Chapter 1: An Introduction to Life on Earth



Bizarre Facts in Biology Blue Bloods Aren’t Just British

Blue-colored blood is found in most arthropods and mollusks. A molecule in their blood called hemocyanin transports oxygen. Hemocyanin differs from the more familiar hemoglobin because of the copper in the molecule that turns blue () when exposed to oxygen.

One particular organism that has this blue blood is the horseshoe crab (). Horseshoe crabs are more closely related to spiders than real crabs and one species (Limulus polyphemus) is commonly found along the Atlantic coast, especially between Virginia and New Jersey, and in the Gulf of Mexico. Horseshoe crabs feed on a variety of organisms like clams, marine worms, and algae and are in turn fed upon by immature Atlantic loggerhead turtles.

Ecologically (), the crabs are of importance to migrating shorebirds that lay over in the Delaware Bay area en route to the birds' Canadian breeding grounds. The birds feast on the energy-rich horseshoe crabs' eggs, enabling the birds to continue their journey northward. Many other species eat the eggs and larvae of horseshoe crabs, or live symbiotically () with the adult crabs.

Economically, the crabs are of great importance to humans. They've been used in eye research, suture material production, the development of wound dressings, and are the primary bait used by eel and conch fisheries. One of the most important uses of the crabs has been for the testing of bacterial contamination of pharmaceutical products. A substance called Limulus Amebocyte Lystate (LAL) () can be isolated from the blood of the crabs and used to detect bacterial endotoxins. The LAL assay replaced the expensive and time-consuming use of rabbits to detect bacterial contamination.

1. When hemoglobin is exposed to oxygen, what color does it become? What mineral is associated with the color of hemoglobin?

2. Since horseshoe crabs are arthropods, what process must they perform in order to grow in size? What is a disadvantage to growing in this fashion?

3. In the 1980s, horseshoe crabs began to recover from a period of overharvesting. How was the Delaware Bay ecosystem impacted by the overharvesting prior to the 1980s and how did the recovery of the crabs affect this ecosystem?

4. What kind of symbiotic relationship does the horseshoe crab appear to have with the Limulus leech, Bdelloura?

5. What specific class of bacteria produces the endotoxins for which the LAL assay tests?

 

Web Investigations: The Search for a Sea Monster

Estimated time: 10 minutes

Many fascinating creatures can be found in the oceans' depths. This exercise looks at the relatively limited information available about a few, better-known species.

1. The first whole giant squid specimen was discovered more than 100 years ago. Why are they so difficult to study ()? One fact is well known. Giant squid are a favorite food of () _______?

2. Probably the most famous deep-sea resident is the coelacanth. Why is it called a "living fossil" ()? Is it the ancestor of mammals ()? The coelacanth has two biological features () more characteristic of mammals than fish. What are they?

3. What is the most unusual feature of the gulper eel ()? Like many deep water species, gulpers have distinctive markers () on their tails. What are they?.

4. Many rare deep-sea species are threatened by fishing, habitat destruction, or other human interventions. What can you do to help ()?

1. Which of the following correctly describes animals?

a. unicellular b. heterotrophs c. sessile or stationary

2. A group of similar cells performing a function is a(n):

a. organ. b. population. c. tissue. d. system.

3. The cells of animals:

a. lack a cell wall. b. contain a nucleus. c. contain mitochondria.

4. The vast majority of animals:

a. are vertebrates. b. lack tissues. c. are producers. d. lack a backbone.

1. The animal phylum characterized by the absence of tissues is:

a. arthropods. b. chordates. c. cnidarians. d. sponges. e. echinoderms.

2. Organisms that can be divided into equal halves on many planes through their central axis have _____ symmetry.

a. no b. radial c. bilateral

3. An animal phylum characterized by radial symmetry is:

a. platyhelminthes or flatworms. b. annelids. c. cnidarians.

d. mollusks. e. chordates.

4. A true body cavity that develops in the mesoderm is a:

a. coelom. b. pseudocoelom.

5. All of these animal phyla have coeloms except:

a. arthropods. b. nematodes or roundworms. c. echinoderms. d. mollusks. e. annelids.

6. In protostomes, the _____ develops from the blastopore.

a. mouth b. coelom c. anus

7. The two phyla characterized by deuterostome development are:

a. annelids and arthropods. b. mollusks and echinoderms.

c. echinoderms and chordates. d. annelids and mollusks.

e. mollusks and arthropods.

1. Which of the following is NOT a characteristic of most animals?

a. heterotrophism b. capable of movement at some point in the life cycle

c. delayed response to external stimuli d. sexual reproduction

2. Which of the following characteristics is NOT shared by plants and animals?

a. multicellular b. eukaryotic c. sexual reproducers d. heterotrophs

3. Which of the following distinguishes animals from fungi?

a. Animals are multicellular. b. Animals are heterotrophs.

c. Animal cells lack a cell wall. d. Animal cells are eukaryotic.

4. How does "radial symmetry" differ from "bilateral symmetry"?

a. A radially symmetrical animal has dorsal and ventral surfaces. Bilaterally symmetrical animals do not.

b. Radially symmetrical animals can be divided into symmetrical halves with any plane through the central axis. Bilaterally symmetrical animals can be divided into equal halves by only one specific plane through a central axis.

c. Radially symmetrical animals possess three embryonic germ layers, while bilaterally symmetrical animals only possess two.

d. Most radially symmetrical animals are active, free-moving organisms throughout their lives, while bilaterally symmetrical animals are not.

5. How many planes through the central axis will divide an organism with bilateral symmetry into roughly equal halves?

a. one b. two c. many

6. Body symmetry is an important criterion for classification purposes. Label the diagrams below indicating plans of symmetry and orientation.

7. Among animals with a fixed body shape, those that are elongated, such as earthworms or scorpions, have which type of symmetry?

a. none

b. bilateral symmetry

c. anterior

d. radial symmetry

e. ventral

8. Animals that have concentrations of sensory organs (or even brains) in a well-defined head are a result of the evolutionary process called ____________________.

9. An animal with cephalization will have which of the following?

a. a cephalic vein b. an anus

c. sensory cells/organs and nerve cells clustered at the anterior end of the animal

d. a completely lined fluid-filled body cavity e. all of the above

10. Which of the following is NOT a function associated with a body cavity?

a. support . digestion c. protection of internal organs

d. allowing internal organs to operate independently of the body wall

11. Which of the following is an example of a coelom?

a. an air-filled cavity b. a fluid-filled cavity

c. a fluid-filled cavity around the digestive tract that is not surrounded by tissues that are mesodermal in origin d. none of the above

12. Species of which of these phyla have a pseudocoelom?

a. Annelida b. Arthropoda c. Mollusca d. Nematoda e. Platyhelminthes

13. Species of which of the following animal phyla are deuterostomes?

a. Annelida b. Arthropoda . Chordata d. Echinodermata

e. All except the first answer above are correct.

f. Both the third and fourth answers are correct.

14. Which of the following is NOT associated with sponges?

a. epithelial cells b. connective tissue c. oscula d. collar cells

e. active larvae

16. The phylum Porifera shares a similar body plan throughout. Label the structures of this body plan in the diagram below.

17. Although Cnidarians have both a polyp and a medusa body form, these two share common structures. Label these structures in the figure above.

18. What are the two functions of the gastrovascular cavity of a cnidarian?

a. digestion and prey capture b. respiration and sexual reproduction

c. digestion and distribution of nutrients d. movement and response to threats

e. filter blood and remove waste

19. A gastrovascular cavity, with a single opening, is the characteristic digestive system of animals in which phylum?

a. Arthropoda b. Nematoda c. Mollusca

d. Platyhelminthes e. Porifera

20. Which of the following is associated with or characteristic of a parasitic flatworm like a tapeworm?

a. hooks and suckers b. eyespots c. a respiratory system d. cilia e. a complex digestive system

22. Some worms (such as flukes) possess both male and female reproductive organs. Flukes are considered ____________________ because of this trait.

24. Animals in which of the following phyla are segmented?

a. Annelida b. Arthropoda . Echinodermata d. Mollusca

e. Both the first and second answers are correct. f. Both the first and fourth answers are correct.

25. Annelids (segmented worms) have many structures comparable to those observed in vertebrates (like you). Which of the following is a vertebrate structure to which there is nothing comparable in an annelid?

a. heart b. kidney c. lung d. teeth

26. Label the typical annelid structures on the earthworm shown on the left.

27. Which of the following is NOT a mollusk?

a. barnacle

b. clam

c. octopus

d. slug

e. snail

28. The success of the cephalopods as predators is supported by the presence of _________.

a. beaklike jaws b. a complex eye

c. a large and complex brain

d. tentacles e. all of the above

29.On the left is a diagram of a typical mollusk. Label the structures indicated.

30. Arthropods are a highly diverse, successful, and fairly complex group of invertebrates. Which of the following evolutionary trends is associated with the arthropods?

a. an absence of tissues

b. a gastrovascular cavity

c. a pseudocoelom

d. cephalization

31. Shedding an old, small exoskeleton to allow a larger one to grow is called ____________________.

32. Insects have a stage that is non-feeding and persists through metamorphosis. An insect in this stage is called a ____________________.

33. Arthropods have a typical body structure exemplified by the grasshopper on the left. Label the structures indicated.

Thinking Through the Concepts

1. The class Insecta is the largest taxon of animals on Earth. Its greatest diversity is in the Tropics, where habitat destruction and species extinction are occurring at an alarming rate. What biological, economic, and ethical arguments can you advance to persuade people and governments to preserve this biological diversity?

2. Discuss at least three ways in which the ability to fly has contributed to the success and diversity of insects.

3. Discuss and defend the attributes you would use to define biological success among animals. Are humans a biological success by these standards? Why?

1. List the distinguishing characteristics of each of the phyla discussed in this chapter, and give an example of each.

2. Briefly describe each of the following adaptations, and explain the adaptive significance of each: bilateral symmetry, cephalization, closed circulatory system, coelom, radial symmetry, segmentation.

3. Describe and compare respiratory systems in the three major arthropod classes.

4. Describe the advantages and disadvantages of the arthropod exoskeleton.

5. State in which of the three major mollusk classes each of the following characteristics is found:

a. two hinged shells b. a radula c. tentacles

d. some sessile members e. the best-developed brains f. numerous eyes

6. Give three functions of the water-vascular system of echinoderms.

7. To what lifestyle is radial symmetry an adaptation? Bilateral symmetry?

Essay Challenge

1. What are some advantages and disadvantages of exhibiting radial symmetry?

2. Why do some species of worms and other animals have both male and female reproductive organs?

3. Explain why a free-living flatworm like a Planarian has cilia, eyespots, and a pharynx which are structures that are absent from a parasitic flatworm like a tapeworm.

4. Why do earthworms die on the dry sidewalks when it stops raining?

5. Most mollusks have open circulatory systems. However, the organisms in the class of cephalopods have closed circulatory systems. Explain why this difference exists.

6. What causes the supply of soft-shelled crabs (for eating purposes) to vary throughout the year?

Figure Caption Questions and Answers

Figure 22-5 The diversity of sponges

Question: Sponges are often described as the most "primitive" of animals. How can such a primitive organism have become so diverse and abundant?

Figure 22-6 Cnidarian diversity

Question: In each of these photos, is the pictured organism a polyp or a medusa?

Figure 22-10 The life cycle of the human pork tapeworm

Question: Why have tapeworms evolved a long, flat shape?

Figure 22-11 An annelid, the earthworm

Question: What advantage does a digestive system with two openings have relative to digestive systems with only a single opening (like that of the flatworms)?

Figure 22-12 Diverse annelids

Question: Why does pouring salt on a leech harm it?

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