Chapter 1

1. Student B is correct. Body temperaturebegins to rise as a result of exposure to thehot environment. Sweating eliminates heatfrom the body and lowers body temperature.Body temperature returning to its idealnormal value is an example of negativefeedback. Student A probably thought itwas positive feedback because sweatingcontinued to increase. However, sweatingis the response. The variable being regulatedby sweating is body temperature.2. Answer e is correct. Positive-feedback mech-anisms continuously stimulate a responseuntil the initial stimulus is removed. Theyare sometimes harmful. The continuallydecreasing blood pressure is an exampleof a harmful positive feedback mechanism.Negative-feedback mechanisms result in areturn to homeostasis. The elevated heartrate is a negative-feedback mechanism thatattempts to return blood pressure to a normalvalue. In this case, the negative-feedbackmechanism is inadequate to restore homeo-stasis, and medical intervention (a transfu-sion) is necessary.3. When a boy is standing on his head, his noseis superior to his mouth. Directional termsrefer to a person’s body in the anatomicalposition, not to the body’s current position.4. The uterus is located in the pelvic cavity. Thepelvic cavity, however, is surrounded by thebones of the pelvis and does not increase insize during pregnancy. Instead, as the fetusgrows, the expanding uterus must move intothe abdominal cavity, thereby crowding theabdominal organs and dramatically increas-ing the size of the abdominal cavity.5. After the pole passes through the abdominalwall, it pierces the parietal peritoneum. Inpassing through the stomach, it penetratesthe visceral peritoneum, the stomach itself,and the visceral peritoneum on the otherside of the stomach. Because the diaphragmis lined inferiorly by parietal peritoneumand superiorly by parietal pleura, these arethe next two membranes pierced. The polethen passes through the pleural space andvisceral pleura to enter the lung.

Chapter 2

1. An atom of iron has 26 protons (the atomicnumber), 30 neutrons (the mass numberminus the atomic number), and 26 electrons(because the number of electrons is equalto the number of protons). If an atom ofiron loses 3 electrons, it has 3 more protons(positive charges) than electrons (negativecharges). Therefore, the iron ion has anoverall charge of + 3, which is representedsymbolically as Fe 3 + .2. The formation of free fatty acids and glycerolfrom a triglyceride is a decomposition reactionbecause a larger molecule breaks down intosmaller molecules. All of the decompositionreactions in the body are collectively referredto as catabolism. This reaction can also beclassified as a hydrolysis reaction because,as part of the reaction, a water molecule issplit into hydrogen, which becomes part ofthe glycerol molecule, and hydroxide, whichbecomes part of a fatty acid molecule. Yes,the reverse anabolic reaction generates water.3. The slight amount of heat functions as acti-vation energy and starts a chemical reaction.The reaction releases a large amount ofheat, causing the solution to become hot.4. Heating (boiling) has destroyed the abilityof the molecules in one or both of the solu-tions to function in the chemical reaction.This is called denaturation. There are twopossibilities as to what is denatured: thereactants themselves or an enzyme thatcatalyzes the reaction.5. Muscle contains proteins. To increasemuscle mass, proteins must be synthesizedfrom amino acids. The synthesis of mol-ecules in living organisms requires the inputof energy. That energy comes from the poten-tial energy stored in the chemical bonds offood molecules, which is released duringthe decomposition of food molecules.6. pH is a measure of H + concentration. If equalamounts of solutions A and B are mixed,the resulting H + concentration is the aver-age value of the two solutions—that is, thepH is (8 + 2) / 2 = 5. A pH of 5 is acidic.This question illustrates an important point:

The pH of a solution can be changed by add-ing a more acidic or more basic solution to it.7. Rapid respiration before diving into thewater causes blood levels of carbon dioxideto decrease. As a result, there is a slightincrease in blood pH. Recall that carbondioxide molecules react with water toproduce carbonic acid, and some of thecarbonic acid molecules dissociate to formhydrogen ions and bicarbonate ions. Thesereactions are reversible. As Ned hyper-ventilates, the blood carbon dioxide levelsdecrease, which causes some hydrogen ionsto react with bicarbonate ions to producecarbonic acid. The carbonic acid then dis-sociates to form water and carbon dioxide, sothere is a net loss of protons. While hold-ing his breath under water, carbon dioxidelevels increased in Ned’s blood. The carbondioxide molecules react with water to formcarbonic acid, which then dissociates toform hydrogen ions and bicarbonate ions.As a result, there is a slight decrease inblood pH. However, the pH of the blooddoes not change dramatically, in partbecause of buffers in the blood.8. As A and B are added to the solution, theenzyme E catalyzes the formation of C.However, when C binds to the active site of E,the ability of E to catalyze the formation of Cis blocked. As more and more C is produced,the rate of formation of C is slowed. Becausethe reaction of C with E is reversible, therewill always be some E that has a functional(not blocked) active site, and some A willtherefore always combine with B.9. Heating the substances might help becauseproteins can be denatured and can coagulate(as in frying an egg). Another possibilityis to try dissolving the substances in water.Most lipids are insoluble in water, whereasmany proteins either are soluble in wateror form colloids with water.

Chapter 3

1. The cells within the wound swell withwater and lyse when a hypotonic solution isintroduced. This kills potentially metastaticcells that may still be present in the wound.

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