The trachea branches into the left and right bronchi which each lead to a lung where the bronchi subdivide into smaller tubes called bronchioles. Each bronchiole ends in a small sac called an alveolus which allows oxygen from the air to enter the bloodstream via tiny blood vessels called capillaries.

Heredity is the passing on of physical or mental characteristics genetically from one generation to another. Heredity is made possible via large strings of chromosomes which carry information encoded in genes.

The broadest classification of life splits all organisms into three groups called domains. The three domains of life are bacteria, archaea and eukaryota.

Heat is always transferred from warmer to cooler environments through conduction, convection, or radiation.

The spinal cord connects the brain to the body's network of nerves. It carries impulses between all organs and the brain and controls simple reflexes.