Light and a plant’s growth
Light is an abiotic factor that plants need to make food. Both how strong the light is and how long it shines matter. In general light helps plants grow, but light that is far too strong can dry and burn leaves. Plants also respond to the length of day and night. Some flower only when the nights are long: the chrysanthemum is an example, so it flowers in autumn. Others flower when the nights are short. To test the effect of light, change only one thing and keep everything else the same. Put two bean or lentil seedlings in identical pots with the same soil and the same amount of water. Put one on a bright window sill and the other in a dark cupboard. Measure their heights and note the colours. The seedling in the dark usually grows tall and thin and looks pale, because it cannot make green colour without light.
| Day | Window (cm) | Dark cupboard (cm) |
|---|---|---|
| 2 | 3 | 4 |
| 4 | 5 | 8 |
| 6 | 7 | 12 |
Seedling test. With a grown-up, plant two lentils or beans in identical cups of soil and give both the same amount of water. Put one on a window sill and one in a dark cupboard. Measure the height every two days with a ruler and note the colour for about a week. Draw a table. Wash your hands after touching soil.