Layman D. Biology Demystified: A Self-Teaching Guide

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nal environment. Insects are important biological inducers (in-DEW-surs) –

‘‘leaders into’’ various states of environmental change.

BUSY POLLINATORS OF FLOWERS

Various insects visit ﬂowers to feed upon their nectar (NEK-tar). Nectar is

named for the ‘‘drink of the gods’’ in Greek and Roman mythology. The

connection is probably the fact that nectar is sweet and ﬁlled with highly

nutritious plant sugars. And busy bees gather this sweet nectar and transform

it into an even-sweeter honey. Bees and butterﬂies visit ﬂowers and feed on

their nectar during the day, while moths show up at night.

During day-or-night visitations, these insects help induce pollination. You

may recall (Chapter 9) that pollination is the process of spreading pollen

grains from male plants to female plants, so the females can be fertilized.

Without insect-induced pollination, many green plants would eventually

die, and with it, most photosynthesis occurring on the Earth. Therefore,

insect-induced pollination of ﬂowering plants is a critical factor in the Web

of Life.

THE MENACING SWARMS

Just as some insects are busy inducers of pollination and promoters of

Biological Order, others attack human crops in menacing swarms.A

swarm is a large group of related insects that ﬂy or move together.

Communication among insects in the swarm may be highly orderly and

eﬃcient, allowing the huge group to carry out important tasks. A swarm

of bees, for instance, may move as a group of thousands from a damaged

hive to a safer area, and build another hive. The new geographic area with

the hive will beneﬁt from an increased pollination of its ﬂowers.

But a swarm of locusts (LOW-kusts) is quite another matter! A locust is a

type of grasshopper with short antennae. Due to their amazing powers of

rapid reproduction, swarms of locusts can darken the sky as they ﬂy.

Wherever they land as a group of billions, whole tracts of ﬁelds and forests

are quickly stripped of their leaves. The entire ecosystem in a particular area

can be eﬀectively destroyed, depriving the region of the beneﬁts of life-giving

photosynthesis. Since the days of Ancient Egypt, farmers have been faced

with the diﬃcult task of repairing the devastation of Biological Disorder

wreaked by insect swarms.

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Quiz

Refer to the text in this chapter if necessary. A good score is at least 8 correct

answers out of these 10 questions. The answers are found in the back of this

book.

1. The arthropods are distinguished from other invertebrates by their:

(a) Lack of jointed backbones

(b) Presence of distinctly jointed legs and feet

(d) Tendency to crawl slowly over the ground

2. By referring to the cephalothorax, it is meant that:

(a) The arthropod body is thoroughly segmented

(b) Invertebrates lack brain tissue

(d) The head and chest segments have been lumped together

3. The lobster can just keep growing bigger and bigger, for as long as it

lives! ‘‘So,’’ you may well ask, ‘‘why doesn’t the lobster rip its own

skin?’’

(a) The lobster doesn’t have any covering or skin!

(b) There is an intermittent period of molting

(d) A rapid healing process takes place

4. The trilobites are most accurately described as:

(a) Primitive, insect-like creatures having two body segments

(b) Arthropods without jointed legs

(d) A vanished group of extremely overdeveloped mollusks

5. As a group, the arachnids:

(a) Consist solely of spiders and their webs

(b) Include practically all types of insects

(d) Involve scorpions, ticks, mites, and spiders

6. As a group, insects:

(a) Have bodies literally ‘‘cut into’’ three major segments

(b) Use eight hollow legs to move around

(d) Fly with at least 5 pairs of wings

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7. Metamorphosis:

(a) Generally involves the shrinkage of an adult back into a larva

(b) Is a mechanism for ﬂuid transport (similar to diﬀusion)

(d) Generally occurs without any need for diﬀerentiation

8. ‘‘Insects (not human beings) are the real monarchs of Planet Earth!’’

Evidence supporting this statement is the fact that:

(a) Insects have far more ‘‘natural intelligence’’ than people

(b) Insecticides often poison humans, as well as insects

(d) There are far more species of insects than any other type of animal

9. Bees can be considered inducers of Biological Order in that:

(a) Pollination resulting from their feeding visits for nectar allows

complex patterns of plant life to grow and thrive

(b) They often live in highly aggressive colonies that ﬁercely attack

hive invaders

(d) Their attractive yellow-and-black body pattern stimulates other

organisms to adopt colorful forms of their own

10. Swarms of insects:

(a) Always attack and destroy whatever lies in their path

(b) Only occur in far northerly regions of the planet

communication and coordination

(d) Show no interactions among their members, whatsoever

The Giraﬀe ORDER TABLE for Chapter 11

(Key Text Facts About Biological Order Within An Organism)

1. ____________________________________________________________

2. ____________________________________________________________

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3. ____________________________________________________________

4. ____________________________________________________________

The Spider Web ORDER TABLE for Chapter 11

(Key Text Facts About Biological Order Beyond The Individual

Organism)

1. ____________________________________________________________

2. ____________________________________________________________

3. ____________________________________________________________

4. ____________________________________________________________

5. ____________________________________________________________

The Broken Spider Web DISORDER TABLE for Chapter 11

(Key Text Facts About Biological Disorder Beyond The Individual

Organism)

1. ____________________________________________________________

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CHAPTER

The Chordata:

Animals with a

‘‘Chord’’ in Their

‘‘Back’’

In the last two chapters (10 and 11), we were discussing the invertebrates. By

deﬁnition, these are animals without any linked bones (called vertebrae)

within their backs. You may remember (Chapter 3) that jellyﬁsh, corals,

sea worms, and other multicellular invertebrates were probably among the

ﬁrst animals to appear during evolution. Only within the last 500 million

years or so have there been any chordates (KOR-dates) – animals with

some kind of ‘‘chord’’ or ‘‘cord’’ present to stiﬀen their backs. It is this

later group, called the Phylum Chordata (kor-DAY-tuh), to which we now

turn with interest.

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The Notochord: Ancient Forerunner of the

Vertebral Column

It is very reasonable for you, the reader, to ask, ‘‘Just what is meant by

having a chord or cord in your back?’’ This concept is best explained by

looking at Figure 12.1, which provides the general body plan of a primitive

chordate. This ﬁgure shows the four general characteristics of all chordates:

1. The presence of a slender notochord (NO-tuh-kord) running down the

back during at least part of the life cycle;

2. A hollow nerve cord that lies immediately dorsal to the notochord;

3. Gill slits along each side of the head; and

4. A post-anal (AY-nul) tail that is very muscular.

The notochord is the key anatomic feature. It is a long, narrow structure in

the ‘‘back’’ (noto-) that looks like a thin ‘‘cord’’ (chord) or rod. The noto-

chord’s chief function is supporting and stiﬀening the body. All chordates

have a notochord in their bodies during at least one stage of their develop-

ment. And it is this notochord that can serve as the basis for development of

a full vertebral column or ‘‘jointed backbone.’’

The Phylum Chordata and Its Groups

The Phylum Chordata can be subdivided into a number of diﬀerent groups.

The major classifying factor is the answer to the following question: ‘‘Does

the particular chordate species being considered keep a notochord in its back

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Fig. 12.1 The general body plan of a primitive chordate.

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throughout its lifetime, or does it replace the notochord with a full vertebral

column after it has passed through the embryo stage?’’

THE SEA SQUIRTS AND LANCELETS: NO ‘‘JOINTED

BACKBONE’’

Figure 12.2 reveals that two of the major groups of chordates keep a noto-

chord in their back throughout their lives. These two groups are called the

Urochordates (YOUR-oh-kor-dates) and the Cephalochordates (SEF-uh-low-

kor-dates).

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Fig. 12.2 Sea squirts and lancelets: Chordates without spines.

The Urochordates are animals that literally have a ‘‘cord’’ (chord) within

their ‘‘tail’’ (uro-). By this it is meant that these creatures have a swimming

larval stage with a notochord in its tail section. The main examples of

Urochordates are the sea squirts. Interestingly enough, the adult stage of

the sea squirt has a body shaped like a ‘‘U,’’ and it remains anchored to a

rock at the bottom of the sea. At one end lies an intake siphon, which sucks in

seawater and ﬁlters out plankton and other tiny creatures during feeding.

And at the other end lies an output siphon, which squirts or shoots out a jet of

water whenever the animal is bothered by a predator.

The Cephalochordates are literally a group of ‘‘cord-heads’’ (cephalo-)!

The implication of this odd name is displayed in Figure 12.2 (B) for the

lancelets (LANS-lits). The lancelets are slender, ﬁsh-like marine animals

that lie partially buried in the sand under shallow water. Their thin, tapered

body is pointed at both ends, making it look much like a small spear or ‘‘little

lance.’’ Because it has no skull, the lancelet doesn’t have a brain, either! Thus,

the notochord extends all the way up into its head, oﬃcially making it a

‘‘cord-head’’ (Cephalochordate). The lancelet is a type of suspension feeder,

meaning that it feeds on small particles suspended in seawater, which it draws

into its mouth with the help of waving, hair-like tentacles (TEN-tuh-kuls).

Both sea squirts and lancelets have notochords in their backs during at

least part of their life cycles, but they are still oﬃcially invertebrates. Many

biologists think that they are important evolutionary ‘‘bridging species’’

between the other invertebrates (which don’t even have a notochord) and

the true vertebrates (whose primitive notochord has been replaced by a

bony vertebral column).

THE VERTEBRATES – CHORDATES WITH A ‘‘JOINTED

BACKBONE’’

In contrast to the Urochordates and Cephalochordates, the Vertebrata (ver-

teh-BRA-tuh) or vertebrates are chordates with both a jointed (segmented)

backbone and a brain case or cranium (KRAY-nee-um) (see Figure 12.3). You

may recall (Chapter 11) that the ‘‘jointed backbones’’ are technically called

the vertebrae. The cranium is just a formal name for the ‘‘skull’’ (crani)

‘‘present’’ (-um) at the top of the vertebral column. Owing to their high

degree of cephalization (concentration of sensory, motor, and other nerve

functions within the head region), vertebrates have a brain in their cranium.

The vertebrates generally have a notochord only as part of their embryonic

stage of development. As their bodies mature, the notochord is replaced by a

vertebral column (linked series of jointed vertebrae).

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The dorsal nerve cord, now protected by a vertebral column, is called the

spinal cord. The skull (brain case or cranium), vertebral column, and ribs

make up what is called the axial (AX-ee-ul) skeleton. The reason for this

name is the pattern set by the bones or cartilage (KAR-tih-lj), commonly

known as ‘‘gristle,’’ which house the brain and spinal cord. This ordered

bone/cartilage pattern forms a longitudinal (long-jih-TWO-duh-nal) axis,or

‘‘lengthwise axle,’’ around which the vertebrate body can turn or pivot.

Finally, vertebrates have a closed circulatory system. The heart serves as a

pump, which sends the blood coursing out through the entire body. After the

body tissues are supplied with oxygen, glucose, and other nutrients, the blood

(now ﬁlled with tissue waste products) returns back to the heart through a

closed loop of vessels.

Wide Diversity in Backboned Creatures: Eight

Different Classes of Vertebrates

Although all vertebrates share a common core of characteristics, they still

show a very wide degree of diversity or diﬀerences among them. This diver-

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Fig. 12.3 Basic elements of the vertebrate body.

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sity is reﬂected in the existence of eight diﬀerent classes of vertebrates. These

are named the Class Agnatha (AG-nuh-thuh), Class Placodermi (PLAK-uh-

derm-ee), Class Chondrichthyes (kahn-DRIK-thees), Class Osteichthyes (ahs-

tee-IK-thee-eez), Class Amphibia (am-FIB-ee-ah), Class Reptilia (rep-TIL-ee-

ah), Class Aves (AY-veez), and Class Mammalia (mah-MAY-lee-uh). [Study

suggestion: The eight diﬀerent vertebrate classes are each labeled with brief

representative pictures in Figure 12.4. Before reading any farther in this

chapter, see if you can match each of the pictures with the appropriate

English translations of their Class names, as follows: the Class of ‘‘birds;’’

the Class of ‘‘cartilage-ﬁshes;’’ the Class of ‘‘livers of a double life {on both

the land and in the water};’’ the Class of ‘‘jawless’’ ﬁshes; the Class of animals

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Fig. 12.4 The eight major classes of vertebrates.