Ch 20-22 lecture

Copyright © 2009 Pearson Education, Inc..

Lectures by

Gregory AhearnUniversity of North Florida

Chapter 20-22

The Diversity of Life

Copyright © 2009 Pearson Education Inc.

20-22.1 How Are Organisms Named And Classified? Organisms are placed into categories on the

basis of their evolutionary relationships.• There are eight major categories.

• Domain, kingdom, phylum, order, class, family, genus, species

• These categories form a nested hierarchy in which each level includes all the ones before it.


20-22.1 How Are Organisms Named And Classified?


20-22.1 How Are Organisms Named And Classified? Each species has a unique, two-part name.

• The scientific name of an organism is formed from the genus and species categories.

• Each genus includes a group of closely related species, and within each species are individuals that can interbreed.


20-22.1 How Are Organisms Named And Classified? Each species has a unique, two-part name

(continued).• Thus, the genus Sialia (bluebirds) includes the

eastern bluebird (Sialia sialis), the western bluebird (Sialia mexicana), and the mountain bluebird (Sialia currucoides)—similar birds that do not interbreed.


20-22.1 How Are Organisms Named And Classified? Three species of bluebird

Fig. 20-22-1


20-22.1 How Are Organisms Named And Classified? Each species has a unique, two-part name

(continued).• Each two-part scientific name is unique;

referring to an organism by its scientific name rules out any chance of ambiguity or confusion.

• By convention, scientific names are underlined or italicized.

• The first letter of the genus name is always capitalized, and the first letter of the species name is always lowercase.

• The species name is never used alone but is always paired with its genus name.


20-22.1 How Are Organisms Named And Classified?

PLAYPLAY Animation—Taxonomic Classification


20-22.1 How Are Organisms Named And Classified? Classification originated as a hierarchy of

categories.• Aristotle (384–322 B.C.) was among the first to

classify living things; he classified about 500 organisms based on structural complexity, behavior, and degree of development at birth.



categories (continued).• Carolus Linnaeus (1707–1778) placed each

organism into a series of hierarchically arranged categories on the basis of its resemblance to other life-forms, and introduced the scientific name composed of genus and species.



categories (continued).• Charles Darwin (1809–1882) demonstrated

that all organisms are connected by common ancestry; the more categories two organisms share, the closer their evolutionary relationship.


20-22.1 How Are Organisms Named And Classified? Biologists identify features that reveal

evolutionary relationships.• Scientists who devise classifications must

distinguish informative similarities caused by common ancestry from uninformative similarities that result from convergent evolution.


20-22.1 How Are Organisms Named And Classified? Biologists identify features that reveal

evolutionary relationships (continued).• In the search for informative similarities,

biologists look at many kinds of characteristics.• Anatomical similarities play a key role in

classification.• Molecular similarities are also useful in

classification.


20-22.1 How Are Organisms Named And Classified? Microscopic structures may be used to

classify organisms.

Fig. 20-22-2


20-22.2 What Are The Domains Of Life?

Before 1970, all forms of life were classified into two kingdoms: Animalia and Plantae.• All bacteria, fungi, and photosynthetic

eukaryotes were considered to be plants, and all other organisms were classified as animals.



The five-kingdom system improved classification.• Robert H. Whittaker’s five-kingdom system

placed all prokaryotic organisms into a single kingdom, and divided the eukaryotes into four kingdoms.

• The prokaryotes were placed in the kingdom Monera.

• The five-kingdom system was an improvement over the two-kingdom system.



A three-domain system more accurately reflects life’s history.• Carl Woese studied the

biochemistry of the Moneran organisms.

• Despite their superficial similarities, these two groups are actually radically different.

Fig. 20-22-3



A three-domain system more accurately reflects life’s history (continued).• He found them to be divided into two groups

based on the nucleotide sequences in the RNA in their ribosomes, and called the two groups the Bacteria and the Archaea.


BACTERIA ARCHAEA EUKARYA

fungi

plants

animals

protists


The tree of life• The five-kingdom system was replaced by one

that divides life into three domains: Bacteria, Archaea, and Eurkarya.

Fig. 20-22-4



Animation—Tree of LifePLAYPLAY



Kingdom-level classification remains unsettled.• Biologists recognize 15 kingdoms among the

Bacteria.• There are three kingdoms in the Archaea.• There are four kingdoms among the Eukarya.

• Animals• Plants• Fungi• Protists


20-22.3 Bacteria And Archaea

Earth’s first organisms were prokaryotes—single-celled microbes that lacked organelles such as a nucleus, chloroplasts, and mitochondria.• In terms of abundance, prokaryotes are

Earth’s predominant form of life.



Bacteria and Archaea are fundamentally different.• Two of life’s domains, Bacteria and Archaea,

consist entirely of prokaryotes; yet there are fundamental differences between them.

• Bacterial cells contain molecules of the polymer peptidoglycan, which strengthens the cell wall.

• These two groups also differ in the structure and composition of the plasma membrane, ribosomes, and RNA polymerases, as well as in the processes of transcription and translation.



Classification of prokaryotes within each domain is difficult.• The biochemical differences between archaea and

bacteria make distinguishing the two domains an easy matter, but classification within each domain poses challenges.

• Prokaryotes have been classified on the basis of such features as shape, means of locomotion, pigments, nutrient requirements, the appearance of colonies, and staining properties.

• More recently, the comparisons of DNA and RNA nucleotide sequences have been used in prokaryotic classification.



Prokaryotic adaptations provide mobility and protection.• Prokaryotes are usually small, 0.2 to 10

micrometers in diameter, compared to 10 to 100 micrometers for eukaryotic cells.



The cell walls that surround prokaryotic cells give characteristic shapes to different types of bacteria and archaea; the most common shapes are spherical, rodlike, and corkscrew-shaped.

Fig. 20-22-5



Prokaryotic adaptations provide mobility and protection (continued).• Some prokaryotes are mobile; some may

have flagella.• Flagella can rotate rapidly and propel the

organism through the environment.

Fig. 20-22-6



Prokaryotic adaptations provide mobility and protection (continued).• Many prokaryotes form films on surfaces.• Some prokaryotes secrete slime that allows

them to adhere to surfaces, or can aggregate into biofilms made up of one or more species in colonies.



Prokaryotic adaptations provide mobility and protection (continued).• Biofilms protect the embedded bacteria

against a variety of attacks, such as from antibiotics and disinfectants.

• Some of the common biofilms are responsible for tooth decay, gum disease, and ear infections.



Protective endospores allow some bacteria to withstand adverse conditions.

Fig. 20-22-7



Prokaryotic adaptations provide mobility and protection (continued).• The endospore forms within the bacterium,

and contains genetic material and a few enzymes encased in a thick protective coat.

• Metabolic activity ceases until the spore encounters favorable conditions, which may take an extremely long period of time.



Prokaryotes are specialized for specific habitats.• Prokaryotes occupy virtually every habitat,

including those where extreme conditions keep out other forms of life.

• Many archaea can live in hot springs at temperatures up to 110°C; they can live at extreme pressures beneath the Earth’s surface, and at very cold temperatures of the Antarctic.

• They can live in the Dead Sea, with salt concentrations seven times those of the ocean.



Prokaryotes exhibit diverse metabolisms.• Many prokaryotes are anaerobes; their

metabolisms do not require oxygen.• Others are opportunistic, using anaerobic

respiration when oxygen is absent and switching to aerobic respiration when oxygen is available.



Prokaryotes exhibit diverse metabolisms (continued).• Prokaryotes feed on many things, including

sugars, proteins, and fats, but also petroleum, methane, benzene, and toluene; some can use hydrogen, sulfur, ammonia, iron, and nitrate.

• Some prokaryotes possess chlorophyll and are photosynthetic.



Prokaryotes reproduce by binary fission.• Most prokaryotes reproduce asexually by

binary fission, which produces identical copies of the original cell.

• They reproduce rapidly and can evolve quickly to adapt to changing conditions.



Prokaryotes affect humans and other organisms.• Prokaryotes play important roles in animal

nutrition.• Many animals that eat plants cannot digest

the cellulose in plants themselves and rely on symbiotic bacteria in their digestive tracts, which are able to digest cellulose, to liberate nutrients from this food source.



Prokaryotes affect humans and other organisms (continued).• Many foods that humans eat are produced by

the actions of bacteria, including cheese, yogurt, and sauerkraut.

• Some bacteria in human intestines feed on undigested food and synthesize nutrients, such as vitamin K and vitamin B12, which the human body absorbs.



Prokaryotes capture the nitrogen needed by plants.• Plants obtain nitrogen for growth from bacteria

that live in the soil, or from nitrogen-fixing bacteria in special nodules on the roots of certain plants.

• These include legumes such as alfalfa, soybeans, lupines, and clover.

• These bacteria capture nitrogen gas from air in the soil and combine it with hydrogen to produce ammonia that plants use directly.



Prokaryotes are nature’s recyclers.• Prokaryotes consume the organic molecules

in the dead bodies of plants and animals, decomposing their wastes and recycling them to the environment.

• Prokaryotes can clean up pollution.



Prokaryotes are nature’s recyclers (continued).• Nearly anything that human beings can

synthesize can be broken down by some prokaryote, including detergents, toxic pesticides, and harmful industrial chemicals.

• Even oil can be broken down by prokaryotes.• The breakdown of pollutants by bacteria is

called bioremediation.



Some anaerobic bacteria produce dangerous poisons.• Some bacteria produce toxins that attack the

nervous system.• Clostridium tetani causes tetanus.• C. botulinum causes botulism (lethal food

poisoning).



Humans battle bacterial diseases old and new.• Pathogenic (disease-causing) bacteria

synthesize toxic substances that cause diseases in humans.• Bubonic plague (“Black death”) killed 100

million people during the fourteenth century.• Tuberculosis, gonorrhea, syphilis, and

cholera are bacterial diseases long associated with humans.



Common bacterial species can be harmful.• Streptococcus causes strep throat.• Another causes pneumonia, which clogs the

lungs with fluid.• A common bacterium of the human digestive

tract, Escherichia coli (E. coli), normally is benign but can transform into a pathogenic form that can be transmitted from human to human.


20-22.4 Protists

The protists are eukaryotes that are not a plant, an animal, or a fungus.• Most protists are single-celled.• While most members of this group are small,

they are incredibly diverse in their modes of reproduction and in their structural and physiological innovations.

• Some of the larger protists are colonies of single-celled individuals, while others are multicellular organisms.


20-22.4 Protists

Protists affect humans and other organisms.• Protists have both positive and negative

effects upon humans.• The primary positive impact comes from the

ecological roles of photosynthetic marine protists.

• On the negative side are the many human diseases caused by parasitic protists.


20-22.4 Protists

Some of the harmful and helpful protists are listed on the slides that follow.• Stramenopiles include photosynthetic and

nonphotosynthetic organisms, and include the diatoms and the brown algae.


20-22.4 Protists

Diatoms encase themselves within glassy (silica) walls, and are photosynthetic phytoplankton that float passively in lakes and oceans.

Fig. 20-22-8


20-22.4 Protists

Brown algae dominate in cool coastal waters and form multicellular aggregations known as brown algae seaweeds.

Fig. 20-22-9


20-22.4 Protists

Alveolates include parasites, predators, and phytoplankton.• Most dinoflagellates are photosynthetic and

move with the use of their two whiplike flagella.

• They are important components of the phytoplankton and are food sources for larger organisms.


20-22.4 Protists

Dinoflagellates

Fig. 20-22-10


20-22.4 Protists

Alveolates include parasites, predators, and phytoplankton (continued).• They cause “red tides” during population

explosions, which kill fish by suffocation due to lack of oxygen from the decay of billions of dinoflagellates.

• Shellfish filter these from the sea and concentrate the toxins that they produce, causing shellfish poisoning.


20-22.4 Protists

A red tide

Fig. 20-22-11


20-22.4 Protists

Apicomplexans are parasitic and have no means of locomotion.• These live inside the bodies or cells of their

hosts.• An example is the malarial parasite

Plasmodium, which lives in the Anopheles mosquito and is transmitted to a human victim by the insect.


20-22.4 Protists

Ciliates are the most complex of the alveolates.• They possess hairlike

outgrowths of the plasma membrane that are used for locomotion.

• Two examples are Paramecium and the predator, Didinium.

Fig. 20-22-12


20-22.4 Protists

Cercozoans have thin pseudopods and elaborate shells.• They possess flexible plasma membranes that

can extend in any direction to form finger-like projections called pseudopods.

• The pseudopods of this group extend through a shell and are threadlike; the largest group is the foraminiferans.


20-22.4 Protists

Cercozoans have thin pseudopods and elaborate shells (continued).• The shells of foraminiferans are made of

calcium carbonate (chalk) that are pierced by many holes through which the pseudopods extend.

• The chalky shells of these organisms may accumulate over millions of years to form deposits of limestone.


20-22.4 Protists

Foraminiferans

Fig. 20-22-13


20-22.4 Protists

Amoebozoans inhabit aquatic and terrestrial environments.• This group moves by extending finger-shaped

pseudopods; they don’t have shells and are composed of the amoebas and the slime molds.

• Amoebas are predators that stalk and engulf prey.

• The dysentery-causing amoeba multiplies in the intestinal wall, triggering severe diarrhea.


20-22.4 Protists

Amoebas

Fig. 20-22-14


20-22.4 Protists

Amoebozoans inhabit aquatic and terrestrial environments (continued).• Slime molds are decomposers that inhabit the

forest floor.• The life cycle goes through two phases: a

mobile feeding stage, and a stationary reproductive stage called a fruiting body.

• There are two kinds of slime molds: acellular and cellular.


20-22.4 Protists

Acellular forms: the organism is a single mass of cytoplasm that may spread over an area of several square yards; this structure is called a plasmodium• Dry conditions stimulate the formation of a

fruiting body, which has haploid spores.

Fig. 20-22-15


20-22.4 Protists

Green algae live mostly in ponds and lakes.• Some forms are small and live in freshwater,

such as Spirogyra, which forms thin filaments from long chains of cells.

Fig. 20-22-20-22


20-22.4 Protists

Green algae live mostly in ponds and lakes (continued).• A marine example, Ulva, or sea lettuce, has

leaves the size of lettuce leaves.• Green algae are important because it is

believed that they were ancestral to the earliest plants.


20-22.5 Plants

What are some of the properties that distinguish plants from other organisms?• Plants have chlorophyll for photosynthesis.• Plant reproduction features alternation of

generations.• Plants have dependent embryos.• Plants have roots or rootlike structures that

anchor it and absorb water and nutrient from the soil.

• Plants have a waxy cuticle that covers the surface of leaves and stems, limiting water loss.


20-22.5 Plants

Two major groups of land plants arose from ancient algal ancestors: the nonvascular plants and the vascular plants.


20-22.5 Plants

Nonvascular plants lack conducting structures, true roots, leaves, or stems.• They have rhizoids that anchor the plant and

bring water and nutrients into the plant body• Body size is limited due to the lack of

conducting tissues, and slow diffusion must distribute water and nutrients throughout the plant body.

• Nonvascular plants include the hornworts, liverworts, and mosses.


20-22.5 Plants

Nonvascular plants

Fig. 20-22-17


20-22.5 Plants

The reproductive structures of nonvascular plants are protected.• An adaptation to terrestrial life is their

enclosed reproductive structures, which prevent the gametes from drying out.

• There are two types of structures, one in which eggs develop and one in which sperm are formed.

• In all vascular plants, the sperm must swim to the egg through a film of water.


20-22.5 Plants

Vascular plants have conducting vessels that also provide support.• The conducting cells of vascular plants are

called vessels, which contain lignin that serve support and conducting functions.

• Vascular plants can grow tall because of vessels, both because of the support these structures provide as well as the conducting of water and nutrients between the roots to the leaves.

• There are two groups of vascular plants: the seedless vascular plants and the seed plants.


20-22.5 Plants

Seedless vascular plants include the club mosses, horsetails, and ferns.• These plants require swimming sperm and

water for reproduction.• They propagate by spores, not seeds.• Their ancestors were larger than present-day

forms, and they dominated the landscape hundreds of millions of years ago.


20-22.5 Plants

Seedless vascular plants

Fig. 20-22-18


20-22.5 Plants

Seed plants dominate the land, aided by two important adaptations: pollen and seeds.• Pollen grains are tiny structures that carry

sperm-producing cells.• Pollen grains are dispersed by wind or by

animal pollinators, such as bees.


20-22.5 Plants

Seeds• Analogous to the eggs of birds and reptiles,

seeds consist of an embryonic plant, a supply of food for the embryo, and a protective outer coat.

• The seed coat keeps the embryo in a state of suspended animation until conditions are good for growth.


20-22.5 Plants

Seed plants are grouped into two general types: gymnosperms, which lack flowers, and angiosperms, the flowering plants.• Gymnosperms evolved earlier than the

flowering plants.


20-22.5 Plants

One group, the conifers, include the pines, firs, spruce, hemlocks, and cypresses that are still very abundant on our planet today.

Fig. 20-22-19a


20-22.5 Plants

The other group of gymnosperms, such as the ginkgos and cycads, have declined to a small remnant of their former range and abundance.

Fig. 20-22-19b,c


20-22.5 Plants

Angiosperms are flowering seed plants.• Three major adaptations have made

angiosperms so successful as plants.

1. Flowers: contain male and female parts of the plant; are used to attract insects as pollinators

2. Fruits: encourage animals to eat the fruit, which contains the fertilized seed of the plant, thus dispersing the plant

3. Broad leaves: collect more sunlight for photosynthesis


20-22.5 Plants

Flowering plants

Fig. 20-22-20


20-22.5 Plants

Animation—Evolution of Plant StructurePLAYPLAY


20-22.6 Fungi

Fungi have distinctive adaptations.• A typical fungus is a mushroom, which is

actually the reproductive part of a more extensive organism.

• Fungi feed off dead material by secreting digestive fluids that break down their food outside of their bodies.


20-22.6 Fungi

Fungi have distinctive adaptations (continued).• The body of a fungus is called a mycelium and

is one-cell thick. • The mycelium is

made up of extensive numbers of filaments called hyphae, which grow across a food source. Fig. 20-22-21

hyphae

(b) Hyphae(a) Mycelium


20-22.6 Fungi

Most fungi can reproduce both sexually and asexually.• Fungi reproduce by

spores that are cast to the wind.

Fig. 20-22-22


20-22.6 Fungi

Most fungi can reproduce both sexually and asexually (continued).• Fungi can reproduce both asexually and

sexually.• Sexual reproduction is reserved for periods of

environmental change or stress.


20-22.6 Fungi

Fungi affect humans and other organisms.• Fungi play a major role in the destruction of

dead plant tissue by being able to digest both lignin and cellulose, the molecules that make up wood.

• Fungi are saprophytes (feeding on dead organisms) and consume the dead of all kingdoms.


20-22.6 Fungi

Fungi affect humans and other organisms (continued).• The activities of fungi and bacteria return

nutrients and minerals to the environment.• Antibiotics—such as penicillin, oleandomycin,

and cephalosporin—are made from fungi to combat bacterial diseases.


20-22.6 Fungi

Fungi make important contributions to gastronomy.• The fungi we consume directly, such as wild

and cultivated mushrooms, make important contributions to human nutrition.

Fig. 20-22-23


20-22.6 Fungi

Fungi make important contributions to gastronomy (continued).• The world’s most famous cheeses—including

Roquefort, Camembert, Stilton, and Gorgonzola—gain their distinct flavors from molds that grow on them as they ripen.

• Other foods and beverages that depend on yeasts for their production are bread, wine, and beer.


20-22.6 Fungi

Fungi attack plants that are important to people.• Fungi cause the majority of plant diseases,

and some of the plants that the infect are important to humans.

• Especially damaging are plant pests called rusts and smuts, which cause billions of dollar’s worth of damage to grain crops annually.


20-22.6 Fungi

Corn smut

Fig. 20-22-24


20-22.6 Fungi

Fungi include parasites that attack humans directly.• Some of these are athlete’s foot, jock itch,

vaginal infections, and ringworm.


20-22.6 Fungi

Fungi can produce toxins.• Molds of the genus Aspergillus produce highly

toxic, carcinogenic compounds known as aflatoxins.

• Some foods, such as peanuts, seem to be especially susceptible to attack by Aspergillus.


20-22.7 Animals

Characteristics of animals• Animals are multicellular.• Animals get their energy by consuming other

organisms.• Animals reproduce sexually.• Animal cells lack a cell wall.• Animals are mobile.• Animals react rapidly to external stimuli.


20-22.7 Animals

For convenience, animals are categorized as either vertebrates (with backbones) or invertebrates (without backbones).• Sponges have a simple body plan, lack

tissues or organs, and are colonies of single-celled organisms.


20-22.7 Animals

Sponges

Fig. 20-22-25


20-22.7 Animals

Sponges (continued)• Water enters through numerous tiny pores in

the body, and leaves through fewer, large openings.

• Oxygen and food is filtered out of the water during passage.

• Reproduction can be asexual through budding, or sexual by the release of eggs and sperm into the water.


20-22.7 Animals

Cnidarians are well-armed predators.• Representatives are jellyfish, corals, and sea

anemones.

Fig. 20-22-26


20-22.7 Animals

Cnidarians are well-armed predators (continued).• Their body parts are arranged in a circle

around the mouth and digestive cavity.• Tentacles are armed with stinging cells that

inject poison into prey and kill it so that it can be eaten.

• Corals form a large calcium carbonate skeleton that can build up over long periods of time and last long after the animal that built it has died.


20-22.7 Animals

Annelids are composed of identical segments.• An example is earthworms with segmented

bodies.• Internally, most of the segments contain

identical copies of nerves, excretory structures, and muscles.

• Representatives are oligochaetes (earthworms), polychaetes (marine worms), and leeches.


20-22.7 Animals

Annelids

Fig. 20-22-27


20-22.7 Animals

Most mollusks have shells.• Snails and slugs are collectively called

gastropods—they crawl on a muscular foot, and many are protected by shells.

• Sea slugs lack shells.• Gastropods feed with a radula, a flexible

ribbon of tissue with spines that scrape algae off rocks.

• A few gastropod species live on land and use a simple lung for breathing.


20-22.7 Animals

Gastropod mollusks

Fig. 20-22-28


20-22.7 Animals

Bivalves are filter feeders.• Scallops, oysters, mussels, and clams are

bivalves.• Bivalves have two shells connected by a hinge.

Fig. 20-22-29


20-22.7 Animals

Bivalves are filter feeders (continued).• They use a muscular foot for burrowing in

sand or mud.• Scallops lack a foot and move by jet

propulsion, achieved by flapping their shells together.

• Water is circulated over the gills, which are covered with mucus that traps food particles and conveys them to the mouth.


20-22.7 Animals

Cephalopods are marine predators.• All cephalopods are predatory carnivores, and

all are marine.• Their foot is developed into tentacles that are

used for detecting and grasping prey. • This group has highly developed brains and

sensory systems.


20-22.7 Animals

The cephalopods include octopuses, nautiluses, cuttlefish, and squids

Fig. 20-22-30


20-22.7 Animals

Arthropods are the dominant animals on Earth.• The Arthropoda includes the insects,

arachnids, and crustaceans.• They all have an exoskeleton; in insects, the

body is divided into three parts: head, thorax, and abdomen.

• Insects are the only flying invertebrates.


20-22.7 Animals

Insects

Fig. 20-22-31


20-22.7 Animals

Arthropods are the dominant animals on Earth (continued).• During their development, insects undergo

metamorphosis, a radical change from a juvenile body form to an adult body form.

• The immature stage of the insect is referred to as a larva, which grows until it reaches maximum size.

• It then forms a nonfeeding stage called a pupa.• An adult emerges from the pupa.


20-22.7 Animals

Most arachnids are predatory meat eaters.• They have eight walking legs and are

carnivorous, feeding on a liquid diet of blood or predigested prey.

• Spiders produce silk from special glands in their abdomens, which they us to build webs to capture prey and to wrap up the prey once it is caught.

• Spider silk is amazingly strong; it can be stronger than steel wire of the same size, but is as elastic as rubber.


20-22.7 Animals

The arachnids include spiders, mites, ticks, and scorpions.

Fig. 20-22-32


20-22.7 Animals

Most crustaceans are aquatic.• The crustaceans include crabs, crayfish,

lobster, shrimp, and barnacles; they only live in the water.

• Crustaceans have two pairs of sensory antennae, but the remaining appendages vary with habitat and lifestyle of the species.


20-22.7 Animals

Crustaceans

Fig. 20-22-33


20-22.7 Animals

The chordates include both invertebrates and vertebrates.


20-22.7 Animals

All chordates have the following features.• The notochord: a stiff, flexible rod that extends

the length of the body and provides attachment for muscles

• The nerve cord: a dorsal hollow tube; one end becomes the brain during development

• Pharyngeal gill slits: these may develop into functional gills or just remain as grooves in early development

• A post-anal tail: extends beyond the body, past the anus


20-22.7 Animals

The invertebrate chordates live in the seas.• The invertebrate

chordates are the lancelets and the tunicates.

Fig. 20-22-34


20-22.7 Animals

The invertebrate chordates live in the seas (continued).• Larvae of lancelets lack a backbone, but the

adults possess all four chordate features.• The tunicates (sea squirts) have a larva that

swims and has all chordate features.• Adults are attached to the sea bottom and do

not move.


20-22.7 Animals

Vertebrates have a backbone.• In vertebrates, the embryonic notochord is

normally replaced during development by a backbone, or vertebral column.

• Vertebrates are represented by fish, amphibians, reptiles, birds, and mammals; there are more ray-finned fishes than any of the other vertebrate groups.


20-22.7 Animals

Ray-finned fishes

Fig. 20-22-35


20-22.7 Animals

Ray-finned fish are an important food source for humans.• Overfishing has sharply reduced the size of

the fish populations in the oceans today; some fish species have been reduced to 10% of their numbers when commercial fishing started.


20-22.7 Animals

The amphibians straddle the boundary between aquatic and terrestrial existence.• Amphibians have a three-chambered heart.• Amphibian lungs are poorly developed and

have to be supplemented by skin respiration.• Amphibians are tied to the water for

reproduction; many undergo metamorphosis with aquatic larval forms and terrestrial adults.


20-22.7 Animals

Amphibians

Fig. 20-22-36


20-22.7 Animals

The reptiles include lizards, snakes, turtles, alligators, and crocodiles.• Many species are completely independent of

water as a result of three adaptations:• Evolution of a tough, scaly skin that resists

water loss and protects the body• Evolution of internal fertilization• Evolution of a shelled egg


20-22.7 Animals

Reptiles

Fig. 20-22-37


20-22.7 Animals

One very distinctive group of reptiles is the birds.• Birds have developed feathers, which are

highly specialized versions of reptilian body scales.

• Modern birds retain scales on their legs, evidence of the ancestry they share with the reptiles.

• Birds have hollow bones for flight, and produce a shelled egg.


20-22.7 Animals

Birds

Fig. 20-22-38


20-22.7 Animals

One branch of reptiles gave rise to a group that evolved hair and diverged to form the mammals.• Mammals are named for the milk-producing

mammary glands used by female members of the group to suckle their young.

• In most mammals, fur protects and insulates the warm body.

• The mammals are divided into three groups: montremes, marsupials, and placentals.


20-22.7 Animals

Monotremes are found only in Australia and New Guinea, and include the platypus and two species of spiny anteaters, also known as echidnas.

Monotremes lay eggs.

Fig. 20-22-39a


20-22.7 Animals

All mammals except monotremes have embryos that develop in the uterus of the female reproductive tract.• In marsupials, embryos are only in the uterus

for a short time and are then born at a very immature stage of development.

• Immediately after birth, they crawl to a nipple, firmly grasp it, and complete their development.

• In many marsupial species, this postbirth development takes place in a protective pouch.


20-22.7 Animals

Marsupials

Fig. 20-22-39b


20-22.7 Animals

Most mammal species are placental mammals.• Compared to marsupials, placental mammals

retain their young in the uterus for a much longer period, so that offspring complete their embryonic development before being born.

• The bat, mole, impala, whale, seal, monkey, and cheetah exemplify the radiation of mammals into nearly all habitats, with bodies adapted to their varied lifestyles.

• The largest group of placental mammals are the bats and rodents.


20-22.7 Animals

Placental mammals

Fig. 20-22-39c,d

Date post:	16-Aug-2015
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