Which of the following points were not explained by Schleiden and Schwann when they formulated their original cell theory ?

Options

A. All plants are composed of different kinds of cells which form the tissues of the plant
B. Animal cells had a thin outer layer which is today known as the ‘plasma membrane’
C. Cells divide and new cells are formed from pre-existing cells
D. The presence of cell wall is a unique character of the plant cells

Answer

To determine which point was not explained by Schleiden and Schwann when they formulated their original cell theory, we can analyze the options provided:

1. **All plants are composed of different kinds of cells which form the tissues of the plant.**
- This statement aligns with the cell theory as Schleiden specifically focused on plant cells and their organization into tissues.

2. **Animal cells had a thin outer layer which is today known as the plasma membrane.**
- This statement is also consistent with the cell theory, as Schwann studied animal cells and recognized the presence of a membrane surrounding them.

3. **Cells divide and new cells are formed from pre-existing cells.**
- This statement was not part of the original cell theory formulated by Schleiden and Schwann. It was introduced later by Rudolf Virchow in 1855, who stated "Omnis cellula e cellula," meaning that all cells arise from pre-existing cells.

4. **The presence of a cell wall is a unique character of plant cells.**
- This statement is correct and aligns with the cell theory, as Schleiden noted the presence of a cell wall in plant cells.

Based on this analysis, the point that was not explained by Schleiden and Schwann in their original cell theory is: **"Cells divide and new cells are formed from pre-existing cells."**