**Core Concept:** Membranes are essential components of cells, consisting of phospholipids, proteins, carbohydrates, and cholesterol. Membrane proteins play crucial roles in cellular functions like transport, signaling, and maintaining cell shape. The protein content in a membrane can vary significantly depending on the cell type and function.

**Why the Correct Answer is Right:** The correct answer is **Option C: Plasma Membrane**. Plasma membranes are the outermost layer of cells and are primarily composed of phospholipids, cholesterol, and glycolipids. However, they contain a significant amount of proteins embedded within their lipid bilayer. These proteins can be classified into three main types: integral proteins, peripheral proteins, and glycoproteins. Integral proteins are directly embedded in the lipid bilayer, while peripheral proteins bind to the membrane's surface. Glycoproteins are proteins that have sugar molecules attached to them.

Plasma membranes serve as selective barriers that regulate the movement of substances in and out of cells, thus maintaining cellular homeostasis. Additionally, they facilitate various physiological processes like transportation, signal transduction, and cell adhesion.

**Why Each Wrong Option is Incorrect:**

A. **Option A: Mitochondrial Membrane**: Although mitochondria contain membrane proteins for energy production (oxidative phosphorylation), the overall protein content per gram tissue is lower than that of plasma membranes.

B. **Option B: Golgi Membrane**: The Golgi apparatus is responsible for processing, sorting, and packaging proteins and lipids destined for secretion or transport to other organelles. However, the protein content per gram tissue is generally lower than that of plasma membranes.

D. **Option D: Endoplasmic Reticulum Membrane**: The endoplasmic reticulum is involved in protein synthesis, folding, and transport. It contains membrane proteins for these functions, but the overall protein content per gram tissue is lower than that of plasma membranes.

**Clinical Pearls:** Membrane proteins play a vital role in maintaining cellular functions and homeostasis. A deeper understanding of membrane proteins is essential for medical students and physicians. In clinical scenarios, knowledge of membrane proteins aids in interpreting clinical findings, formulating differential diagnoses, and determining treatment strategies.