Autotrophic organisms are able to produce their own food using simple inorganic substances like carbon dioxide and energy from external sources like sunlight or inorganic chemicals. Option 1, photosynthesis, is the correct answer as it is the process by which autotrophs convert light energy into chemical energy to synthesize organic molecules, such as glucose, using carbon dioxide and water. During photosynthesis, the energy from sunlight is absorbed by pigments, such as chlorophyll, and used to power the conversion of carbon dioxide and water into glucose and oxygen. Glucose is used as an energy source to fuel cellular processes, while oxygen is released as a byproduct.

Option 2, gluconeogenesis, is a metabolic pathway that occurs in some heterotrophic organisms where glucose is synthesized from non-carbohydrate precursors. This process is not used by autotrophic organisms to fulfill their carbon and energy requirements.

Option 3, glycogenesis, is the process of glycogen synthesis where excess glucose is stored as glycogen in liver and muscle cells. This process is not directly related to fulfilling the carbon and energy requirements of autotrophic organisms.

Option 4, external sources, is a vague and broad option. While autotrophic organisms do rely on external sources of