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 important process helps plants and some tiny organisms create food and release oxygen into the air, which is vital for life on Earth.

Scientists believe that at first, the pigments used in photosynthesis were used to protect living things from harmful light, especially strong ultraviolet rays. The basic idea of photosynthesis was first described by Jan Ingenhousz, a scientist from the Netherlands working in Britain, 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

Available evidence from studies of very old rocks suggests 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 the ones we know today and did not produce oxygen. They used different substances to get energy.

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

Symbiosis and the origin of chloroplasts

See also: Symbiogenesis

Some animals have formed 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 even take tiny parts from algae called chloroplasts and keep them in their own bodies. This helps the mollusks live for months just by using sunlight.

One idea explains how chloroplasts first appeared in plant cells. Chloroplasts look a lot 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 process plants use to turn water and carbon dioxide into sugars and oxygen using sunlight. A special enzyme called RuBisCO helps attach carbon dioxide to make sugars, but it can also attach oxygen by mistake. This mistake wastes energy for the plant.

Some plants have special ways to help RuBisCO work better. The C₄ pathway concentrates carbon dioxide around RuBisCO, which helps it work more efficiently. This is common in about 3% of plants, especially grasses. Another pathway, called CAM photosynthesis, helps plants save water by collecting carbon dioxide at night and using it during the day. This is used by about 7% of plants, including many cacti and succulents.

C₄ and CAM pathways evolved separately many times in different plants. C₄ became common around 6 to 7 million years ago, likely because of changes in climate and more fires that helped grasses grow. Scientists study the ratio of two carbon types in plant material to learn about these ancient plants.