Two nuclides are isotones if they have the same neutron number, but different proton number. For example, boron-12 and carbon-13 nuclei both contain 7 neutrons, and so are isotones.

A pure substance has a constant composition and cannot be separated into simpler substances by physical means. There are two types of pure substances: elements and compounds. Atoms of the same element are identical in properties. The periodic table contains a list of the only elements which is known to man.

"Itai-Itai disease" was coined by locals for the severe pains victims felt in the spine and joints, and caused by cadmium. Cadmium poisoning can also cause softening of the bones and kidney failure. The cadmium was released into rivers by mining companies in the mountains, which were successfully sued for the damage. Itai-Itai disease is known as one of the Four Big Pollution Diseases of Japan.

Magnesium is bound as the central atom of the porphyrin ring of the green plain pigment chlorophyll. Magnesium is the element that causes plants to be able to convert light into energy and is the powerhouse behind photosynthesis in plants. Magnesium is also used by plants for the metabolism of carbohydrates and in the cell membrane stabilization.

Three types of proteins form myofibrils- contractile, regulatory, and structural. Contractile proteins generate force for muscle contraction. The two contractile proteins in myofibrils are actin (part of the thin filament) and myosin (part of the thick filament).

Nitrogenous wastes tend to form toxic ammonia, which raises the pH of body fluids. The animals must detoxify ammonia by converting it into a relatively-nontoxic form such as urea or uric acid. Nitrogenous waste is excreted in different forms by different species.

A homologous structure is an organ, system, or body part that shares a common ancestry in multiple organisms. This definition is found in evolutionary biology and uses the meaning of having a similar structure or origin.

The average speed of an object is the total distance traveled by the object divided by the elapsed time to cover that distance. It's a scalar quantity which means it is defined only by magnitude. A related concept, average velocity, is a vector quantity. A vector quantity is defined by magnitude and direction.

An amylase is an enzyme that catalyses the hydrolysis of starch into sugars. Amylase is present in the saliva of humans and some other mammals, where it begins the chemical process of digestion.

sphincter prevents the acidic contents of the stomach from moving upward into the esophagus.