fermentation doesn't produce ant ATP so what is its importance?

Answer 1

Actually, you are incorrect. Fermentation, or anaerobic respiration, does produce small amounts of ATP. Of course, respiration in the presence of oxygen produces much larger amounts. So "aerobic" respiration is always more efficient if oxygen is available. However, there are many environments in which there is no oxygen, and fermenation would be an absolute requirement for life.

Answer 2

Fermentation follows glycolysis. Glycolysis has a net gain of 2 ATP, and sometimes that's the only choice cells have because no oxygen is available.

Fermentation takes away the end products of glycolysis so glycolysis can continue. Glycolysis uses NAD+ as an electron carrier and will not continue without NAD+. Fermentation "empties" it so NAD+ is available for glycolysis again.

Lactic acid fermentation changes the pyruvate into lactic acid. When oxygen becomes available, the lactic acid can be used to form pyruvate so the cell can use it in aerobic respiration to get the rest of the ATP gain.

Answer 3

Fermentation is a process that occurs in the absence of oxygen. In the absence of oxygen, ATP can only be produced by substrate level phosphorylation during glycolysis. The problem is, that, in addition to producing 2ATP, glycolysis also converts NAD+ to NADH. Thus, unless there is a mechanism to convert NADH back to NAD+, the cell would eventually run out of NAD+ and die, since it would no longer be able to perform glycolysis, and hence produce ATP.

This is where fermentation comes into place. During fermentation, the pyruvate produced from glucose by glycolysis is converted to either lactic acid or ethanol (depending on the type of cell). In either case, fermentation converts 2NADH into 2NAD+. These 2NAD+ in turn can now be reused in glycolysis, and the balance is maintained!