When out of oxygen, vertebrate muscle :

Options

A. produces lactic acid
B. produces more carbon dioxide
C. stops functioning
D. degrades protein

Explanation

**Step-by-Step Solution:**

1. **Understanding the Context**: When vertebrate muscles are subjected to intense activity, they require oxygen to produce energy through aerobic respiration. However, during prolonged or vigorous exercise, the oxygen supply can become insufficient.

2. **Anaerobic Conditions**: In the absence of sufficient oxygen (anaerobic conditions), the muscles cannot perform aerobic respiration effectively. This leads to a shift in the metabolic pathway.

3. **Lactic Acid Production**: Under anaerobic conditions, the muscles switch to anaerobic respiration. This process primarily involves the conversion of glucose into energy, resulting in the production of lactic acid as a byproduct.

4. **Effects of Lactic Acid**: The accumulation of lactic acid in the muscles can lead to muscle fatigue and pain. This is often experienced as a burning sensation during intense exercise.

5. **Conclusion**: Therefore, when vertebrate muscles are out of oxygen, they primarily produce lactic acid.

**Final Answer**: When out of oxygen, vertebrate muscle produces lactic acid.

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