What is the primary structural feature of the Golgi body?

The primary structural feature of the Golgi body, also known as the Golgi apparatus, is its arrangement of stacked, flattened sacs called cisternae. These stacks resemble a series of pancakes and are key to the Golgi body's function in processing and packaging proteins and lipids that have been synthesized in the endoplasmic reticulum.

Each cisterna is involved in various stages of modification and sorting of these biomolecules before they are dispatched to their respective destinations within or outside the cell. The unique structure of the stacked, flattened sacs allows for a large surface area, which facilitates the efficient processing of materials as they move through the Golgi apparatus in a directional manner—from the cis face (entry side) to the trans face (exit side).

In contrast to the correct answer, the other options do not accurately describe the structure of the Golgi body. Spherical bodies and solid granules do not reflect the distinctive morphology of the Golgi apparatus, and long tubules are not characteristic of its structure either. This specific arrangement is vital to the function of the Golgi in the cell, highlighting the importance of understanding cellular structures in relation to their roles.