Final answer:
Alpha channels allow the creation, storage, and manipulation of masks in an image which isolates and protects specific parts. Layers, layer comps, and quick mask mode all serve different functions within image editing but do not provide the same storage capability for masks as alpha channels do.
Step-by-step explanation:
The feature that enables you to create, store, and manipulate masks to isolate and protect specific parts of an image is alpha channels. An alpha channel is an additional channel in a digital image that stores selections as grayscale images. This allows you to save various masks within the same file and easily switch between them for different purposes such as adjusting transparency, compositing, or making complex selections. Layers are like sheets of stackable glass that you can work on independently, and layer comps are used to capture the visibility, position, and appearance of layers to save different states of your work. The quick mask mode is a temporary way to create and edit selections within the image; it doesn't store the masks for long-term use.