Topic 4 Excretory System: Invertebrate Excretion

Question 1

• All cells in contact with external, aqueous environment
• Have water soluble wastes (ammonia, CO2) that exit via simple diffusion
• Protists such as Paramecium and Amoebas possess contractile vacuoles for excess H2O excretion via active transport

Answer 1

1. Protozoans and Cnidarians

Question 2

• Excrete CO2 directly through moist skin
  a. Nephridia (metanephridia): functional unit of excretion that occur in pairs within each segment of annelids (earthworms)
• Interstitial fluids enter nephridium through ciliated opening called nephrostome and concentrate through a collecting tubule due to selective secretion into surrounding coelomic fluid. Blood that surrounds the tubule reabsorbs the fluid. Water, salts, and urea are excreted through an excretory pore

Answer 2

2. Annelids

Question 3

• Possess flame cells/flame bulbs, which are bundles of flame cells that combine to form protonephridia
• Distributed along branched tube system that permeated the flatworm
• Body fluids are filtered across flame cells, whose cilia move fluids through the tube system; wastes exit through pores of tube

Answer 3

3. Platyhelminthes

Question 4

• CO2 is released from tissue via trachea which lead to the external air via spiracles
  a. Malpighian Tubules: found in terrestrial arthropods; tubules that attach at junction between midgut and hindgut. Collect body fluids from hemolymph that bathes cells. Fluids are deposited at junction
• Fluids include nitrogenous wastes including uric acid crystals (formed from water and retained salts). As fluids pass through the hindgut, retained materials pass out of walls and wastes continue down the tract for excretion through anus
• Aquatic crustaceans use green glands instead, which function similar to malpighian tubules

Answer 4

4. Arthropods

Question 5

• Nitrogenous waste is usually converted to ammonia, which is toxic
• Excretion handling is varied depending on organism

Answer 5

Note