Core overview
Living organisms are built from one or more cells. In animals, cells share a plasma membrane, a watery cytosol, and (in most human cells) a nucleus that houses DNA. That arrangement separates reactions, stores genetic instructions, and allows groups of cells to specialise into tissues.
Key membrane-bound compartments (organelles) include mitochondria for energy conversion, the endoplasmic reticulum and Golgi apparatus for synthesis and shipping of proteins and lipids, and lysosomes for degrading worn-out parts. Together they keep metabolism organised.
How it works
Cells sense their environment using receptors on the surface or inside the cell. Signals are relayed through molecular pathways that change gene activity, metabolism, or the cytoskeleton. This is how hormones, immune cues, and local neighbour cells coordinate behaviour.
For growth and repair, many cells progress through a regulated cell cycle. DNA is copied only when checks indicate the genome is intact; then the cell can divide. When cells stop dividing, they often enter specialised states needed for muscle, nerve, or immune function. Disruption of checkpoints can contribute to disease when division runs out of control.
Why it matters
Understanding cell biology clarifies how infections hijack cellular machinery, how medicines target specific pathways, and why genetic changes can alter a single cell type with wide effects on the body. It also links basic science to regenerative research and cancer biology, where the goal is to restore normal signalling or stop harmful proliferation.