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The liver is supplied by the hepatic artery bringing oxygenated blood to it. The liver is also supplied by the hepatic portal vein. This brings the absorbed nutrients from the small and large intestine...

A zymogen is the inactive form of an enzyme. For instance the enzyme pepsinogen is produced by chief cells in the gastric pits. Pepsinogen is a zymogen. Hydrochloric acid produced by the parietal cells...

Alpha helices and Beta pleated sheets. 

There are a number of reasons why it is necessary to open and close the air vents. These include; allowing oxygen in, which is also necessary for respiration and allowing heat to escape. Closing the ai...

For the exams, the definition you will need to know is that "diffusion is the net movement of a substance from an area of high concentration to an area of low concentration, down a diffusion gradi...