Protists

Reading PreviewKey Concept0 What are the characteristics of

animal-like, plantlike, andfunguslike protists?

flab

, ZONE

DiscovermArctiVity

L!Lives in a Drop of Pond Water? I ‘1. Use a plastic dropper to place a drop of pond

water on a microscope slide.2. Put the slide under your microscope’s low-

power lens. Focus on the objects you see.3. Find at least three different objects that

you think might be organisms. Observethem for a few minutes.

4. Draw the three organisms in your notebook.Below each sketch, describe the movements orbehaviors of the organism. Wash your hands thoroughly whenyou have finished.

Think It OverObserving What characteristics did you observe that madeyou think that each organism was alive?

Key Terms0 protist 0 protozoan0 pseudopod0 contractile vacuole 0 cilia0 symbiosis 0 mutualism0 algae 0 spore

Target Reading SkillOutlining As you read, make anoutline about protists that you canuse for review. Use the red sectionheadings for the main topics andthe blue headings for thesubtopics.

l Look at the objects in Figure 13. What do they look like to you?Jewels? Beads? Stained glass ornaments? You might be sur-prised to learn that these beautiful, delicate structures are thewalls of unicellular organisms called diatoms. Diatoms live in

‘. both fresh water and salt water and are an important foodsource for many marine organisms. They have been called the

2 “jewels of the sea.”

I. What is a protist?

ll. Animal-like protists

A. Protozoans with pseudopods

B.

C.

FIGURE 13DiatomsThese glasslike organismsare classified as protists.

226 O

tuami M Protistsl'ltlll'.l'.ltttltttlt'nlllllhll ltlw, [tlatlllllkt‘,o1t|tlhaulinhlm otnnntnni'.tuiiilmtmtl .mtl l HlIll.|'.llllt| [It W/Ml WHY‘»do pluttsl'. «III/w hum uln' .umthw /

A thew shells ate the tt‘lthtlll" olnmu‘llnlai, .mtmal like plottststailed loiamtmleia.

What Is a Protist?lliatotns are only one of the vast v.'n'ieties ol protists. Protists are l(‘l|l\.ll"\'0ll‘.\' that cannot he classilied as .‘lltllllttlh'. plants. or lnngi.Because prolists are so dillel'ent from one another. you can thinkof them as the "odds and ends" kingdom. Ilowever. pl'ollsls doshare some characteristics. In addition to heing eukaryotes. all pldmhko pron.“ mund onprotists live in moist snrronndings. : mm” “no”

The word that best descrilws protists is diversity. l‘or exam 1ple. most protists are unicellular. hut some are nmlticellnlan'.Some are heterotrophs. some are .‘llllUll'UpllS. and others areboth. Some protists cannot move. while others loom aroundtheir moist snrrotnidings.

Because of the great variety of protists. scientists have proposed several ways ol'gronping these organisms. One useful wayol‘gronping protists is to divide them into three categories, hasedon characteristics they share with organisms in other l\'lll},,'(l()lll.\'.'.‘lltlllttll-lllx‘t‘ protists. plantlike protists. and l'nngnslike protists.

A This red alqa is a multlcellular,

HandingChuckpuint ) In what kind of environment do all protists live?

Animal-Like ProtistsWhat image pops into your head when you think olan animal?A tiger chasing its prey? A snake slithering onto a rock? Most lpeople immediately associate animals with movement. In tact. lmovement is often involved with an important characteristic of lanimals ~ ohtan'ning lood. All animals are heterotrophs that l 001"”.90l’l'll‘0"ml "5“

l

‘ The. yellow slime mold

must obtain lood by eating other organisms. hmgug'ke pron“Like animals, am'nml-lilw protists are lwterot‘rophs, and

most are able to move from place to place to obtain food. Butunlike amimals, .‘nn'mallike protists. or protoz.’0xt|1s (proh luh lZUII tin/2). are nnicellulan: l’l'olol’oalns can he classilied into tourgroups, hased on the way they move and live.

Chapter 7 O 227

FIGURE 15

AmoebaAmoebas are sarcodines that livein either water or soil. They feedon bacteria and smaller protists.

Food VacuoleWhen the ends of two pseudopods

PseudopodAn amoeba uses pseudopods

form when cytoplasm flowstoward one location andthe rest ofthe amoebafollows.

’

Cell MembraneBecause the cell membraneis very thin and flexible, anamoeba's shape changes constantly.

Go ‘Dnlm'e

act:ve k“part.KFor: Amoeba and Paramecium activityVisit: PHSchool.comWeb Code: cep-1031

fuse, they form a food vacuole. Foodis broken down inside the food vacuole

to move and feed. Pseudopods in the Cytoplasm-

NucleusThe nucleus controls thecell’s functions and isinvolved in reproduction.Amoebas usually reproduceby binary fission.

Cytoplasm

Contractile VacuoleThe contractile vacuole collectsexcess water from the cytoplasmand expels it from the cell.

Protozoans With Pseudopods The amoeba in Figure 15belongs to the group of protozoans called sarcodines. Sarco-dines move and feed by forming pseudopods (SOO duhpahdz)—temporary bulges of the cell. The word pseudopodmeans “false foot.” Pseudopods form when cytoplasm flowstoward one location and the rest of the organism follows.Pseudopods enable sarcodines to move. For example, amoebasuse pseudopods to move away from bright light. Sarcodinesalso use pseudopods to trap food. The organism extends apseudopod on each side of the food particle. The two pseudo-pods then join together, trapping the particle inside.

Protozoans that live in fresh water, such as amoebas, have aproblem. Small particles, like those of water, pass easflythrough the cell membrane into the cytoplasm. If excess waterwere to build up inside the cell, the amoeba would burst. FOPtunately, amoebas have a contractfle vacuole (kun TRAK “1'VAK yoo ohl), a structure that collects the extra water and thef1expels it from the cell.

FIGURE 16

Parameciumn. Paramecia are ciliates that live

Pe icle . _ mostly in fresh water. LikeA st'fi but flex'ble Cover'ng' amoebas, paramecia feed onCalled the Pemde: surrounds a bacteria and smaller protists.paramecium and gives It shape.

Large NucleusContractile VacuolesTwo contractile vacuoles collectexcess water from the cytoplasmand expel it from the cell.

Small Nucleus

Cytoplasm

Anal Pore \ . I

Wastes leave N 3;;through the 17-1277: :5 :1?

anal pore.

r/Irr(rmy /OralGroove

The oral groove is a funnel-likeindentation lined with cilia. The ciliamove water containing food into thevacuole that forms at the end of theoral groove.

Food VacuoleThousands of cilia project through A food vacuole forms and pinches offthe pellicle. The beating cilia enable from the oral groove. It moves into thea paramecium to move smoothly cytoplasm. Inside the vacuole, the foodin one direction. is broken down and then distributed.

Protozoans With Cilia The second group of animal—likeprotists are the ciliates. Ciliates have structures called c11'ia (SILee uh), which are hairlike projections from cells that move witha wavehk'e motion. Ciliates use their cilia to move and obtainfood. Cilia act something like tiny oars to move a ciliate. Theirmovement sweeps food into the organism.

The cells of ciliates, like the paramecium in Figure 16, arecomplex. Notice that the paramecium has two contractile vac—uoles that expel water from the cell. It also has more than onenucleus. The large nucleus controls the everyday tasks of thecell. The small nucleus functions in reproduction.

Paramecia usually reproduce asexually by binary fission.Sometimes, however, pzu‘amecia reproduce by conjugation.This occurs when two paramecia join together and exchangesome of their genetic material.

#Jcnheecadk'pnogimi What are cilia?

Protozoans With Flagella The third group of protozoan;are flagellates (FLAI uh lits), protists that use long, whiplike fla‘gella to move. A flagellate may have one or more flagella.

Some of these protozoans live inside the bodies of otherorganisms. For example, one type of flagellate lives in the intes-tines of termites. There, they digest the wood that the termiteseat, producing sugars for themselves and for the termites. Inturn, the termites protect the protozoans. The interactionbetween these two species is an example of symbiosis (sim beeOH sis)—a close relationship in which at least one of the spe-cies benefits. When both partners benefit from living together,the relationship is a type of symbiosis called mutualism.

Sometimes, however, a protozoan harms its host. Forexample, Giardia is a parasite in humans. Wfld animals, such as

beavers, deposit Giardia in freshwater streams, rivers, andlakes. When a person drinks water containing Giardia, theseprotozoans attach to the person’s intestine, where they feedand reproduce. The person develops a serious intestinal con-

dition commonly called hlk'er’s disease. FIGURE 17GiardiaWhen people drink from Protozoans That Are Parasites The fourth type of proto-freShwat,er Streams and l,akes',they zoans are characterized more by the way they live than by thecan get hikers disease. Giardia T. .I intestinal-S (inset) is the protozoan way they move. hey are all paras1tes that feed on the cells andresponsible for this disease_ body fluids of their hosts. These protozoans move in a varietyInferring Why is it important for of ways. Some have flagella, and some depend on hosts forhikers to filter Stream Water? transport. One even produces a layer of slime that allows it to

slide from place to place!Many of these parasites have more than one host. For exam—

ple, Plasmodium is a protozoan that causes malaria, a disease ofthe blood. Two hosts are involved in Plasmodium’s life cycle—humans and a species of mosquitoes found in tropical areas.The disease spreads when a healthy mosquito bites a personwith malaria, becomes infected, and then bites a healthy person.Symptoms of malaria include high fevers that alternate withsevere chil'ls. These symptoms can last for weeks, then disap-pear, only to reappear a few months later.

Reading

WWHCheck‘pflorint; What is symbiosis?

FIGURE 18Malaria MosquitoAnopheles mosquitoes can carry theparasitic protozoan Plasmodium,which causes malaria in people.

230 0

Plantlike .Prc.')ti'5't..splantlike protists, which are commonly called algae(Al. jee),are extremely diverse. Like plant's, algae are autotrophs. Mostare able to use the sun’s energy to make their own food.

Algae play a signilicant role in many environments. Foremmple, algae that live near the surlace of ponds, lakes, andoceans are an important lood source lor other organisms in thewater. in addition, much ofthe oxygen in [Earth’s atmosphere ismade by these algae.

Algae vary greatly in size. Some algae are unicellular, whileothers are multicellular. Still others are groups of unicellular

. muttZONE

1

Watching ProtistsIn this activity you will watchthe interaction betweenparamecium, an animal-likeprotist, and ChloreI/a, aplantlike protist.

1. Use a plastic dropperto place 1 drop of

paramecium culture on amicroscope slide. Addorganisms that live together in colonies. Colonies can contain

from a le'w cells up to thousands of cells. In a colony, most cellscarry out all functions. But, some cells may become specializedto perform certain functions, such as reproduction.

some cotton fibers to slowdown the paramecia.

. Use the microscope’s low-power objective to findsome paramecia.

. Add 1 drop of Chlore/la tothe paramecium cultureon your slide.

. Switch to high power andlocate a paramecium.Observe what happens.Then wash your hands.

Inferring What evidence doyou have that paramecia areheterotrophs? That Chlore/laare autotrophs?

Algae exist in a wide variety of colors because they containmany types of pigments. You may recall that pigments arechemicals that produce color. Depending on their pigments,algae can be green, yellow, red, brown, orange, or even black.

Diatoms Diatoms are unicellular protists with beautifulglasslike cell walls. Some float near the surface of lakes oroceans. Others attach to objects such as rocks in shallow water.Diatoms are a food source for heterotrophs in the water. Manydiatoms can move by oozing chemicals out of slits in their cellwalls. They then glide in the slime.

When diatoms die, their cell walls collect on the bottoms ofoceans and lakes. Over time, they form layers of a coarse sub—stance called diatomaceous (dy uh tuh MAY shus) earth. Diato-maceous earth makes a good polishing agent and is used inhousehold scouring products. It is even used as an insecticide—the diatoms’ sharp cell walls puncture the bodies of insects.

fori it

ill- Dinoflagellates Dinoflagellates (dy noh FLA] uh lits) areunicellular algae surrounded by stiff plates that look like a suitof armor. Because they have different amounts of green,orange, and other pigments, dinoflagellates exist in a varietyof colors.

All dinoflagellates have two flagella held in groovesbetween their plates. When the flagella beat, thedinoflagellates twirl like toy tops as they move (tripthrough the water. Many glow in the dark. Theylight up the ocean’s surface when disturbed by apassing boat or swimmer.

Flagella

FIGURE 19DinoflagellatesDinoflagellates whirl throughthe water with their flagella.

Chapter 7 O 231

Chloroplast(used in foodproduction)

FIGURE 20EuglenaThe euglena is a common euglenoid that livesin fresh water. In sunlight, many euglenas canmake their own food. Without sunlight, theyobtain food from their environment.interpreting Diagrams What structures help aeuglena find and move toward light?

{inningPredict what will happenwhen you pour a culture ofeuglena into a petri dish, andthen cover half the dish withaluminum foil. Give a reasonfor your prediction.

. Then carry out the experi-ment with a culture ofeuglena in a plastic petri dish.Cover half the dish with a|u~minum foil. After 10 minutes,uncover the dish. What doyou observe? Was your pre-diction correct? Explain whyeuglena behave this way.

232 O

Euglenoids Euglenoids (yoo GLEE noydz) are green, unicel—lular algae that are found mostly in fresh water. Unlike otheralgae, euglenoids have one animal—like characteristic—theycan be heterotrophs under certain conditions. When sunlightis available, most euglenoids are autotrophs that produce theirown food. However, when sunlight is not available, euglenoidswill act like heterotrophs by obtaining food from their envi-ronment. Some euglenoids live entirely as heterotrophs.

In Figure 20, you see a euglena, which is a common eugle-noid. Notice the long, whiplike flagellum that helps the organ-ism move. Locate the eyespot near the flagellum. Although theeyespot is not really an eye, it contains pigments. These pig—ments are sensitive to light and help the euglena recognize thedirection of a light source. You can imagine how importantthis response is to an organism that needs light to make food.

Red Algae Almost all red algae are multicellular seaweeds.Divers have found red algae growing more than 260 metersbelow the ocean’s surface. Their red pigments are especiallygood at absorbing the small amount of light that is able toreach deep ocean waters.

People use red algae in a variety of ways. Carrageenan(ka ruh IEE nun) and agar, substances extracted from red algae:are used in products such as ice cream and hair conditioner.For people in many Asian cultures, red algae is a nutrient-richfood that is eaten fresh, dried, or toasted.

Green Algae Green algae, which contain green pigments, arequite diverse. Most green algae are unicellular. Some, however,form colonies, and a few are multicellular. Most green algae livein either fresh water or salt water. The few that live on land arefound on rocks, in the crevices of tree bark, or in moist sorl's.

Green algae are actually very closely related to plants that liveon land. Green algae and plants contain the same type of chloro-phyll and share other important similarities. In fact, some scien—tists think that green algae belong in the plant kingdom.

Brown Algae Many of the organisms that are commonlycalled seaweeds are brown algae. In addition to their brown pig—ment, brown algae also contain green, yellow, and orange pig-ments. As you can see in Figure 22, a typical brown alga hasmany plantlike structures. Holdfasts anchor the alga to rocks.Stalks support the blades, which are the leaflike structures of thealga. Many brown algae also have gas—filled sacs called bladdersthat allow the algae to float upright in the water.

Brown algae flourish in cool, rocky waters. Brown algaecalled rockweed live along the Atlantic coast of North America.Giant kelps, which can grow as long as 100 meters, live in somePacific coastal waters. The giant kelps form large underwater“forests” where many organisms, including sea otters and aba—lone, live.

Some people eat brown algae. In addition, substances calledalgins are extracted from brown algae and used as thickeners inpuddings and other foods.

ReadingCheckpoinjt What color pigments can brown algae contain?

FIGURE 22 Brown AlgaeGiant kelps are brown algae that havemany plantlike structures.Interpreting Diagrams What plant structuresdo the kelps’ ho/dfasts and blades resemble?

FIGURE 21Green AlgaeGreen algae range in size fromunicellular organisms tomulticellular seaweeds. Thismulticellular sea lettuce, Ulva,lives in oceans.

Blade Holdfast

Chapter 7 O 233

Funguslike Protistsi

l The third group of protists are the funguslike protists. You mayrecall that fungi include organisms such as mushrooms andyeast. Until you learn more about fungi, you can think of fungias the “sort of like” organisms. Fungi are “sort of like” animalsbecause they are heterotrophs. They are “sort of like” plantsbecause their cells have cell walls. In addition, most fungi usespores to reproduce. A spore is a tiny cell that is able to growinto a new organism.

Lik'e fungi, funguslik'e protists are heterotrophs, have cellwalls, and use spores to reproduce. All funguslike protistsare able to move at some point in their lives. The three typesof funguslik'e protists are slime molds, water molds, and downymil'dews.

ll

Slime Molds Slime molds are often brilliantly colored. Theylive on forest floors and other moist, shady places. They oozealong the surfaces of decaying materials, feeding on bacteriaand other microorganisms. Some slime molds are so small thatyou need a microscope to see them. Others may cover an areaof several meters!

Slime molds begin their life cycle as tiny, individualamoeba—like cells. The cells use pseudopods to feed and creeparound. Later, the cells grow bigger or join together to form agiant, jellylike mass. In some species, the giant mass is multi-

‘ xvx‘ cellular and forms when food is scarce. In others, the giant.\ mass is actually a giant cell with many nuclei.

The mass oozes along as a single unit. When environ-mental conditions become harsh, spore—producing struc-tures grow out of the mass and release spores. Eventually

the spores develop into a new generation of slime molds.

FIGURE 23Slime MoldsThe chocolate tube slime moldfirst forms a tapioca-like mass(top). When conditions becomeharsh, the mass grows spore-producing stalks (right). The stalks,or "chocolate tubes, " are coveredwith millions of brown spores.

Water Molds and Downy Mildews Most water moldsand downy mildews live in water or moist places. 'l‘hese organ-isms often grow as tiny threads that look like fuzz. Figure 24shoWs a lish attacked by a water mold and a leaf covered bydowny mildew.

Water molds and downy mildews attack many food crops,such as potatoes, corn, and grapes. A water mold impacted his-tory when it destroyed the lrish potato crops in 1845 and 1846.The loss of these crops led to a famine. More than one million

A Water mold on fish

people in lreland died, and many others moved to the UnitedStates and other countries.

Readin———Jg=Checkpoint )

FIGURE 24Water Molds and Downy MildewsMany water molds are decomposersof dead aquatic organisms. Others areparasites of fish and other animals.Downy mildews are parasites of manyfood crops.

Section Assessment

@ Target Reading Skill Outlining Use your outline aboutprotists to help you answer the questions below.

Reviewing Key Concepts1. a. Listing List the four types of animal—like protists. How

does each type move or live?b. Comparing and Contrasting How are these four types

of protists similar to animals? How are they different?c. Classifying You observe an animal—like protist under

the microscope. It has no hairlike or whiplikestructures. It moves by forming temporary bulges ofcytoplasm. How would you classify this protist?

2. a. Reviewing In what way are diatoms, dinoflagellates,and other plantlike protists similar to plants?

b. Making Generalizations Why is sunlight important toplantlike protists.?

c. Making Judgments Would you classify euglena as ananimal-like protist or as a plantlike protist? Explain.

3. a. Listing What are the three types of funguslike protists.?b. Describing In what ways are funguslike protists similar

to fungi?

In what environments are water molds found?

Lzone\

V Downy mildew on grape leaf

Lab At-Home Activity

Algae Scavenger Hunt Look aroundyour house with a family memberto find products that containsubstances made from algae. Lookat both food and nonfood items.Before you begin, tell your familymember that substances such asdiatomaceous earth, algin, andcarrageenan are products that comefrom algae. Make a list of theproducts and the algae—basedingredient they contain. Share yourlist with the class.