Photosynthesis is the process by which carbon dioxide and water are converted into oxygen and carbohydrates, using solar energy from the sun. In plants, photosynthesis occurs in a part of the cell called the chloroplast. Chloroplasts contain chlorophyll, a green pigment molecule that harnesses sunlight to drive photosynthesis. Chlorophyll is what lends plants their green color.

A leading theory states that the ancestor of all plants engulfed a cyanobacterium, a simple organism that evolved photosynthesis billions of years ago. Over time, the engulfed cyanobacterium lost most of its features and became permanently enslaved in the plant’s cellular system as the chloroplast.

Trees, shrubs, ferns, flowers, mosses, and other familiar green things all share the narrow definition of "plant." They are multicellular organisms that photosynthesize and live on land. But how do scientists define the organisms that live in water, yet also have a nucleus and can photosynthesize? These have traditionally been classified as "algae."

Most algae live in the world’s oceans. They represent a very diverse group of organisms whose evolutionary relationships are not clear. They can be unicellular (consisting of only one cell), multicellular, or live in connected colonies. Some notable algae include diatoms (whose cells are made of silicon dioxide—which means their bodies are made of glass), dinoflagellates (which form an important partnership with corals), and stoneworts (the closest relative to land plants). “Seaweed” is a general term for marine multicellular algae, such as the giant kelp and nori.

While it is widely known that tropical forests and grasslands provide a significant amount of the Earth’s oxygen, it is the ocean’s algae, little engines of photosynthesis, which produce the majority of the world’s oxygen.

Biological diversity is not spread evenly across the planet. Some regions, called biodiversity “hotspots,” contain more unique species and are at greater risk from human impact. These hotspots can still be saved if action is taken.

In 1998, Conservation International (CI) presented a strategy to focus conservation efforts in areas where they will have the greatest impact. A biological hotspot is defined by CI as an area containing at least 1,500 species of plants found nowhere else in the world, and has also already lost at least 70% of its original habitat.

Today, CI lists 34 regions as terrestrial hotspots, and Academy scientists have a strong history of research in many of them. The California Floristic Province, Caribbean Islands, Mesoamerica, Atlantic rainforest and tropical savanna of Brazil, South African Cape, Madagascar, and the Yunnan Province in China are just a few of the hotspots where Academy expeditions have landed. By documenting and analyzing the species that live in these habitats, scientists can help local governments and conservation groups save these unique flora and fauna before they disappear forever.