Tardigrades: Tiny Survivors — Reading Comprehension Worksheet

Read the passage

The same text as the printed sheet, with the same paragraph numbers the questions refer to — for reading aloud from a screen or a board.

1. If you scooped up a clump of damp moss and looked at it under a microscope, you might spot a tiny creature lumbering along on eight stubby legs. It is a tardigrade. Most tardigrades are less than one millimeter long, and because of their slow, clumsy walk, people often call them water bears.
2. Tardigrades live almost everywhere: in moss and soil, at the bottom of the ocean, on mountaintops, and even in Antarctica. Scientists have described more than a thousand different kinds. To stay active, though, a tardigrade must be surrounded by a thin film of water. That makes its real talent all the more surprising, because many tardigrades can survive drying out completely.
3. When its home dries up, a tardigrade pulls in its head and legs and curls into a shriveled ball called a tun. It loses almost all the water in its body, and its activity slows until it is barely alive. In this state it can wait for years. When water returns, the tun soaks it up, and within hours the tardigrade can be walking again as if nothing had happened.
4. As a tun, a tardigrade can survive conditions that would kill almost any other animal, including freezing cold and strong radiation. In 2007, scientists even sent dried tardigrades into space, outside the protection of a spacecraft. When the tardigrades returned to Earth and were given water, some of them came back to life.
5. Tardigrades are not unbreakable, however. An active water bear crawling through wet moss is soft and easily harmed. Its toughness depends on the tun. Scientists have found that a drying tardigrade fills its body with special proteins and a sugar called trehalose, which help protect it until water returns.

The questions

The answers, and the paragraph each one comes from, are on the last page of the PDF — not here, so a student reading on screen cannot see them.

1. In paragraph 3, what is a tun?
   1. a tardigrade's dried, curled-up form
   2. a kind of moss that tardigrades eat
   3. the microscope used to find tardigrades
   4. a drop of water on a leaf
2. What does a tardigrade need around it in order to stay active?
   1. bright sunlight
   2. a thin film of water
   3. warm, dry air
   4. a crowd of other tardigrades
3. Based on the passage, which tardigrade is MOST likely to survive a sudden, hard freeze?
   1. one crawling through wet moss
   2. one that has dried out into a tun
   3. one swimming in a puddle
   4. one that has just hatched
4. Why did the scientists give the tardigrades water after their trip to space? (written answer)
5. In one or two sentences, write the main idea of the passage. (written answer)

How the reading level was set

This passage was written to the Grades 5–6 band: Longer sentences with more than one clause, more subject vocabulary (mochila, telegraph, radiation), some of it explained only by its context, and an explanation that runs across the whole passage — cause and effect, or a claim and its limits — so the main idea has to be put together rather than found in one sentence. The band is a judgement, not a readability score — no Lexile measure or grade-level formula has been applied. These are the counts it rests on, taken from the text itself:

Words:

286

Sentences:

18

Average sentence:

15.9 words

Longest sentence:

28 words

Words of seven letters or more:

20%

Sources for the facts in this passage

The passage is original writing, not an excerpt or an adaptation. Its facts were checked against these pages:

• University of Florida, IFAS Featured Creatures — Tardigrades, Water Bears, Moss Piglets — Tardigrades are 0.1 to 1 mm long with eight legs and are called water bears; they live worldwide, including Antarctica; most need water to be active; in drought they enter a dried state protected by special proteins and the sugar trehalose; over 1,300 species are described; they can survive the vacuum of space.
• European Space Agency — Tiny animals survive exposure to space — Tardigrades flew on the Foton-M3 mission in September 2007 and were exposed on the outside of the capsule; they can go years without water and are highly resistant to radiation.

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Or see every passage, grouped by reading level, on the reading comprehension worksheets page.