The walls of capillaries are only one cell thick. The lifespan of a red blood cell is about 120 days. Impulses travel through nerves because of ions. Latitude describes locations north or south of the equator. The highest elevation in Oklahoma is in the southeast corner of the state.
Estuaries are where rivers meet the sea and fresh water mixes with salt water.
Intraspecies competition occurs between organisms of the same species. The population in a given area at a given time is known as carrying capacity. Ninety five percent of all mammals are placental mammals. Bats are the only mammal that can actually fly.