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: -In biology, cell theory is a scientific theory first formulated in the mid-nineteenth century, that living organisms are made up of cells, that they are the basic structural/organizational unit of all organisms, and that all cells come from pre-existing cells.

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: -The Cell Theory Is a Unifying Principle of Biology The cell theory states that all biological organisms are composed of cells; cells are the unit of life and all life come from preexisting life. The cell theory is so established today that it forms one of the unifying principles of biology.

Detailed explanation-5: -Robert Hooke, one of the first scientists to use a light microscope, discovered the cell in 1665. In all life forms, including bacteria, plants, animals, and humans, the cell was defined as the most basic structural and functional unit.