Evolution of photosynthesis

The evolution of photosynthesis refers to how the process of using light energy to make sugars from carbon dioxide and water developed over time. This process helps plants and some tiny organisms create food and release oxygen into the air, which is very important for life on Earth.

Scientists think that at first, the pigments used in photosynthesis helped protect living things from harmful light. The basic idea of photosynthesis was first described by Jan Ingenhousz, a scientist from the Netherlands, in 1779.

The first organisms that could do photosynthesis probably appeared very early in the history of life. These early life forms likely used simple substances like hydrogen instead of water. There are three main ways that photosynthesis happens today: C₃ photosynthesis, C₄ photosynthesis, and CAM photosynthesis. C₃ photosynthesis is the oldest and most common way, using the Calvin cycle to start turning carbon dioxide into food. C₄ and CAM plants have special tricks to save water, which helps them survive in dry places.

Origin

Evidence from very old rocks shows that life existed more than 2.5 billion years ago. Fossils from this time show what might be early plants that used sunlight. These first plants were different from plants today and did not produce oxygen. They used different things to get energy.

Later, some of these plants began to use water to make energy. This made oxygen for the first time in our atmosphere. This big change happened a long time ago and helped shape our world. Cyanobacteria, a type of simple plant, were important in this change and stayed important for life in the oceans.

Symbiosis and the origin of chloroplasts

See also: Symbiogenesis

Some animals have helpful relationships with algae that can make food from sunlight. This is most common in corals, sponges, and sea anemones. A few sea mollusks like Elysia viridis and Elysia chlorotica can take tiny parts from algae called chloroplasts and keep them in their own bodies. This helps the mollusks live for months using just sunlight.

One idea explains how chloroplasts first appeared in plant cells. Chloroplasts look like tiny photosynthetic bacteria. The endosymbiotic theory suggests that very early eukaryotic cells took in these bacteria. Over time, the bacteria changed to become chloroplasts inside plant cells. Like mitochondria, chloroplasts still have their own DNA, separate from the rest of the cell. This DNA is similar to that found in cyanobacteria.

Evolution of photosynthetic pathways

Photosynthesis is the way plants use water and carbon dioxide to make sugars and oxygen with sunlight. A special enzyme called RuBisCO helps turn carbon dioxide into sugars, but sometimes it makes a mistake and uses oxygen instead. This mistake uses up the plant's energy.

Some plants have special tricks to help RuBisCO work better. The C₄ pathway gathers extra carbon dioxide around RuBisCO, so it can work more efficiently. This is common in about 3% of plants, especially grasses. Another trick is called CAM photosynthesis. It helps plants save water by collecting carbon dioxide at night and using it during the day. Many cacti and other thick, fleshy plants use this method.

C₄ and CAM pathways developed separately in many different plants. C₄ became more common around 6 to 7 million years ago, probably because of changes in the weather and more fires that helped grasses grow. Scientists study the types of carbon in old plants to learn more about these ancient plants.