The term that can be used to describe evolution by natural selection is SCIENTIFIC THEORY.
Theory means "the best explanation so far."
Scientific theory is a work in progress. It is a well-substantiated explanation of some aspect of the natural world that is acquired through the scientific method, and repeatedly confirmed through observation and experimentation.
Algae and nitrogen-fixing bacteria are photosynthetic organisms.
The three methods of carbon dioxide transport in the blood are dissolution in blood plasma, binding to hemoglobin, and carried in the form of bicarbonate. About 7% of the carbon dioxide is dissolved in the blood plasma. The majority of the remaining 93% is carried as part of the bicarbonate buffer system while the rest binds to hemoglobin.