1. Glycolysis is the catabolism of glucose to pyruvate and takes place with or without oxygen. In the presence of oxygen, pyruvate is further metabolized through the Krebs Cycle (TCA cycle) and the electrons/reducing equivalents are used to generate more ATP via oxidative phosphorylation. In the absence of oxygen, you only get the net 2ATPs produced in glycolysis.
2. In the absence of oxygen, pyruvate accumulates. In some organisms—notably in yeast—pyruvate is fermented/reduced to ethanol and carbon dioxide.
3. The ATP used to start glycolysis is just “hanging around” as you say. It comes either from prior rounds of glycolysis or from prior rounds oxidative phosphorylation.
4. I think your formula is wrong. There could be Pi on the left side of the net reaction, which stands for inorganic phosphate, but “Piruvate” should be “Pyruvate.” There is more than one way to show the overall reaction. The net reaction for glycolysis (ignoring the two ATPs that are consumed and regeneratated—they “cancel out,” if you will) is:

Glucose + 2 ADP + 2 NAD+ + 2 Pi —–> 2 Pyruvate + 2 ATP + 2 NADH + 2 H+

glycolysis (or Embden-Meyerhoff) pathway is consisted by a 10-enzymatic reactions (which 3 of thew are non-reversible reactions) which converts glucose into pyruvate. In this glycolysis pathway, definetly no oxygen in the form of O2 is consumed, so it’s said as an anaerobic pathway.

reduction of pyruvate in anaerobic condition not only yields ethanol and CO2 which is performed by an example, Saccharomyces cerevisiae. another microorganisms like Lactobacillus lactis can reduce pyruvate directly into lactic acid (compare with ethanol which need a decarboxylation process before it can be yielded). Another microorganisms which live in a high reducing soil (anaerobic condition) like Clostridium sp. converts pyruvate into acetate. And many mooooreee…. 😆

1)No,glycolysis does not require oxygen.
2)Not,the absence of oxygen,it is its availability,which is crucial.
3)Require ATP,comes from previous cycle.
4)Pi,in orignal equation represents,inorganic phospate.

ATP is present at stable concentrations in the cell and thus is not necessarily derived from previous metabolic pathways.