Concept:Cell theory is a fundamental principle of biology that describes the basic unit of life.
Explanation:Schleiden and Schwann jointly proposed the cell theory in the 1830s.
Schleiden studied plant cells, and Schwann studied animal cells.
They concluded that all living organisms are made of cells.
This theory was later refined by Rudolf Virchow.
Antonie van Leeuwenhoek first observed living cells, but did not formulate the theory.
Robert Brown discovered the nucleus, not the cell theory.
Singer and Nicolson proposed the fluid mosaic model of the cell membrane.
Answer:B. Schleiden and Schwann
