The Question is from neet-zoology animal-kingdom cnidaria, and it was created by the author K SUNKANNA

Question

Which specific cellular mechanism in cnidarians allows for the rapid discharge of nematocysts, considering the internal osmotic pressure is significantly higher than the surrounding seawater?

K SUNKANNA · Accepted Answer

## CORE INFORMATION
✓ **Answer**: C
## CONCEPT FRAMEWORK
 **Primary Concept**: Nematocyst discharge mechanism in cnidarians
 **Related Topics**: Osmosis, Calcium signaling, Myonemes, Cnidocyte structure
 **Prerequisites**: Understanding of cellular processes, osmosis, and muscle contraction.
## SOLUTION PATHWAY
**Given Information**:
  Higher internal osmotic pressure in cnidocytes compared to seawater.
  Need to explain rapid nematocyst discharge.
**Method & Steps**:
 1. Analyze the options considering the given information.
  Reasoning: The question highlights the higher internal osmotic pressure, implying a mechanism that doesn't rely on osmotic changes for rapid discharge.
 2. Evaluate each option's plausibility.
  Working: 
        * Option A (Passive diffusion): This would increase internal pressure, but slowly and not necessarily trigger rapid discharge.  It also contradicts the already high internal pressure.
        * Option B (Active transport of sodium): This could create an osmotic gradient, but this process is usually slower than the extremely rapid nematocyst discharge.
        * Option C (Calcium influx and myoneme contraction):  A rapid influx of calcium ions is a well-known trigger for muscle contraction. Myonemes are muscle-like cells surrounding the nematocyst.  This mechanism offers a fast and efficient way to discharge the nematocyst.
        * Option D (Enzymatic breakdown): While enzymatic processes are involved in nematocyst formation, this is not the primary trigger for the rapid discharge itself. 
  Key Point: The speed of nematocyst discharge requires a fast acting mechanism.
 3. Select the most plausible mechanism.
  Result: Option C, rapid calcium influx triggering myoneme contraction, provides the fastest and most plausible explanation for the rapid nematocyst discharge.
  Verification: This mechanism is well-supported by biological evidence.
 ## OPTION ANALYSIS
A :x: Passive diffusion is too slow and contradicts the high internal pressure.
B :x: Active sodium transport is too slow for the rapid discharge observed.
C ✓: Rapid calcium influx and myoneme contraction are a well-established mechanism for rapid nematocyst discharge.
D :x: Enzymatic breakdown is involved in nematocyst formation, but not the immediate trigger for discharge.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing osmosis with other cellular mechanisms:  Osmosis is a slow process, not suitable for rapid discharge.
  2.Ignoring the role of myonemes: Myonemes are crucial for the forceful ejection of nematocysts.
 **Quick Tips**:
  1.Remember the speed requirement for nematocyst discharge to narrow down the options.
  2.Calcium ions are key triggers for many rapid cellular processes, including muscle contraction.

K SUNKANNA · Answer

Passive diffusion of water into the cnidocyte, increasing internal pressure

K SUNKANNA · Answer

Active transport of sodium ions out of the cnidocyte, creating an osmotic gradient

K SUNKANNA · Answer

The correct Option is "Rapid influx of calcium ions triggering forceful contraction of surrounding myoneme cells"

K SUNKANNA · Answer

Enzymatic breakdown of the cnidocil cap, releasing stored elastic energy

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