As air rises, it cools and condenses into small droplets of water or ice, which make up clouds. When the particles of ice or water become too heavy, they fall in the form of precipitation.
A water molecule is made of a relatively large oxygen atom and two smaller hydrogen atoms.
The water table moves up and down depending on how much water is in the ground. During droughts, the water table sinks. During times of heavy precipitation, the water table rises.
When a parent plant forms sex cells, the genes of the parent separate. According to the Law of Segregation a gene from each pair goes to each sex cell.
A mutation is a change in a gene.
Chromosomes contain genetic material made up of many genes.
Chromosomes are located in the nucleus of every cell in a living thing.
Scientists refer to the shape of a DNA molecule as a double helix. Rungs on the double helix are formed by substances called nitrogen bases.
A male sex cell unites with a female sex cell to form a fertilized egg.
There are four different types of nitrogen bases in DNA, which combine in specific ways. The sequence of nitrogen bases determines the particular genes on a chromosome and the genetic code.
Recombinant DNA is created by inserting a DNA segment or gene from one organism into another. DNA is usually transferred from a complex organism to a simple organism, such as bacterium.
Plains are large, flat areas with little difference in elevation. Coastal plains are located relatively close to the coastline of the ocean. The highlighted area indicates coastal plains along the Atlantic and Gulf coast.
From time to time, throughout North American history, a large portion of the continent has been covered with massive sheets of ice called glaciers. The ice sheet pictured here covered all of Canada and extended as far south as Iowa and Illinois.
Most of the water from the Interior Plains drains into the Mississippi River watershed. The Mississippi River travels south to the Gulf of Mexico, where it deposits sediments in the Mississippi River delta.
The Appalachian mountains stretch from Alabama, along the eastern United States, to Newfoundland, Canada. The Rocky Mountains stretch from New Mexico to Alberta and British Columbia.
Desert grasslands exist in Arizona, New Mexico, and parts of Texas and Mexico.
This map demonstrates the worldwide distribution of grasslands.
The map illustrates two major groups of grasslands in the Great Plains: shortgrass prairie and mixed prairie.
Asthma is an allergic and inflammatory response in which airways constrict, making it hard to breathe.
Blood vessels are tubes that transport blood throughout the body.