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. The second part states that cells are the basic units of life.

Detailed explanation-2: -Theodor Schwann was the one who proposed that all animals are made up of cells., and that cells are the basic unit of structure and function of animals. His contributions paved the way for the development of the cell theory.

Detailed explanation-3: -Schwann concluded three things that became vital components of the cell theory. First, Schwann concluded that both plants and animals were composed of cells. Second, these cells have independent lives. Third, these independent lives are subject to the organism’s life.

Detailed explanation-4: -However the cell theory of Schleiden differed from modern cell theory in that it proposed a method of spontaneous crystallization that he called “Free Cell Formation". In 1858, Rudolf Virchow concluded that all cells come from pre-existing cells, thus completing the classical cell theory.

Detailed explanation-5: -In it Schwann declared that “All living things are composed of cells and cell products". He drew three further conclusions about cells, which formed his cell theory or cell doctrine. The first two were correct: The cell is the unit of structure, physiology, and organization in living things.