Get the dark energy definition and explanation. See how dark energy accounts for the accelerating expansion of the universe.

# Anne Helmenstine

Learn about purines and pyrimidines in biochemistry, including their structures, properties, functions, and sources.

## Purines and Pyrimidines

Compare alkaline vs acidic in chemistry and everyday life with the definitions of the terms and examples. See how they relate to pH.

## Alkaline vs Acidic

Learn about mitosis vs meiosis. Compare and contrast the two forms of cell division, focusing on the difference between them.

## Mitosis vs Meiosis Recently updated !

Learn about the commutative property in math. Get the definition and examples of the property and compare it to the associative property.

## Commutative Property in Math – Definition and Examples

Learn the difference between concave vs convex for lenses, mirrors, polygons, and mathematical functions. See how to remember the difference.

## Concave vs Convex

Learn whether two atoms of the same element are identical and see how they can vary. Discover how to identify an atom.

## Are Two Atoms of the Same Element Identical?

Learn how many bones are in the human body. Get the number for both adults and infants and learn why the number varies between people.

## How Many Bones Are in the Human Body?

Learn what Planck's constant is and why it is important in quantum mechanics. Get the definition and value of h.