Capillaries are small thin-walled vessels that permit the exchange of oxygen, carbon dioxide, nutrients, and waste between blood and the body's cells. This process of exchange is called diffusion.

An ecosystem is a biological community of interacting organisms and their physical environment. This includes both the biotic (living) and abiotic (non-living).

Simple magnets have two poles, north and south, and opposite poles attract each other (N attracts S, S attracts N). Likewise, the same pole of two magnets repel (N repels N, S repels S). The Earth has a magnetic field and North and South Poles which enables the use of a magnetic compass to determine direction.

A substance undergoes a phase transition when it moves from one state of matter to another, for example, when water freezes or boils.

Temperatures again increase with altitude in the thermosphere which is the hottest (4,530 °F / 2,500 °C) atmospheric layer due to direct exposure to the Sun's radiation. However, the gas in this layer is highly diluted so even though the atoms of gas may be very high in temperature, there are too few of them to effectively transfer much heat.