Using Autumn leaves to learn about Photosynthesis

Autumn_foliage_2012_(8253653780)Most secondary school children, and many primary school children too, will have learnt about photosynthesis in class: if you need a refresher, this is the process that makes a leaf green.

What many of us don’t know is why the leaves turn other colours in autumn, and you can use this time of year to teach them why but in a way that doesn’t involve any sitting in a classroom or writing chemical equations (unless they really want to!). Take a walk with your children in the woods and talk about the different colours they can see: brilliant reds, burnt oranges, purples and more. Ask them why they think this happens; is it something that has been added to the leaves, or something that is missing? Were the colours always there? Have they changed over time and why?

They may come up with some lovely ideas but the truth is that a tree’s leaves are always orange and yellow, even in summer. In the sunnier months, the greenness is more present because the pigment chlorophyll is stronger than the pigment that makes up the other colours (xanthophyll makes the yellow and carotene the orange if you want to get clever). In autumn, the leaves produce less chlorophyll when there is less sunlight and the other colours are able to burst through. The reds and purples we see are from the pigment anthocyanin, which isn’t present all year and just appears when the night’s get cooler, so is a real sign that winter is on the way.

Thinking about these signs that photosynthesis is slowing down, you might then like to talk with your children about what they think happens with there isn’t enough sunlight and water for the process that gives life to trees to occur: the trees ‘shut down’ and  rest until spring when the process starts all over again. You might also like to talk about the word deciduous and why dentists use this word to apply to milk teeth too.

While you’re in the woods, you could try some other fun activities: collect some leaves and use them for a collage or press them when you get home. Draw them or take photographs, trying to capture the amazing range of colours you can see. Buy or download a tree guide and walk the woods seeing what you can find. Or just have a good time traipsing through piles of leaves.


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