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Table of Contents – pages iii. Unit 1: What is Biology? Unit 2: Ecology Unit 3: The Life of a Cell Unit 4: Genetics Unit 5: Change Through Time Unit 6: Viruses, Bacteria, Protists, and Fungi Unit 7: Plants Unit 8: Invertebrates Unit 9: Vertebrates Unit 10: The Human Body.

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Table of contents pages iii

Table of Contents – pages iii

Unit 1:What is Biology?

Unit 2:Ecology

Unit 3:The Life of a Cell

Unit 4:Genetics

Unit 5:Change Through Time

Unit 6:Viruses, Bacteria, Protists, and Fungi

Unit 7:Plants

Unit 8:Invertebrates

Unit 9:Vertebrates

Unit 10:The Human Body


Table of contents pages vii xiii

Table of Contents – pages vii-xiii

Unit 1: What is Biology?

Chapter 1:Biology: The Study of Life

Unit 2: Ecology

Chapter 2:Principles of Ecology

Chapter 3:Communities and Biomes

Chapter 4:Population Biology

Chapter 5:Biological Diversity and Conservation

Unit 3:The Life of a Cell

Chapter 6:The Chemistry of Life

Chapter 7:A View of the Cell

Chapter 8:Cellular Transport and the Cell Cycle

Chapter 9:Energy in a Cell


Table of contents pages vii xiii1

Unit 4: Genetics

Chapter 10:Mendel and Meiosis

Chapter 11:DNA and Genes

Chapter 12:Patterns of Heredity and Human Genetics

Chapter 13:Genetic Technology

Unit 5: Change Through Time

Chapter 14:The History of Life

Chapter 15:The Theory of Evolution

Chapter 16:Primate Evolution

Chapter 17:Organizing Life’s Diversity

Table of Contents – pages vii-xiii


Table of contents pages vii xiii2

Unit 6: Viruses, Bacteria, Protists, and Fungi

Chapter 18:Viruses and Bacteria

Chapter 19:Protists

Chapter 20:Fungi

Unit 7: Plants

Chapter 21:What Is a Plant?

Chapter 22:The Diversity of Plants

Chapter 23:Plant Structure and Function

Chapter 24:Reproduction in Plants

Table of Contents – pages vii-xiii


Table of contents pages vii xiii3

Table of Contents – pages vii-xiii

Unit 8: Invertebrates

Chapter 25:What Is an Animal?

Chapter 26:Sponges, Cnidarians, Flatworms, and Roundworms

Chapter 27:Mollusks and Segmented Worms

Chapter 28:Arthropods

Chapter 29:Echinoderms and Invertebrate Chordates


Table of contents pages vii xiii4

Table of Contents – pages vii-xiii

Unit 9: Vertebrates

Chapter 30:Fishes and Amphibians

Chapter 31:Reptiles and Birds

Chapter 32:Mammals

Chapter 33:Animal Behavior

Unit 10: The Human Body

Chapter 34:Protection, Support, and Locomotion

Chapter 35:The Digestive and Endocrine Systems

Chapter 36:The Nervous System

Chapter 37:Respiration, Circulation, and Excretion

Chapter 38:Reproduction and Development

Chapter 39:Immunity from Disease


Unit overview pages 670 671

Sponges, Cnidarians, Flatworms, and Roundworms

Unit Overview – pages 670-671

What Is an Animal?

Sponges, Cnidarians, Flatworms, and Roundworms

Mollusks and Segmented Worms

Arthropods

Echinoderms and Invertebrate Chordates


Chapter contents page xi

Chapter Contents – page xi

Chapter 26Sponges, Cnidarians, Flatworms, and Roundworms

26.1:Sponges

26.1:Section Check

26.2:Cnidarians

26.2:Section Check

26.3:Flatworms

26.3:Section Check

26.4:Roundworms

26.4:Section Check

Chapter 26Summary

Chapter 26Assessment


Chapter intro page 692

Chapter Intro-page 692

What You’ll Learn

You will identify and compare and contrast the characteristics of sponges, cnidarians, flatworms, and roundworms.

You will describe and evaluate the significance of sponge, cnidarian, flatworm, and roundworm adaptations.


26 1 section objectives page 693

26.1 Section Objectives – page 693

Section Objectives:

  • Relate the sessile life of sponges to their food-gathering adaptations.

  • Describe the reproductive adaptations of sponges.


Section 26 1 summary pages 693 697

Section 26.1 Summary – pages 693-697

What is a sponge?

  • Sponges are asymmetrical aquatic animals that have a variety of colors, shapes, and sizes.

  • Many are bright shades of red, orange, yellow, and green.


Section 26 1 summary pages 693 6971

Section 26.1 Summary – pages 693-697

What is a sponge?

  • Although sponges do not resemble more familiar animals, they carry on the same life processes as all animals.


Section 26 1 summary pages 693 6972

Section 26.1 Summary – pages 693-697

Sponges are pore-bearers

  • Sponges are classified in the invertebrate phylum Porifera, which means “pore bearer.”

  • Most live in marine biomes, but about 150 species can be found in freshwater environments.


Section 26 1 summary pages 693 6973

Section 26.1 Summary – pages 693-697

Sponges are pore-bearers

Water out

  • Sponges are mainly sessile organisms.

Central

cavity

  • Because most adult sponges can’t travel in search of food, they get their food by a process called filter feeding.

Water

in


Section 26 1 summary pages 693 6974

Section 26.1 Summary – pages 693-697

Sponges are pore-bearers

Water out

  • Filter feeding is a method in which an organism feeds by filtering small particles of food from water that pass by or through some part of the organism.

Central

cavity

Water

in


Section 26 1 summary pages 693 6975

Section 26.1 Summary – pages 693-697


Section 26 1 summary pages 693 6976

Section 26.1 Summary – pages 693-697

Cell organization in sponges

  • For some sponge species, if you took a living sponge and put it through a sieve, not only would the sponge’s cells be alive and separated out, but these cells would come together to form new sponges.

  • It can take several weeks for the sponge’s cells to reorganize themselves.


Section 26 1 summary pages 693 6977

Section 26.1 Summary – pages 693-697

Cell organization in sponges

  • Many biologists hypothesize that sponges evolved directly from colonial, flagellated protists, such as Volvox.

Volvox


Section 26 1 summary pages 693 6978

Section 26.1 Summary – pages 693-697

Cell organization in sponges

  • More importantly, sponges exhibit a major step in the evolution of animals—the change from unicellular life to a division of labor among groups of organized cells.


Section 26 1 summary pages 693 6979

Section 26.1 Summary – pages 693-697

Reproduction in sponges

  • Sponges can reproduce asexually and sexually.

  • Depending on the species, asexual reproduction can be by budding, fragmentation, or the formation of gemmules.


Section 26 1 summary pages 693 69710

Section 26.1 Summary – pages 693-697

Reproduction in sponges

  • An external growth, called a bud, can form on a sponge.

  • If a bud drops off, it can float away, settle, and grow into a sponge.

  • Sometimes, buds do not break off. When this occurs, a colony of sponges forms.

  • Often, fragments of a sponge break off and grow into new sponges.


Section 26 1 summary pages 693 69711

Section 26.1 Summary – pages 693-697

Reproduction in sponges

  • Some freshwater sponges produce seedlike particles, called gemmules, in the fall when waters cool.

  • The adult sponges die over the winter, but the gemmules survive and grow into new sponges in the spring when waters warm.


Section 26 1 summary pages 693 69712

Section 26.1 Summary – pages 693-697

Reproduction in sponges

  • Most sponges reproduce sexually.

  • Some sponges have separate sexes, but most sponges are hermaphrodites. A hermaphrodite (hur MAF ruh dite) is an animal that can produce both eggs and sperm.


Section 26 1 summary pages 693 69713

Section 26.1 Summary – pages 693-697

Reproduction in sponges

  • Eggs and sperm form from amoebocytes.

  • During reproduction, sperm released from one sponge can be carried by water currents to another sponge, where fertilization can occur.


Section 26 1 summary pages 693 69714

Section 26.1 Summary – pages 693-697

Reproduction in sponges

  • Fertilization in sponges may be either external or internal.

  • A few sponges have external fertilization—fertilization that occurs outside the animal’s body.

  • Most sponges have internal fertilization, in which eggs inside the animal’s body are fertilized by sperm carried into the sponge with water.


Section 26 1 summary pages 693 69715

Section 26.1 Summary – pages 693-697

Egg

cell

Sperm

cells

Flagella

Larvae

New sponge


Section 26 1 summary pages 693 69716

Section 26.1 Summary – pages 693-697

Reproduction in sponges

  • In sponges, the collar cells collect and transfer sperm to amoebocytes.

  • The amoebocytes then transport the sperm to ripe eggs.


Section 26 1 summary pages 693 69717

Section 26.1 Summary – pages 693-697

Support and defense systems in sponges

  • Sponges are soft-bodied invertebrates, that can be found at depths of about 8500 m.

  • Their internal structure gives them support and can help protect them from predators.


Section 26 1 summary pages 693 69718

Section 26.1 Summary – pages 693-697

Support and defense systems in sponges

  • Some sponges have sharp, hard spicules located between the cell layers.

  • Spicules may be made of glasslike material or of calcium carbonate.

Spicules


Section 26 1 summary pages 693 69719

Section 26.1 Summary – pages 693-697

Support and defense systems in sponges

  • Other sponges have an internal framework made of silica or of spongin, a fibrous protein-like material.

  • Sponges can be classified according to the shape and makeup of their spicules and/or frameworks.


Section 26 1 summary pages 693 69720

Section 26.1 Summary – pages 693-697

Support and defense systems in sponges

  • Besides sharp spicules, some sponges may have other methods of defense.

  • Some sponges contain chemicals that are toxic to fishes and to other predators.


Section 1 check

Section 1 Check

Question 1

What is the major evolutionary step in animals that sponges exhibit?


Section 1 check1

Section 1 Check

Sponges are the first animals to exhibit the change from a unicellular life to a division of labor among groups of organized cells.


Section 1 check2

Section 1 Check

Question 2

In sponges, where do fertilized eggs develop into zygotes?

A. in the sponge’s osculum

B. in the pore cells

C. in the collar cells

D. in the jelly between the cell layers


Section 1 check3

Section 1 Check

The answer is D, in the jelly between the cell layers.


Section 1 check4

Section 1 Check

Question 3

How many layers of cells make up a sponge?

A. two

B. three

C. four

D. five

The answer is A, two.


26 2 section objectives page 698

26.2 Section Objectives – page 698

Section Objectives

  • Analyze the relationships among the classes of cnidarians.

  • Sequence the stages in the life cycle of a cnidarian.

  • Evaluate the adaptations of cnidarians for obtaining food.


Section 26 2 summary pages 698 705

Section 26.2 Summary – pages 698-705

What is a cnidarian?

  • Cnidarians (ni DARE ee uns) are a group of invertebrates made up of more than 9000 species of jellyfishes, corals, sea anemones, and hydras.

  • They can be found worldwide, and all but a few cnidarians live in marine biomes.


Section 26 2 summary pages 698 7051

Section 26.2 Summary – pages 698-705

Body structure

Mouth

Tentacle

  • A cnidarian’s body is radially symmetrical. It has one body opening and is made up of two layers of cells.

Cavity

Inner cell layer

Jellylike layer

Bud

Outer cell layer

Disc


Section 26 2 summary pages 698 7052

Section 26.2 Summary – pages 698-705

Body structure

Mouth

  • The two cell layers are organized into tissues with specific functions.

Tentacle

Cavity

Inner cell layer

  • The inner layer is adapted mainly to assist in digestion.

Jellylike layer

Bud

Outer cell layer

Disc


Section 26 2 summary pages 698 7053

Section 26.2 Summary – pages 698-705

Body structure

  • Because a cnidarian’s body is only two layers of cells, no cell is ever far from water.

  • Oxygen dissolved in water can diffuse directly into body cells.

  • Carbon dioxide and other wastes can move out of a cnidarian’s body cells directly into the surrounding water.


Section 26 2 summary pages 698 7054

Section 26.2 Summary – pages 698-705

A Cnidarian

  • Cnidarians display a remarkable variety of colors, shapes and sizes. Some can be as small as the tip of a pencil.

  • Most cnidarians have two distinct body forms during their life cycles.

  • A polyp is the sessile form of a cnidarian. Its mouth is surrounded by tentacles.

  • Examples of polyps include sea anemones, corals, and hydras.


Section 26 2 summary pages 698 7055

Section 26.2 Summary – pages 698-705


Section 26 2 summary pages 698 7056

Section 26.2 Summary – pages 698-705

Body form

  • Most cnidarians undergo a change in body form during their life cycles.

Polyp

Medusa


Section 26 2 summary pages 698 7057

Section 26.2 Summary – pages 698-705

Body form

  • There are two body forms, the polyp and the medusa.

Polyp

Medusa


Section 26 2 summary pages 698 7058

Section 26.2 Summary – pages 698-705

Body form

  • In cnidarians, one body form may be more observable than the other. In jellyfishes, the medusa is the body form usually observed.

  • The polyp is the familiar body form of hydras.


Section 26 2 summary pages 698 7059

Section 26.2 Summary – pages 698-705

Reproduction in cnidarians

  • All cnidarians have the ability to reproduce sexually and asexually.

  • Sexual reproduction occurs in only one phase of the life cycle.

  • It usually occurs in the medusa stage, unless there is no medusa stage then the polyp can reproduce sexually.


Section 26 2 summary pages 698 70510

Section 26.2 Summary – pages 698-705


Section 26 2 summary pages 698 70511

Section 26.2 Summary – pages 698-705

Digestion in cnidarians

  • Cnidarians are predators that capture or poison their prey using nematocysts.

  • A nematocyst (nih MA tuh sihst) is a capsule that contains a coiled, threadlike tube.

  • The tube may be sticky or barbed, and it may contain toxic substances.

  • Nematocysts are located in stinging cells that are on tentacles.


Section 26 2 summary pages 698 70512

Section 26.2 Summary – pages 698-705

Digestion in cnidarians

  • Once captured by nematocysts, prey is brought to the mouth by contraction of the tentacles.

Mouth

Gastrovascular cavity

Polyp

Mouth

Medusa


Section 26 2 summary pages 698 70513

Hydra eating daphnia

Section 26.2 Summary – pages 698-705

Digestion in cnidarians

  • The inner cell layer of cnidarians surrounds a space called a gastrovascular (gas troh VAS kyuh lur) cavity.

  • Cells adapted for digestion line the gastrovascular cavity and release enzymes over captured prey. Any undigested materials are ejected back out through the mouth.


Section 26 2 summary pages 698 70514

Section 26.2 Summary – pages 698-705

Nervous system in cnidarians

  • A cnidarian has a simple nervous system without a control center, such as a brain like that of other animals.

  • In cnidarians, the nervous system consists of a nerve net that conducts impulses to and from all parts of the body.

  • The impulses from the nerve net cause contractions of musclelike cells in the two cell layers.


Section 26 2 summary pages 698 70515

Section 26.2 Summary – pages 698-705

Diversity of Cnidarians

There are four classes of cnidarians:

  • Hydrozoa, Scyphozoa, Cubozoa, and Anthozoa. Cubozoans once were classified as scyphozoans.


Section 26 2 summary pages 698 70516

Section 26.2 Summary – pages 698-705

Most hydrozoans form colonies

  • The class Hydrozoa includes two groups—the hydroids, such as hydra, and the siphonophores, including the Portuguese man-of-war.

  • Most hydroids are marine animals that consist of branching polyp colonies formed by budding, and are found attached to pilings, shells, and other surfaces.


Section 26 2 summary pages 698 70517

Section 26.2 Summary – pages 698-705

Most hydrozoans form colonies

  • The siphonophores include floating colonies that drift about on the ocean’s surface.

  • The Portuguese man-of-war, Physalia, is an example of a siphonophore hydrozoan colony.

  • Each individual in a Physalia colony has a function that helps the entire organism survive.


Section 26 2 summary pages 698 70518

Section 26.2 Summary – pages 698-705

Scyphozoans are the jellyfishes

  • The fragile and sometimes luminescent bodies of jellyfishes can be beautiful.

  • Some jellyfishes are transparent, but others are pink, blue, or orange.

  • The medusa form is the dominant stage in this class.


Section 26 2 summary pages 698 70519

Section 26.2 Summary – pages 698-705

Scyphozoans are the jellyfishes

  • The gastrovascular cavity of scyphozoans has four internal divisions.

  • Like other cnidarians, scyphozoans have musclelike cells in their outer cell layer that can contract. When these cells contract together, the bell contracts, which propels the animal through the water.


Section 26 2 summary pages 698 70520

Section 26.2 Summary – pages 698-705

Most anthozoans build coral reefs

  • Anthozoans are cnidarians that exhibit only the polyp form.

  • All anthozoans have many incomplete divisions in their gastrovascular cavities.

Sea Anemone


Section 26 2 summary pages 698 70521

Section 26.2 Summary – pages 698-705

Most anthozoans build coral reefs

  • Sea anemones are anthozoans that live as individual animals, and are thought to live for centuries.

Sea Anemone


Section 26 2 summary pages 698 70522

Section 26.2 Summary – pages 698-705

Most anthozoans build coral reefs

  • Corals are anthozoans that live in colonies of polyps in warm ocean waters around the world.

  • They secrete protective, cuplike calcium carbonate shelters around their soft bodies.

  • Colonies of many coral species build the beautiful coral reefs that provide food and shelter for many other marine species.


Section 26 2 summary pages 698 70523

Section 26.2 Summary – pages 698-705

Most anthozoans build coral reefs

  • Corals that form reefs are known as hard corals.

  • Other corals are known as soft corals because they do not build such structures.


Section 26 2 summary pages 698 70524

Section 26.2 Summary – pages 698-705

Most anthozoans build coral reefs

  • The living portion of a coral reef is a thin, fragile layer that grows on top of the shelters left behind by previous generations.


Section 26 2 summary pages 698 70525

Section 26.2 Summary – pages 698-705

Most anthozoans build coral reefs

  • Although corals are often found in relatively shallow, nutrient-poor waters, they thrive because of their symbiotic relationship with microscopic, photosynthetic protists called zooxanthellae (zoh oh zan THEH lee).


Section 26 2 summary pages 698 70526

Section 26.2 Summary – pages 698-705

Most anthozoans build coral reefs

  • The zooxanthellae produce oxygen and food that the corals use, while using carbon dioxide and waste materials produced by the corals.

  • These protists are primarily responsible for the bright colors found in coral reefs.


Section 26 2 summary pages 698 70527

Section 26.2 Summary – pages 698-705

Most anthozoans build coral reefs

  • Because the zooxanthellae are free-swimming, they sometimes leave the corals.

  • Corals without these protists often die.


Section 26 2 summary pages 698 70528

Section 26.2 Summary – pages 698-705

Origins of Sponges and Cnidarians

  • The earliest fossil evidence for sponges dates this group to late in the Precambrian, about 650 million years ago.

  • The earliest known cnidarians also date to the Precambrian, about 630 million years ago.


Section 26 2 summary pages 698 70529

Section 26.2 Summary – pages 698-705

Origins of Sponges and Cnidarians


Section 26 2 summary pages 698 70530

Section 26.2 Summary – pages 698-705

Origins of Sponges and Cnidarians

  • The earliest coral species were not reef builders, so reefs cannot be used to date early cnidarians.

  • The larval form of cnidarians resembles protists, and because of this, scientists consider cnidarians to have evolved from protists.


Section 2 check

Section 2 Check

Question 1

Which of the following features is NOT common to both sponges and cnidarians?

A. body made up of two layers of cells

B. radial symmetry

C. sessile

D. reproduce both sexually and asexually

The answer is B.


Section 2 check1

Section 2 Check

Question 2

Explain the difference between the ways cnidarians and sponges take in food.

Answer

Sponges passively filter food particles from the water when the particles flow through the sponge. Cnidarians actively seek food with tentacles that capture or paralyze the prey and take it to the cnidarian’s mouth for ingestion.


Section 2 check2

Section 2 Check

Question 3

Explain how each of the two forms in the figure below benefits from contractions of muscle-like cells caused by impulses from its nerve net.

Mouth

Gastrovascular cavity

Polyp

Mouth

Medusa


Section 2 check3

Section 2 Check

In the sessile polyp form, cell contractions cause tentacles to move prey toward the mouth. In the free-swimming form, cell contractions help the medusa to swim and find food.

Mouth

Gastrovascular cavity

Polyp

Mouth

Medusa


Section 2 check4

Section 2 Check

Question 4

Which of the following is NOT true of cnidarian budding?

A. it can form colonies of individuals

B. it produces clones of the parents

C. it produces haploid organisms

D. it is part of asexual reproduction


Section 2 check5

Section 2 Check

The answer is C. Budding produces diploid organisms.


26 3 section objectives page 706

26.3 Section Objectives – page 706

Section Objectives:

  • Distinguish between the structural adaptations of parasitic flatworms and free-living planarians.

  • Explain how parasitic flatworms are adapted to their way of life.


Section 26 3 summary pages 706 710

Section 26.3 Summary– pages 706-710

What is a flatworm?

  • The least complex worms belong to the phylum Platyhelminthes (pla tee HEL min theez).

  • These flatworms are acoelomates with thin, solid bodies.

Planarian


Section 26 3 summary pages 706 7101

Section 26.3 Summary– pages 706-710

What is a flatworm?

  • There are approximately 14,500 species of flatworms found in marine and freshwater environments and in moist habitats on land.

Planarian


Section 26 3 summary pages 706 7102

Section 26.3 Summary– pages 706-710

What is a flatworm?

  • The most well-known members of this phylum are the parasitic tapeworms and flukes, which cause diseases in other animals, among them frogs and humans.

  • The most commonly studied flatworms in biology classes are the free-living planarians.


Section 26 3 summary pages 706 7103

Section 26.3 Summary– pages 706-710

Nervous control in planarians

  • Most of a planarian’s nervous system is located in its head—a characteristic common to other bilaterally symmetrical animals.

Nerve cell mass


Section 26 3 summary pages 706 7104

Section 26.3 Summary– pages 706-710

Nervous control in planarians

  • Some flatworms have a nerve net, and others have the beginnings of a central nervous system.

Nerve cell mass


Section 26 3 summary pages 706 7105

Section 26.3 Summary– pages 706-710

Nervous control in planarians

  • A planarian’s nervous system includes two nerve cords that run the length of the body.

Ganglia

Eyespots

Nerve cord

Muscle cells


Section 26 3 summary pages 706 7106

Section 26.3 Summary– pages 706-710

Nervous control in planarians

  • It also includes eyespots that can detect the presence or absence of light and sensory cells that can detect chemicals and movement in water.

Ganglia

Eyespots

Nerve cord

Muscle cells


Section 26 3 summary pages 706 7107

Section 26.3 Summary– pages 706-710

Nervous control in planarians

  • At the anterior end of the nerve cord is a small swelling called a ganglion (plural, ganglia). The ganglion receives messages from the eyespots and sensory pits, then communicates with the rest of the body along the nerve cords.

Ganglia

  • Messages from the nerve cords trigger responses in a planarian’s muscle cells.


Section 26 3 summary pages 706 7108

Section 26.3 Summary– pages 706-710

Reproduction in planarians

  • Like many of the organisms studied in this chapter, most flatworms including planarians, are hermaphrodites.

  • During sexual reproduction, individual planarians exchange sperm, which travel along special tubes to reach the eggs.


Section 26 3 summary pages 706 7109

Section 26.3 Summary– pages 706-710

Reproduction in planarians

  • Fertilization occurs internally. The zygotes are released in capsules into the water, where they hatch into tiny planarians.


Section 26 3 summary pages 706 71010

Section 26.3 Summary– pages 706-710

A Planarian

  • Planarians have many characteristics common to all species of flatworms.

  • The bodies of planarians are flat, with both a dorsal and a ventral surface. All flatworms have bilateral symmetry.


Section 26 3 summary pages 706 71011

Section 26.3 Summary– pages 706-710


Section 26 3 summary pages 706 71012

Section 26.3 Summary– pages 706-710

Reproduction in planarians

  • Planarians also can reproduce asexually.

  • When a planarian is damaged, it has the ability to regenerate, or regrow, new body parts. Regeneration is the replacement or regrowth of missing body parts.


Section 26 3 summary pages 706 71013

Section 26.3 Summary– pages 706-710

Reproduction in planarians

  • If a planarian is cut horizontally, the section containing the head will grow a new tail, and the tail section will grow a new head.


Section 26 3 summary pages 706 71014

Section 26.3 Summary– pages 706-710

Reproduction in planarians

  • Thus, a planarian that is damaged or cut into two pieces may grow into two new organisms—a form of asexual reproduction.


Section 26 3 summary pages 706 71015

Section 26.3 Summary– pages 706-710

Feeding and digestion in planarians

  • A planarian feeds on dead or slow-moving organisms.

Extended

pharynx

  • It extends a tube-like, muscular organ, called the pharynx (FAHR inx), out of its mouth. Enzymes released by the pharynx begin digesting food outside the animal’s body.


Section 26 3 summary pages 706 71016

Section 26.3 Summary– pages 706-710

Feeding and digestion in planarians

  • Food particles are sucked into the digestive tract, where they are broken up.

  • Cells lining the digestive tract obtain food by endocytosis.

  • Food is thus digested in individual cells.


Section 26 3 summary pages 706 71017

Section 26.3 Summary– pages 706-710

Feeding and digestion in parasitic flatworms

Hooks

  • A parasite is an organism that lives on or in another organism and depends upon that host organism for its food.

Scolex

Sucker

Proglottid

  • Parasitic flatworms have mouthparts with hooks that keep the flatworm firmly attached inside its host.

Mature proglottid

with fertilized eggs


Section 26 3 summary pages 706 71018

Section 26.3 Summary– pages 706-710

Feeding and digestion in parasitic flatworms

  • They do not need to move to seek out or find food.

  • Parasitic flatworms do not have complex nervous or muscular tissue.


Section 26 3 summary pages 706 71019

Section 26.3 Summary– pages 706-710

Tapeworm bodies have sections

Hooks

  • The body of a tapeworm is made up of a knob-shaped head called a scolex (SKOH leks), and detachable, individual sections called proglottids.

Scolex

Sucker

Proglottid

Mature proglottid

with fertilized eggs


Section 26 3 summary pages 706 71020

Section 26.3 Summary– pages 706-710

Tapeworm bodies have sections

Hooks

  • A proglottid (proh GLAH tihd) contains muscles, nerves, flame cells, and male and female reproductive organs.

Scolex

Sucker

Proglottid

Mature proglottid

with fertilized eggs


Section 26 3 summary pages 706 71021

Section 26.3 Summary– pages 706-710

Tapeworm bodies have sections

  • Some adult tapeworms that live in animal intestines can be more than 10 m in length and consist of 2000 proglottids.


Section 26 3 summary pages 706 71022

Section 26.3 Summary– pages 706-710

The life cycle of a fluke

  • A fluke is a parasitic flatworm that spends part of its life in the internal organs of a vertebrate, such as a human or sheep.

  • It obtains its nutrition by feeding on cells, blood, and other fluids of the host organism.


Section 26 3 summary pages 706 71023

Section 26.3 Summary– pages 706-710

The life cycle of a fluke

Adult flukes

Larva

Embryos

released

Human

host

Snail host

Larva


Section 26 3 summary pages 706 71024

Section 26.3 Summary– pages 706-710

The life cycle of a fluke

  • Blood flukes of the genus Schistosoma cause a disease in humans known as schistosomiasis.

  • Schistosomiasis is common in countries where rice is grown.

  • Blood flukes are common where the secondary host, snails, also are found.


Section 3 check

Section 3 Check

Question 1

In order to survive and reproduce, a parasite must have a _______.

A. pharynx

B. proglottid

C. scolex

D. host


Section 3 check1

Section 3 Check

The answer is D, host.


Section 3 check2

Section 3 Check

Question 2

Explain the way planarians can reproduce asexually.


Section 3 check3

Section 3 Check

When a planarian is damaged, it can regenerate new body parts. It can also regenerate new organisms if cut into separate pieces.


26 4 section objectives page 711

26.4 Section Objectives – page 711

Section Objectives:

  • Compare and contrast the structural adaptations of roundworms and flatworms.

  • Identify the characteristics of four roundworm parasites.


Section 26 4 summary pages 711 713

Section 26.4 Summary– pages 711-713

What is a roundworm?

  • Roundworms belong to the phylum Nematoda.

  • They are widely distributed, living in soil, animals, and both freshwater and marine environments.

  • Most roundworm species are free-living, but many are parasitic.

Roundworm


Section 26 4 summary pages 711 7131

Section 26.4 Summary– pages 711-713

What is a roundworm?

  • Roundworms are tapered at both ends.

  • They have a thick outer covering, which they shed four times as they grow, that protects them in harsh environments.

Intestine

Anus

Mouth

Round body

shape


Section 26 4 summary pages 711 7132

Section 26.4 Summary– pages 711-713

What is a roundworm?

  • They lack circular muscles but have lengthwise muscles.

  • As one muscle contracts, another muscle relaxes. This alternating contraction and relaxation of muscles causes roundworms to move in a thrashing fashion.


Section 26 4 summary pages 711 7133

Section 26.4 Summary– pages 711-713

What is a roundworm?

  • Roundworms have a pseudocoelom and are the simplest animals with a tubelike digestive system.

  • Roundworms have two body openings—a mouth and an anus.

Intestine

Anus

Mouth

Round body

shape


Section 26 4 summary pages 711 7134

Section 26.4 Summary– pages 711-713

What is a roundworm?

  • The free-living species have well-developed sense organs, such as eyespots, although these are reduced in parasitic forms.

Intestine

Anus

Mouth

Round body

shape


Section 26 4 summary pages 711 7135

Section 26.4 Summary– pages 711-713

Diversity of Roundworms

  • Approximately half of the described roundworm species are parasites, and about 50 species infect humans.


Section 26 4 summary pages 711 7136

Section 26.4 Summary– pages 711-713

Roundworm parasites of humans

  • Infection by Ascaris (ASS kuh ris) is the most common roundworm infection in humans.

  • Children become infected more often than adults do.

  • Eggs of Ascaris are found in soil and enter a human’s body through the mouth.


Section 26 4 summary pages 711 7137

Section 26.4 Summary– pages 711-713

Roundworm parasites of humans

  • The eggs hatch in the intestines, move into the bloodstream, and eventually to the lungs, where they are coughed up, swallowed, and begin the cycle again.


Section 26 4 summary pages 711 7138

Section 26.4 Summary– pages 711-713

Roundworm parasites of humans

  • Pinworms are the most common human roundworm parasites in the United States.

  • Pinworms are highly contagious because eggs can survive for up to two weeks on surfaces.


Section 26 4 summary pages 711 7139

Section 26.4 Summary– pages 711-713

Roundworm parasites of humans

  • Its life cycle begins when live eggs are ingested. They mature in the host’s intestinal tract.

  • Female pinworms exit the host’s anus—usually as the host cell sleeps—and lay eggs on nearby skin.

  • These eggs fall onto bedding or other surfaces.


Section 26 4 summary pages 711 71310

Section 26.4 Summary– pages 711-713

Roundworm parasites of humans

  • Trichinella causes a disease called trichinosis (tri keh NOH sis).

  • This roundworm can be ingested in raw or undercooked pork, pork products, or wild game.

Trichinella


Section 26 4 summary pages 711 71311

Section 26.4 Summary– pages 711-713

Roundworm parasites of humans

  • Hookworm infections are common in humans in warm climates where they walk on contaminated soil in bare feet.

  • Hookworms cause people to feel weak and tired due to blood loss.


Section 26 4 summary pages 711 71312

Section 26.4 Summary– pages 711-713

Roundworm parasites of other organisms

  • Nematodes can infect and kill pine trees, cereal crops, and food plants such as potatoes.

  • They are particularly attracted to plant roots and cause a slow decline of the plant.


Section 26 4 summary pages 711 71313

Section 26.4 Summary– pages 711-713

Roundworm parasites of other organisms

  • They also can infect fungi and can form symbiotic associations with bacteria.

  • Nematodes also can be used to control pests.


Section 4 check

Section 4 Check

Question 1

Which of the following is NOT a feature of roundworms?

A. pseudocoelom

B. anus

C. outer covering that can be shed

D. scolex


Section 4 check1

Section 4 Check

The answer is D, scolex.


Section 4 check2

Section 4 Check

Question 2

Which of the following parasites embeds itself inside the host’s muscle tissue?

A. Tapeworms

B. Trichinella

C. Ascaris

D. Pinworms


Section 4 check3

Section 4 Check

The answer is B. Trichinella is found in pork muscle tissue and can invade the muscle tissue of humans who eat undercooked infected pork.


Chapter summary 26 1

Chapter Summary – 26.1

Sponges

  • A sponge is an aquatic, sessile, asymmetrical, filter-feeding invertebrate.

  • Sponges are made of four types of cells. Each cell type contributes to the survival of the organism.

  • Most sponges are hermaphroditic with free-swimming larvae.


Chapter summary 26 2

Chapter Summary – 26.2

Cnidarians

  • All cnidarians are radially symmetrical, aquatic invertebrates that display two basic forms: medusa and polyp.

  • Cnidarians sting their prey with cells called nematocysts located on their tentacles.

  • The three primary classes of cnidarians include the hydrozoans, hydras; schyphozoans, jellyfishes; and anthozoans, corals and anemones.


Chapter summary 26 3

Chapter Summary – 26.3

Flatworms

  • Flatworms are acoelomates with thin, solid bodies. They are grouped into three classes: free-living planarians, parasitic flukes, and tapeworms.

  • Planarians have simple nervous and muscular systems. Flukes and tapeworms have structures adapted to their parasitic existence.


Chapter summary 26 4

Chapter Summary – 26.4

Roundworms

  • Roundworms are pseudocoelomate, cylindrical worms with lengthwise muscles, relatively complex digestive systems, and two body openings.

  • Roundworms can be parasites of plants, fungi, and animals, including humans.


Chapter assessment

Chapter Assessment

Question 1

Which of the following is NOT a method of asexual reproduction in sponges?

A. budding

B. fragmentation

C. gemmule formation

D. flagellated larvae


Chapter assessment1

Chapter Assessment

The answer is D. Flagellated larvae result from sexual reproduction.


Chapter assessment2

Chapter Assessment

Question 2

In hermaphroditic sponges, eggs and sperm form from _______.

A. larvae

B. epithelial cells

C. amoebocytes

D. collar cells


Chapter assessment3

Chapter Assessment

The answer is C, amoebocytes.

Amoebocyte


Chapter assessment4

Chapter Assessment

Question 3

Describe the symbiotic relationship between corals and zooxanthellae.


Chapter assessment5

Chapter Assessment

Zooxanthellae produce oxygen and food that the corals use. The corals produce carbon dioxide and waste materials that the zooxanthellae use.


Chapter assessment6

Chapter Assessment

Question 4

The cnidarians with many incomplete divisions in their gastrovascular cavities are the _______.

A. Scyphozoans

B. Hydrozoans

C. Anthozoans

D. Siphonophores


Chapter assessment7

Chapter Assessment

The answer is C, Anthozoans.


Chapter assessment8

Chapter Assessment

Question 5

The medusa is the body form usually observed in _______.

A. Scyphozoans

B. Hydrozoans

C. Siphonophores

D. Anthozoans


Chapter assessment9

Chapter Assessment

The answer is A, Scyphozoans.


Chapter assessment10

Chapter Assessment

Question 6

How is a secondary host involved in the life cycle of a tapeworm?

Answer

The eggs of the tapeworm hatch when a secondary host eats them.


Chapter assessment11

Chapter Assessment

Question 7

The secondary host for the blood fluke is a _______.

A. human

B. sheep

C. snail

D. dog


Chapter assessment12

Chapter Assessment

The answer is C, snail.


Chapter assessment13

Chapter Assessment

Question 8

The simplest animals with a tube-like digestive system are _______.

A. Nematodes

B. Platyhelminthes

C. Hydrozoans

D. Anthozoans


Chapter assessment14

Chapter Assessment

The answer is A, Nematodes.

Roundworm


Chapter assessment15

Chapter Assessment

Question 9

Which of the following is not a roundworm infection in humans?

A. hookworm

B. ringworm

C. pinworm

D. ascaris


Chapter assessment16

Chapter Assessment

The answer is B. Ringworm is a fungal infection.


Photo credits

Photo Credits

Photo Credits

  • Digital Stock

  • Ward's Natural Science Est.  

  • Kip Evans/NOAA

  • Florida Keys National Marine Sanctuary/NOAA  

  • Carolina Biological Supply Co.  

  • Dr. John Crites

  • David M. Dennis

  • Alton Biggs


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