Moving and breathing in water

When humans go under water they use special equipment to supply them with air. Some pond minibeasts have a similar system. Water boatmen carry air trapped in hairs on their underside and water spiders make an underwater air supply by collecting air at the surface and putting this in an underwater web.

Alternatively, some pond minibeasts have a thin body wall or a special region that absorbs oxygen directly from the surrounding water, e.g. water fleas (body surface), mayfly nymphs (external gills) and dragonfly nymphs (internal gills at their back end).

Moving through water is more difficult than moving through air and animals living under water have developed different ways of swimming, floating and crawling.

At the water surface, animals can take advantage of "surface tension" - a sort of special film that can support gentle weights. Pond skaters and whirligig beetles skate on the surface and water boatmen hang below the surface.

Descriptions of each animal's adaptations are given in the notes included with this pack.

Aims: To show that animals are adapted in different ways to living in water.

Activities

1. How do pond minibeasts move?

This can be done at the edge of the pond or back in the classroom if a suitable tank is available. By asking simple questions like the following, differences in animals and their lifestyles will emerge:

Where is the animal in the water? On the surface, under the surface, on the bottom or amongst the plants?
How does the animal move? Steady, jerkily, quickly, slowly?
What are the movements? Walk, run, crawl, swim, wriggle, flip, skate?
How many legs does it have? Are all the legs the same? Does it have feelers (antennae)?
Can you separate the herbivores (plant-eaters) from the carnivores (meat-eaters)? In general, carnivores tend to move quickly and have conspicuous eyes and jaws.

2. How does a pond skater skate?

The pond skater is a common bug that skates around on the water surface. To see how the surface of the water can support gentle weights, float a piece of blotting-type paper in a bowl of clean water and place a needle on it. As the papers sinks, the needle should be supported by the surface film. Detergents break up the surface film, and so after adding a drop of washing-up liquid the needle should sink.

Try floating other objects on the water to see what floats and what sinks, e.g. stones and leaves.

3. How does pollution disrupt the water's surface?

Pollutants such as detergents destroy the surface tension of water. A novel way of demonstrating this is by making a soap-powered boat. Simply cut out a piece of card to the shape shown then float it on the water - the boat does not move. Then remove it from the water and wedge a small piece of soap in the notch at the back. Watch how the boat moves through the water as the surface tension behind it is disrupted by the soap.

4. How does a water boatman breathe?

Fill a jar with pond water, then collect a water boatman and some pond weed and transfer them to the jar. Watch the water boatman come to the surface for air. How long does it stay under water before coming up for air?

Pond Pack Introduction Why study ponds? Pond-dipping Safety for teachers Safety for kids Animal variety Moving and breathing Cycles of life Webs of life Plant life Maths English Geography History Art and design Make a pond Plant identification Animal identification Activity sheets Bug dial Where to go Acknowledgements EDUCATION NATURE SEARCH . . . . . . . . .