Most of a plant's surface area contributing to the photosynthetic process occurs in the leaves. Hundreds of millions of years of natural selection have shaped leaves into efficient structures that maximize their exposure to light, control their gas exchange, minimize water loss, and help move water, minerals, and carbohydrates up from the roots and to other parts of the plant.
About 10 percent of all the photosynthesis that occurs is the product of higher plants, those that we regularly see around us, and the other 90 percent is the product of algae, most of which occur ini the ocean.
Homeostasis - Environment of the Earliest Cell
All life forms are thought to share a marine origin because the fluids found in cells have a salt concentration comparable to that of salt water. The majority of freshwater environments, the ocean presents a stable environment with regard to salt concentration, pH, and temperature.
Most organisms are very sensitive to even slight changes in their external environment, and are unable to survive seemingly minor changes in their surrounding medium.
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