What plants need to grow

Plants are living things, yet they seem to just stand there. In fact they breathe, respire, make their own food and reproduce. This chapter looks at how.

We know animals eat food to grow. But have you ever seen a plant eating the way an animal does? Still, as a plant grows, new leaves and branches appear, it gets taller, and its stem gets thicker. What makes that happen?

The students in the book have three ideas:

• water helps, because plants grow better when watered regularly;
• sunlight plays a part;
• plants take food from the soil through their roots.

Activity 10.1 tests them. Fill three clay pots of the same size with garden soil and plant a young sapling of a fast-growing plant, like chilli or tomato, in each. Use the same kind of plant, of similar size, in all three, so that the only thing that differs is the condition you are testing. Label them A, B, C and count their leaves.

• Pot A: direct sunlight, watered every day so the soil stays slightly moist.
• Pot B: direct sunlight, no water.
• Pot C: kept in the dark, watered every day.

Watch for two weeks, noting the height, the number of leaves and the colour of the leaves.

The plant in pot A (sunlight and water) grows better than the plant in pot C (water but no sunlight). The plant in pot B may even have died: plenty of sunlight, but no water.

So plants need both sunlight and water to grow. Neither one alone is enough.