When production of `CO_2` is more than intake of `O_2`, the respiratory substrate is

Options

A. sucrose
B. organic acid
C. glucose
D. fat/protein

Answer

To determine the respiratory substrate when the production of CO2 is more than the intake of O2, we need to analyze the respiratory quotient (RQ) which is defined as the ratio of the volume of carbon dioxide produced to the volume of oxygen consumed during respiration.

### Step-by-Step Solution:

1. **Understand the Concept of Respiratory Substrate**:
- A respiratory substrate is a compound that is oxidized during respiration to produce energy. Common substrates include carbohydrates, fats, and proteins.

2. **Define Respiratory Quotient (RQ)**:
- RQ = (Volume of CO2 produced) / (Volume of O2 consumed)
- If RQ > 1, it indicates that more CO2 is produced than O2 is consumed.

3. **Analyze Different Respiratory Substrates**:
- **Sucrose**: The chemical equation shows that the volume of CO2 produced is equal to the volume of O2 consumed (RQ = 1). Therefore, sucrose does not fit our criteria.
- **Glucose**: Similarly, the respiration of glucose also results in an RQ of 1 (6 CO2 produced for 6 O2 consumed). Thus, glucose is also not the correct answer.
- **Organic Compounds**: When organic compounds are metabolized, they typically produce more CO2 than the O2 consumed, resulting in an RQ greater than 1. This indicates that organic compounds can be a potential respiratory substrate.
- **Fats and Proteins**: The metabolism of fats and proteins generally results in an RQ less than 1, as they consume more O2 than CO2 produced.

4. **Conclusion**:
- Since we are looking for a respiratory substrate where the production of CO2 exceeds the intake of O2, the correct answer is **organic acids**. They are the substrates that lead to an RQ greater than 1.

### Final Answer:
The respiratory substrate when the production of CO2 is more than the intake of O2 is **organic acids**.