"Despite these common properties, and the fundamental unity of life they reveal, it is difficult to make generalizations about living organisms."

“The remarkable similarity of metabolic pathways and gene sequences across the phyla argues strongly that all modern organisms are derived from a common evolutionary progenitor by a series of small changes , each of which conferred a selective advantage to some organism in some ecological niche.”

“The unity and diversity of organisms become apparent even at the cellular level.”

“As a result, there is an electrostatic attraction between the oxygen atom of one water molecule and the hydrogen of another , called a hydrogen bond.”

“The chemistry of living organisms is organized around carbon, which accounts for more than half the dry weight of cells.”

“The current understanding that all organisms share a common evolutionary origin is based in part on this observed universality of chemical intermediates and transformations, often termed "biochemical unity.”

“The upper limit of cell size is probably set by the rate of diffusion of solute molecules in aqueous systems.”