Which of these pairs of processes are anaerobic?

Options

A. A) Fermentation and glycolysis
B. B) Fermentation and the Krebs cycle
C. C) Glycolysis and the Krebs cycle
D. D) The Krebs cycle and
the electron transport system

Explanation

To determine which pairs of processes are anaerobic, we first need to understand the definitions and characteristics of the processes involved in respiration.

### Step-by-Step Solution:

1. **Understand Types of Respiration**:
- There are two main types of respiration: aerobic and anaerobic.
- **Aerobic respiration** requires oxygen and involves the complete oxidation of organic food into carbon dioxide and water.
- **Anaerobic respiration** occurs in the absence of oxygen and involves the incomplete oxidation of organic food.

2. **Identify the Processes**:
- The processes mentioned in the question are:
- **Glycolysis**: This is the first step in both aerobic and anaerobic respiration. It does not require oxygen.
- **Fermentation**: This is an anaerobic process that occurs after glycolysis when oxygen is not available.
- **Krebs Cycle**: This process occurs only in aerobic respiration and requires oxygen.
- **Electron Transport System**: This process also requires oxygen and is part of aerobic respiration.

3. **Evaluate Each Option**:
- **Option A**: Fermentation and Glycolysis
- Both processes can occur without oxygen. Glycolysis is common to both aerobic and anaerobic respiration, while fermentation is strictly anaerobic.
- **Conclusion**: This pair is anaerobic.
- **Option B**: Fermentation and the Krebs Cycle
- Fermentation is anaerobic, but the Krebs Cycle requires oxygen.
- **Conclusion**: This pair is not anaerobic.
- **Option C**: Glycolysis and the Krebs Cycle
- Glycolysis is anaerobic, but the Krebs Cycle is aerobic.
- **Conclusion**: This pair is not anaerobic.
- **Option D**: The Krebs Cycle and the Electron Transport System
- Both of these processes require oxygen.
- **Conclusion**: This pair is not anaerobic.

4. **Final Answer**:
- The correct answer is **Option A: Fermentation and Glycolysis** as both processes are anaerobic.