Organic acids are indeed used as respiratory substrates in biological processes.
Understanding Respiratory Substrates
Respiratory substrates are molecules that can be broken down through cellular respiration to release energy (ATP). While carbohydrates, lipids, and proteins are well-known respiratory substrates, organic acids also serve this crucial role.
Based on the provided information:
- Confirmation: The reference explicitly states, "Carbohydrates, lipids, proteins, and organic acids act as respiratory substrates." It further confirms, "So, yes organic acids are respiratory substrates."
- Examples: Common types of organic acids that function as respiratory substrates, as mentioned in the reference, include:
- Carboxylic acids
- Lactic acid
- Etc. (implying other organic acids can also be used)
- Respiratory Quotient (R.Q.): A characteristic feature when organic acids are respired is their Respiratory Quotient (R.Q.), which is the ratio of carbon dioxide produced to oxygen consumed. The reference notes that the R.Q. for organic acids "is more than 1".
Key Takeaways
When considering which organic acid is used as a respiratory substrate, it's important to understand that it's not limited to just one specific acid. Instead, the category of organic acids as a whole functions in this capacity, with various specific organic acids participating depending on the organism and metabolic conditions.
Some common examples highlighted, consistent with the reference, are:
- Lactic Acid: Famously produced during anaerobic respiration in muscles and some microorganisms, lactic acid can also be further metabolized aerobically as a substrate.
- Carboxylic Acids: This is a broad class, and many intermediates of metabolic pathways like the Citric Acid Cycle (Krebs Cycle), such as citric acid, malic acid, fumaric acid, and succinic acid (which are carboxylic acids or dicarboxylic/tricarboxylic acids), can directly enter the respiratory pathway and be oxidized.
While the question asks for "Which organic acid", the reference indicates that organic acids collectively serve this purpose, listing specific types like carboxylic acids and lactic acid as common examples. Therefore, rather than a single name, the answer points to a category and specific examples within it based on the provided source.
