Advanced Placement (AP) Biology Practice Exam

The endoplasmic reticulum (ER) has several critical roles within the cell, primarily centered around the synthesis and processing of proteins and lipids. The rough endoplasmic reticulum is particularly involved in protein synthesis and initial post-translational modifications, while the smooth endoplasmic reticulum is responsible for lipid synthesis and the metabolism of carbohydrates. Additionally, the smooth ER plays a role in detoxifying potentially harmful substances. Energy production through ATP is primarily associated with mitochondria, not the endoplasmic reticulum. Mitochondria are the organelles responsible for cellular respiration, where they convert biochemical energy from nutrients into ATP, which cells use as an energy currency. Thus, energies are not produced by the endoplasmic reticulum, making it clear why this function does not belong to it.