In the latter case the resistance is caused by dissipation of mechanical energy when the configuration or the direction of flow is sharply changed, by the formation of vortices and secondary flows as a result of the flow breaking away, by the centrifugal forces, etc.
Animals depend on plants for food as plants produce food and energy which animals can't, so, herbivores eat plants to get energy, carnivores eat herbivores and other carnivores for energy and omnivores eat all four, plants, herbivores, carnivores and also other omnivores for energy.
Moving air (wind) is also important for some plants to pollinate. Animals Animals including humans need oxygen to live. We breathe in oxygen and breathe out Carbon Dioxide. There are also air pockets in soils and water that help tiny living things survive in water and beneath the soils. For example, fishes absorb Oxygen from water with their gills.