GoalMake a prediction about where a plant will grow best, test it fairly and say what the results show.
New words
predict · to say what you think will happenfair test · a test where you change only one thingresult · what you find out at the end
Explanation
Scientists test their ideas. First they predict what will happen. In a fair test you change only one thing. Everything else stays the same. Mia wants to find out if a plant needs light. She puts one plant in the light and one in a cupboard. The pots, the soil and the water are the same for both plants. Only the light is different. After two weeks she looks at both plants and writes down her results. The plant in the light grew well, so plants need light.
Plant A
Plant B
light
yes
no
same pot and soil
✓
✓
same water
✓
✓
result after 2 weeks
?
?
Worked examples
Mia changes the light. She keeps the pot, the soil and the water the same, so the test is fair.
Mia’s results after two weeks: the plant in the light is 12 cm tall and green. The plant in the dark is 5 cm tall and pale.
If Mia gave one plant a lot of water and the other none, she could not tell if the light or the water made the difference. That would not be a fair test.
Class activity
Fair test (with an adult): does a plant grow better in a warm place or a cool place? Plant the same number of seeds in two identical pots with the same soil. Put one pot indoors and one in a cool shady spot outdoors (not freezing). Give them the same amount of water. Predict first. Measure the tallest seedling in each pot every two days with a paper strip and write the lengths in a table. Which place was better?
Practice
1
In a fair test, how many things do you change?
Only one.
2
Sara tests if seeds grow better in sand or in soil. Which two things must she keep the same?
Any two of: the water, the light, the pot, the kind of seed. She changes only what the seeds grow in.
3
Look at the results. Which plant grew taller, and how many centimetres taller?
The warm plant, by 3 cm.
4
Before you start a test, you say what you think will happen. What is this called?
