**Core Concept**
Putrescine is a polyamine involved in various cellular processes, including cell growth and proliferation. Its biosynthesis occurs through the decarboxylation of an amino acid.

**Why the Correct Answer is Right**
Putrescine is formed by the decarboxylation of ornithine, an amino acid, through the action of the enzyme ornithine decarboxylase (ODC). This process is a crucial step in the biosynthesis of polyamines, which play a significant role in cell growth, differentiation, and survival. The reaction involves the removal of a carboxyl group from ornithine, resulting in the production of putrescine.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because decarboxylation of arginine results in the production of agmatine, not putrescine.
**Option B:** This option is incorrect because the decarboxylation of glutamate does not produce putrescine.
**Option C:** This option is incorrect because the decarboxylation of aspartate results in the production of alanine, not putrescine.

**Clinical Pearl / High-Yield Fact**
Ornithine decarboxylase is a key enzyme in the biosynthesis of polyamines, and its activity is often upregulated in cancer cells, contributing to their rapid growth and proliferation.

**Correct Answer:** C. Ornithine.