An air mass is a large body of air that has similar moisture (density) and temperature characteristics. A front is a transition zone between two air masses.

An electron is a subatomic particle that orbits the nucleus of an atom. It carries a negative electric charge. Generally, an atom has the same number of negative electrons orbiting the nucleus as it does positive protons inside.

The narrowest classification of life, species, contains organisms that are so similar that they can only reproduce with others of the same species.

Tough fibrous cords of connective tissue called tendons connect muscles to the skeleton while another type of connective tissue called ligaments connect bones to other bones at joints (elbow, knee, fingers, spinal column).

Minterals, vitamins, and fiber are micronutrients while proteins, carbohydrates, and fats are macronutrients.