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.
Why do animals depend on plants. Plants give animals the food and shelter they need. Herbivores, which are plant eating animals, rely on plants to provide them with a regular source of food. They also provide shelter to may animals, both large and small.
Plants utilize the sun's energy, animals eat plants and utilize the plants' energy, and some animals eat other animals and utilize their energy. The food chain is a cycle of predation, and although it is necessary for life to exist, it has to have limits.