What process allows certain organisms to manufacture carbohydrates without sunlight?

Chemosynthesis is the correct answer because it refers to a process by which certain organisms, particularly some bacteria and archaea, can produce carbohydrates by using energy derived from chemical reactions, often involving inorganic substances, instead of relying on sunlight. This process typically occurs in environments where sunlight is not accessible, such as deep-sea hydrothermal vents.

In chemosynthesis, these organisms utilize chemical energy to convert carbon dioxide and water into glucose and other organic compounds. This ability allows them to thrive in extreme environments, contributing to primary production in ecosystems that do not receive sunlight.

In contrast, photosynthesis relies on sunlight to generate sugars and oxygen from carbon dioxide and water, making it unsuitable for organisms in dark environments. Respiration is a metabolic process where organisms break down organic molecules to release energy, but it does not produce carbohydrates. Fermentation is a form of anaerobic respiration, which converts sugars into energy, but similarly does not generate carbohydrates de novo.