1. Plasma Membrane: This is the outer boundary of the cell, acting as a barrier between the cell's internal environment and the external environment. It controls what enters and exits the cell, ensuring the cell's survival and function.

2. Cytoplasm: This is the gel-like substance that fills the cell and contains all the organelles. It provides a medium for chemical reactions to occur and supports the cell's structure.

3. Ribosomes: These are tiny structures responsible for protein synthesis, the building blocks of cells. They are found in all cells, from bacteria to humans.

4. DNA: This is the genetic material of the cell, containing instructions for all the cell's activities. It is organized into chromosomes in eukaryotic cells, while it is found as a single circular molecule in prokaryotic cells.