AP BIOLOGY

Detailed explanation-1: -By the late 1830s, botanist Matthias Schleiden and zoologist Theodor Schwann were studying tissues and proposed the unified cell theory. The unified cell theory states that: all living things are composed of one or more cells; the cell is the basic unit of life; and new cells arise from existing cells.

Detailed explanation-2: -Cell theory, as formulated by Theodor Schwann in 1839, implied that this relationship was a specific and lawful one, i.e. that germs of a certain kind, all else being equal, would produce adult organisms of the same kind, and vice versa.

Detailed explanation-3: -Schleiden said in his textbook that the cell is the most general expression of the concept of the plant, so it is necessary to study the cell as the foundation of the plant world. This theory started a branch of biology that focused on the study of plant cells called plant cytology.

Detailed explanation-4: -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.