Consider the roles of valves and blood vessel walls in moving blood through the body. if you were given a piece of flexible tubing and a small piece of plastic, how might you design a simple model that would simulate those roles?

The tube is like a blood vessel, and the plastic is just like the valves. The plastic piece in the tube opens when the water flows in the correct direction and close when water backflows. I hope that this is the answer that you were looking for and it has helped you.

The answer is a because - is an direction

This type of galaxy is an approximately ellipsoidal shape and a smooth, nearly featureless image. they are the largest single star systems, in the universe and are built by the collisions of many smaller galaxies.