1. Plasma membrane: This thin, flexible barrier encloses the cell, regulating what enters and exits. It's made of a phospholipid bilayer with embedded proteins.
2. Cytoplasm: This gel-like substance fills the cell and contains the cell's internal structures (organelles). It's composed mostly of water, along with salts, enzymes, and other molecules.
3. DNA: This genetic material carries the instructions for building and maintaining the cell. In prokaryotes, the DNA is circular and found in a region called the nucleoid. In eukaryotes, it's organized into chromosomes within a nucleus.
