Why should human population be a concern?

Four types of motile cells in human body?

How many species of living things are alive on earth today? more than 1,000,000 none of these answers are correct 100-500 1,000 –500,000 o 500,000 -1,000,000

The earths core is made up mainly of what 2 substances? 2. like an egg, earth has a core, a layer surrounding the core, and a thin, hard outer layer. which layers of the earth match the layers of an egg?