Compare and contrast the structure and function of the osmoregulatory organs of flatworms, earthworms, and insects, detailing where and how the processes of filtration, reabsorption, secretion, and excretion occur.

●Flatworm

Protonephridia: this are tubes that branch all through the body into bulb-like flame cells; only open to exterior and not the interior of the body; cilia take in fluid from the body; it helps in preventing loss of ions

Reabsorption of water and metabolic waste product

Excretion is aided by excretory pores

●Earthworms

(Meta)nephridia: its tube system open to both inward and outside area of the body; it iundergies the closed circulatory system

Filtration: derive fluid in coelom via nephrostomes (bigger molecules are not included)

Reabsorption of salt takes place in nephrostomes

Nephrostomes is also involved in secretions.

Excretion: urine is excreted through the nephridiopores

●Insects

Malpighian tubules: it is a continuation of digestive tract that branch off; urine is not produced by filtration due to the fact that no pressure difference (open circulatory system) occurs admist the blood in body cavity and tubules; and can preserve water till a large degree.

Reabsorption: water and K+ is recollected into circulatory system through the tubules.

Secretion will result in water absorption through osmosis

Secretion: substances such as waste molecules, Na+, and K+ have an inflow into the tubules through active transport

Excretion of small molecules and waste products take the appearance of feces

i think the answer is

mass

well, that's easy; the answer's c, "it reduces contamination of the water and substrate of the estuary."