Answer: They help control what enters and leaves the cell.
Explanation: carbohydrates also help the immune system identify if the cell is foreign or not.
Certain fossils, called index fossils, help geologists match rock layers. To be useful as an index fossil, a fossil must be widely distributed and represent a type of organism that existed for a brief time period. Index fossils are useful because they tell the relative ages of the rock layers in which they occur.