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Cress in the dark - why does it grow so fast???

Discussion in 'Primary' started by Emnemz, Jun 16, 2008.

  1. We're doing a cress experiment in Year 1 and after planting it on Friday already the cress that's grown in the dark has grown the most. The cress that has everything (water, warmth, sunlight and nutrients) has grown a little bit, and the other 2 (in the cold and in the sand) haven't grown at all. There's loads of cress in the dark one, more so than the one that has everything. I know about it not being as green because of the lack of sunlight/chlorophyll but how can I explain about the fact that it's grown at all?

    I can only think that it's growing towards the tiny gap where the light is coming in because it's striving to get to the sun - plus I know I'll be able to physically show the kids this because it's literally bending over towards the gap.

    I've tried googling but can't really find any child-friendly terminology.

    Any help would be much appreciated!!
     
  2. The cress fairy makes it grow and grow and grow;)
     
  3. Germination is the process by which seeds sprout. Seeds must go through several stages of development before being ready to sprout. When seeds are ready to be planted warmth, water, and oxygen are all needed for seed to germinate. This is because the seed contains the plant embryo, which stores enough food to give the baby plant all the energy it needs to sprout. After the seeds sprout and use up all the stored food, they do need light to grow. The light is needed for photosynthesis, which thereafter provides the plant?s food source. ( http://wow.osu.edu/experiments/plants/sprout.html )

    Roots respond to gravity and move downwards, but a special event called tropism occurs which makes the plant look for light (in effect) so if in the dark it will grow and grow to look for the light as it needs to light to make its food in a process called photosynthesis. So if it is in the dark it will search for the light and respond to the light which is why plants in the dark are often longer, paler and weaker as they are looking for the light, overgrowing and until photosynthesis can occur (once it has used up all the nutrients in the seed) it will be pale and weak.
     
  4. Find this thread title amusing as wotsit4 is known to us as cress! But she doesn't grow? Maybe we should experiment with cress a bit!
    Sorry to bring tone of thread down!
     
  5. I like MP's explanation best. Nice and simple.
     
  6. Still think my idea is best!
     
  7. I knew I was right!
     
  8. nomad

    nomad Star commenter

    In child-friendly terms, the cress can tell the difference between light and dark.

    If it is kept in the dark, it 'believes' that it is still under the ground and so it grows as fast as possible to get to the light so that it can start making food properly.
     
  9. Right can anyone now explain in child friendly terms why on earth the seeds that were kept dry and in the dark and then others that were kept dry and in the light have grown really well. The others (light and watered and then dark and watered) haven't grown at all. And I did a science degree!
     
  10. Your classroom is damp so the 'dry' ones were a bit damp and grew happily. Your 'wet' ones have had the kind of attention my littlest carrot gives to all plants - a good 2 inches of water and advice to 'swim'!
     
  11. Very funny! Wet ones were only watered when the soil was dry and a small amount of water. Surprisingly giving over task to children meant they did it properly and diligently and didn't overwater so not sure why it happened. We even dried out the soil as children thought it needed to be really dry. Therefore, not sure why it happened. But hey gave us lots to talk about. Planted cress seeds too and they worked fine so at least we saw seeds do what they were supposed to do. It even happened with the sunflower seeds so maybe my classroom is damp! Bizarre.
     
  12. The dry seeds growing seems very odd - maybe there were also mould spores in there, that needed a bit more moisture than the seeds, so the watered seeds rotted (and the dry ones managed on the minimal amount left in the 'dry' soil)? As you say, at least it gives an interesting discussion! Maybe the children had very damp, sweaty hands?!
     
  13. nomad

    nomad Star commenter

    Always use rain water when germinating seeds. the aluminium sulphate in the drinking water supply acts as a growth retardant.
     
  14. Thanks nomad for that snippet. I may be a scientist but not a gardener! Our cress has worked as expected but the beans haven't. But we ended up having a very interesting chat about our results today. We were observed by some older children who were amazed by how knowledgeable my year 1s were!
     

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