Plants Around Us
Primary 2 · Science and Elementary Technology
Plants Around Us
Lesson 2 of 3
12 min
Let's begin
Keza planted two bean seeds on the same morning. Same soil. Same size cup. Same amount of water every day.
She put one cup on the windowsill, where the sun comes in. She put the other cup in a dark box under her bed.
Two weeks later she looked at both. One plant was short, strong and dark green. The other was pale, thin and floppy, and it fell over when she touched it.
Why? Let's find out.
Look again at what Keza did. The soil was the same. The cup was the same. The water was the same. The seeds were the same.
Only one thing was different: one plant had light, and one plant had no light.
So the difference in the plants must come from the light. Nothing else could have caused it!
That is how a scientist thinks. Change one thing. Keep everything else the same. Then you know what caused what. Remember this — you will use it in your own experiment.
Keza's dark-box plant was pale and thin because its leaves could not do their job. Leaves need sunlight to make food. No light means no food. A hungry plant grows thin and weak, and then it dies.
This is why farmers plant their beans in an open field, and not underneath a thick shady tree. The tree would block the sunlight, and the beans would go hungry.
Uwase forgot to water her plant for a whole week. She came back and the soil was dry as dust. The leaves were hanging down, soft and floppy, like a tired flag.
She poured water on the soil. By evening, the leaves were standing up again.
Water goes in through the root, travels up the stem, and reaches the leaves. Water is what keeps a plant firm and standing.
Yes! This surprises many people.
If you pour water into the cup every hour, the soil turns into mud. The roots sit in water all day. And roots need to breathe air — air that hides in the little gaps between the bits of soil. In mud, there are no gaps, and no air.
The roots rot, and the plant dies. So do not drown your plant with kindness.
The rule: keep the soil damp, not swimming. Touch the top of the soil. If it feels dry, add a little water. If it still feels wet, wait.
You breathe air. So does a plant.
The leaves take in air, and the leaf uses that air, together with water and sunlight, to make the plant's food. And as you just learned, the roots need air down in the soil too.
That is why farmers dig and loosen the soil before planting. They are letting air into the ground for the roots.
Soil does three jobs at once:
Soil can run out of that goodness after many harvests. That is why your family digs compost or manure into the garden. They are putting the goodness back.
Mugisha's bean plant looks sad. Here is exactly what he sees:
Let's work it out together.
Is it thirsty? No — the soil is damp, so it has water.
Is it leaning towards the window? Yes. A plant leans towards light, because it is reaching for it. So it is not getting enough light where it is standing.
Pale + thin + leaning towards the window = not enough light.
What should Mugisha do? Move the plant to the sunny windowsill. Not water it more — that would only make things worse!
See what you just did? You looked at the clues, and you worked out the cause. That is real science.
Tip
A plant needs four things every day, just like you:
a drink (water), a sunbath (light), a breath (air), and a bed (soil).
Drink, sunbath, breath, bed. Say it four times and you will never forget it.
Work each one out first. The answer is right underneath.
Name the four things a plant needs to grow well.
Answer: water, light, air and soil.
Umutoni's plant has soft leaves hanging down, and the soil is dry as dust. What does it need?
Answer: water. Water keeps a plant firm and standing up.
Gatete waters his plant ten times a day. The soil is like mud. The plant is dying. Why?
Answer: the roots are sitting in water and cannot get air, so they rot. Soil should be damp, not swimming.
Why do farmers not plant their beans under a big shady tree?
Answer: the tree blocks the sunlight. Without sunlight, the bean leaves cannot make food, and the plants grow thin and weak.
Keza wants to find out if a plant needs soil. She fills one cup with soil and puts a seed in it. What must she put in the second cup, and what must stay the same?
Answer: the second cup gets no soil — just the seed (you can rest it on damp cotton or cloth). Everything else must stay the same: same seed, same water, same light, same place. Change only one thing!
Note
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