Living and Nonliving Things and Habitats: Two Wren and Sitka Lessons, Grades 3-5

It sounds like an easy question until somebody makes you answer it. A raven is alive. A boot is not. But saying why takes more than pointing.

Scientists settled on a list. A living thing grows, uses energy, gets rid of waste, responds to what happens around it, reproduces, is made of cells, and keeps its insides steady even when the weather changes.

Here is the tricky part. A thing has to do all of them. A river moves and changes, but it never eats and it never has baby rivers. A candle flame uses energy and grows, but it is not made of cells.

Some things used to be alive and are not anymore. A fallen log, a feather, a dry leaf. Scientists call those things once-living, and they are their own category.

An ecosystem is every living thing in one place plus all the nonliving parts they depend on. Water, soil, air, sunlight, temperature, and rock all count.

A habitat is where one particular kind of animal or plant lives inside that ecosystem. A niche is the job it does there, which is a different question entirely.

Two species cannot hold exactly the same niche in the same place for long. One always does it a little better and the other shifts, moves, or disappears.

Ecosystems handle change up to a point. Remove one common species and something else usually fills the gap. Remove a keystone species and much more falls apart.

Nothing in an ecosystem is separate. That is not a nice sentiment. It is the actual finding, and it is why a change in one place shows up somewhere you did not expect.