When testing the best conditions for seed germination, controlled variables are the factors you keep constant to ensure a fair test. These variables do not change throughout the experiment so that any differences in germination can be attributed to the independent variable you are testing.

Examples of Controlled Variables in Seed Germination Experiments

• Type of seed: Use seeds from the same species and batch.
• Amount of water: Provide the same volume of water to each seed or group.
• Soil type or growth medium: Use the same soil or medium for all seeds.
• Temperature (if not the variable being tested): Keep the temperature constant.
• Light exposure (if not the variable being tested): Keep light conditions the same.
• Container size: Use identical pots or trays.
• Planting depth: Plant seeds at the same depth.
• Air humidity: Maintain consistent humidity levels.

By controlling these variables, you ensure that the only factor affecting germination is the one you are intentionally changing (e.g., temperature, light, water amount, soil type). This allows you to draw valid conclusions about the best conditions for seed germination.