Plants and what they need
Biology · Early Years · The School
Parts with jobs
Roots drink water. They hold the plant down too. The stem carries water up, and it 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
A plant needs four things. Light. Water. Air. Warmth. Take away any ONE and the plant suffers. That is worth testing, not just believing. Grow four cress pots. Give one no light. Give one no water. Put one on a cold windowsill. Give one everything. A week later the pots tell you the answer themselves.
Change one thing only
In that cress test, keep everything the same. Change only the ONE thing you are testing. Say the dark pot also got less water. Then you would not know which one caused the difference. Scientists call this a fair test. It is the single most important idea in all of practical science.
Plant four identical seedlings. Pot 1 gets everything: light, water and warmth. Pot 2 gets no light. Pot 3 gets no water. Pot 4 goes in the fridge. Come back 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 pot. That is why you can say what caused each result. Change two at once and you learn nothing.