AP BIOLOGY

Detailed explanation-1: -The classical cell theory was proposed by Theodor Schwann in 1839. There are three parts to this theory. The first part states that all organisms are made of cells.

Detailed explanation-2: -His research led to the discovery of the cell that produces the myelin sheath that envelops the axon. In honor of his contribution, this was later eponymously named the Schwann cell [3, 7, 9]. He also found that during embryonic development individual cells unite to form the muscle fiber [10].

Detailed explanation-3: -German scientists Theodore Schwann and Mattias Schleiden studied cells of animals and plants respectively. These scientists identified key differences between the two cell types and put forth the idea that cells were the fundamental units of both plants and animals.

Detailed explanation-4: -Schwann also discovered pepsin, the first animal enzyme known, and revealed that yeast is a living organism. All of his discoveries were made between 1834 and 1839, before he was 30 years old.

Detailed explanation-5: -In 1838, German scientist Matthias Schleiden concluded that all plants are made of cells. The next year Theodor Schwann, another German, concluded that all animals were also made of cells.