The same process occurs in marine or aquatic food chains and it is the phytoplankton that performs photosynthesis in the open water. The chemical process of making sugar by plants is aided by chlorophyll, a green pigment, which acts as a catalyst for the reaction. Carbon dioxide from the air, and water, are chemically transformed into glucose, a simple carbohydrate, with the byproduct oxygen also being produced. This is a reversible reaction because when glucose is burned or used by an organism, the energy is released and the byproducts carbon dioxide and water are excreted. When the glucose is stored for later use by the plant, the molecules of glucose are linked together and become a larger molecule called starch.
Potatoes are an excellent example of plant starch.
You can test for the presence of starch by using household iodine solution. If a drop of brown iodine comes in contact with starch, a reaction occurs and a color change from brown to blue indicates starch is present. The color intensifies with an increased amount of starch. Try the iodine experiment to test your hypothesis. The production or growth rate of phytoplankton in the open sea is known as the primary productivity.