Download 3.12 THE EXCRETORY SYSTEM

3.12 THE EXCRETORY SYSTEM
SECTION 3.12 QUESTIONS
(Page 214)
Understanding Concepts
1. Excess amino acids are broken down in the liver in a process called deamination.
2. The amino group left over from the deamination process is converted into ammonia. Nitrogen compounds, such
as
ammonia, are poisonous. Two molecules of ammonia can combine with carbon dioxide to form urea. Urea is much
less (100 000 times) toxic than ammonia.
3. Nephrons carry filtered fluids from the blood to the urinary bladder. Nephrons permit the selective reabsorption
of
filtered fluids and are the functional unit of the kidney.
4. (a) D—the kidney
(b) E—the ureter
(c) C—the renal artery
(d) F—the urinary bladder
5. Filtration involves the movement of fluids from the glomerulus into the Bowman’s capsule. Reabsorption
involves the
movement of fluids from the nephron into the extracellular fluid and eventually the capillary network. Secretion
involves the selective transport of fluids from the capillary network into the nephron (the collecting duct).
6. Kidney stones are formed by the precipitation of dissolved minerals from the blood. They are a problem because
they
may become lodged in the renal pelvis or move into the narrow ureter, blocking the flow of urine from the kidney
to
the bladder. Sharp-edged stones may also cut or tear delicate tissue as the stone moves toward the bladder, causing
terrible pain in the process.
7. Blood containing a drug would be force-filtered in the glomerulus. Liquid with the drug dissolved in it would
thus be
forced out into the cavity of the Bowman’s capsule. From there, the liquid containing the drug would move down
the
descending arm of the loop of Henle. The drug would become more concentrated because water is moving out of
the
tubule at this part of the nephron. In the loop of Henle and in part of the ascending arm, some of the drug might
move
back into the tissues, depending on its solubility in the tubular liquid and its permeability with respect to the tubule
tissues. Any of the drug that remained in the tubule would become more concentrated as more water was removed
from
the tubule during its passage to the collecting ducts. Eventually, the drug would enter the urinary bladder and be
excreted in the urine.
NEL Section 3.12 105
8. In fish, ammonia never builds up to a toxic level because it diffuses directly out of the circulatory system through
the
gills. However, fish have to regulate the amount of salt in their bodies. Salts in the ocean are more concentrated
than
the salts found in the extracellular fluid of the fish, so marine fish tend to lose water through osmosis. To
compensate
for this, they drink seawater and excrete the excess salt through specialized cells in their gills. Freshwater fish have
the
opposite problem. The salt in their bodies is more concentrated than the surrounding water so they tend to gain
water
by osmosis. They get rid of the excess water by excreting large amounts of urine.
Applying Inquiry Skills
9. Student answers will vary. One possible experimental design is as follows:
(i) Set up a control and an experimental group. Care should be taken to ensure that control and experimental
groups
are similar in age, gender, health, and so on.
(ii) Provide all members of the control group with 100 mL of water.
(iii) Provide all members of the experimental group with 100 mL of caffeine drink.
(iv) Collect and compare urine output over the next 5 h. All members of both groups should be placed under
similar
conditions (e.g., no exercise, no additional food or drink).
(v) Graph the urine output over time for both groups and analyze the results.
Making Connections
10. One kidney is able to excrete the wastes from the human body. It is beneficial to have two kidneys because it
provides
a backup system should one kidney fail.
11. Alcohol is a diuretic, that is, it causes the body to lose water through the excretion of urine. Alcohol increases
urine
volume and the urine formed is dilute. The concentration of dissolved materials in the blood rises which increases
the
likelihood that it will precipitate out in the form of kidney stones. Alcohol can contribute to dehydration and it also
inhibits the ability of the kidneys to excrete uric acid. Beer is high in oxalates which combine with calcium to form
calcium oxalate, the most common kidney stone-forming compound. Binge drinking increases the level of uric acid
and the risk of formation of kidney stones.
12. Student responses will vary. A possible PMI chart on urine testing is shown below.
PMI
Ethical The right to privacy does Urine testing is an A list should be generated
not supercede the responsibility infringement of the identifying jobs and professions
for the safety of others. Urine individual’s right to that affect the safety or the lives
testing is no different than the privacy. of others. People entering
breathalyzer. It is used in the these jobs should be required
interest of public safety. to sign an agreement allowing
regular or random urine testing.
Health Mandatory urine testing could Urine testing is not What if all persons using
prevent health problems mandatory for legal drugs (including alcohol
(e.g., addiction, cancer) that drugs such as alcohol and nicotine) were required
are associated with drug use and nicotine, so why to pay a portion of their
and abuse. should it be mandatory health care expenses?
for other (illegal) drugs
that may not be as
dangerous as the
legal drugs?
Technology The current technology can People are continuously The government could
determine with 100% certainty finding new ways to develop new legislation
that a person has used specific mask the presence imposing stiff penalties
drugs. of specific drugs in on companies developing
the body so the processes or products
technology is not aimed at beating drug
reliable. tests.
Recommendation Urine testing should be used only when there are risks to human lives or public safety,
e.g., in public transportation—airline pilots, train engineers, car drivers; in medical practice;
in public protection—police officers, firemen, military personnel.
106 U nit 3 Student Book Solutions NEL