Gymnosperms evolved seeds as a wayto protect their youngAfter mosses and ferns, the next group of plants to

evolve was the gymnosperms [JIM-nuh-sperms] . This

group includes pine trees and other conifers (cone-

bearing plants ; see Figure 3 .8), as well as cycads and

ginkgos.

Gymnosperms were the first plants to evolve seeds,

structures in which plant embryos are encased in a pro-

tective covering and provided with a stored supply of

nutrients (Figure 3 .10) . Gymnosperms (gymno, "naked";

sperm, "seed") have seeds that are relatively unpro-

tected compared with those of angiosperms, the next

major group of plants to arise. Gymnosperms were the

dominant plants 250 million years ago, and the evolu-

tion of seeds was probably an important part of their

success . Seeds provided nutrients that plant embryos

could use to grow before they were able to produce

their own food via photosynthesis . Seeds also provided

embryos with protection from drying or rotting and

from attack by predators.

Angiosperms produced the world's first flowersAlthough typically we think of flowers when we think of

plants, flowering plants are a relatively recent develop-

ment in the history of life . Today the flowering plants, or

angiosperms [Awjee-oh-sperms], are the most dominant

and diverse group of plants on the planet, including

orchids, grasses, corn plants, and apple and maple trees.Angiosperms produce seeds that are well protected (angio

means "vessel," referring to the tissues that encase the

plant's embryo).

Highly diverse in size and shape, angiosperms live

in a wide range of habitats—from mountaintops to

deserts to salty marshes and fresh water. Almost any

plant we can think of that is not a moss, a fern, or a

cone-producing tree is an angiosperm . The key to the

success of angiosperms, and their defining feature, is

the flower . Flowers are specialized structures for sexual

reproduction, or pollination, where the male and the

female gametes meet (Figure 3 .11).

Some flowers provide food, such as the sugary liquid

known as nectar, to attract animals to visit them and in

the process transport pollen (male gametes) from flower

to flower. The transported pollen can fertilize another

flower's ovules (structures containing female gametes).

Thus animals can provide a means of sexual reproduc-

tion between even very distant plants . Plants also use

wind to disperse their pollen from flower to flower.

People with hay fever are reacting to this method of

Light-gathering leavesare the main site ofphotosynthesis . Leavesabsorb carbon dioxidethrough tiny openings.

A waxy covering(cuticle) on leavesand stems preventsunnecessarywater loss byevaporation .

Most plants possess vasculartissues . The vascular systemtransports water and mineralsthroughout the plant and addsto its sturdiness.

Flowers are the structuresin which reproduction takesplace and in which fruitsare produced.

Fruits contain theyoung of the nextgeneration, the seeds . j

The stem providessupport and extends theplant toward the sun.

Roots anchor plantsto the ground andallow them to absorbwater and criticalnutrients from the soil.

Figure 3 .9 The Basic Structures of a PlantShown here is a familiar garden vegetable, a pepper plant . Because itis a member of the angiosperms, the last of the major plant groups toevolve, all the evolutionary innovations that distinguish plants can beshown on this one plant.

plant sex, which sends nose-irritating pollen blowing

through the air.

In addition to increasing the efficiency of fertilization

through flowers, angiosperms have evolved a variety of

ways to distribute their seeds to distant places in order

to get their young off to a good start . One of these is the

use of tasty fruits that attract animals . As the embryos

of some angiosperms are developing, the surrounding

ovary develops into a ripening fruit (see Figure 3 .11).

Animals eat the fruit and later excrete the seeds in their

feces . These nutrient-rich wastes provide a good place for

the seeds to begin life, often far from their parent plant

where they will not compete with that parent for water,

Chapter 3 Major Groups of Living Organisms

Plants are the basis of land ecosystemsand provide many valuable productsIt is difficult to overstate the significance of plants . As

photosynthesizing organisms, plants use sunlight and

carbon dioxide to make sugars, food that they and the

organisms that eat them can use. Nearly all organisms

on land ultimately depend on plants for food, either

directly by eating plants or indirectly by eating other

organisms (such as animals) that eat plants or that eat

other organisms that eat plants, and so on . Many organ-

isms live on or in plants, or on or in soils largely made up

of decomposed plants.

Flowering plants provide humans with materials such

as cotton for clothing and with pharmaceuticals such as

morphine. Essentially all agricultural crops are flower-

ing plants, and the entire floral industry rests on the

reproductive structures of angiosperms . Gymnosperms

such as pines, spruces, and firs are the basis of forestry

industries, providing wood and paper.

As valuable as plants are when harvested, they are

also valuable when left in nature . By soaking up rain-

water in their roots and other tissues, for example, plants

prevent runoff and erosion that can contaminate streams.

Plants also produce the crucial gas oxygen.

nutrients, or light . But hitching a ride in an animal's gut

is not the only means plants have for overcoming their

immobility ; plant seeds have evolved many other ways to

travel (Figure 3 .12).

Figure 3 .12 Getting Around

Plants have evolved many ways of spreading to new areas. (a) A palmtree seed in a coconut can float for hundreds of miles until it reachesa new beach where it can take root and grow . (b) Some seeds havewings (for example, maple "keys") or other structures (such asdandelion fluff, shown here) that allow them to be carried by thewind, sometimes over great distances .

3.5 The Fungi : A Worldof Decomposers

Most people are familiar with fungi as the

'BACTERIA' 'ARCHAEA)

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'BACTERIA' (ARCHAEA)

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ing from their lawns. However, the Fungi,

a kingdom within the domain Eukarya,

also includes yeasts (single-celled fungi)

and molds . In fact, the familiar mushroom

is just a small part of a fungus. Most fungal

tissues typically are woven through what-

ever substance—often the tissues of

c 2

another organism—the fungus is digest-

ing and making its living from . Because fungal tissues

are largely hidden from view, fungi are among the most

poorly understood of the major groups of organisms.

Fungi can be costly to human society. They can cause

diseases, contaminate crops, rot food, and force us to

clean our bathrooms more often than we might like. Otherfungi are beneficial, providing us with pharmaceuticals,

including antibiotics such as penicillin . Yeasts such as

Saccharomyces cerevisiae [sAK-ah-roh-MICE-eez Bair-uh-

VEE-see-eye] can feed on sugars and produce two impor-

tant products : alcohol and the gas carbon dioxide, both

crucial to the rising of bread and the brewing of beer.

Fungi also provide highly sought-after delicacies such as

truffles, whose underground growing locations can be

found only by specially trained dogs or pigs.

As Figure 3.13 shows, the fungi are divided into three

distinct groups : zygomycetes, which evolved first,

ascomycetes, and basidiomycetes . Each group differs in—

and is named for—its unique reproductive structures.

Fungi play several roles in terrestrial ecosystems.

Many fungi are decomposers . Playing the role of garbage

processor and recycler, these fungi speed the return of

the nutrients in dead and dying organisms to the ecosys-

tem. Some fungi are parasites (organisms that live in or

on other organisms and harm them), while others are

mutualists (organisms that benefit from, and provide

benefits to, the organisms they associate with) . Sometimes

the benefits and harms in these associations involve nutri-

tion, sometimes not . Do not confuse these terms, how-

ever, with the categories of decomposer, consumer, and

producer, even though they describe how organisms get

their nutrition . Mutualist and parasite are a separate,

unrelated pair of words to describe whether organisms

are good or bad for the organisms they associate with.

For example, consumers can be mutualists or parasites;

likewise, mutualists can be consumers, producers, or

decomposers .

Chapter 3 Major Groups of Living Organism

In humans, fungi can cause mild diseases such as ath-

lete's foot . Fungal diseases can also be deadly, like the

pneumonia caused by the fungus Pneumocystis carinii

[woo-moh-szss-tiss kuh-REE-nee], the leading killer of

people suffering from AIDS . Fungi attack plants, too.

Ceratocystis ulmi [BARE-uh-toh-srss-tiss ooL-mee] causes

Dutch elm disease, which has nearly eliminated the elm

trees that once formed arching canopies over streets all

across the United States. Rusts and smuts are fungi that

attack crops . Still other fungi are specialized for eating

insects, and biologists are trying to use these fungi to kill

off insects that are crop pests (Figure 3.16).

Some fungi live in beneficial associations withother speciesSome fungi are mutualists, living in association with

other organisms to their mutual benefit . One broad

group of mutualists—found in all three groups of fungi

(zygomycetes, ascomycetes, and basidiomycetes)—is

known as mycorrhizal [MY-koh-RYE-zul] fungi . These

species live in mutually beneficial associations with

plants . The fungi form thick, spongy mats of mycelium

on and in the plants' roots that help the plants absorb

more water and nutrients . The fungi receive sugars

and amino acids, the building blocks of proteins, from

the plants . More than 95 percent of ferns (and their

close relatives), gymnosperms, and angiosperms have

mycorrhizal fungi living in association with their roots.

ire 3.16 Fungal Parasitese fungi are parasites, making their living by attacking the tissuesher living organisms . This beetle, a weevil in Ecuador, has been1 by a Cordyceps [Koe-duh-seps] fungus, the stalks of which arering out of its back .

Figure 3 .17 Mutua list FungiA lichen consists of an alga and a fungus intimately entwined In amutually beneficial association . This lichen, known as British soldiersis shown growing on an old log.

For example, morels—a group of mushrooms highh

prized as food by some—are the reproductive struc-

tures of mycorrhizal fungi.

Another familiar fungal association is the lichen [a-

kin], a lacy, orange or gray-green growth often seen on

tree trunks or rocks . A lichen is an association of an alga

(a photosynthetic protist, as we learned earlier) anda

fungus (Figure 3 .17) . Both ascomycetes and basid-

iomycetes are known to form lichens . The alga and fungus

in a lichen grow with their tissues intimately entwined,

allowing the fungus to receive sugars and other carbon

compounds from the alga . In return, the fungus produces

lichen acids, a mixture of chemicals that scientists believe

may function to protect both the fungus and the alga from

being eaten by predators.

3 .6 The Animalia : Complex,Diverse, and Mobile

The Animalia, or the animals, are

a kingdom within the domain Eu-

karya. The Animalia is the most

familiar major group, and the one

to which humans belong. All ani-

mals are multicellular, and many

of them are quite complex . The

animals include flashy creatures

such as Bengal tigers, peacocks,

and you, as well as worms, sea

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Unit 1 The Diversity of Life

stars, snails, insects, and other creatures that are less obvi-ously animal-like, such as sponges and corals.

The sponges, the most ancient of animal lineages,were the first to branch off the evolutionary tree (Figure

3 .18 on the next page) . Next to evolve were the cnidar-ians [nye-DARE-ee-uns] (including jellyfish, sea

anemones, and corals), and then the flatworms . Thenext group to evolve was the protostomes, a group thatcomprises more than 20 separate subgroups, includ-ing mollusks (such as snails and clams), annelids (seg-mented worms), and arthropods (including crustaceans,spiders, and insects), the three shown in Figure 3 .18.These three protostome groups are depicted branchingoff together because it is unclear which of them evolvedfrom the others first . What is known is that they arepart of a single lineage descending from an ancestorthat branched off the tree after flatworms, but beforeechinoderms [ee-KYE-noh-derms] . Next to evolve werethe echinoderms (sea stars and the like) and the ver-tebrates (animals with backbones, such as fish, birds,and humans), both deuterostomes [goo-ter-oh-stomes].

Like all fungi and some bacteria and protists, animalsare consumers, making their living by eating the tissuesof other organisms, from which they derive both carbonand energy. Animals differ from fungi and plants in thatanimal cells do not have cell walls surrounding theirplasma membranes . Typically mobile and often in searchof either food or mates, animals have evolved a huge diver-

sity in their ways of life.

Animals evolved true tissuesSponges are among the simplest of animals . They repre-sent a time in the evolution of animals before tissues—specialized, coordinated collections of cells—had evolved.A sponge is a loose collection of cells (Figure 3 .19) . If it isput through a sieve and broken apart into individualcells, it will slowly reassemble as a whole sponge.Widespread and highly successful, sponges feed on amoe-bas and other tiny organisms in their aquatic environ-ment, filtering a ton of water just to get enough food togrow an ounce.

One of the earliest animal groups to evolve true tissueswas the cnidarians . Their name—Cnidaria—comes fromthe Greek word for "nettle," a stinging plant found on land.Cnidarians are characterized by stinging cells they useto immobilize prey and to protect themselves from pred-ators. Like other cnidarians, jellyfish (Figure 3 .20) havespecialized nervous tissues, musclelike tissues, and diges-tive tissues. This specialization allows behavior—such asgracefully and rapidly swimming away from predators—that requires the coordination of many cells .

Outgoing water

Animals evolved organs and organ systemsAfter tissues, the next level of complexity to evolve wasorgans and organ systems . Recall that organs are bodyparts composed of different tissues organized to carryout specialized functions . Usually organs have a definedboundary and a characteristic size and shape ; an exam-ple is the kidney.

An organ system is a collection of organs functioningtogether to perform a specialized task . The human diges-tive system, for example, is an organ system that includesthe stomach as well as other digestive organs, such as thepancreas, liver, and intestines . Flatworms, a group of fairlysimple wormlike animals, were one of the earliest groupsto evolve true organs and organ systems (Figure 3 .21).

Animals evolved complete body cavitiesStill later in the history of this group, animals evolved acomplete body cavity—an interior space with a mouth atone end and an anal opening at the other . The two dis-

tinct evolutionary lineages that exhibit such cavities arethe protostomes and the deuterostomes (see Figure 3 .18).Protostomes include such animals as insects, worms, and

Chapter 3 Major Groups of Living Organisms

One type of specialized cell,the collar cell, has a tail-likeappendage, known as aflagellum, which keeps waterflowing through the sponge.Collar cells also trap food andpass it to other cells, which

idigest it.

Figure 3 .19Sponges Have Specialized Cells but Lack TissuesSponges are loose associations of cells . Although some of thesecells are specialized, none are organized as tissues, as in mostother animals .

riew the tissuewrs of a jellyfish .

I The endoderm is specialized tofacilitate digestion, dischargingproteins that break down food,which is then taken up by the cells

f The mesoglea isan inner layer ofjellylike material .

snails. Deuterostomes include animals such as sea stars

(echinoderms) and all the animals with backbones (ver-

tebrates), such as humans, fish, and birds.

The names for these two lineages refer to which of

the two openings in the early embryo becomes the

mouth . In protostomes (from proto, "first" ; stome,"opening"), the mouth forms from the first opening to

develop, and the anus forms elsewhere later . hndeuterostomes (deutero, "second"), the first opening

develops into the anus, while the second opening

becomes the mouth. This developmental difference has

led to radically different patterns of tissue organiza-

tion in these two groups.

The tentacles contain specializedstinging cells that are used to injectpoisons into prey and subdue them.

Figure 3 .20 Jellyfish Have True Tissue LayersCnidarians (including jellyfish) were one of the earliest groups toevolve true tissues . These tissues include the ectoderm (ecto, "outer";derm, "skin") and the endoderm (endo, "inner") . For clarity, these twolayers are color-coded blue and yellow, respectively . Sandwichedbetween them is an inner (red) layer of secreted material known as themesoglea (meso, "middle" ; glee, "jelly") . In addition to serving asnervous tissue, the ectoderm coordinates with the endoderm tocontract like muscle tissue . Tentacles bring food into the internal cavitythrough a single opening, which serves as both a mouth and an anus.

Figure 3 .21 Flatworms Evolved Organs and OrganSystems

One of several organ systems in the flatworm is the reproductivesystem . It contains both male and female structures, since everyflatworm can function as both a male and a female . For clarity, wehave color-coded the female structures pink (ovary, oviduct, andgenital pore) and the male structures blue (penis and testis).

Unit 1 The Diversity of Life

Animal body forms exhibit variationson a few themesAnimals exhibit a great variety of shapes and sizes, many

of which are variations on a few basic body plans.

Arthropods (arthro, "jointed" ; pod, "foot") have a hard

outer skeleton called an exoskeleton (exo, "outer"), which

is made of chitin [KYE-tin], the same material found in the

cell walls of fungi.

One feature that has facilitated the evolution of arthro-

pod bodies is their segmented body plan . Over time, indi-

vidual body segments have evolved different combinations

of legs, antennae, and other specialized appendages,

resulting in a huge number of different types of animals,

some of them extremely successful . Probably the best-

known arthropod group is the insects (grasshoppers,beetles, butterflies, and ants, among others), which have

six legs and live on land . Whereas prokaryotes dominate

Earth in sheer numbers of individuals, insects dominate

in number of species, having many more species than

any other group of organisms.

Other arthropod groups include the arachnids [uh-

RACK-nids] (spiders, scorpions, and ticks), which have

eight legs and also live on land; the crustaceans (lob-

sters, shrimps, and crabs), which have ten or more legs

and live primarily in water ; and millipedes and cen-tipedes, which live on land and have many more legs—

but less specialization—than the previously mentioned

groups. Arthropods are a wonderful illustration of how

evolution can modify a basic body plan to produce many

variations over time (Figure 3 .22) . Looking just at theevolution of the last segment (the rear ends) of these

animals, one can see that the changes support a hugevariety of shapes and lifestyles . The last segment has

evolved into the delicate abdomen of a butterfly, the

piercing abdomen of a wasp (which has a huge structure

Figure 3.22 Variations on a ThemeFrom a simple segmented body plan, arthropods have evolved a hugediversity of forms and sizes . The millipede can be viewed as thesimplest form of these segmented animals, as all of its segments aresimilar. As segments have evolved and diversified, a variety oforganisms have arisen, from lobster to swallowtail butterfly toparasitoid wasp.

for inserting and laying eggs deep in another animal'sbody), and the delicious tail of the lobster.

Such segmentation can also be seen in the annelids

(segmented worms ; see Figure 3 .18) . This group includesthe familiar earthworm, whose body is made up of a

repeated series of segments (Figure 3 .23a).Vertebrates—animals with an internal backbone—

are also built on a (less obvious) segmented body plan

(Figure 3.23b) . The major vertebrate groups include fish,amphibians (frogs and salamanders), reptiles (snakes,

lizards, turtles, and crocodiles), birds, and mammals(including humans and kangaroos) . Like annelids andarthropods, vertebrates illustrate how a variety of very

different forms can evolve from one basic body plan . The

front appendage of vertebrates has evolved as an arm inhumans, a wing in birds, a flipper in whales, an almostnonexistent nub in snakes, and a front leg in salaman-ders and lizards.

Animals exhibit an astounding varietyof behaviorsAnother fascinating characteristic of animals is theirability to move, which allows for a wide range of behav-iors . Animals have evolved varied ways to capture prey,

eat prey, avoid being captured, attract mates and carefor young, and migrate to new habitats . As we saw earlier,animals are quite useful to immobile organisms, such asplants, which have evolved ways to get animals to carrytheir pollen and seeds.

Animals play key roles in ecosystemsand provide products for humansBecause they live by eating other organisms, andbecause most are mobile, animals play many roles inecosystems . Most serve as consumers, preying on manyspecies of plants and animals . Some animals, such as

carrion beetles, serve as decomposers of dead animals.

(a)

(b)

Figure 3.23 Many Animals Are SegmentedSegmentation, a body plan in which segments repeat and often canevolve independently of one another, is shown here in (a) anearthworm (an annelid, or segmented worm), and (b) a vertebrate.

Chapter 3 Major Groups of Living Organisms

Test your knowledgeof the properties of

multicellulareukaryotes .