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How do plants find 'up'?

You will need:

  • A dark cupboard and blanket
  • 2 Tomato plants that are about 10 cm tall
  • 1 plastic bag


  1. Water both plants well.
  2. Leave one plant in full sunlight.
  3. Place the other plant on the floor of the cupboard.
  4. Cover the cupboard with the blanket to exclude light.
  5. Turn the plant pot on it's side and wait 2-3 days.
  6. You should find that the plant stem has 'bent', i.e. growing vertically again.
  7. Place the plant pot inside the plastic bag and tie the ends around the plant stem (to trap the soil)
  8. Tip the plant pot upside down and see if it tries to grow vertically again.
Gravitropism of a plant

Image courtesy

The movement of plants due to gravity is called 'gravitropism'. 'Tropism' means to move. No-one really knows exactly why plants can sense gravity.

Experiments by NASA have shown that plants in space grow in weird spirals. One idea is that gravity makes heavy starch granules inside plant cells fall to the bottom of cells. This may trigger the plants ability to find 'up. For more information see Science@NASA

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