A biome is a large naturally occurring community of flora (plants) and fauna (animals) occupying a major habitat (home or environment).

Hard bones provide primary support for the endoskeleton while more flexible cartilage is found at the end of all bones, at the joints, and in the nose and ears. In addition to providing support and protecting bodily organs, bones also produce blood cells and store minerals like calcium.

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.

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:

The four planets closest to the Sun (Mercury, Venus, Earth, and Mars) are called terrestrial (Earth-like) planets because, like the Earth, they're solid with inner metal cores covered by rocky surfaces.