Describe the process of respiration occurring in the cytoplasm,or describe the anaerobic phase of aerobic respiration.

(N/A) Definition: Glycolysis is the phase of respiration that involves the breakdown of one molecule of glucose into two molecules of pyruvic acid.
Origin: The term 'glycolysis' is derived from the Greek words 'glycos' (sugar) and 'lysis' (splitting).
The scheme of glycolysis was proposed by Gustav Embden,Otto Meyerhof,and $J$. Parnas,and is commonly referred to as the $EMP$ pathway.
In anaerobic organisms,only glycolysis occurs. Glycolysis takes place in the cytoplasm of the cell,where glucose undergoes partial oxidation to form two molecules of pyruvic acid. In plants,this glucose is derived from sucrose (the end product of photosynthesis) or from storage carbohydrates.
Both glucose and fructose are phosphorylated to form Glucose-$6$-phosphate by the enzyme hexokinase.
Glucose + $ATP$ $\xrightarrow{\text{Hexokinase}}$ Glucose-$6$-Phosphate
This phosphorylated glucose then isomerizes to produce Fructose-$6$-phosphate.
Glucose-$6$-Phosphate $\longrightarrow$ Fructose-$6$-Phosphate
Subsequent steps for the metabolism of glucose and fructose are identical.
Glycolysis consists of a chain of ten reactions,controlled by different enzymes,to produce pyruvate from glucose.
Fructose-$6$-phosphate is converted into Fructose-$1,6$-bisphosphate in the presence of $ATP$.
$ATP$ is consumed at two steps: first,in the conversion of glucose to Glucose-$6$-phosphate,and second,in the conversion of Fructose-$6$-phosphate to Fructose-$1,6$-bisphosphate.
Fructose-$1,6$-bisphosphate is then split into Dihydroxyacetone phosphate $(DHAP)$ and $3$-phosphoglyceraldehyde $(PGAL)$.
Fructose-$1,6$-Bisphosphate $\longrightarrow$ $DHAP$ $(3C)$ + $PGAL$ $(3C)$
In one step,$NADH + H^+$ is formed from $NAD^+$ when $3$-phosphoglyceraldehyde is converted to $1,3$-bisphosphoglycerate $(BPGA)$.
$3$-phosphoglyceraldehyde $\longrightarrow$ $1,3$-bisphosphoglycerate + $NADH + H^+$
Two redox-equivalents are removed from $PGAL$ and transferred to a molecule of $NAD^+$.
$PGAL$ is oxidized and combined with inorganic phosphate to form $BPGA$.
The conversion of $BPGA$ to $3$-phosphoglyceric acid $(PGA)$ is an energy-yielding process,where energy is trapped by the formation of $ATP$.
Another $ATP$ is synthesized during the conversion of phosphoenolpyruvate $(PEP)$ to pyruvic acid.
Pyruvic acid is the key product of glycolysis. Its metabolic fate depends on cellular needs. There are three major ways cells handle pyruvic acid:
$(1)$ Lactic acid fermentation
$(2)$ Alcoholic fermentation
$(3)$ Aerobic respiration
Fermentation occurs under anaerobic conditions in many prokaryotes and unicellular eukaryotes. For complete oxidation of glucose to $CO_2$ and $H_2O$,organisms adopt the Krebs cycle (aerobic respiration),which requires $O_2$.