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In the beginning there was water, sand...

A workshop on a miniature ecosystem offers a beautiful and near-perfect biology lesson for primary classes, writes Douglas Blane

Making planets is a messy business. No matter how well prepared you think you are, there is always some debris left at the end. So, as the pupils at St Cuthbert's Primary school, Glasgow, head home with their bottled planets under their arms, their teachers swoop on the scattered sand, salt and sticky tape and in minutes return the classroom to its pristine condition.

If only there had been a few teachers around when the solar system was created it wouldn't be the cluttered place it is. ("Get those meteors tidied up before they have somebody's eye out.") Of course the children haven't made a whole living planet in a bottle. But with the help of presenters Mathew Castle and Georgina Bell, they have created a miniature ecosystem.

Once algae, water, sand and eggs have been brought together and a little fertiliser and starter food added, the children need only shake their bottles - which they all manage with enthusiasm - then keep them warm, well-lit and undisturbed for two days. This might be harder for pupils with pesky little brothers, suggests young Chantelle.

If all goes well the eggs will hatch into dozens of translucent brine shrimps and, like a machine but with living parts, the self-contained system will begin to operate. The algae will make food from sunlight. The shrimps will graze on the algae. The oxygen given off by the algae will e used by the shrimps for respiration. The carbon dioxide exhaled by the shrimps will be used by the algae in photosynthesis. And shrimps that die will be broken down by micro-organisms and replaced by some of the 75 young ones to which the prolific females give birth in a day.

It's beautiful. It is also quite technical, scientific and at first sight maybe too advanced for Primary 4. But the presenters blend theory and practice so well, using questions to draw out previous knowledge, that the children absorb the science almost as naturally as the shrimps take in oxygen. It is not far from being a perfect biology lesson, with the added bonus that, once self-sustaining, the ecosystems in the bottles can be used again and again to explore aspects of living things and the processes of life.

The presenters are lively, patient and knowledgeable, but in the children's eyes are effortlessly upstaged by the bottled beasts, which give birth, fight for female favours, mate enthusiastically, and scuttle around like demented orange aliens. "It's amazing the effect they have on kids," says Mathew. "The worst class in the world will settle down when they see the brine shrimps."

Bottled Planet is supported by the Marine Conservation Society and aimed at Primary 4-6 and P7.More information on using the brine shrimp Artemia in 5-14 science can be found in the Journal of Biological Education 34, p117-122, as well as on various websites, such as www.homerton.cam.ac.ukresearchbsep

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