Question

Nephridiopores of an earthworm occur in all segments except
A) First
B) Last
C) Both First and last
D) First two and last

Answer 1

Hint: The nephridiopore is the external opening of a nephridium, from where waste is excreted from the cell. It is an excretory organ that has been found in many species, such as flatworms and annelids.

Complete Answer:
Nephridium or nephridia is an invertebrate organ that is found in pairs and performs a function close to that of the vertebrate kidney. Nephridia expel the metabolic waste from the body of the animal.

Earthworms (annelids) have slightly more advanced excretory structures called nephridia. Each section, excluding the first two and last of the earthworm, contains a pair of nephridia. They are similar to flame cells in that they do have cilia tubules and behave like a kidney to remove waste. In more advanced segmented worms, such as earthworms, nephridia are usually clustered in pairs around parts of the body of the worm. Each category shares similarity. All of them act as waste ducts, but each has distinctive functions as well.

The nephridium consists of an opening called a nephrostome, a long convoluted tubule, and then a further opening called a nephridiopore. Body fluids are pumped through the nephrostome and moved via the complex tubular framework. Critical substances are reabsorbed by active mechanisms, and waste products are returned to the lumen of the tube. The subsequent excretory fluid or urine is carried through the nephridiopore.

The three main regions found in the body of an earthworm are the Preclitellar Region, the Clitellar Region and the Postclitellar Region. The clitellar segment has around 2000 nephridiopores per segment, so it is called a forest of nephridia.

Note: Nephridia is epicly similar to nephrons or urinary tubules found in human kidneys. Nephridia aids in controlling the amount of water through reabsorption from excreted products during summers and winters, so that the blood flows into hypertonic urine.