Model Answer
0 min readIntroduction
Cnidocytes, also known as stinging cells, are characteristic of cnidarians like Hydra, responsible for prey capture and defense. These cells contain organelles called cnidoblasts, which house the nematocysts – complex intracellular structures that deliver a stinging impulse. The nematocyst is a unique feature of this phylum, enabling efficient predation and protection. Understanding the structure of both the cnidoblast and the diverse types of nematocysts is fundamental to comprehending the biology and ecological role of Hydra. This answer will detail the structure of the cnidoblast and the various types of nematocysts found in Hydra.
Structure of Cnidoblast
The cnidoblast is the specialized cell responsible for producing and discharging nematocysts. Its structure can be described as follows:
- Capsule: This is the main body of the cnidoblast, containing the coiled nematocyst. It’s a secretory product of the Golgi apparatus.
- Operculum: A lid-like structure covering the opening of the capsule. It controls the discharge of the nematocyst.
- Cnidocil: A hair-like trigger extending from the capsule. Mechanical or chemical stimulation of the cnidocil initiates the discharge process.
- Filopodia: These are microvilli-like projections surrounding the cnidocil, increasing the surface area for sensory input.
- Nucleus: Located at the base of the cell, controlling cellular functions.
The cytoplasm contains mitochondria and other organelles necessary for cellular metabolism and nematocyst formation.
Types of Nematocysts in Hydra
Hydra possesses several types of nematocysts, each adapted for a specific function. These are categorized based on their morphology and mechanism of action:
1. Penetrants (Gladiolus)
These are the most common type of nematocyst in Hydra. They are thread-like and used for prey capture. Upon discharge, the thread penetrates the prey’s skin, allowing Hydra to hold onto it.
2. Volvents (Desmos)
These nematocysts are sticky and coiled. They are used for entanglement and adhesion. When discharged, the thread wraps around the prey, securing it to the tentacles.
3. Glutinous (Colloblast)
These nematocysts are unique to some freshwater hydroids, including Hydra. They are smaller and have a bulbous tip covered in adhesive secretions. They are primarily used for adhesion to surfaces and prey.
4. Volvent-Penetrants (Heteroneme)
These are a combination of volvent and penetrant types. They possess both sticky and penetrating capabilities, providing a dual function in prey capture and defense.
The following table summarizes the key differences between these nematocyst types:
| Nematocyst Type | Morphology | Function |
|---|---|---|
| Penetrant (Gladiolus) | Thread-like, barbed | Prey capture – penetration |
| Volvent (Desmos) | Coiled, sticky | Prey capture – entanglement |
| Glutinous (Colloblast) | Small, bulbous, adhesive | Adhesion to surfaces & prey |
| Volvent-Penetrant (Heteroneme) | Combination of coiled & thread-like | Dual function – entanglement & penetration |
The discharge of a nematocyst is a remarkably rapid process, occurring within milliseconds. It involves a complex interplay of ion fluxes and osmotic pressure changes within the capsule, leading to the forceful eversion of the thread.
Conclusion
In conclusion, the cnidoblast and its contained nematocysts are crucial for the survival of Hydra, enabling it to effectively capture prey and defend itself. The diverse types of nematocysts, each with specialized morphology and function, demonstrate the remarkable evolutionary adaptations within this phylum. Further research into the molecular mechanisms governing nematocyst discharge could have implications for biomedical applications, such as the development of novel drug delivery systems or bio-inspired adhesives.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.