Cellula

Cellula is the term used in biology to denote the basic unit of life. In many languages, including Italian and Latin, cellula refers to a living cell. The cell is the smallest unit that can perform all vital functions, from energy metabolism to reproduction. In eukaryotes, the cell is delimited by a plasma membrane and contains cytoplasm in which organelles are suspended, while DNA is stored in the nucleus.

Cell theory, established in the 19th century, states that all organisms are composed of cells, that cells are the fundamental units of life, and that new cells arise from preexisting ones. The theory traces to the observations of Hooke in 1665, and later, Matthias Schleiden, Theodor Schwann, and Rudolf Virchow, who formalized the core principles.

Prokaryotic cells lack a defined nucleus and most membrane-bound organelles, whereas eukaryotic cells have a nucleus and complex organelles. Plant and fungal cells have cell walls and chloroplasts; animal cells lack chloroplasts and usually have a smaller vacuole. Unicellular organisms perform all life processes within a single cell; multicellular organisms rely on specialized cells and tissues for function.

Key organelles include the nucleus, which houses DNA; mitochondria for energy production; ribosomes for protein synthesis; endoplasmic reticulum and Golgi apparatus for protein processing and trafficking; lysosomes and peroxisomes for digestion and detoxification; and, in plants and algae, chloroplasts and large central vacuoles. Communication between cells occurs via signaling molecules and receptors, while transport across membranes relies on diffusion, osmosis, and active transport.

Genetic material in eukaryotes is linear DNA organized into chromosomes; prokaryotes contain a circular chromosome in the nucleoid region. Cell division includes mitosis and cytokinesis in somatic cells, and meiosis in germ cells, enabling growth, tissue maintenance, and sexual reproduction.