https://www.khanacademy.org/science/telangana-class-10-biologyin/x58e314ef7f27e124:transportation-and-circulation/x58e314ef7f27e124:evolution-of-circulatory-system/e/evolution-of-circulatory-system 2026-01-11T08:44:04.593456302Z Evolution of circulatory system This section traces the evolution of transport systems from simple intracellular movement in unicellular organisms to true circulatory systems in annelids. It shows how increasing body size and complexity led to new strategies—such as cytoplasmic streaming, gastrovascular cavities, body fluids, and pressurized blood flow—to deliver nutrients, oxygen, and wastes efficiently to all cells. Khan Academy exercise