Antoine-Laurent de Lavoisier, the "father of modern chemistry, was a French nobleman prominent in the histories of chemistry and biology. He discovered that, although matter may change its form or shape, its mass always remains the same.
Shmoop Chemistry explains The Atomic Theory. Part of our Atoms, Molecules, and Ions Learning Guide. Learning and teaching resource for The Atomic Theory written by PhD students from Stanford, Harvard, Berkeley
Barbara McClintock, Nobel Laureate Barbara McClintock discovered the ability of genes to change places within the chromosome ("genetic transposition") and earned a Nobel Prize for it, making her the first American woman to win an unshared prize.