**Photo-autotrophy** is the process by which organisms use **light energy** (primarily from the sun) to synthesize their own food from inorganic substances, such as carbon dioxide (CO₂) and water (H₂O). This process is most commonly associated with **photosynthesis**, where light energy is captured by pigments (such as chlorophyll) and converted into chemical energy in the form of glucose or other carbohydrates. ![[d8ae5ac477e1973d16eb8b18ea35e50a.jpg]] ### Key Features of Photo-autotrophy: 1. **Energy Source**: The primary energy source for photo-autotrophic organisms is sunlight. 2. **Carbon Source**: They obtain carbon from CO₂ in the atmosphere, which they convert into organic compounds. 3. **Oxygen Release**: In the case of oxygenic photosynthesis (as seen in plants, algae, and cyanobacteria), oxygen (O₂) is released as a byproduct of splitting water molecules. 4. **Pigments**: Photo-autotrophic organisms contain pigments like **chlorophyll** that absorb light energy to drive the photosynthetic reactions. ### Examples of Photo-autotrophic Organisms: - **Plants**: All green plants are photo-autotrophic, using photosynthesis to produce food. - **Algae**: Algae (like seaweed and phytoplankton) are key marine photo-autotrophs. - **Cyanobacteria**: These bacteria were some of the earliest organisms to evolve photosynthesis and are still crucial to many ecosystems today. ### Photosynthesis Process: Photo-autotrophy is largely synonymous with **photosynthesis**, which can be broken into two stages: 1. **Light-Dependent Reactions**: Light energy is absorbed by chlorophyll and used to produce ATP (energy currency of cells) and NADPH (electron carrier), with water molecules being split to release oxygen. 2. **Calvin Cycle** (Light-Independent Reactions): ATP and NADPH generated in the first stage are used to convert CO₂ into glucose and other carbohydrates, which serve as energy and carbon storage. ![[ad73617487c9b074cf0259caeeaa0f0d.jpg]] ### Role in Ecosystems: - **Primary Producers**: Photo-autotrophs form the base of most food chains by producing organic compounds that are consumed by heterotrophic organisms (organisms that cannot produce their own food). - **Carbon Sequestration**: By converting atmospheric CO₂ into organic material, they play a crucial role in regulating carbon levels and mitigating climate change. ### Contrast with Chemo-autotrophy: While photo-autotrophs use sunlight as their energy source, **chemo-autotrophs** obtain energy from the oxidation of inorganic compounds (like sulfur or ammonia), a process that is independent of light. Chemo-autotrophs are often found in extreme environments, such as deep-sea hydrothermal vents. Photo-autotrophy is fundamental to life on Earth as it not only provides food and energy for autotrophic organisms themselves but also supports entire ecosystems by supplying the base energy required for other organisms.