**Core Concept**
Peripheral cell membrane proteins are a class of proteins that are loosely attached to the cell membrane and are not embedded within it. These proteins play crucial roles in various cellular processes, including cell signaling, cell-cell interactions, and protein transport. They are often involved in the regulation of cell growth, differentiation, and apoptosis.

**Why the Correct Answer is Right**
Peripheral cell membrane proteins are typically attached to the cytoplasmic side of the cell membrane via ionic bonds, hydrogen bonds, or hydrophobic interactions. This attachment is often mediated by specific domains or motifs within the protein, such as the PEST domain or the PDZ domain. Examples of peripheral cell membrane proteins include annexins, spectrin, and talin, which are involved in cell signaling, cytoskeletal organization, and cell adhesion, respectively.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because peripheral cell membrane proteins are not embedded within the cell membrane, unlike integral membrane proteins.
**Option B:** This option is incorrect because peripheral cell membrane proteins are not necessarily involved in transport across the cell membrane.
**Option C:** This option is incorrect because peripheral cell membrane proteins are not solely involved in cell-cell interactions.

**Clinical Pearl / High-Yield Fact**
Peripheral cell membrane proteins are often involved in disease processes, including cancer, cardiovascular disease, and neurological disorders. For example, annexin A2 has been implicated in the pathogenesis of various cancers, including breast and lung cancer.

**Correct Answer: D. Peripheral cell membrane proteins are loosely attached to the cell membrane via ionic bonds, hydrogen bonds, or hydrophobic interactions.**