Materials move down a concentration gradient . Passive or active ?

What would happen to the nutrients in an ecosystem if decomposers, such as bacteria, didn’t exist there?

How energy move through ecosystem ?

Which of the following must be true for a fossil organism to be useful as an index fossil? a. the fossil organism must be widespread geographically. b. the fossil organism must be abundant. c. the fossil organism must be limited to a short span of geologic time. d. all of the above.