**Core Concept**
Bilirubin is a breakdown product of heme, a component of hemoglobin found in red blood cells. The degradation of heme involves a series of enzyme-catalyzed reactions that ultimately lead to the formation of bilirubin. This process is crucial for the normal metabolism of red blood cells.

**Why the Correct Answer is Right**
The breakdown of heme to bilirubin is initiated by the enzyme heme oxygenase, which cleaves the porphyrin ring of heme to produce biliverdin, a green pigment. Biliverdin is then reduced to bilirubin by the enzyme biliverdin reductase. This process occurs primarily in the spleen, liver, and bone marrow. Bilirubin is then conjugated in the liver and excreted into the bile, where it is eventually eliminated from the body.

**Why Each Wrong Option is Incorrect**
**Option A:** Albumin is a protein synthesized by the liver, but it is not a source of bilirubin.
**Option B:** Globulin is another protein synthesized by the liver, but it is not directly involved in the production of bilirubin.
**Option D:** Transferrin is a protein that binds and transports iron in the bloodstream, but it is not a precursor to bilirubin.

**Clinical Pearl / High-Yield Fact**
Bilirubin toxicity can occur when levels become excessively high, leading to kernicterus, a condition characterized by brain damage and neurological dysfunction. This highlights the importance of normal bilirubin metabolism and the potential consequences of its disruption.

**✓ Correct Answer: C. Heme. Bilirubin is the degradation product of heme.**