Question

Which of the following is not an example of a filtration mechanism for removing soluble wastes from the body fluids of animals? a. Malpighian tubules b. the vertebrate kidney c. the excretory system of annelids d. metanephridia

Short answer

All of the listed options; Malpighian tubules, the vertebrate kidney, the excretory system of annelids and metanephridia, are examples of filtration mechanisms for removing soluble wastes from the body fluids of animals.

Step-by-step solution

Identify the function of each option

a. Malpighian tubules - These are found in insects and are used to remove soluble wastes from the body.\n b. The vertebrate kidney - This organ filters blood and removes waste products which are expelled as urine.\n c. The excretory system of annelids - This system is present in segmented worms like earthworms, it includes a pair of kidneys which are responsible for osmoregulation and excretion.\n d. Metanephridia - These are excretory organs found in some invertebrates which serve to uptake waste and excess water.

Analyse the options

Based on the functions identified above, all options serve as filtration mechanisms used to remove waste from the body of animals, hence none of the provided options should be considered as incorrect.

Key concepts

Malpighian Tubules

The Malpighian tubules are a critical part of the excretory system in many arthropods, such as insects and spiders. These tubules are hair-like projections that extend from the digestive tract into the body cavity. Malpighian tubules are adept at removing nitrogenous wastes such as uric acid from the insect's hemolymph (a fluid equivalent to blood in vertebrates), effectively functioning without filtration. Instead, they secrete waste into the digestive tract, from where it exits the body with the feces.

Understanding the unique nature of Malpighian tubules can clarify why they are not filtration organs in the traditional sense, as they do not filter blood or body fluid through a filtration barrier. They selectively secrete certain substances to concentrate waste, conserving water and essential ions, which is crucial for survival, especially in terrestrial environments where water conservation is important.

• Found in insects and spiders.
• Extend from the digestive tract, secreting wastes into it.
• Conserve water and ions, vital for land-dwelling arthropods.

Vertebrate Kidney

In vertebrates, the kidney is the principal organ responsible for excretion and osmoregulation. This sophisticated bean-shaped organ filters blood, removes excess water, salts, and waste products, and returns necessary substances to the blood through a process known as reabsorption.

The vertebrate kidney operates through a complex network of nephrons, each of which is a microscopic filtration unit. Blood enters a nephron through the glomerulus, a cluster of capillaries, where the filtration of blood occurs. This initial filtrate then travels through the renal tubule, where useful substances are reabsorbed, and waste is concentrated into urine. Finally, the urine is collected in the bladder before excretion.

• Principal organ for excretion in vertebrates.
• Filtration occurs in numerous nephrons within each kidney.
• Functions in both excreting wastes and regulating bodily fluids.

Annelid Excretory System

Annelids, such as earthworms, possess a segmented excretory system that includes a paired organ called nephridia in each segment. There are two main types of nephridia: metanephridia and protonephridia. In the case of common earthworms, metanephridia are responsible for osmoregulation and excretion.

Each metanephridium in an earthworm consists of a funnel-like opening, the nephrostome, which collects bodily fluids. These fluids then pass through a tubular structure where useful substances are absorbed back into the body, and waste is expelled through the nephridiopore. This system is highly efficient for the worm's life in moist soil environments, as it not only gets rid of wastes but also helps in maintaining the worm's fluid balance.

• Segmented organisms with paired nephridia in each segment.
• Metanephridia manage osmoregulation and waste excretion.
• Efficient in moist soil environments for maintaining balance.

Metanephridia

Metanephridia are a type of nephridia found in some invertebrates, such as annelids (segmented worms) and mollusks. They serve as the organism's excretory system by collecting waste materials from the coelom (body cavity) and facilitating their excretion from the body. The structure of metanephridia includes a ciliated funnel that filters coelomic fluid.

This tubular system not only gets rid of nitrogenous waste but also plays a key role in balancing the animal's water and ionic concentration. It is a demonstration of how excretory systems can be closely adapted to the environmental and physiological needs of an organism, supporting the efficient removal of waste while conserving valuable resources, a critical aspect of survival for these invertebrates.

• Found in annelids and mollusks.
• Filter waste from the coelom, critical for maintaining ionic balance.
• Contribute to the homeostasis of invertebrate organisms.