An exoskeleton (external skeleton) is common in arthropods like insects, spiders, and crustaceans.

Clouds are categorized based on their shape, size, and altitude. Stratus clouds are low-altitude clouds characterized by horizontal layering with a broad flat base. When stratus clouds occur on the ground the result is fog.

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

Anemia, which may cause weakness, dizziness, and headaches is caused by a lack of iron in the diet.

Velocity and displacement are vector quantities which means each is fully described by both a magnitude and a direction.  In contrast, scalar quantities are quantities that are fully described by a magnitude only.  A variable indicating a vector quantity will often be shown with an arrow symbol:  \(\vec{v}\)