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.

Cells are classified into one of two groups based on whether or not they have a nucleus. Eukaryotic cells have a nucleus, prokaryotic cells do not have a nucleus and therefore have a less complex structure than eukaryotic cells.

The acids produced by the pancreas contain several enzymes that aid in digestion. Lipase converts fat to glycerol and fatty acids. Pancreatic amylase breaks down complex carbohydrates into simple sugars. Trypsin converts polypeptides (the building blocks of protein) into amino acids.

The respiratory system manages respiration which is the process by which blood cells absorb oxygen and eliminate carbon dioxide.