**Core Concept**
The transport of molecules across cell membranes, particularly those that are lipid-soluble or have a large molecular size, often requires the assistance of carrier proteins to facilitate diffusion. This process is essential for maintaining cellular homeostasis and regulating the concentration of essential substances.

**Why the Correct Answer is Right**
The correct answer requires a carrier protein because it is a polar molecule that cannot dissolve in the lipid bilayer of the cell membrane. Carrier proteins, also known as transport proteins, bind to the molecule and undergo a conformational change to facilitate its transport across the membrane. This process is essential for the transport of molecules such as glucose, amino acids, and other nutrients that are essential for cellular function. The specific carrier protein involved in this process is the sodium-glucose cotransporter (SGLT), which uses the concentration gradient of sodium ions to drive the transport of glucose into the cell.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not require a carrier protein. Molecules that are lipid-soluble, such as oxygen and carbon dioxide, can diffuse directly across the cell membrane without the assistance of a carrier protein.
**Option B:** This option is incorrect because it is a charged molecule that can diffuse through the phospholipid bilayer of the cell membrane without the assistance of a carrier protein.
**Option C:** This option is incorrect because it is a large molecule that requires active transport, which involves the use of energy to transport the molecule against its concentration gradient. This process requires the assistance of a carrier protein and an energy source, such as ATP.

**Clinical Pearl / High-Yield Fact**
The transport of glucose into cells is facilitated by the sodium-glucose cotransporter (SGLT), which uses the concentration gradient of sodium ions to drive the transport of glucose into the cell. This process is essential for maintaining normal blood glucose levels and is impaired in conditions such as diabetes mellitus.

**Correct Answer:** C.