Science Sparks: Cress Caterpillars

This is our cress caterpillar! You can see in the photo that 3 of the segments are a lighter shade of green than the other three. Can you guess why this might be?


What you need:

  • Cress seeds
  • An egg box, cut into segments
  • Water


  • Place some cress seeds in each segment of the egg box.
  • Place 3 segments on one plate or tray and 3 on another plate or tray.
  • Add water to all, and place one plate on a windowsill and one in the dark.
  • Water frequently.

The cress should grow within a few days. I did give my ‘in the dark seeds’ a little bit of light to help them grow which is why they are slightly green.

The Science Bit

We were very surprised that the seeds grew so well without any soil. They got everything they needed to grow from the water and nutrients stored in the seed.

Green plants make sugar for growth by a process called photosynthesis.

Carbon dioxide + water  (and light ) ———> glucose and oxygen

Photosynthesis takes place in choroplast cells which contain a substance called chlorophyll which makes plants green.

Sunlight is also needed to make chlorophyll, this is why the cress seeds which have been exposed to less sunlight are less green than the seeds kept in the sun.

Thanks Science Sparks!


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