Chapter 1: An Introduction to Life on Earth
Bizarre Facts in Biology Busy Birds
Most birds fly and flying requires LOTS of energy (remember your study of ATP synthesis back in Chapter 8?). If you've already read Chapter 23, you know that birds have many adaptations like hollow bones, four-chambered hearts, and lungs supplemented by air sacs that enable them to fly.
The energy to fly requires high metabolism, and high metabolism requires lots of food and oxygen. The metabolism of hummingbirds () is especially high, so they spend a great deal of time eating. They will visit hundreds of flowers a day in search of nectar. If the hummingbirds are unable to collect enough food, they must do something to conserve energy.
The hummingbirds' four-chambered heart prevents oxygenated and deoxygenated blood from mixing, so more oxygen can be delivered to the tissues that use it to make ATP. More oxygen can also be delivered if the heartbeat () is faster and the respiratory rate is high. When a hummingbird is flying, its heart rate may increase to 1220 beats per minute.
1. Hummingbirds weigh 1/10 of an ounce and need 10 calories per day. That equates to 100 calories per ounce. So that you can better relate to the hummingbird's eating dilemma, complete the following activity.
A. Indicate the number of calories per serving in your favorite food. Be sure to share what your favorite food is too.
B. Indicate the number of calories per day you would need if you burned energy at the same rate as a hummingbird. Show all your work.
C. Indicate the number of servings of your favorite food you'd have to consume per day if you burned energy at the same rate as a hummingbird. Show all your work.
2. What do hummingbirds do to conserve energy when they have a bad food-finding day or when the weather is not conducive to feeding?
3. How does the ruby-throated hummingbird's resting heart rate and respiratory rate compare with the average human's resting heart rate and respiratory rate?
Web Investigations: Fish Story
Estimated time: 10 minutes
If you read the case study in Chapter 23, you know the coelacanth () was once believed to be extinct. The scientific community was amazed when one was discovered () in the waters off South Africa in 1938. Fourteen long years went by before a second coelacanth was found. Now there are estimated to be 1000 or fewer coelacanths living in the waters off South Africa. The most recent find () in September, 2003 was off southern Tanzania, so the range of coelacanths off the coast of Africa may be more extensive than previously believed.
In 1997 a coelacanth was noticed at a fish market by Dr. Mark Erdmann who was honeymooning in Indonesia () 6000 miles from where coelacanths were known to live. Dr. Erdmann spoke briefly with the fisherman and photographed the fish, but did nothing else because he thought he must have missed the announcement about a second group of coelacanths off Indonesia. When he returned to Berkeley () a week later he realized that he'd made an important new find in Indonesia. Genetic analysis of a second Indonesian fish indicated that the Indonesian coelacanth was indeed a different species of coelacanth.
Today many people may only be familiar with the coelacanth thanks to the attention it received in a Volkswagen commercial (). In the commercial the coelacanth was compared by an auto mechanic to the "extinct" full-size tire. However, the scientific community is very interested in the coelacanths because there are many unanswered questions about them and further study of them may provide insight into the evolution of the tetrapods (four-legged animals).
1. How are the paired fins of coelacanths similar to our arms and legs?
2. What did scientists believe the fleshy fins of the coelacanths indicated about the fish?
3. Coelacanths are ovoviviparous meaning they give birth to live offspring (known as pups). What advantage is there to bearing live offspring as opposed to practicing external development, which is typical of many fish?
1. Which of the following is a characteristic of chordates?
a. ventral, hollow nerve cord b. radial symmetry c. protostome development
d. a true body cavity (coelom) e. all of the above
2. Species of which of the following animal phyla are deuterostomes?
a. Annelida b. Arthropoda c. Chordata d. Echinodermata
e. All except the first answer above are correct.
f. Both the third and fourth answers are correct.
3. All members of the phylum Chordata, whether human or lancelet, share certain key features. Which of the following traits is NOT characteristic of all chordates?
a. dorsal, hollow nerve cord b. notochord c. pharyngeal gill slits d. tail
e. bony endoskeleton
4. The only chordate feature present in adult humans is the _________.
a. post-anal tail b. dorsal, hollow nerve cord c. pharyngeal gill slits d. notochord
5. The invertebrate chordates lack _________.
a. pharyngeal gill slits b. a post-anal tail c. a backbone d. a dorsal, hollow nerve cord
e. all of the above
6. Which of the following enables you to identify the lamprey species that are parasitic?
a. suckerlike mouths lined with teeth b. complex eyes c. fleshy fins d. bony skeletons
e. jaws with rows of razor-sharp teeth
7. Cartilaginous fish are characterized by _________.
a. a three-chambered heart b. poorly developed lungs
c. a skeleton formed entirely of cartilage d. milk-producing mammary glands
8. Which of the vertebrate groups is the most diverse, but often overlooked because of humans' habitat bias?
a. bony fish b. jawless fish c. mammals d. birds
9. The range of amphibian habitats on land is limited by _________.
a. eggs protected by a jellylike coating b. use of their skin as a supplementary respiratory organ
c. external fertilization d. All of these are correct.
10. Amphibians are most like _________.
a. mosses b. flowering plants c. conifers d. ferns
11. Reptiles are well adapted to living in drier habitats because of their _________.
a. hollow bones b. production of a shelled amniotic egg c. two-chambered heart
d. moist skin used as a supplemental respiratory organ e. external fertilization
12. The ability of birds to fly is facilitated by their _________.
a. four-chambered heart b. lungs supplemented by air sacs
c. external development in a shelled egg d. hollow bones e. All of these are correct.
13. Which of the following characteristics are shared by both arthropods and mammals?
a. a well-developed nervous system b. a closed circulatory system
c. an internal skeleton d. compound eyes
14. What defines, or distinguishes, a mammal from other vertebrates?
a. its hairless exterior b. its primitive, simple brain c. milk-producing glands
d. the fact that most mammals complete the great majority of their development outside the uterus
15. A long period of uterine development and gas, nutrient, and waste exchange between the mother and embryo are characteristic of _________.
a. all mammals b. birds c. marsupials d. placental mammals e. monotremes
16. The group of terrestrial vertebrates that may be indicators of environmental degradation is the _________.
a. amphibians b. bony fishes c. lancelets
Thinking Through the Concepts
1. Briefly describe each of the following adaptations, and explain the adaptive significance of each: vertebral column, jaws, limbs, amniote egg, feathers, placenta.
2. List the vertebrate groups that have each of the following:
a. a skeleton of cartilage b. a two-chambered heart c. an amniote egg d. warm-bloodedness
e. a four-chambered heart f. a placenta g. lungs supplemented by air sacs
3. List four distinguishing features of chordates.
4. Describe the ways in which amphibians are adapted to life on land. In what ways are amphibians still restricted to a watery or moist environment?
5. List the adaptations that distinguish reptiles from amphibians and help reptiles adapt to life in dry terrestrial environments.
6. List the adaptations of birds that contribute to their ability to fly.
7. How do mammals differ from birds, and what adaptations do they share?
8. How has the mammalian nervous system contributed to the success of mammals?
Issues in Biology What Is Happening to the Frogs?
The spectacular golden toad, once found in the montane preserve of Monte Verde, Costa Rica, has not been seen since 1989. The gastric brooding frog of Queensland, Australia (), whose bizarre parenting activity involved the female swallowing her fertilized eggs (her stomach stopped secreting digestive enzymes and she brooded her eggs there until they were tiny, but fully formed froglets, capable of life on their own), disappeared about the same time. In California a recent search for frog populations first studied 75 years before found that there were only four of seven species at 26 of 70 documented locations. Similarly, at various South American sites, once abundant species have become rare or extinct. In Minnesota, deformed frogs () are becoming common. All over the world, it appears, amphibians are in trouble. What catastrophe is responsible? Are the frogs vanishing?
Scientists first became aware of a problem in the late 1980s. Presentations at international conferences in 1989 and 1990 made it clear that there might be a problem. (Remember that in any scientific query, the answers are no better than the data, and in 1990 good, quantitative data were in short supply.) Although many herpetologists—those who study amphibians and reptiles—believed that they had witnessed declines in amphibian populations, there were very few long-term studies to address the issue. The result was that herpetologists organized a response to the perceived loss of the animals that they studied. An international organization, the Declining Amphibian Populations Task Force (), and a North American organization, the North American Amphibian Monitoring Program (), were established to coordinate research efforts.
First, there was the question of whether or not the numbers of amphibians really were declining. Of course, it is pretty hard to argue that extinction is not a decline and that the golden toads and the gastric brooding frogs were not species that were merely being overlooked. But the losses of these species were not enough on which to base an argument for the existence of a worldwide decline of amphibian populations. The problem is that amphibians, especially most salamanders (but many frogs as well) are secretive animals that are not regularly or frequently seen by very many people unless they are closely observed (studied). The argument was made that populations being studied were probably quite abundant when they were chosen, and that there is evidence that at least some amphibian populations undergo dramatic size fluctuation, remaining small for several years. Therefore, herpetologists ought to expect decline in some of their study populations. That argument did not really explain why impressions of decline were so widespread among herpetologists, nor did it explain the California study.
Currently, we are getting better data. Recent studies of the frog fauna of the Monteverde Cloud Forest Preserve in Costa Rica found that it was "highly improbable" that the 20 species (of an original fauna of 50 species) that disappeared after 1987 population crashes that claimed the golden toad could be the result of normal population changes. Even those previously abundant species that survived the crash do not appear to be recovering. Another study of a nearby montane ecosystem in Costa Rica also found "atypical population fluctuations" (declines) of aquatic breeding amphibian species.
Why should we care about what is happening to amphibians? One reason to care is that amphibians have been compared to the canaries miners took with them into mines. When oxygen levels declined too far, the sensitive canaries quit singing, thus warning the miners to leave. Amphibians, with their dual lives on land and in water and their thin permeable skins, may be very sensitive to degradation of their habitat. Although many populations of amphibians have disappeared as a result of habitat loss (the United States has lost more than 50% of its wetlands; some states like California and Ohio have lost nearly 95%), the population declines and extinctions that have occurred in montane areas of the western United States, Costa Rica, South America, and Australia have occurred in preserved habitats. Pollution is suspected as one cause of the Minnesota frog deformities. Some evidence exists that UVB radiation, increasing as a result of ozone loss, may harm sensitive amphibians (), though not all populations are sensitive and some are not exposed to much sunlight. Similarly, some amphibian populations have demonstrated a sensitivity to waters acidified by acid deposition. Therefore, another reason to care is that, since human fingerprints seem to be all over the mystery of the amphibian declines, humans have a moral obligation to figure out the problem and correct it—before the amphibians are all gone!
1. Why are amphibians "caught between two worlds," namely aquatic and terrestrial habitats?
2. Why do amphibians have thin, permeable skins?
3. How do environmental changes to their habitats actually threaten the life or health of amphibians?
Essay Challenge
1. Identify four features of chordates and explain why these features are important.
2. Explain why it might be important for an animal to be amphibious.
3. Mosses are often referred to as the amphibians of the plant kingdom. What are the similarities between mosses and amphibians that cause people to say that?
4. Why do some scientists believe that birds are recent descendants of reptiles?
5. Why are lungs supplemented by air sacs and a four-chambered heart essential to a bird's ability to fly?
6. Why are birds and mammals warm-blooded?
7. What are some benefits and disadvantages of being "warm-blooded"?
Figure Caption Questions and Answers
Figure 23-5 The diversity of the bony fishes
Question: In terms of water regulation (maintaining the proper amount of water in the body), how does the challenge faced by a freshwater fish differ from that faced by a saltwater fish?
Figure 23-6 Amphibian means “double life”
Question: What advantages might amphibians gain from their "double life"?
FIGURE 23-9 The diversity of birds
Question: Although the ancestor of all birds could fly, many bird species—such as the ostrich—cannot. Why do you suppose flightlessness has evolved repeatedly among birds?
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