CK-12 Foundation
Ck 12: Biology: Invertebrate Evolution
[Free Registration/Login may be required to access all resource tools.] An overview of the major events in invertebrate evolution.
Khan Academy
Khan Academy: Prokaryote Interactions & Ecology
Learn about cooperation and "multicellularity" in prokaryotes including mutualisms, commensalisms, parasitisms. Also find out the role of prokaryotes in the carbon and nitrogen cycles.
CK-12 Foundation
Ck 12: Biology: Late Precambrian Period
[Free Registration/Login may be required to access all resource tools.] Describes how events during the late Precambrian impacted life on Earth.
CK-12 Foundation
Ck 12: Biology: Organization of Cells
[Free Registration/Login may be required to access all resource tools.] Learn how multicelled organisms have specialized cells that do specific jobs and single celled organisms exist without the help of other cells.