Concept 6 Genes are real things.

Hugo de Vries, Carl Correns and Erich von Tschermak-Seysenegg were the three scientists who rediscovered Mendel's laws in 1900. They were all working independently on different plant hybrids, and came to the same conclusions about inheritance as Mendel. Robert Hooke was one of the first scientists to describe a cell. Theodor Schwann redefined the cell as a living unit.

Theodor Schwann (1810-1882)

Theodor Schwann was born in Neuss, Germany. He studied medicine in Berlin, and after graduation went on to do an assistantship in anatomy. In 1838, Schwann and Matthias Jakob Schleiden (1804-1881) developed the "cell theory." Schwann went on and published his monograph Microscopic Researches into Accordance in the Structure and Growth of Animals and Plants in 1839. In the monograph, Schwann identified the common features of all cells — plants and animals, and he illustrated many different cell types. Although Schwann did change the definition of cell by stressing the internal cellular components, he believed incorrectly that cells could arise from assembly of cellular fluids. In 1839, Schwann was appointed Professor of Anatomy at the University of Louvain. In 1848 he moved to Liège where he taught physiology and comparative anatomy.

Theodor Schwann recognized that eggs, ova, are cells. In 1841, sperm were classified as cells when they were seen developing from testis cells.

What is the largest single cell in existence?