Temperature Regulation in Marine Organisms

 

There are two extremes of temperature regulation in organisms. Homeotherms are organisms that regulate body temperature to a constant level, usually above that of the ambient (surrounding) environment. A constant and relatively high body temperature enables biochemical reactions to occur in a relatively constant internal environment and at a relatively high rate. Most birds have a body temperature of about 40°C, whereas the temperature of most marine mammals is about 38 °C. Because such temperatures are much higher than that of most seawater, marine homeotherms lose heat rapidly to the surrounding environment. 

 

 

There is another completely different style of living. Poikilotherms are organisms whose body temperature conforms to that of the ambient environment. All subtidal marine invertebrates and most fishes fit into this category. There is an interesting intermediate status in which body temperature is usually somewhat higher than ambient temperature. Strong-swimming fishes, such as skipjack tuna and yellowfin tuna, have this intermediate status. Their rise in temperature above ambient conditions stems from metabolic heat generated by muscular activity (swimming) combined with a heat retention mechanism. The temperature rise is probably necessary to generate the increased biochemical reaction rates that are needed for sustained activity. In contrast, some intertidal animals are not true Poikilotherms, they maintain themselves at lower-than-ambient body 

temperature, using both evaporation and circulation of body fluids to avoid being heated at low tide by the Sun. Their body temperatures, therefore, differ from that of an inanimate object of the same size and shape that might be placed on the shore. 

Intertidal organisms absorb and lose heat directly to the air. Darker-colored forms can absorb more heat than can light-colored forms; therefore, variation in color can reflect differences in adaptation to the capture of solar energy at different latitudes. 

 

 

Ocean temperatures are usually less than 27°C and may be less than 0°C in some locations and during some seasons. Therefore, most homeothermic mammals and birds must lose heat continuously to the environment. Their skin is the main pathway of 

heat loss, especially by direct conduct of heat from the skin to the contacting colder water. Because animals have a circulatory system, heat loss from the body surface also occurs as warm interior blood is transferred and moves into contact with the 

periphery of the body. Their bodies also radiate heat, usually in the infrared part of the spectrum. Finally, as animals exhale, the resulting evaporation of water involves a considerable loss of heat. 

 

 

The first line of defense against heat loss is a well-insulated body surface. Marine birds deal with this problem by means of specially adapted feathers. A series of interlocking contour feathers encloses a thick layer of down feathers that traps stationary air, which in turn acts as an insulating layer. Whales, porpoises, and seals are insulated against the lower sea temperatures by a thick layer of subcutaneous fat. Sea otters lack such a layer, but they constantly preen and fluff up a relatively thick layer of fur. Such mechanisms are only partly successful, however, and to generate more body heat to maintain a constant temperature, marine mammals usually must have a higher metabolic rate than similarly sized terrestrial (land) animals. 

 

 

In marine mammals that have limbs, the limbs are the principal sources of heat loss because they expose a relatively greater amount of body surface area per unit volume to cold water. However, warm arterial blood must be supplied to limbs, such as the flipper of a porpoise. Heat loss in porpoises is minimized by a countercurrent heat exchanger. The arteries are surrounded by veins, within which blood is returning to the core of the animal. At any contact point, the artery, which is on the inside, is warmer than a surrounding vein, so heat is lost to the returning venous blood flow. Heat is thus reabsorbed and returned to the porpoise’s body core. This spatial relationship of circulatory vessels minimizes heat loss to the flipper and thence to the water. Although the anatomical details are quite different, fishes such as skipjack tuna have a circulatory anatomy based on the same overall design. Arteries and veins in the near-surface musculature are in contact, and in arteries and veins, respectively, blood flows in opposite directions.

 

 

 

【Paragraph 2】

There is another completely different style of living. Poikilotherms are organisms whose body temperature conforms to that of the ambient environment. All subtidal marine invertebrates and most fishes fit into this category. There is an interesting intermediate status in which body temperature is usually somewhat higher than ambient temperature. Strongswimming fishes, such as skipjack tuna and yellowfin tuna, have this intermediate status. Their rise in temperature above ambient conditions stems from metabolic heat generated by muscular activity (swimming) combined with a heat retention mechanism. The temperature rise is probably necessary to generate the increased biochemical reaction rates that are needed for sustained activity. In contrast, some intertidal animals are not true Poikilotherms, they maintain themselves at lower-thanambient body temperature, using both evaporation and circulation of body fluids to avoid being heated at low tide by the Sun. Their body temperatures, therefore, differ from that of an inanimate object of the same size and shape that might be placed on the shore. Intertidal organisms absorb and lose heat directly to the air. Darker-colored forms can absorb more heat than can light-colored forms, therefore, variation in color can reflect differences in adaptation to the capture of solar energy at different latitudes. 

 

1. According to paragraph 2, the body temperature of strong-swimming fishes is usually above that of their surroundings probably so they can 

A. generate heat to warm themselves in cold waters 

B. have enough energy for prolonged activity 

C. generate metabolic heat for muscular activity 

D. retain heat for later use when the surrounding conditions change 

 

 

【Paragraph 3】

Ocean temperatures are usually less than 27°C and may be less than 0°C in some locations and during some seasons. Therefore, most homeothermic mammals and birds must lose heat continuously to the environment. Their skin is the main pathway of heat loss, especially by direct conduct of heat from the skin to the contacting colder water. Because animals have a circulatory system, heat loss from the body surface also occurs as warm interior blood is transferred and moves into contact with the periphery of the body. Their bodies also radiate heat, usually in the infrared part of the spectrum. Finally, as animals exhale, the resulting evaporation of water involves a considerable loss of heat. 

 

2. According to paragraph 3, all of the following contribute to heat loss in homeothermic animals EXCEPT 

A. heat transfer from the skin to the water 

B. the movement of blood to the animal’s periphery 

C. an increase in their activity during certain seasons 

D. the evaporation of water during breathing 

 

 

【Paragraph 4】

The first line of defense against heat loss is a well-insulated body surface. Marine birds deal with this problem by means of specially adapted feathers. A series of interlocking contour feathers encloses a thick layer of down feathers that traps stationary air, which in turn acts as an insulating layer. Whales, porpoises, and seals are insulated against the lower sea temperatures by a thick layer of subcutaneous fat. Sea otters lack such a layer, but they constantly preen and fluff up a relatively thick layer of fur. Such mechanisms are only partly successful, however, and to generate more body heat to maintain a constant temperature, marine mammals usually must have a higher metabolic rate than similarly sized terrestrial (land) animals.

 

 

3. The word “stationary” in the passage is closest in meaning to 

A. warm 

B. surface 

C. nonmoving 

D. nearby 

 

4. All of the following are mentioned in paragraph 4 as defenses against heat loss EXCEPT 

A. subcutaneous fat 

B. layers of feathers 

C. a thick layer of fur 

D. constant metabolic rates 

 

5. What can be inferred from the comparison of terrestrial animals to marine animals in the last sentence of paragraph 4? 

A. An animal’s size is not the only factor affecting its metabolic rate. 

B. An animal’s size determines what mechanism can be successfully used to prevent heat loss. 

C. Smaller animals are more successful than larger ones at preventing heat loss. 

D. Terrestrial animals have a wider variety of mechanisms for preventing heat loss than marine animals do. 

 

6. Paragraph 4 expands on paragraph 3 by 

A. presenting various reasons why first-time defenses are inadequate to deal with the problem described in paragraph 3 

B. discussing mechanisms that marine animals use to reduce the problem described in paragraph 3 

C. identifying specific ways that the problem described in paragraph 3 harms marine animals 

D. explaining why the problem described in paragraph 3 harms some marine animals more than others 

 

 

【Paragraph 5】

In marine mammals that have limbs, the limbs are the principal sources of heat loss because they expose a relatively greater amount of body surface area per unit volume to cold water. However, warm arterial blood must be supplied to limbs, such as the flipper of a porpoise. Heat loss in porpoises is minimized by a countercurrent heat exchanger. The arteries are surrounded by veins, within which blood is returning to the core of the animal. At any contact point, the artery, which is on the inside, is warmer than a surrounding vein, so heat is lost to the returning venous blood flow. Heat is thus reabsorbed and returned to the porpoise’s body core. This spatial relationship of circulatory vessels minimizes heat loss to the flipper and thence to the water. Although the anatomical details are quite different, fishes such as skipjack tuna have a circulatory anatomy based on the same overall design. Arteries and veins in the near-surface musculature are in contact, and in arteries and veins, respectively, blood flows in opposite directions. 

 

7. According to paragraph 5, some marine mammals that have limbs minimize heat loss by using a system in which 

A. vessels that return blood to the animal’s core absorb heat from warm interior arteries 

B. blood returning to the core is warmer than blood flowing from the core 

C. the placement of the arteries reduces blood flow to the veins 

D. both arteries and veins are in contact with near-surface musculature 

 

 

8. Why does the author discuss “fishes such as skipjack tuna”? 

A. To explain by contrast why the circulatory anatomy of porpoises is efficient 

B. To show that marine animals other than mammals use a countercurrent exchange system to minimize heat loss 

C. To identify and illustrate a type of circulatory anatomy that is common in fishes 

D. To provide evidence that the amount of heat marine animals lose increases with increased body surface area

 

 

【Paragraph 2】

There is another completely different style of living. ■Poikilotherms are organisms whose body temperature conforms to that of the ambient environment. ■All subtidal marine invertebrates and most fishes fit into this category. ■There is an interesting intermediate status in which body temperature is usually somewhat higher than ambient temperature. ■Strong-swimming fishes, such as skipjack tuna and yellowfin tuna, have this intermediate status. Their rise in temperature above ambient conditions stems from metabolic heat generated by muscular activity (swimming) combined with a heat

retention mechanism. The temperature rise is probably necessary to generate the increased biochemical reaction rates that are needed for sustained activity. In contrast, some intertidal animals are not true Poikilotherms, they maintain themselves at

lower-than-ambient body temperature, using both evaporation and circulation of body fluids to avoid being heated at low tide by the Sun. Their body temperatures, therefore, differ from that of an inanimate object of the same size and shape that might

be placed on the shore. Intertidal organisms absorb and lose heat directly to the air. Darker-colored forms can absorb more heat than can light-colored forms, therefore, variation in color can reflect differences in adaptation to the capture of solar

energy at different latitudes.

 

9. Look at the four squares【■】that indicate where the following sentence can be added to the passage.

However, not all marine organisms can be easily classified as either homeotherms or poikilotherms.

Where would the sentence best fit?

 

10.【Directions】An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some answer choices do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points. Drag your choices to the spaces where they belong.

 

Marine and other organisms are classified as homeotherms if they maintain a constant body temperature and as poikilotherms if their body temperature matches that of the environment.

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Answer Choices

A. Although strong-swimming fishes and intertidal organisms have body temperatures that are higher or lower than ambient temperatures, most fishes and subtidal marine organisms are poikilotherms.

B. There are no homeotherms in cold ocean waters because it is too difficult for homeotherms to prevent heat loss in these environments.

C. Features such as fur help reduce heat loss, but marine homeotherms require a higher metabolism than do terrestrial homeotherms of similar size to maintain a constant body temperature.

D. Some organisms are thought to have various methods of heat regulation in order to maintain different body temperatures at different times of year.

E. Marine homeotherms lose heat to the environment through respiration and other means, the most important being skin contact with colder seawater.

F. Animals with disadvantage limbs are regarding at a body temperature because their circulatory anatomy is poorly designed for managing heat loss.

 

 

 

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