Ask most children what plants need to grow, and you’ll usually get the answer “sunshine and water” straight back, but not as many of them will be so quick to tell you why. Photosynthesis has been described as the most important process on the planet and it is very easy to see why. The ability of plants to make their own food by turning carbon dioxide and water into sugar and oxygen, using sunlight and a spot of clever chemistry is quite remarkable and forms the basis of all food chains in nature – not to mention making breathing possible!
While the chemistry itself is fairly complex, the good news is that the basic idea is easy to grasp and kids know most of the important points already – although they’ve probably never really thought about it. To get started on the photosynthesis path, asking them if they like eating vegetables can sometimes be a good start – whether they enthuse wildly or just simply say “yuck” really doesn’t matter! Once you’ve got them talking about eating plants, if you can lead the discussion away from vegetables and on to their favourite fruits – you’re almost there. Of course, the sweetness of fruits tends to be the reason children like them – and sweetness means sugar, and sugar means photosynthesis – but how do you explain that to a bunch of little inquiring minds?
Ever Wondered Why Plants Are Green?
Every kid knows that plants are green (well, mostly), but asking them to think about why can be a good way to bring up the idea of that special plant pigment, chlorophyll. Once you have done that, it should be a whole lot easier to explain the whole process. It’s worth spending a bit of time getting the idea over that this green plant pigment is trapping the sun’s energy and using it – a bit like a factory uses electricity – to make something new. Children know that plants don’t eat anything, so the idea of them making their own food shouldn’t be too hard to introduce to youngsters – and that, of course brings you back to green plant pigment once again. The actual chemistry isn’t necessarily just so important for children to understand at this stage, (though if they do, so much the better) but something along the lines of :
“Water and carbon dioxide make sugar and oxygen, in the presence of sunlight and green plant pigment” should do very nicely for a start.
Having reached this point, it’s a really good time to remind children just how important oxygen is for us and all the other animals on the planet, and what trouble we’d all be in if plants didn’t photosynthesise.
Nothing makes the point quite so well as seeing it for yourself, so if you have a small aquarium or vacant fish tank, here’s a useful little activity you might like to try with your kids. You’ll need a few sprigs of pond weed – Canadian Pond Weed (Elodea) which you can buy from most pet shops works really well – and a jam or coffee jar. Fill the aquarium with water and submerge the jam jar, place the weed inside the jar and then stand the jar on its open end, so the weed is left sitting underneath. It’s best to set this up an hour or two before you want to use it, keeping the aquarium cool and for best results, covered with a towel or small cloth to keep out the light.
If you then uncover the aquarium and stand it in sunlight, as the weed photosynthesises, bubbles of oxygen will start appearing on the leaves and if you leave it long enough, they should rise up to the jam jar, pushing out the water as they gradually collect inside the glass. It’s a nice and simple way of making it possible to see something which normally goes on invisibly and unnoticed.
These days it’s a very rare child indeed who has not heard about carbon dioxide – at least in its role as “villain” in global warming, but teaching kids about its pivotal role in photosynthesis is a sure-fire way of introducing the whole idea of cycles in nature. It can also help them make sense of a lot of other things too – from how to look after plants in the garden to just what an important role plants play by giving us food and oxygen, and why conserving rainforests is such a good thing to do. Today’s eco-aware youngsters should lap it up.