Describe the first stage of respiration.

(N/A) The first stage of respiration is known as glycolysis.
Definition: Glycolysis is the process in which one molecule of glucose is broken down into two molecules of pyruvic acid.
Origin: The term glycolysis originates from the Greek words 'glycos' (sugar) and 'lysis' (splitting).
History: The scheme of glycolysis was proposed by Gustav Embden,Otto Meyerhof,and $J$. Parnas,and is commonly referred to as the $EMP$ pathway.
Location and Process: Glycolysis occurs in the cytoplasm of the cell. In this process,glucose undergoes partial oxidation to form two molecules of pyruvic acid. In plants,glucose is derived from sucrose (the end product of photosynthesis) or from storage carbohydrates.
Key Steps:
$1$. Phosphorylation: Glucose and fructose are phosphorylated to form $Glucose-6-phosphate$ by the enzyme hexokinase,utilizing $ATP$.
$Glucose + ATP \xrightarrow{\text{Hexokinase}} Glucose-6-Phosphate$
$2$. Isomerization: $Glucose-6-phosphate$ isomerizes to $Fructose-6-phosphate$.
$3$. Second Phosphorylation: $Fructose-6-phosphate$ is converted into $Fructose-1,6-bisphosphate$ in the presence of $ATP$.
$4$. Splitting: $Fructose-1,6-bisphosphate$ is split into two triose phosphates: $Dihydroxyacetone$ $phosphate$ $(DHAP)$ and $3-phosphoglyceraldehyde$ $(PGAL)$.
$5$. Subsequent Steps: Through a series of ten enzymatic reactions,these triose phosphates are eventually converted into two molecules of pyruvic acid,producing $NADH + H^+$ and $ATP$ in the process.