Q.101 Five dialysis bags (DB1-DB5), impermeable to sucrose, were filled with various concentrations of
sucrose. The bags were placed in separate beakers containing 0.6 M sucrose solution. Every 10
minutes, the bags were weighed and the percent change in mass of each bag was plotted as a
function of time.
Which plot in the graph (X-axis representing time in minutes and Y-axis representing mass change
in percentage) represent(s) bags that contain a solution that is hypertonic at 50 minutes?
(A) DB2 (B) DB4 (C) DB3 (D) DB4 and DB5
Introduction
Osmosis-based questions involving dialysis bags are very common in NEET, CBSE Class 11 Biology, and competitive exams. These questions test your understanding of hypertonic, hypotonic, and isotonic solutions by analyzing mass change vs time graphs.
In this article, we will clearly explain Question 16, analyze the graph, define the key concept of hypertonicity, and evaluate each option step by step to arrive at the correct answer.
Understanding the Question
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Five dialysis bags (DB1–DB5) contain different sucrose concentrations.
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The bags are impermeable to sucrose, but permeable to water.
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All bags are placed in 0.6 M sucrose solution.
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Mass change (%) vs time (minutes) is plotted.
The question asks:
Which dialysis bag(s) contain a solution that is hypertonic at 50 minutes?
Key Concept: What Does Hypertonic Mean?
A solution is hypertonic when:
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It has a higher solute concentration than the surrounding solution.
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Water moves out of the bag by osmosis.
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The bag loses mass, resulting in a negative percent change in mass.
📌 Important Rule:
Negative mass change = hypertonic solution inside the bag
Analyzing the Graph
At 50 minutes, observe the mass change values:
| Dialysis Bag | Mass Change (%) | Interpretation |
|---|---|---|
| DB1 | Positive | Hypotonic |
| DB2 | Positive | Hypotonic |
| DB3 | ~0 | Isotonic |
| DB4 | Negative | Hypertonic |
| DB5 | Strongly Negative | Hypertonic |
Correct Answer
✅ (D) DB4 and DB5
Both DB4 and DB5 show a negative percentage change in mass, which clearly indicates that water moved out of the bags. Hence, the solutions inside these bags are hypertonic compared to the external 0.6 M sucrose solution.
Explanation of All Options
Option (A): DB2 ❌
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DB2 shows a positive mass change.
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Water entered the bag.
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This means the solution inside is hypotonic, not hypertonic.
Option (B): DB4 ❌ (Partially Correct)
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DB4 is hypertonic, but the option lists only DB4.
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Since DB5 is also hypertonic, this option is incomplete.
Option (C): DB3 ❌
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DB3 shows no significant mass change.
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This indicates an isotonic solution.
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No net movement of water occurs.
Option (D): DB4 and DB5 ✅ (Correct)
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Both bags show negative mass change.
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Water exits the bags due to higher internal solute concentration.
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Therefore, both are hypertonic.
Final Conclusion
✔ Dialysis bags DB4 and DB5 contain hypertonic solutions at 50 minutes.
This question reinforces the concept that mass decrease in osmosis experiments always indicates a hypertonic internal solution.
