AP BIOLOGY

Detailed explanation-1: -One glucose molecule yields four ATP molecules in total during glycolysis. Since 2 ATP molecules are used up in the first phase of glycolysis, there is a net gain of 2 ATP molecules.

Detailed explanation-2: -Although four ATP molecules are produced in the second half, the net gain of glycolysis is only two ATP because two ATP molecules are used in the first half of glycolysis.

Detailed explanation-3: -The ATP yield of glycolysis is not problematic: the net yield is two ATPs per glucose converted to pyruvate.

Detailed explanation-4: -2 molecules of ATP are utilised in the glycolysis. One molecule of ATP is utilised when glucose is converted to glucose-6-phosphate and the other is utilised when fructose-6-phosphate is converted to fructose-1, 6-bisphosphate. So, the net gain of ATP molecules during glycolysis is 2.

Detailed explanation-5: -Thus, two ATPs are used in the first three steps of glycolysis. Hence, to split the glucose 2 molecules of ATPs are used.