Lesson 5

Question 1

How do aquatic animals release nitrogenous waste?

Answer 1

• Excrete ammonia itself
• Ammonia is very soluble in water
• Can quickly diffuse across the gills of fish into water
• Then diluted to a non-toxic level

Question 2

How do birds, reptiles and insects release nitrogenous waste?

Answer 2

• Excrete uric acid which is almost insoluble in water
• Use lots of energy to do this but very little water needed
• Allows them to survive in dry environments

Question 3

How do mammals release nitrogenous waste?

Answer 3

• Excrete urea
• Requires lots of water but less toxic then ammonia
• So body tissues can tolerate it in higher concentration for short periods of time

Question 4

Why do desert mammals have longer loops of Henle and produce more concentrated urine?

Answer 4

More opportunity to pump ions into medulla tissue fluid:
• Conc of ions in tissue fluid of medulla increased when ions pumped from asc. limb
• Low WP in medulla tissue fluid enhances water reabsorption from desc. limb and duct
• So more concentrated urine released

Question 5

Describe and explain volume and conc of various mammals

Answer 5

• Beaver - aquatic - short loop (doesn’t extend to medulla) so large volume of dilute urine
• Human - terrestrial - intermediate (extends into medulla) - Medium volume of intermediate conc
• Kangaroo rat - Desert - long (extends deep into medulla) - Very small volume of concentrated urine