Final answer:
The front end of an earthworm is thicker, darker in color, and usually more rounded in shape, while the back end is pointed or tapered. The front end contains the mouth and prostomium, while the back end contains the anus for waste elimination.
Step-by-step explanation:
The difference between the front end and the back end of an earthworm can be distinguished by the presence of certain features. The front end, also known as the anterior end, is typically thicker and darker in color compared to the back end, also known as the posterior end.
Additionally, the front end may have a more rounded shape, while the back end is usually pointed or tapered. Another distinguishing feature is the presence of the worm's mouth and prostomium at the front end, which is used for feeding and sensory perception. On the other hand, the back end of the earthworm contains the anus, through which waste is eliminated as castings. Overall, these physical and anatomical characteristics can help identify the front and back ends of an earthworm.