26th May 2006 at 01:00
KS3 Look at illustrations of pond food chains. Get pupils to look in a pond dip sample for some of the animals and records their size, movement and colour. It is not easy to count the animals but pupils may get some idea of relative numbers and you can link this to pyramids of numbers. Investigate surface tension by floating pins on water; add a drop of detergent and watch the pins sink. Find out if other common liquids (vinegar, soap, bleach) have the same effect. Put a drop of water on a feather and observe.

Treat the feather with solvent to remove the oily coating and add the water again. Watch what happens to the drop. Link the observations to the description of pondskaters in the article.

KS4 The animals found in water are linked to its quality. Rat-tailed maggots, blood worm larvae and Tubifex worms indicate polluted water, while stone fly and may fly nymphs show it is clean. Test water for these species as well as pH, turbidity, odour and colour. Always carry out risk assessments, especially if you are sampling polluted water where there is a chance of Weil's disease.

KS5 Fill washing up bowls, cover with fine mesh and leave in a sheltered place.

Introduce quantitative sampling and counting techniques and over a period of weeks record the changes in the micro - organism populations. Identify the pioneer species and the changes during population succession. Link this to nutrient recycling and phytoplankton changes in lakes and oceans.

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