The Question is from neet-botany respiration-in-plants rq, and it was created by the author Mr. NARESH KUMAR K

Question

During seed germination, the R.Q. is initially high but gradually declines. This shift is primarily attributed to the change in:

Mr. NARESH KUMAR K · Accepted Answer

## CORE INFORMATION
✓ **Answer**: C
## CONCEPT FRAMEWORK
 **Primary Concept**: Respiratory Quotient (R.Q.) and seed germination
 **Related Topics**: Cellular respiration, carbohydrate metabolism, lipid metabolism, protein metabolism
 **Prerequisites**: Understanding of R.Q. ($\frac{CO_2 	ext{ produced}}{O_2 	ext{ consumed}}$), the process of seed germination, and the different substrates used during different stages of germination.
## SOLUTION PATHWAY
**Given Information**:
  R.Q. is initially high and then declines during seed germination.
  This indicates a shift in the substrate being used for respiration.
**Method & Steps**:
 1. **Initial Stage (High R.Q.):**  During the early stages of germination, the seed primarily utilizes stored carbohydrates (starch) for respiration.  The breakdown of carbohydrates produces a relatively high amount of $CO_2$ compared to the amount of $O_2$ consumed.  The R.Q. for carbohydrates is approximately 1 ($\frac{CO_2}{O_2} \approx 1$).
  Reasoning: Carbohydrate respiration involves complete oxidation.
  Formula/Rule: $C_6H_{12}O_6 + 6O_2 ightarrow 6CO_2 + 6H_2O$
 2. **Later Stage (Declining R.Q.):** As germination progresses, the seed begins to utilize stored lipids and proteins for respiration. The oxidation of lipids and proteins produces less $CO_2$ relative to $O_2$ consumed. The R.Q. for lipids is less than 1 (typically between 0.7 and 0.9), and for proteins, it's even lower (around 0.9).
  Working: The shift from carbohydrate to lipid and protein metabolism leads to a decrease in the $CO_2/O_2$ ratio.
  Key Point: The change in R.Q. reflects a shift in the respiratory substrate, not a change in oxygen availability, temperature, or hydration levels (although these factors influence germination). 
 3. **Final Conclusion:** The gradual decline in R.Q. is directly linked to the change in the substrate being respired, from primarily carbohydrates to lipids and proteins.
  Result: Option C is correct.
  Verification: The explanation aligns with the established understanding of seed germination and metabolic shifts.
 ## OPTION ANALYSIS
[A] :x: Ambient temperature affects the rate of respiration, but not the R.Q. directly.
[B] :x: Oxygen availability influences the rate of respiration, but not the R.Q.  A change in oxygen availability would affect both $CO_2$ and $O_2$ proportionally (at least initially).
[C] ✓: The substrate being respired directly determines the ratio of $CO_2$ produced to $O_2$ consumed, thus influencing the R.Q.
[D] :x: Seed hydration is essential for germination, but doesn't directly explain the change in R.Q. ratio.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing R.Q. with respiration rate: R.Q. is a ratio, while the respiration rate is the amount of $O_2$ consumed or $CO_2$ produced per unit time.
  2.Ignoring the different R.Q. values for different substrates:  Different substrates have different R.Q. values, leading to a change in the overall R.Q. during germination.
 **Quick Tips**:
  1.Remember the approximate R.Q. values for carbohydrates (1), lipids (<1), and proteins (<1).
  2.Relate the change in R.Q. to the metabolic shift during seed germination.

Mr. NARESH KUMAR K · Answer

Ambient temperature

Mr. NARESH KUMAR K · Answer

Availability of oxygen

Mr. NARESH KUMAR K · Answer

The correct Option is "Substrate being respired"

Mr. NARESH KUMAR K · Answer

Seed hydration levels

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