Photosynthesising primary producers require sunlight. Therefore, in the ocean, phytoplankton would be concentrated within the surface layers of the ocean where the sunlight penetrates. Phytoplankton support a wide range of marine life: zooplankton feed on phytoplankton, which in turn support fish and so on.
These are macrophytes that grow entire in the freshwater and become fossilized by the calcification oozes, going back to the Paleozoic era about 250 million years ago.
And they are unicellular to multi-cellular organisms also found in moist terrestrial habitats.
The pancreas detects that the blood sugar level is higher and releases insulin. It tells the liver to store glucose in the blood as glycogen. This regulates the blood sugar levels
