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.
It's really important for you to remember that cellular respiration in eukaryotic cells takes place in the mitochondria. Both animal cells and plant cells depend on cellular respiration for their energy needs, because both animal cells and plant cells need ATP. Plant cells may be able to use the energy from the sun to make sugar, but they can't use the sun's energy as fuel.