Question

Which of the following is a tube where nutrients are reabsorbed and where fluid waste is excreted from the mollusk body?

1) nephridia
2) radula
3) siphon
4) foot

Answer 1

The tube in mollusks where nutrients are reabsorbed and where fluid waste is excreted in the nephridia (option 1). Nephridia filter waste from body fluids, reabsorb nutrients, and excrete waste through a pore on the body's side. Other mollusk structures like the radula, siphon, and foot serve different functions and are not involved in excretion.

Step-by-step explanation:

In mollusks, the tube where nutrients are reabsorbed and fluid waste is excreted is the nephridia. Mollusks have a coelom and a complete digestive system, and the nephridia play a crucial role in their excretory system. These organs filter waste from body fluids and release it into the coelom. Terrestrial mollusks perform gas exchange across the lining of their mantle cavity, while aquatic mollusks use gills for respiration. The nephridia function similarly to the kidneys in vertebrates, filtering fluid from the coelom and then reabsorbing nutrients and solutes as the filtrate passes down the tubules. The end product, containing nitrogenous and other wastes, is eventually secreted through a pore in the side of the body.

Other structures in mollusks include the radula, a rasping organ used for feeding, the siphon used in aquatic species for water intake and expulsion during respiration and feeding, and the foot, a muscular structure used for locomotion. However, these are not involved in the reabsorption of nutrients or excretion of waste. Therefore, the correct answer to the student's question is nephridia.

Answer 2

The nephridia (option 1) are tube-like organs in mollusks that filter waste from body fluids, facilitate nutrient reabsorption, and excrete fluid waste. They are part of the excretory system and are critical for the organism's osmoregulation.

Step-by-step explanation:

The tube where nutrients are reabsorbed, and fluid waste is excreted from the mollusk body is called nephridia. Mollusks, along with other members of the animal kingdom such as earthworms (annelids), have this excretory structure. Nephridia function by filtering waste from body fluids, allowing for the reabsorption of nutrients and the expulsion of nitrogenous and other wastes.

They perform a critical role in both excretion and osmoregulation within the mollusk's body. Unlike nephridia, the other options such as radula, siphon, and foot serve different purposes. The radula is a tongue-like organ found in mollusks used for feeding; the siphon is involved in water intake and expulsion and in filter-feeding processes in bivalves; and the foot is a muscular structure used for locomotion.