Final answer:
The smooth endoplasmic reticulum (SER) is specialized for lipid and steroid synthesis, and cells producing steroid hormones would have an especially high concentration of SER.
Step-by-step explanation:
The organelle specialized for lipid and steroid synthesis is the smooth endoplasmic reticulum (SER). The SER is involved in the synthesis of carbohydrates, lipids including phospholipids and cholesterol, and steroid hormones without the presence of ribosomes on its surface, which gives it a smooth appearance. This differentiates it from the rough endoplasmic reticulum (RER) which is studded with ribosomes and is primarily involved in protein synthesis. Among cells with a high concentration of SER, those that make steroid hormones, like the Leydig cells in the testes, would have an especially abundant SER due to their need to produce hormones such as testosterone.