Example Questions
Example Question #1 :Understanding Other Excretory Physiology
Nitrogenous wastes are produced from the degradation of DNA and proteins, and released from the body via the excretory system. Which of the following is the primary nitrogenous waste produced by aquatic animals?
Urea
Nitric acid
Ammonia
Uric acid
Ammonia
氨是高度水溶性,可以有毒to cells at low concentrations due to presence of its ammonium ion, which can interfere with oxidative phosphorylation. Ammonia is small and can easily diffuse through cell membranes, making it easy to excrete. Essentially, there is a trade off of easy excretion and toxicity levels.
For aquatic animals, however, toxicity is negligible due to the large volume of water available to dilute ammonia wastes. The high solubility of ammonia wastes and the abundance of water solvent allow for the ammonia to be transported out of cells in an very dilute concentration, without harming the organism. This allows aquatic organisms to conserve energy, compared to terrestrial organisms that must convert ammonia wastes to other forms.
两栖动物和哺乳动物氨转化为尿素,which can be excreted with less water, but must still be relatively dilute. These animals release liquid wastes from the body, resulting in water loss, but conserve energy compared to organisms that continue to convert urea into uric acid. Birds and reptiles excrete uric acid, which requires very little water waste, but uses a larger amount of energy in conversion. This is beneficial to animals that may not have ready access to fresh water.
Example Question #2 :Understanding Other Excretory Physiology
Ammonia is a toxic form of excreted nitrogenous waste. What would be a key reason that an organism would preferentially excrete ammonia instead of urea or uric acid?
Ammonia excretion benefits its environment and habitat
Energy is required to convert ammonia to a less toxic form
Ammonia is selectively reabsorbed better than urea or uric acid during excretion
Less water is lost when ammonia is excreted
Energy is required to convert ammonia to a less toxic form
There is a key trade-off between energy consumption and toxicity in the excretion of nitrogenous wastes. Ammonia is the simplest form of the waste product, and requires very little energy to produce; however, it is highly toxic and must be diluted to extremely low concentrations in order to be safe to the cells. Many aquatic animals excrete ammonia because of their proximity to water. Access to large amounts of water means that these organisms can safely excrete dilute ammonia without needing to use energy in conversions.
Terrestrial animals, with less access to water, excrete urea or uric acid. These wastes are derived from ammonia, but require an input of energy for the conversion. They are less toxic and require less water loss for dilution, making them ideal for animals that must conserve fluids. Uric acid is the least toxic of the nitrogenous wastes, but also requires the greatest energy investment.
Example Question #3 :Understanding Other Excretory Physiology
The consumption of alcohol has what effect on the human urinary system?
It completely blocks the flow of fluids through the kidney tubules
It has no effect on the human urinary system
It increases the activity of antidiuretic hormone (ADH), decreasing urine production
It decreases the activity of antidiuretic hormone (ADH), increasing urine production
它导致黑暗,concentrated urine
It decreases the activity of antidiuretic hormone (ADH), increasing urine production
Alcohol decreases the activity of antidiuretic hormone (vasopressin). A diuretic increases the production of urine and thus, inhibition of thisantidiuretic hormone results in an increase in the production of highly diluted urine.
Alcohol does not block the flow of fluids through the kidney tubules.
Example Question #4 :Understanding Other Excretory Physiology
Which of the following would be filtered by the kidney and not found in urine?
Urea
Proteins
Water
Potassium
Sodium
Proteins
Proteins would not be found in the urine because these molecules are too large to pass through the glomerulus of the nephron of the kidney. They would be filtered out and remain in the bloodstream. Meanwhile, all of the other compounds would be present in normal urine.