Question

Select the correct option representing the excretory organs present in (i) earthworm, (ii) centipede, (iii) prawn, and (iv) flatworm. (a) Malpighian Flame Nephridia Green tubules cell gland (b) Flame Green Malpighian Nephridia cell gland tubules (c) Nephridia Malpighian Green Flame tubules gland cell (d) Green Nephridia Flame cell Malpighian gland tubules

Short answer

The correct answer is (c) Nephridia, Malpighian tubules, Green gland, Flame cell.

Step-by-step solution

Identify Excretory Organs for Earthworm

Determine the excretory organ present in earthworms. For earthworms, the answer is nephridia, organs that filter fluid in the coelom (body cavity).

Identify Excretory Organs for Centipede

Identify the excretory structure in centipedes. Centipedes use Malpighian tubules, which are part of the arthropod body system for excreting wastes.

Identify Excretory Organs for Prawn

Determine the excretory system used by prawns. Prawns (crustaceans) have green glands (also known as antennal or maxillary glands) for excretion.

Identify Excretory Organs for Flatworm

Find the excretory organ characteristic of flatworms. Flatworms excrete waste through cells known as flame cells.

Match Each Organism with Its Corresponding Excretory Organ

Match excretory organs to the correct organism in each option. (i) Earthworm - Nephridia, (ii) Centipede - Malpighian tubules, (iii) Prawn - Green gland, (iv) Flatworm - Flame cell.

Select the Correct Option

Use the matches made in the previous step to find the correct option which lists all excretory organs in the order of the organisms mentioned: earthworm, centipede, prawn, and flatworm. The correct sequence based on steps 1-5 is Nephridia, Malpighian tubules, Green gland, Flame cell.

Key concepts

Nephridia

Earthworms have a complex system for managing waste, which includes tiny tubular structures called nephridia. Acting much like kidneys in humans, nephridia play a critical role in both excretion and osmoregulation in earthworms. Each earthworm segment, except the first three and the last one, contains a pair of nephridia.

The nephridia filter out waste from the fluid in the coelomic cavity – the fluid-filled space that runs through the worm's body. This waste includes excess salts and urea, which is soluble in water and therefore easy for the nephridia to handle. The processed waste is then excreted through pores on the earthworm's body surface. A similar structure is found throughout various annelids, showcasing how nature has adapted this efficient system for maintaining internal balance in different environments.

Malpighian Tubules

Within the world of insects and arachnids, such as centipedes, the Malpighian tubules are the primary organ for dealing with metabolic waste. These tubules, named after the Italian biologist Marcello Malpighi, are hair-like structures that extend from the digestive tract and float in the hemolymph (a fluid analogous to blood in invertebrates).

Malpighian tubules work by absorbing wastes and converting them into uric acid or other solid nitrogenous compounds, which are then excreted into the gut. This method of excretion is advantageous because it conserves water, an essential adaptation for terrestrial life. Insects like centipedes are thus able to survive in dry environments thanks to this efficient excretory system.

Green Glands

Prawns and other crustaceans possess specialized excretory organs known as green glands, which are sometimes termed antennal or maxillary glands due to their anatomical location. Each gland consists of a glandular end sac and a bladder, connected to an excretory pore at the base of the antennae.

These glands perform the dual function of removing waste materials such as ammonia from the blood, as well as helping in osmoregulation, the process by which organisms regulate the water and ionic composition of their body fluids. The name 'green glands' is derived from the greenish tinge of their interior membrane, which is not always visibly green from the outside. Their role is crucial in allowing these aquatic creatures to control their internal environment despite changes in the external aquatic environment.

Flame Cells

Flame cells are the specialized cells responsible for excretion and osmoregulation in flatworms, including planarians and tapeworms. These cells line the branched tubules that run throughout the flatworm's body, and their primary job is to filter and remove excess water and metabolic waste.

Named for the flickering movements observed within them, which resemble a flame, flame cells contain cilia - tiny hair-like projections - that beat to create currents drawing fluid through ducts which open on the surface of the worm's body. This network, resembling a primitive kidney, is a simple yet effective way for these animals to maintain fluid balance and remove toxins from their tissues, a necessity for their survival in a variety of habitats, from freshwater to salty seawater and even within host organisms, in parasitic varieties.