Changes cause an unbalanced ecosystem.    

Living things get what they need from the ________________________________in which they live.

Animals provide the oxygen that plants need to live.   

Ecosystems are healthy when all their parts are in ______________________________.

The organism that is harmed in a close relationship between two living things is called a _____________________________________.

An organism that competes successfully is more likely to ___________________________ and reproduce.

Organisms in an ecosystem ____________________ for and share resources.

Parasites ______________________________ the organism they live on.

As a population __________________________, more food, more water, and more living space are needed.

A gradual change in an ecosystem is called a _____________________________.

A species that is reduced and may die out is placed in the ___________________________________ list.

Climates change very _________________________________.

Strip-mining is an environmentally friendly way to get coal from Earth.

Federal law requires that land disturbed by mining must be ____________________________________.

_________________________________ in rivers and streams can move into Earth’s oceans.

The National Parks System preserves the ____________________________________ of many animals.

__________________________________ are substances that are very harmful to humans and other organisms.

Fossils show that woolly mammoths are very similar to today's __________________

Fossils show that Earth has __________ over time.