Reading a Grade 4 Fact Text
RI.4.10
Read the text, then answer the questions.
What a Beaver Dam Does
A beaver does not build a dam for shelter. It builds one to make a pond, and it lives in a lodge in the pond. The dam raises the water so the lodge entrance stays underwater. A predator that cannot swim cannot get in. But the pond does far more than protect one family. Behind a dam, water slows, and slow water drops the silt it carries. Over years this builds rich wet ground. That ground holds water in a drought and holds it back in a flood. It supports plants, insects, amphibians and birds that were not there before. Where beavers have been reintroduced, the number of species in a valley typically rises within five years.
- 1. Why does a beaver build a dam?
- 2. What keeps a predator out of the lodge?
- 3. What overall structure does this text use?
- 4. How soon does species number typically rise after beavers return?
Lichen
A lichen is not one organism. It is a fungus and an alga living as one body. The fungus provides the structure and holds water. The alga photosynthesises and makes sugar. Separated, the fungus starves and the alga dries out. Because it needs no soil, a lichen can grow on bare rock, on gravestones and on the roofs of cars that have not moved for a decade. Lichens grow extremely slowly — some crustose species less than a millimetre a year. Scientists use that rate to date rock surfaces, a method called lichenometry. Lichens also absorb whatever is in the air. Where the air is dirty, they disappear, which makes them a living measure of pollution.
- 1. The text says lichens are a living measure of pollution. What reason is given?
- 2. What two organisms make up a lichen?
- 3. Determine the main idea of this text and explain how key details support it.
- 4. How slowly can a crustose lichen grow?
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