In a eukaryotic cell, which membrane-enclosed organelle is the primary site of lipid (phospholipid and steroid) synthesis?

• A. Golgi apparatus
• B. Mitochondrion
• C. Smooth endoplasmic reticulum (SER)
• D. Rough endoplasmic reticulum (RER)

Answer: (C)

Verified step by step guidance

1. Understand the function of each organelle listed: The Golgi apparatus is mainly involved in modifying, sorting, and packaging proteins and lipids for secretion or delivery to other organelles.
2. Recall that mitochondria are primarily responsible for energy production through cellular respiration, not lipid synthesis.
3. Recognize that the rough endoplasmic reticulum (RER) is studded with ribosomes and primarily synthesizes proteins destined for membranes or secretion.
4. Identify that the smooth endoplasmic reticulum (SER) lacks ribosomes and is specialized in the synthesis of lipids, including phospholipids and steroids.
5. Conclude that the primary site of lipid synthesis in a eukaryotic cell is the smooth endoplasmic reticulum (SER).