Blood is created in bone marrow and is made up of cells suspended in liquid plasma. Red blood cells carry oxygen, white blood cells fight infection, and platelets are cell fragments that allow blood to clot.

To provide oxygen to the body, blood flows through the heart in a path formed by the right atrium → right ventricle → lungs → left atrium → left ventricle → body. When blood enters the right side of the heart it is deoxygenated. It enters the left side of the heart oxygenated after traveling to the lungs.

An endoskeleton (internal skeleton) is a charateristic of vertebrate animals, including humans.

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

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