The Question is from neet-botany respiration-in-plants rq, and it was created by the author B VENKAT

Question

A succulent xerophyte exhibiting Crassulacean Acid Metabolism (CAM) is kept in a sealed, transparent container with a CO2 sensor.  The container is exposed to a 12-hour light/12-hour dark cycle.  At which point during the cycle would the CO2 concentration within the container be LOWEST, assuming no other influencing factors?

B VENKAT · Accepted Answer

## CORE INFORMATION
✓ **Answer**: D
## CONCEPT FRAMEWORK
 **Primary Concept**: Crassulacean Acid Metabolism (CAM) photosynthesis
 **Related Topics**: Photosynthesis, gas exchange in plants, CO2 uptake
 **Prerequisites**: Understanding of the basic principles of photosynthesis and the differences between C3, C4, and CAM pathways.
## SOLUTION PATHWAY
**Given Information**:
  * CAM plant in a sealed container.
  * 12-hour light/12-hour dark cycle.
  * CO2 sensor monitoring the container's atmosphere.
  * No other influencing factors (e.g., respiration by other organisms).
**Method & Steps**:
 1. **Understanding CAM photosynthesis:** CAM plants, adapted to arid conditions, open their stomata at night to minimize water loss.  They take in $CO_2$ at night and store it as malic acid in vacuoles.
  Reasoning: This is the key to understanding the CO2 levels in the container.
  Formula/Rule:  No specific formula is needed, but understanding the process of CAM is crucial.
 2. **CO2 uptake and release:** During the night, the plant takes up $CO_2$ from the atmosphere.  During the day, the stored malic acid is used in photosynthesis, releasing $CO_2$ as a byproduct.
  Working: Since the container is sealed, the CO2 absorbed at night is not replenished from the outside. The CO2 released during the day is consumed in photosynthesis.
  Key Point: The $CO_2$ concentration will decrease as the plant takes it in during the night and will increase as it's released during the day. 
 3. **Lowest CO2 concentration:** The lowest $CO_2$ concentration will occur near the end of the dark period, just before the light period begins, because the plant has been actively absorbing $CO_2$ throughout the night.
  Result: The CO2 concentration will be lowest near the end of the dark period.
  Verification: The logic aligns with the known mechanism of CAM photosynthesis.
 ## OPTION ANALYSIS
A :x: Near the end of the light period: $CO_2$ is being released during the light period.
B :x: Near the beginning of the light period: $CO_2$ levels would be relatively high since the plant has just started releasing the $CO_2$ from the malic acid.
C :x: Midway through the dark period:  $CO_2$ uptake is ongoing throughout the dark period, but the lowest level would be reached at the end.
D ✓: Near the end of the dark period: The plant has been actively absorbing $CO_2$ for the entire night, leading to the lowest concentration before the light period begins.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing CAM with C3 or C4 photosynthesis: Remember that CAM plants open their stomata at night.
  2.Ignoring the sealed container: The sealed container is crucial because it prevents the replenishment of $CO_2$ from the external environment.
 **Quick Tips**:
  1.Focus on the timing of stomatal opening and $CO_2$ uptake in CAM plants.
  2.Visualize the $CO_2$ levels changing over the 24-hour cycle.

B VENKAT · Answer

Near the end of the light period

B VENKAT · Answer

Near the beginning of the light period

B VENKAT · Answer

Midway through the dark period

B VENKAT · Answer

The correct Option is "Near the end of the dark period"

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