Nematode Systems: Identifying the Absent Respiratory System

Nematodes, commonly known as roundworms, are a diverse group of invertebrates. Understanding their anatomy is key to biology exams. Let's examine the systems mentioned:

Key Nematode Systems

• Digestive System: Nematodes possess a complete digestive system, typically consisting of a mouth, pharynx, intestine, caecum, rectum, and anus. This system allows them to process food.
• Reproductive System: Reproduction is primarily sexual. Most nematodes have distinct male and female individuals (dioecious), although some are hermaphroditic or parthenogenetic. They feature well-developed reproductive organs.
• Excretory System: Nematodes have a specialized excretory system, often involving one or two renette cells or a tubular gland connected to a ventral pore. This system regulates osmotic balance and removes waste.
• Respiratory System: Nematodes LACK a specialized respiratory system (like lungs or gills). Gas exchange (uptake of oxygen and release of carbon dioxide) occurs primarily through diffusion across their moist body surface.

Conclusion

Based on their biology, nematodes do not have a dedicated respiratory system. Gas exchange is achieved via diffusion. Therefore, the Respiratory system is the correct answer.