If there is no oxygen present, how can cells make ATP? glycolysis cell respiration fermentation

## Step 1: <br />Understand the question. The question is asking about the process by which cells can produce ATP (Adenosine Triphosphate), the primary energy currency of cells, in the absence of oxygen.<br /><br />## Step 2: <br />Review each option. <br /><br />- Glycolysis: This is the first step in both aerobic and anaerobic respiration. It occurs in the cytoplasm of the cell and does not require oxygen. It breaks down one molecule of glucose into two molecules of pyruvate, producing a net gain of 2 ATP molecules.<br /><br />- Cell respiration: This term generally refers to aerobic respiration, which requires oxygen to produce ATP. Therefore, this option is not correct.<br /><br />- Fermentation: This is an anaerobic process that allows cells to produce ATP without oxygen. There are two types of fermentation: lactic acid fermentation and alcoholic fermentation. Both start with glycolysis, followed by a different pathway to regenerate NAD+, which is needed for glycolysis to continue.<br /><br />## Step 3: <br />Based on the above analysis, the correct answer is "glycolysis" and "fermentation". Both processes allow cells to produce ATP without oxygen.