Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Excretion is the removal from organisms of the waste products of metabolism (chemical reactions in cells including respiration), toxic materials, and substances in excess of requirements.
The lungs excrete carbon dioxide (), which is a waste product of aerobic respiration: .
The kidneys excrete urea, excess salts, and excess water (). These are passed out of the body in the form of urine.
Urea is produced in the liver from the breakdown of excess amino acids through a process called deamination. The nitrogen-containing part of the amino acid is converted into ammonia () and then into the less toxic urea ().
It is important to distinguish between excretion and egestion; egestion is the removal of undigested food (feces) that has never entered the cells or participated in metabolism.
Accumulation of in the body is dangerous because it dissolves in blood plasma to form carbonic acid (), which lowers the and can denature enzymes.
📐Formulae
💡Examples
Problem 1:
Identify the excretory organ responsible for the removal of urea and state the metabolic process that produces urea.
Solution:
The excretory organ is the kidney. Urea is produced in the liver via the process of deamination of excess amino acids.
Explanation:
Urea () is the primary nitrogenous waste in humans. While produced in the liver, it is filtered from the blood and excreted by the kidneys.
Problem 2:
Calculate the amount of water excreted if a person consumes of , loses through sweat and through exhalation, assuming they stay in water balance and produce of metabolic water.
Solution:
Total in = . Total out = . For balance: . .
Explanation:
Water balance involves equating the total water intake and metabolic production to the total output through skin, lungs, and kidneys.