I-oh-dine

I’ve never understood why some teachers give the students a leaf and let them test for starch. How does a green leaf being boiled in water, boiled in ethanol and washed in water before drowning it in brown iodine until it turns black really convince students that green plants make starch?

I think a much better idea is to destarch a plant (put it in the dark for a week, but don’t forget it), then make a mask and cover the leaf with the card mask. Cutting out the shapes can make it fun. Put the plant under some nice photosynthetically active radiation, eg sunlight. Leave the mask over the leaf for a week and then test the leaf for starch. Now only the parts of the leaf that have been in the sun ought to have made the starch and students can tell it isn’t the act of boiling, washing and destroying that is turning iodine blue black.

Gracie, Jayden and Libby did a fab job with their leaf as you can see. It then is obvious to the students that the leaf requires light and produces starch. Be impressed and well done girls, you deserve the honourable mention.

got to show all of their photos or there will be uproar!
another cracking photo showing light is needed for starch production.

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February 2019

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