7.2 Circulatory systems in animals | Transport systems in animals

7.2 Circulatory systems in animals (ESG8X)Transport systems are crucial to survival. Unicellular organisms rely on simple diffusion for transport of nutrients and removal of waste. Multicellular organisms have developed more complex circulatory systems.Open and closed circulation systems (ESG8Y)There are two types of circulatory systems found in animals: open and closed circulatory systems.Open circulatory systemsIn an open circulatory system, blood vessels transport all fluids into a cavity. When the animal moves, the blood inside the cavity moves freely around the body in all directions. The blood bathes the organs directly, thus supplying oxygen and removing waste from the organs. Blood flows at a very slow speed due to the absence of smooth muscles, which, as you learnt previously, are responsible for contraction of blood vessels. Most invertebrates (crabs, insects, snails etc.) have an open circulatory system. Figure 7.1 shows a schematic of an open circulatory system delivering b...