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4. Cells And Tissues eLearn.Punjab

Sub-cellular or Acellular Particles: According to the first principle of the cell theory all

organisms are composed of one or more cells. Virus, prions and viroids are not composed of cells;
rather they are sub-cellular or acellular particles. They do not run any metabolism inside them. They
show some characteristics of living organisms i.e. they can increase in number and can transmit
their characters to next generations. We know that such acellular particles are not classified in any
of the five kingdoms of organisms.

History of the formulation of cell theory

4.2 Cellular Structures And Functions

We are well familiar with the basic organization of a eukaryotic cell. Here we will get some detailed
learning about cellular structure and functions. A cell is made by the assemblage of organelles.
There are some structures in cell that are not organelles, but are still very important for cell. These
structures are cell wall, cell membrane, cytoplasm, and cytoskeleton.

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