OwlSheets Students

Living Things in a Clump of Moss

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Living Things in a Clump of Moss

Use microscope evidence to decide what is made of one cell, many cells or none.

What the moss water held

Read about the moss study and the class's findings, then answer the questions.

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.

What We Found in the Moss Water
Thing found	Size (µm)	Cells seen	Nucleus?	Moved or grew?
Tardigrade	300	Many, several kinds	Yes	Yes
Rotifer	200	Many, several kinds	Yes	Yes
Ciliate	60	One	Yes	Yes
Bacterium	2	One	No	Yes
Sand grain	300	None	No	No
Oak leaf bit	2,000	Empty cell walls	No	No

1.

Sort each thing using the evidence in the passage and the table.

2.

How many ciliates, lined up end to end, would be as long as one tardigrade? ciliates

3.

Use Wren's cell count and the size of the field of view. About how wide is one moss leaf cell? µm

4.

The sand grain and the tardigrade are about the same size. Which evidence best shows that the tardigrade is a living thing and the sand grain is not?

A. The sand grain came from the wall, not the moss.B. The tardigrade is larger than the sand grain.C. The sand grain is harder to see on the slide.D. The tardigrade is made of many cells with nuclei.

5.

When water was first added, the tardigrades were curled up and still. Which conclusion best fits all of the class's evidence?

A. They were alive but inactive while dry, then became active in water.B. They were bits of sand shaped like animals until the water wet them.C. They were nonliving until the water turned them into living cells.D. They were dead, and new ones came in with the bottled water.

6.

Which observation is the best evidence that a tardigrade is multicellular and not one very large cell?

A. It crawls through the water on eight stubby legs.B. Its gut, muscles and legs are built from many small cells.C. It stretched out and moved after half an hour in water.D. It is about 300 µm long, much longer than a ciliate.

Using cell evidence

Use the evidence from the moss study to complete each task.

7.

Complete the summary. Use words from the word bank. One word is not used.

The ciliate is because its whole body is cell. The rotifer is . The sand grain has no cells, so it is .

8.

The bit of oak leaf showed empty cell walls, no nucleus and no change in two days. What is the best conclusion?

A. It came from a living thing made of cells but is no longer alive.B. It is a unicellular organism, since each of its cells is empty.C. It did not come from a living thing, since it did not move.D. It is still alive, since it has cell walls like the moss leaf.

9.

Mateus says, "Any living thing too small to see clearly without a microscope is just one cell." Which finding best shows he is wrong?

A. A bacterium, about 2 µm across, is a single cell.B. A sand grain, about 300 µm across, has no cells.C. A rotifer, about 200 µm long, has many kinds of cells.D. A ciliate, about 60 µm long, is a single cell.

10.

Mateus said the brown, crunchy moss clump "looks dead." Was the clump a home for living things, and were they all the same kind of organism? Write a claim, give at least three pieces of evidence from the passage and the table, and explain your reasoning about cells.