Autotrophic nutrition:
Autotrophic nutrition is the process by which organisms are capable of producing their own food using simple inorganic substances such as carbon dioxide and water, with the help of sunlight or chemical energy. Autotrophs, also known as producers, are able to synthesize their own organic molecules, such as glucose, through the process of photosynthesis or chemosynthesis.

Photosynthesis:
Photosynthesis is the main process by which autotrophs convert light energy into chemical energy in the form of glucose. It occurs in the chloroplasts of plant cells and certain bacteria. The process involves several steps:

1. Light absorption: Chlorophyll, a pigment present in chloroplasts, captures light energy from the sun.

2. Conversion of light energy: The captured light energy is converted into chemical energy and stored in the form of ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate).

3. Water splitting: Water molecules are split into hydrogen ions (H+) and oxygen (O2) through a process called photolysis. The released oxygen is released into the atmosphere.

4. Carbon fixation: Carbon dioxide (CO2) from the atmosphere enters the chloroplasts and combines with the hydrogen ions and chemical energy from ATP and NADPH to produce glucose (C6H12O6).

5. Release of oxygen: The glucose produced is stored in the plant cells for energy, while oxygen is released into the atmosphere as a byproduct.

Chemosynthesis:
Chemosynthesis is another form of autotrophic nutrition that occurs in certain bacteria and archaea. Unlike photosynthesis, which utilizes light energy, chemosynthesis uses chemical energy obtained from inorganic compounds such as hydrogen sulfide or ammonia.

Significance of autotrophic nutrition:
Autotrophic organisms play a vital role in the food chain as they provide energy and organic molecules for heterotrophic organisms, which are unable to produce their own food. Autotrophic nutrition is the basis of all ecosystems, as it forms the foundation of the food web and allows energy to flow through the ecosystem. It also contributes to the oxygen content in the atmosphere, making it suitable for aerobic organisms to survive.

In conclusion, autotrophic nutrition is the process by which organisms produce their own food using inorganic substances and energy sources. This process is mainly achieved through photosynthesis in plants and certain bacteria, and chemosynthesis in specific bacteria and archaea. Autotrophic nutrition is essential for the survival of ecosystems and the balance of energy flow within them.