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1

Protista: Learning Objectives

• What features are common to the members

of kingdom Protista?

• Diversity among Protists

Three-Domain Classification

Six-Kingdom ClassificationEukaryote Phyla

Sizes of Protists

Mostly unicellular eukaryotic organisms that

live in aquatic environments

• Unicellular organisms (most)

• microscopic

• Colonies

• loosely connected groups of cells

• Coenocytes

• multinucleate masses of cytoplasm

• Multicellular organisms

• composed of many cells

• A unicellular protist

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Diversity in the Kingdom Protists.

• Classification based on:

• means of locomotion

• modes of nutrition

• interactions with other organisms

• habitats

• modes of reproduction

Locomotion

• Pseudopodia

• Flagella

• Cilia

• Some are nonmotile

Nutrition

• Protists are:

• Heterotrophs

• Autotrophs

Interactions

• Protists are free-living or symbiotic

• Symbiotic relationships vary

- A close relationship between 2 unrelated

organisms

Mutualism + +

Commensalism + -

Parasitism + -

Habitats

• Most protists live in

• ocean

• freshwater ponds

• lakes

• streams

• Parasitic protists live in body fluids of hosts

Reproduction

• Many protists reproduce both sexually and

asexually

• Others reproduce only asexually

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Chloroplast EvolutionRelationships Among Protists

• Protist kingdom

• paraphyletic group:

- group of orgs with common ancestor

and some but not all of its descendents

• Determined by

• ultrastructure (electron microscopy)

• comparative molecular data

Eukaryote Phyla

Protists are descendants of early eukaryotes

Giardia

Fig. 25-5b, p. 536

Nucleus

Flagella

50 µm

Trichonympha – live in

gut of termites

Discicristates

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Ciliates Cilliates - Conjugation

Dinoflagellates Plasmodium

A Water Mold Diatoms: some form floating plankton

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Heterokonts: Golden Algae Heterokonts: Brown Algae

• Multicellular - important in cooler ocean

waters

• Kelps (largest brown algae)

• leaflike blades

• stemlike stipes

• anchoring holdfasts

• gas-filled bladders for buoyancy

Brown Algae Foraminiferans

Cercozoa: Actinopods

• Mostly marine

plankton

• Obtain food

with axopods

• slender

cytoplasmic

projections

Plants

• Monophyletic group including

• red algae

• green algae

• land plants

• Based on

• molecular data

• presence of chloroplasts bounded by outer

and inner membranes

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Red Algae: Mostly multicellular seaweeds

important in warm tropical ocean waters Green Algae

• Wide diversity in size, structural

complexity, and reproduction

• Botanists hypothesize that ancestral green

algae gave rise to land plants

Green Algae

Fig. 25-17, p. 547

5 Both mating types reproduce

asexually by mitosis; only (-)

strain is shown.–

–

– Zoospores

ASEXUAL

REPRODUCTION

(by mitosis)

–

–

4 Four haploid

cells emerge,

two (+)

and two

(-).

1 Gametes are

produced by

mitosis.+

–

– – SEXUAL

REPRODUCTION

+HAPLOID (n)

GENERATION

–

+–

from a different

strainDIPLOID (2n)

GENERATION 2 (+) and (-)

gametes fuse,

forming a

diploid zygote.

+Meiosis Fertilization

3Meiosis

occurs.Zygote (2n)

Amoebazoa: Amoebas

• Entamoeba histolytica

• parasitic amoeba

• causes amoebic dysentery

Fig. 25-22, p. 549

Green alga

Pseudopodia

100 µm

Amoebas: Use cytoplasmic extensions (pseudopodia) to move and obtain

food by phagocytosis

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Omoebozoa:

• Feeding stage is multinucleate plasmodium

Plasmodial Slime Molds

Slime molds Opisthokonts: Choanoflagellates

• single posterior flagellum in flagellate cells

• collar of microvilli surrounds base of flagellum

• Choanoflagellates

• are related to fungi and animals

Choanoflagellate