A Safari in a Clump of Moss
Wren Kowalczyk peeled a clump of moss off the old brick wall behind Eastfield Middle School. It had not rained for two weeks, and the moss was brown and crunchy. "It looks dead," said her classmate Mateus Ferreira. Their teacher, Ms. Oyelaran, suggested they find out what was really in it.
The class soaked the moss clump in a dish of bottled water. Within an hour, the brown moss had turned green again. The next morning they squeezed water from the moss onto slides and looked at it under microscopes at 100× and 400×. At 400×, the field of view was about 400 µm across. They also looked at a stained slide of each kind of small animal they found.
Most of a moss leaf was a single layer of boxy cells, each with a cell wall, a nucleus and green chloroplasts. Wren counted about 20 cells across the field of view at 400×. In the moss water, the class found tiny animals called tardigrades. When the water was first added, the tardigrades were curled up and still, but after about half an hour many of them stretched out and crawled on eight stubby legs. On the stained slides, a tardigrade's gut, muscles and legs were made of many small cells with different shapes. The class also found rotifers, which swirl water toward their mouths with a crown of tiny hairs, and stained rotifers also showed many kinds of cells.
Smaller still were ciliates. Each ciliate was a single cell with a nucleus and a coat of tiny hairs, and some split in two while the class watched. The tiniest living things were bacteria, single cells with no nucleus whose numbers grew over two days. A grain of sand from the wall and a bit of dry oak leaf from the gutter were also in the water. The sand had no membrane and no nucleus. The oak leaf showed empty cell walls with no nucleus, and nothing about either one changed in two days.