Question

which of these is thought to be the first group of organisms able to use h₂o as an electron donor in photosynthesis?
land plants
algae
cyanobacteria
aquatic plants

Explanation:

Cyanobacteria are believed to be the first organisms to use water as an electron - donor in photosynthesis. They were crucial in the oxygenation of the Earth's atmosphere through this process. Land plants, algae, and aquatic plants evolved later and also use water in photosynthesis but were not the first.

Answer:

cyanobacteria