We need pictures in our minds to help us understand biology. Here are two examples. One is enzyme. This is a chemical that makes a reaction go fast by participating in the reaction. After the reaction, it is restored to its original state. This like a car battery. It gets used up a little bit in starting the car. While driving, it is restored to its original state. See A cell is like a car.

 

Another example is gene. Imagine you did a thousand word crossword puzzle. Now someone gave you another box of the same puzzle. If you take a few parts from the first puzzle, like a house near a river, put it on the table with the second puzzle, built around it, and then returned it, then take another few parts and built around it, it would be much faster to do the second puzzle. A gene is like the puzzle.

 

For a quote, see Imagery.