Two types of genes play major roles in regulating the cell cycle: proto-oncogenes encourage cell division, while tumor-suppressor genes inhibit cell division. the balance between these two types of genes may be disrupted by naturally occurring or environmentally caused a) proteins. b) mutations. c) inhibitors. d) cell cycle clocks.

Wetlands form where water and land meet. a lake with a wetland fringe can fill in with decayed plant and animal material to become a wet meadow. a pond can fill in to become a bog or fen. sediment can fill in a river marsh to become a swamp.flooding of coastal lowlands from rising sea levels has created broad coastal marshes that are protected from wave action by barrier islands or reefs. coastal wetlands also form when rivers deposit sediment as they reach the ocean. plants then take root and hold the soil firm against the forces of tides and waves.

The equator absorbs the most sunlight