In order for glucose to be used as an energy source, it is necessary that -

Options

A. Glucose be formed from fructose
B. Glucose be degraded to `CO_(2)`
C. 2 molecules of ATP be invested in the system
D. None

Answer

To answer the question "In order for glucose to be used as an energy source, it is necessary that -", we can break down the process of glucose metabolism and its conversion into usable energy (ATP) in a step-by-step manner.

### Step-by-Step Solution:

1. **Understanding Glucose as an Energy Source**:
- Glucose is a simple sugar and a primary source of energy for cells. It is essential for cellular respiration, which is the process through which cells convert glucose into energy.

2. **The Role of ATP**:
- ATP (adenosine triphosphate) is the energy currency of the cell. For glucose to be utilized as an energy source, it must be converted into ATP.

3. **The Process of Respiration**:
- The process of respiration involves two main phases: the physical phase (gas exchange) and the chemical phase (ATP production).
- In the physical phase, gases like oxygen and carbon dioxide are exchanged.
- In the chemical phase, glucose is broken down to produce ATP.

4. **Glycolysis**:
- The first step in the breakdown of glucose is glycolysis. Glycolysis occurs in the cytoplasm and involves the conversion of one glucose molecule into two molecules of pyruvate.
- During glycolysis, a total of 4 ATP molecules are produced, but 2 ATP molecules are initially invested to start the process.

5. **Net ATP Production**:
- Therefore, the net gain of ATP from glycolysis is 4 ATP (produced) - 2 ATP (invested) = 2 ATP.
- Thus, the investment of 2 ATP molecules is crucial for the overall ATP production from glucose.

6. **Conclusion**:
- In summary, for glucose to be used as an energy source, it is necessary to invest 2 ATP molecules during glycolysis, which allows for the production of ATP from glucose.

### Final Answer:
In order for glucose to be used as an energy source, it is necessary that 2 ATP molecules are invested during the glycolysis process.