Answer:
Energy investment phase of Glycolysis is necessary so that reaction can occur Spontaneously or in Thermodynamically favorable manner.
Explanation:
Coupling Reaction helps an Endergonic reaction to take place by coupling that reaction with an Exergonic reaction that generates energy such as hydrolysis of ATP.
The first step of Glycolysis is an energy investment step because the ist step of Glycolytic pathway deals with attachment of inorganic phosphate with glucose molecule(endergonic reaction) with the help of ATP hydrolysis(exergonic reaction) that generates energy to carry out the formation of Glucose 6 phosphate from glucose.