During glycolysis, one molecule of glucose is converted into two molecules of pyruvate. The process of glycolysis occurs in the cytoplasm of the cell and involves a series of enzymatic reactions. Among these reactions, there are two steps where ATP molecules are directly synthesized. Let's break down the process to understand how many ATP molecules are produced.

1. Glycolysis Overview:
Glycolysis is the first step in cellular respiration, which is the process by which cells convert glucose into energy. It can be divided into two phases: the energy investment phase and the energy payoff phase.

2. Energy Investment Phase:
During this phase, two molecules of ATP are consumed to activate glucose, which is then split into two three-carbon molecules called glyceraldehyde-3-phosphate (G3P).

3. Energy Payoff Phase:
In this phase, the G3P molecules are further metabolized to generate ATP and NADH.

- Step 1: G3P oxidation
Each G3P molecule is oxidized to form 1,3-bisphosphoglycerate, producing two molecules of NADH in the process.

- Step 2: ATP synthesis
In this step, 1,3-bisphosphoglycerate is converted into 3-phosphoglycerate, and one molecule of ATP is directly synthesized. This reaction occurs twice, resulting in the synthesis of two ATP molecules.

- Step 3: ATP synthesis
In the next step, 3-phosphoglycerate is converted into 2-phosphoglycerate, and one more molecule of ATP is directly synthesized. Again, this reaction occurs twice, resulting in the synthesis of two more ATP molecules.

- Step 4: Conversion of 2-phosphoglycerate to phosphoenolpyruvate
In this step, 2-phosphoglycerate is converted into phosphoenolpyruvate without the production of ATP.

- Step 5: ATP synthesis
Phosphoenolpyruvate is then converted into pyruvate, and one last molecule of ATP is directly synthesized. This reaction also occurs twice, resulting in the synthesis of two additional ATP molecules.

Therefore, the total number of ATP molecules directly synthesized during glycolysis from one molecule of glucose is 2 + 2 + 2 = 6 ATP molecules.

Hence, the correct answer is option D) 6.

There are two substrate level phosphorylations during glycolysis. So one glucose yields 4 ATPs.