Cell theory was propounded byA. Schleiden and SchwannB. Watson and CrickC. Mendel and MorganD. Wallace and Darwin

The correct answer is:

A. Schleiden and Schwann

Explanation: Cell theory was proposed by two scientists, Matthias Schleiden and Theodor Schwann, in the 19th century. Schleiden, a botanist, stated that all plants are made of cells, and Schwann, a zoologist, extended this idea by stating that all animals are made of cells. Together, they formulated the basic principles of cell theory, which include:

All living organisms are made up of one or more cells.
The cell is the basic unit of structure and function in living organisms.
All cells arise from pre-existing cells.
This theory laid the foundation for the study of biology and the understanding of life at the cellular level.