Describe the difference between bottom up and top down controls on a food chain

This video (about 20 minutes) provides some in-depth details about ecological research behind the concept of a

https://youtu.be/hRGg5it5FMI

Please watch the video and answer the following questions:

1) Describe the difference between “bottom up” and “top down” controls on a food chain. How does this relate to the “green world hypothesis”?

2) Why was Robert Paine throwing starfish into the ocean? How did the results of his experiment help to demonstrate the idea of a “keystone species”?

3) What is the role of sea otters in regulating the marine kelp ecosystem of the Pacific Ocean? How does this relate to the idea of trophic cascade?

4) How did 20th century Pacific whaling further demonstrate the trophic cascade hypothesis?