Ch. 20 Sec. 1

Protists

Protists are eukaryotes that are not members of the Plant, Animal, or Fungi kingdoms.

I. What Is a Protist?

A. May include more than 200,000 species

B. Most are unicellular

A. The first eukaryotic organisms on EarthB. Mitochondria and chloroplasts in eukaryotic

cells may have descended from prokaryotes that lived inside larger cells

II. Evolution of Protists

ChloroplastPlants and plantlike protists

A. Classified by how they obtain nutrition

1.Heterotrophs - animal-like protists 2.Photosynthesizers – plantlike

protists3.Decomposers and parasites -

funguslike protists

III. Classification of Protists

Ch. 20 Sec. 2

Animallike Protists: Protozoans

• There are four phyla of animal-like protists:• zooflagellates• sarcodines• ciliates• Sporozoans

Animal-like protists are classified by their means of

movement

I. ZooflagellatesA. Animal-like protists (heterotrophs)B. Swim using flagella

1. Long, whiplike projections2. Allow a cell to move3. Most have one or two flagella4. Some species have many

Fluorescence photomicrographs of chonaoflagellates

C. Most reproduce asexually1. Mitosis2. Cytokinesis

D. Some may reproduce sexually1. Gametes form through meiosis2. Gametes fuse

II. SarcodinesPseudopods - temporary cytoplasmic

projections used for feeding or movement

A. Amoebas1. Flexible, active cells2. Thick pseudopods

a. Extend out of the central mass of the cell

3. Amoeboid movementa. Cytoplasm streams into the pseudopodb. The rest of the cell follows

Structures of an Amoeba

Fig. 20-4 Page 500 Sarcodines use pseudopods for feeding and movement. The amoeba, a common sarcodine, moves by first extending a pseudopod away from its body. The organism’s cytoplasm then streams into the pseudopod. Amoebas also use pseudopods to surround and ingest prey.

4. Amoebas surround food and engulf ita. Food vacuole - small cavity in the cytoplasm

that temporarily stores foodb. Food digestedc. Nutrients passed to cell d. Waste stays in vacuole until released outside

the cell5. Amoebas reproduce by mitosis and cytokinesis

B . Other sarcodines 1.Foraminiferans2.Heliozoans (“sun animals”)

III. CiliatesA. Ciliates use cilia for feeding and

movement1. Short hairlike projections2. Propel a cell

B. Paramecia1. Cilia

a. Grouped into rows and bundlesb. Beat in a regular pattern

Structures of a Paramecium

Fig. 20-5 Page 501 Ciliates use hairlike projections called cilia for feeding and movement. Ciliates, including this paramecium, are covered with short, hairlike cilia that propel them through the water. Cilia also line the organism’s gullet and move its food—usually bacteria—to the organism’s interior. There, the food particles are engulfed, forming food vacuoles. The contractile vacuoles collect and remove excess water, thereby helping to achieve homeostasis, a stable internal environment.

1. Trichocystsa. Bottle-shaped structures b. Below the surface of the cell membranec. Used for defense

C. Internal Anatomy

2. Paramecia possess two types of nuclei:a. Macronucleus keeps multiple copies of

most genes for its day-to-day existence b. Micronucleus contains a “reserve copy”

3. Gulleta. Cilia sweep food inb. Traps the particles and

forces them into food vacuoles

c. The food vacuoles fuse with lysosomesi. contain digestive enzymes

4. Anal porea. After digestion, the waste material empties

through the anal pore

5. Contractile vacuoles - cavities in the 5. Contractile vacuoles - cavities in the cytoplasmcytoplasm

a. Specialized to collect watera. Specialized to collect waterb. In fresh water: osmosisb. In fresh water: osmosisc. Excess collected in vacuoles c. Excess collected in vacuoles d. Contract, pumping water outd. Contract, pumping water oute. Maintain homeostasise. Maintain homeostasis

D. Conjugation1. Reproduction is usually asexual by

mitosis and cytokinesis2. Conjugation - When placed under stress

• Two paramecia attach themselves to each other.

• Meiosis produces four haploid micronuclei, three of which disintegrate.

• The remaining micronucleus in each cell divides again.

Macronucleus

Micronucleus

MEIOSIS

See Fig. 20-6 Page 502 During conjugation, two paramecia attach themselves to each other and exchange genetic information. The process is not reproduction because no new individuals are formed. Conjugation is a sexual process, however, and it results in an increase in genetic diversity.

• The two cells exchange one micronucleus from each pair.

• The macronuclei disintegrate, and each cell forms a new macronucleus from its micronucleus.

• Conjugation is not a form of reproduction. In large populations, conjugation helps produce and maintain genetic diversity.

Genetically identical paramecia form

IV. SporozoansA. ImmobileB. Parasitic

1. Worms2. Fish3. Birds4. Humans

• Many sporozoans have complex life cycles that involve more than one host.

• Sporozoans reproduce by sporozoites.• A sporozoite can attach itself to a host cell,

penetrate it, and then live within it as a parasite.

V. Animal-like Protists and DiseaseSome animal-like protists cause serious diseases, including malaria and African sleeping sickness.

A. MalariaA. Malaria1.1. Malaria is one of the world’s most serious Malaria is one of the world’s most serious

infectious diseases, killing as many as 2 infectious diseases, killing as many as 2 million people each year. million people each year.

2.2. The sporozoan The sporozoan PlasmodiumPlasmodium, which causes , which causes malaria, is carried by the female malaria, is carried by the female AnophelesAnopheles mosquito. mosquito.

• Malarial Infection

Fig. 20-7 Animal-like protists can cause serious diseases, including malaria. The bite of an Anopheles mosquito can transmit Plasmodium sporozoites. Once in the human body, Plasmodium infects liver cells and red blood cells and multiplies.

• A female Anopheles mosquito bites a human infected with malaria and picks up Plasmodium gamete cells.

• The sexual phase of the Plasmodium life cycle takes place inside the mosquito.

• Gametes fuse to form zygotes, meioses occurs, and sporozoites are produced and migrate to salivary gland.

• Infected mosquito bites another human, injecting saliva that contains Plasmodium sporozoites.

Plasmodium sporozoites

• Sporozoites infect liver cells and multiply asexually.

Liver

Plasmodium sporozoites

• Infected liver cells burst, releasing Plasmodium cells called merozoites that infect red blood cells.

Plasmodium sporozoites

Liver

Liver cells burst

Merozoites

Red blood cells

Merozoites

• Merozoites reproduce asexually inside red blood cells.

• Infected red blood cells burst, releasing merozoites that infect other red blood cells. Some cells release gametes that can infect mosquitoes.

Red blood cells

Merozoites

B. Other Diseases Caused byB. Other Diseases Caused by Protists Protists

1.1.African sleeping sicknessAfrican sleeping sickness2.2.Amebic dysenteryAmebic dysentery3.3.GiardiaGiardia

VI. Ecology of Animal-like ProtistsA. Many animal-like protists are essential

to the living world 1. Some live symbiotically within other

organisms 2. Some recycle nutrients from dead

organic matter3. Some live in water, where they are eaten

by tiny animals, which in turn serve as food for larger animals

B. ex: Trichonympha 1. Lives in the digestive systems of termites2. Breaks down cellulose3. Allows termites to digest wood

20–1 The Kingdom ProtistaThe kingdom Protista is a diverse group. Protists are eukaryotes that are not members of the kingdoms

Plantae, Animalia, or Fungi. Most protists are unicellular. Earth’s first eukaryotes were protists. One way protists are classified is according to how

they obtain nutrition. Thus, many protists that are heterotrophic are called

animallike protists. Protists that produce their own food by

photosynthesis are called plantlike protists. Protists that obtain their food by external digestion

are called funguslike protists.

20–2 Animallike Protists: ProtozoansAnimallike protists are called protozoans. Protozoans are

heterotrophs.There are four phyla of animallike protists. They are

classified according to how they move.• Protists that swim using flagella are classified in the

phylum Zoomastigina. They are called zooflagellates. Flagella are long, whiplike projections that allow a cell to move.

• Members of the phylum Sarcodina move by using pseudopods. Sarcodines also use pseudopods for feeding.

Pseudopods are temporary projections of cytoplasm.Sarcodines called amoebas have thick pseudopods. An

ameoba moves by first extending its psuedopod. The cell’scytoplasm flows into the pseudopod. The rest of the cellthen follows. This type of movement is called amoeboid

movement.

• Members of the phylum Ciliophora, known as ciliates, use cilia for feeding and

movement. Cilia are short, hairlike projections similar to

flagella. Some of the best-known ciliates belong to the

genus Paramecium. The cilia of a paramecium are organized into

evenly spaced rows and bundles. Just under the cell membrane, a paramecium

has small defense structures called trichocysts. When a paramecium is in danger, the

trichocysts release stiff projections that protect the cell.

• Members of the phylum Sporozoa do not move on

their own. They are parasites that reproduce by means of sporozoites. Some animallike

protists cause serious diseases. For example, Plasmodium is a sporozoan that causes malaria.

Trypanosoma is a zooflagellate. It causes African sleeping sickness.

Some animallike protists are helpful. Trichonympha lives in the digestive system of

termites. This protist helps termites digest wood.