What is it called when protein carriers are used with diffusion to move things across the cell membrane?

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.

Which statement is true about the two stars labeled in this diagram?

If the type of food available changes, then…