For fatty acids to be able to enter the pathways of cellular respiration, they must be:

Options

A. deaminated
B. combined with glycerol
C. combined with ATP
D. broken into acetyl groups

Explanation

To answer the question, "For fatty acids to be able to enter the pathways of cellular respiration, they must be:", we will follow these steps:

### Step-by-Step Solution:

1. **Understanding Fatty Acids**:
- Fatty acids are long-chain molecules that serve as important energy sources in the body. They cannot directly enter the Krebs cycle due to their structure.

2. **Role in Cellular Respiration**:
- In cellular respiration, fatty acids need to undergo a transformation before they can be utilized for energy production.

3. **Beta-Oxidation Process**:
- The process through which fatty acids are broken down is called beta-oxidation. This process occurs in the mitochondria and involves the sequential removal of two-carbon units from the fatty acid chain.

4. **Formation of Acetyl Coenzyme A**:
- During beta-oxidation, fatty acids are converted into acetyl CoA (acetyl coenzyme A). Each two-carbon unit that is removed forms one molecule of acetyl CoA.

5. **Entry into Krebs Cycle**:
- Once converted into acetyl CoA, these molecules can then enter the Krebs cycle (also known as the citric acid cycle), where they are further processed to produce ATP, the energy currency of the cell.

6. **Conclusion**:
- Therefore, for fatty acids to enter the pathways of cellular respiration, they must be broken down into acetyl groups (acetyl CoA).

### Final Answer:
Fatty acids must be **broken down into acetyl groups** to enter the pathways of cellular respiration.

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