Plants and what they need
Biology · Early Years · The School
Parts with jobs
Roots drink water and hold the plant down. The stem carries water up and holds the plant tall. Leaves catch sunlight to make food. Flowers make seeds so there can be new plants. Every part has a job — pull up a weed and look at the roots before you throw it away.
Four things a plant needs
Light, water, air and warmth. Take away any ONE and the plant suffers. That is worth testing rather than believing: grow four cress pots, and give one no light, one no water, one a cold windowsill, and one everything. A week later, the pots tell you the answer themselves.
Change one thing only
In that cress test, keep everything the same except the ONE thing you are testing. If the dark pot also got less water, you would not know which caused the difference. Scientists call this a fair test, and it is the single most important idea in all of practical science.
Plant four identical seedlings. Pot 1 gets everything: light, water, warmth. Pot 2 gets no light. Pot 3 gets no water. Pot 4 goes in the fridge. After a week, pot 1 is healthy, pot 2 is pale and floppy, pot 3 is dry and drooping, pot 4 has barely grown. Only ONE thing was changed in each, which is why you can say what caused each result. Change two at once and you learn nothing.