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.
One of the most important functions of animals is to help disperse seeds and pollinate plants. This provides vital support to a variety of fruit and vegetable crops, many of which would not survive without the help of animals. Primates, for example, help to disperse seeds through the fruits they eat. Bats also help spread seeds and pollinate a variety of plants. Bees are the most important animal to plant ecosystems.