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A plant is respiring with an RQ of greater than 1.  What substrate is it likely using?

NISHANTH · Accepted Answer

## CORE INFORMATION ✓ **Answer**: D ## CONCEPT FRAMEWORK **Primary Concept**: Respiratory Quotient (RQ) **Related Topics**: Plant respiration, metabolic substrates, carbohydrate, fat, protein, organic acid metabolism **Prerequisites**: Understanding of cellular respiration and the calculation of RQ. ## SOLUTION PATHWAY **Given Information**: RQ > 1 The plant is respiring. **Method & Steps**: 1. Understanding Respiratory Quotient (RQ) Reasoning: RQ is the ratio of the volume of carbon dioxide produced to the volume of oxygen consumed during respiration. It varies depending on the substrate being oxidized. Formula/Rule: $RQ = \frac{Volume\,of\,CO_2\,produced}{Volume\,of\,O_2\,consumed}$ 2. Analyzing RQ values for different substrates Working: * Carbohydrates: RQ = 1 (e.g., glucose: $C_6H_{12}O_6 + 6O_2 ightarrow 6CO_2 + 6H_2O$) * Fats: RQ < 1 (e.g., palmitic acid) * Proteins: RQ ≈ 0.9 * Organic acids: RQ > 1 (e.g., malic acid, citric acid) Key Point: An RQ greater than 1 indicates that more carbon dioxide is being produced than oxygen is being consumed. This is characteristic of the oxidation of organic acids. 3. Determining the likely substrate Result: Since the RQ is greater than 1, the plant is likely using organic acids as a respiratory substrate. Verification: The calculation of RQ for various substrates confirms that only organic acids yield an RQ greater than 1. ## OPTION ANALYSIS A :x: Carbohydrates have an RQ of 1. B :x: Fats have an RQ less than 1. C :x: Proteins have an RQ of approximately 0.9. D ✓: Organic acids have an RQ greater than 1 because their oxidation produces more $CO_2$ than $O_2$ is consumed. This is due to their pre-existing carboxyl groups. ## LEARNING AIDS **Common Mistakes**: 1.Confusing RQ with other metabolic ratios: Ensure you understand the specific definition of RQ and don't confuse it with other ratios. 2. Incorrectly calculating RQ: Pay close attention to the units and ensure the volumes are accurately measured or obtained. **Quick Tips**: 1.Remember the general ranges of RQ for different substrates: Carbohydrates (1), Fats (<1), Proteins (≈0.9), Organic acids (>1). 2.Visualize the balanced chemical equations for respiration of different substrates to understand the ratio of $CO_2$ to $O_2$.

NISHANTH · Answer

Carbohydrate

NISHANTH · Answer

Fat

NISHANTH · Answer

Protein

NISHANTH · Answer

The correct Option is "Organic acid"

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