The biosphere is the global ecological system integrating all living beings and their relationships. This includes their interactions with the lithosphere (the rigid outer part of the earth, consisting of the crust and upper mantle), hydrosphere (all surface water), and atmosphere (the envelope of gases surrounding the planet).

Deoxyribonucleic acid (DNA) is the molecule that contains genetic information. DNA is encoded through a combination of nucleotides that bind together in a specific double helix pattern.

In contrast to the Celsius scale (measured in degrees centigrade) that fixes 0° at the freezing point of water and the Fahrenheit scale that uses 32°, the Kelvin scale fixes 0° at absolute zero (-273°C) which is the lowest temperature possible in the universe.

Small quantities of certain minerals like iron, calcium, magnesium, and salt are important for nutrition and health.

A neutron is a subatomic particle found in the nucleus of an atom. It is neutral as it carries no electric charge.

A prefix is added to the base units of the metric system to indicate variations in size. Each prefix specifies a value relative to the base unit in a multiple of 10. Common prefixes are:

Primary consumers (herbivores) subsist on producers like plants and fungus. Examples are grasshoppers, cows, and plankton.

Secondary consumers (carnivores) subsist mainly on primary consumers. Omnivores are secondary consumers that also eat producers. Examples are rats, fish, and chickens.

A population is a group of organisms of the same species who live in the same area at the same time. A community is a group of populations living and interacting with each other in an area.

The water (hydrologic) cycle describes the movement of water from Earth through the atmosphere and back to Earth. The cycle starts when water evaporates into a gas from bodies of water like rivers, lakes and oceans or transpirates from the leaves of plants.