Bioreactors have

Options

A. Foam control system, temperature control system
B. Oxygen delivery system
C. pH control system
D. All the above

Answer

### Step-by-Step Solution:

1. **Understanding Bioreactors**:
- Bioreactors are large vessels used for biological processes where raw materials are converted into specific products through the action of microorganisms, plant cells, or animal cells.

2. **Key Functions of Bioreactors**:
- They provide optimum conditions for the growth of host cells, which is crucial for producing desired products such as enzymes and antibiotics.

3. **Factors Affecting Growth and Productivity**:
- Several environmental factors are critical for the growth of organisms in bioreactors. These include:
- **pH**: The acidity or alkalinity of the environment must be maintained at an optimal level for the organisms to thrive.
- **Temperature**: The temperature must also be controlled to ensure that it remains within the optimal range for the specific organism being cultured.
- **Oxygen**: For aerobic processes, a constant supply of oxygen is necessary for the growth of aerobic organisms.
- **Foam Control**: Foam can form during fermentation processes, which can affect the efficiency of the bioreactor and needs to be controlled.

4. **Analyzing the Options**:
- **A. Foam control system**: Necessary to manage foam formation.
- **B. Temperature control system**: Essential to maintain optimal temperature.
- **C. Oxygen delivery system**: Critical for aerobic processes.
- **D. pH control system**: Important for maintaining the right pH level.
- Since all these systems are essential for the effective functioning of a bioreactor, the correct answer is **D. all of the above**.

### Final Answer:
**D. all of the above**

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