Which of the following is an example of membrane bound little structures present in a cell?

The correct option is Lysosome.

To understand why this is the correct answer, let us break down the concept of membrane-bound structures within a cell:
Cells contain various internal structures known as organelles, which perform specific functions. These organelles can be either membrane-bound (enclosed by a lipid bilayer membrane) or non-membrane-bound (lacking a membrane wrapping).

Let us analyze each of the given options:
1. Lysosome: Lysosomes are small, spherical, membrane-bound vesicles containing digestive (hydrolytic) enzymes. The membrane is critical because it keeps the acidic enzymes inside, preventing them from destroying the rest of the cell. Therefore, a lysosome is a membrane-bound structure.
2. Ribosome: Ribosomes are molecular machines responsible for protein synthesis. They are made of RNA and proteins and do not have any surrounding membrane. They are non-membrane-bound structures found in both prokaryotic and eukaryotic cells.
3. Cytoplasm: The cytoplasm is the jelly-like fluid that fills the cell and surrounds the organelles. It is a region/medium, not a membrane-bound organelle itself.
4. Nucleoplasm: Nucleoplasm is the fluid substance found inside the nucleus. Similar to cytoplasm, it is a fluid medium rather than an individual membrane-bound structure.

Thus, out of the choices provided, the Lysosome is the only example of a membrane-bound organelle/structure present in a cell.