Biological organisation increases in complexity: cell → tissue → organ → organ system. A specialised cell has features suited to its job; cooperating cells form tissues; different tissues combine in organs; organs coordinate in systems.
Use the chain structure → immediate function → system effect → survival. A root hair cell has a long projection that increases surface area for uptake. Xylem forms hollow strengthened pathways for water transport, while phloem moves dissolved sugars. In animals, alveoli provide a large surface area and thin exchange surfaces; villi increase absorptive area; narrow capillaries support exchange with tissues.
Artificial systems replace selected functions rather than perfectly copying an organ. Dialysis removes selected wastes and excess water from blood, supporting part of kidney function but not reproducing all kidney roles continuously.