Final answer:
Ribosomes are to proteins as the smooth endoplasmic reticulum (SER) is to lipids, because ribosomes synthesize proteins, whereas lipids are made in the smooth ER.
Step-by-step explanation:
The student asks about the function of ribosomes in comparison to another cellular structure. Ribosomes are to proteins as lipids are to the endoplasmic reticulum (ER). Ribosomes are the cellular structures responsible for protein synthesis.
When viewed through an electron microscope, ribosomes appear either as clusters or as single, tiny dots that float freely in the cytoplasm or are attached to the endoplasmic reticulum. Lipids, on the other hand, are synthesized in the smooth portion of the ER, which is aptly named the smooth endoplasmic reticulum (SER). Thus, the correct analogy would be that ribosomes are to proteins as the smooth ER is to lipids, making the answer to the question #2) endoplasmic reticulum.