm, 16 cm, and 26 cm. Label the fourth pot “Control.”
2. Add soil samples and seeds
Put the soil samples you collected from various depths during Activity 1 into the correctly-labeled pots.
In the control pot fill the rest of the volume with potting mix and sprinkle 10 lettuce seeds on top.
3. Situate the filled pots on the Experiment Station
A circle designates where to put each pot—this will help keep the assay organized.
Using a 150 mL irrigation syringe, pull 30 mL of water and use it to evenly wet the soil surface of the pot. Water twice a day—morning and evening—or as needed to dampen the soil surface.
5. Record your data
Create a table where you can write down the results from your experiment. Record how many plants each pot has, amount of water you added and the soil temperature for each pot. Collect data for at least 9 days.
What is a “Control?”
A control is the element of an experiment that stays consistent throughout, indicating how variables impact results.
The control in this assay is designed to determine whether conditions are suited for seed germination. If the lettuce seeds germinate, your conditions are right for seed germination. If they do not germinate think about how some variables (sun, temperature, water) could cause low germination rates and try the assay again after you alter the variables.