How does a virus differ from a common cell?Immersive Reader It has no nucleus, cell wall, or organelles. It has two nuclei and no cell wall or organelles. A virus has no cell wall, no nucleus, and only organelles for movement. A virus differs from a cell only in shape.

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.