Which process is a non-carbon source of glucose synthesis?

The correct answer is Gluconeogenesis. Gluconeogenesis is the metabolic process by which glucose is synthesized from non‑carbon sources such as amino acids, glycerol, and lactate. This is in contrast to photosynthesis, which uses carbon dioxide as the carbon source. Among the options:

• Photosynthesis: Uses CO₂ (a carbon source) to produce glucose.
• Glycolysis: Breaks down glucose, it does not synthesize it.
• Gluconeogenesis: Correct; it synthesizes glucose from non‑carbohydrate (non‑carbon) precursors.
• Fermentation: Breaks down glucose without oxygen, not a glucose synthesis pathway.

Therefore, the correct answer is "Gluconeogenesis".