Final answer:
Nematodes possess a simple digestive system stretching from mouth to anus, featuring a mouth with lips and teeth, a muscular pharynx, a straight intestine, and a rectum leading to the anus. Their protective cuticle lines the digestive tract, and they absorb nutrients via extracellular digestion followed by phagocytosis.
Step-by-step explanation:
Digestive System of Nematodes
The nematodes, also known as roundworms, exhibit a simple yet effective digestive system that extends from the mouth to the anus, making them pseudocoelomates with a complete digestive tract. Beginning at the anterior end, the mouth has three or six lips and may be equipped with teeth or a stylet for piercing. The mouth leads into the stomodeum, which is the foregut comprising a muscular pharynx that pumps food into the intestine where digestion and absorption occur. The intestine is a simplistic tube forming the majority of the digestive tract, with certain species having diverticular pouches for increased surface area. At the posterior end of the nematode, the proctodeum—or hindgut—comprises the rectum that leads to the anus, where waste is expelled from the body.
Nematodes have an epidermis that may be a single layer of cells or a syncytium which is protected by a cuticle rich in collagen and chitin. This cuticle also lines the pharynx and rectum, acting as a continuation of the external protective layer. Their cylindrical body shape, visible in diagrams such as Figure 28.32, aids in movement and digestion. The digestion process in nematodes involves extracellular enzymes secreted into the intestinal space for breaking down food, and the subsequent phagocytosis of digested materials by lining cells.
Overall, nematodes' digestive systems function efficiently to support their free-living or parasitic lifestyles. This system showcases nematodes' evolutionary adaptations for their ecological roles, including nutrient absorption and waste elimination.