Which of the following statements about anaerobic respiration is incorrect ?

Options

A. In animal cells, like muscles during exercise, when oxygen is inadequate for cellular respiration pyruvic acid is reduced to lactic acid by lactate dehydrogenase .
B. The net gain of ATP is 2 molecules.
C. In this process , less than seven percent of the energy in glucose is released .
D. If the concentration of alcohol is seven percent, it becomes toxic to yeast .

Answer

To determine which statement about anaerobic respiration is incorrect, let's analyze each option step by step.

### Step 1: Understand Anaerobic Respiration
Anaerobic respiration occurs in the absence of oxygen. It is a process by which cells convert glucose into energy without using oxygen, resulting in the production of byproducts such as lactic acid or ethanol.

### Step 2: Evaluate Each Statement

1. **Statement 1**: "In animal cells like muscles during exercise when oxygen is inadequate for cellular respiration, pyruvic acid is reduced to lactic acid by the lactate dehydrogenase."
- **Analysis**: This statement is correct. During intense exercise, when oxygen levels are low, pyruvic acid is converted into lactic acid in muscle cells, facilitated by the enzyme lactate dehydrogenase.

2. **Statement 2**: "The net gain of ATP is 2 ATP."
- **Analysis**: This statement is also correct. Anaerobic respiration, such as lactic acid fermentation or alcoholic fermentation, typically results in a net gain of 2 ATP molecules from one molecule of glucose.

3. **Statement 3**: "In this process, less than 7% of the energy in glucose is released."
- **Analysis**: This statement is correct. Anaerobic respiration is less efficient than aerobic respiration, and it releases only about 2-5% of the energy stored in glucose.

4. **Statement 4**: "If the concentration of alcohol is 7%, it becomes toxic to yeast."
- **Analysis**: This statement is incorrect. Yeast can tolerate alcohol concentrations up to about 13% before it becomes toxic. At 7%, yeast is not significantly affected.

### Conclusion
The incorrect statement about anaerobic respiration is **Statement 4**.

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