Through a process called homeostasis.
If there is not enough glucose the pancreas secrete glucagon (a hormone) which causes the liver to convert stored glycogen into glucose.
If there is too much glucose, the pancreas release insulin. The insulin binds to insulin receptors on cells telling them to take in glucose. The insulin also tells the liver to convert glucose into glycogen.
The Precambrian time refers to the time 4.5 billion to 542 millions year ago. This period is characterized by having reduced atmosphere and included reduced compounds. Scientists believed that atmosphere at that time was devoid of free oxygen and CO2 was present in excess. Before the complex life evolved on the Earth, the Precambrian Earth's ocean contained dissolved carbon dioxide.
I believe the answer is a
Cyanobacteria were the first organisms to introduce oxygen into Earth's atmosphere. They were also known as blue-green algae, and is estimated that they first appeared around 3 billion years ago.
