CHAPTER 28: PROTISTSAP Biology 2013

ProtistsSingle-celled (mostly - some colonial or multicellular)

Eukaryotes

Extremely diverse (more diverse than any other classification of eukaryotes)

Contain: photoautotrophs, heterotrophs, mixotrophs (both heterotrophic and autotrophic)

Diverse habitats (freshwater and marine species)

Both sexual and asexual life cycles

Figure 28.2a–d

100 µm

100 µm

4 cm

500 µm

The freshwater ciliate Stentor, a unicellular protozoan (LM)

Ceratium tripos, a unicellular marine dinoflagellate (LM)

Delesseria sanguinea, a multicellular marine red alga

Spirogyra, a filamentous freshwater green alga (inset LM)

(a)

(b)

(c)

(d)

Table 28.1

Secondary EndosymbiosisCauses much of the diversity

Plastid-bearing lineages evolved into red algae and green algae

Cyanobacterium

Heterotrophic eukaryote

Primary endosymbiosis

Membranes are represented as dark lines in the cell.

1 2 3

One of these membranes was lost in red and green algal descendants.

Plastid

Red alga

Secondary endosymbiosis

Secondary endosymbiosis

Secondary endosymbiosis

Green alga

Dinoflagellates

Apicomplexans

Stramenopiles

Plastid

Euglenids

Chlorarachniophytes Fig. 28.2

1

2

3

Eukaryotic Clades Diplomonads

Parabasalids

Euglenozoans

Dinoflagellates

Apicomplexans

Ciliates

Diatoms

Golden algae

Brown algae

Oomycetes

Cercozoans

Forams

Radiolarians

Red algae

Chlorophytes

Charophytes

Land plants

Slime molds

Gymnamoebas

Entamoebas

Nucleariids

Fungi

Choanoflagellates

Animals

Alveolates

Stramenopiles

Green

algae

Am

oebozoans O

pisthokonts

Excavata C

hromalveolata

Rhizaria

Archaeplastida

Unikonta

Fig. 28.3

Understanding of protists continues to change rapidly

One hypothesis divides all eukaryotes into five supergroups

Diatom diversity

50 µm

Volvox, a colonial freshwater green alga

20 µm 50 µm

A unikont amoeba 100 µm

Excavata

Characterized by its cytoskeleton

Have modified mitochondria that lack DNA, electron transport chain, and citric acid cycle enzymes

Adapted to anaerobic environments

Lack plastids

Diplomonads - two nuclei and multiple flagella

Parabasalids - move by means of flagella and undulating plasma membrane

Flagella

5 µ

m

Undulating membrane

Fig. 28.4

EugenozoansInclude predatory heterotrophs, photosynthetic autotrophs, and pathogenic parasites

Main distinguishing characteristic is a spiral or crystalline rod of unknown function inside the flagella

Kinetoplastids - single large mitochondrion (kinetoplast) (ex. Trypanosoma - parasitic causes sleeping sickness in humans)

Euglenids - have one or two flagella

Crystalline rod (cross section)

Flagella

Ring of microtubules (cross section)

8 µm

0.2 µm

Fig. 28.5

9 µm

Fig. 28.6

Long flagellum

Eyespot

Short flagellum

Contractile vacuole

Nucleus

Chloroplast

Plasma membrane

Euglena (LM) 5 µm Pellicle

Light detector Fig.

28.7

4

5

6

ChromalveolatesMay be monophyletic and originated by a secondary endosymbiosis event

Like many protist clades, it is controversial.

Alveolates - membrane bound sacs (alveoli) under the plasma membrane

Dinoflagellates - aquatic photoautotrophs and heterotrophs that have a characteristic shape (reinforced by internal plates of cellulose), two flagella that make them spin as they move, and rapid growth causes “red tides” (can be toxic to humans)

Ciliates - use cilia to move and have macronuclei and micronuclei (use conjugation to exchange micronuclei)

Flagellum Alveoli

Alveolate

0.2 µ

m

Fig. 28.8

Flagella

3 µ

m

Fig. 28.9

Conjugation Asexual reproduction

Key

MEIOSIS

MICRONUCLEAR FUSION

Diploid micronucleus

Diploid micronucleus

Haploid micronucleus

Compatible mates

The original macronucleus disintegrates.

(b) Conjugation and reproduction

Fig. 28.11

ChromalveolatesApicomplexans - parasites of animals

Ex. Plasmodium is the parasite that causes malaria

Requires both mosquitos and humans to complete life cycle

900,000 people die each year from malaria

Sporozoites (n)

Oocyst

Zygote (2n)

Merozoite (n)

Gametes

Liver

Liver cell

Red blood cells

Gametocytes (n)

Merozoite

Apex

0.5 µm Red blood cell

Key

Haploid (n) Diploid (2n)

Inside mosquito Inside human

MEIOSIS

FERTILIZATION

Fig. 28.10

ChromalveolatesStramenopila - photoautotrophs and heterotrophs

Most have “hairy” flagellum paired with a “smooth” flagellum

Diatoms - glass-like wall of hydrated silica, reproduce both sexually and asexually (major component of phytoplankton)

Golden Algae - some unicellular some colonial

Oomycetes - water molds, downy mildews, and white rusts

Smooth flagellum

Hairy flagellum

5 µm

Fig. 28.12

40 µ

m

Flagellum

Outer container

Living cell

25 µm

Fig. 28.14

Apicomplexans Ciliates

Diatoms

Stramenopiles

Alveolates

Chrom

alveolata

Rhizaria Archaeplastida Unikonta

Dinoflagellates

Golden algae Brown algae Oomycetes

Excavata

Germ tube

Cyst

Hyphae ASEXUAL REPRODUCTION

Zoospore (2n)

Zoosporangium (2n)

Zygote germination SEXUAL

REPRODUCTION

Key

Haploid (n) Diploid (2n)

MEIOSIS

FERTILIZATION Zygotes (oospores) (2n)

Antheridial hypha with sperm nuclei (n)

Egg nucleus (n)

Oogonium

Fig. 28.13

Fig. 28.17

7

8

9

ChromalveolatesBrown Algae - largest and most complex algae

Multicellular and mostly marine (commonly referred to as seaweeds)

Algal body is plant-like but lack true roots, stems, and leaves

Has a holdfast (rootlike), stipe (stemlike), and blades (leaflike)

Alteration of generations

Blade

Stipe

Holdfast

Fig. 28.15

10 cm

Mature female gametophyte (n)

Developing sporophyte

Zygote (2n)

Haploid (n) Diploid (2n)

Key

Sporangia

Gametophytes (n)

Zoospore

Female

Male

Sperm

MEIOSIS

FERTILIZATION

Sporophyte (2n)

Egg

Fig. 28.16

RhizariansDNA evidence supports this as a monophyletic clade

Amoebas - move and feed by pseudopodia

Radiolarians - pseudopodia radiate from central body

Foraminiferans - multichambered shells

Cercozoans - most are heterotrophic parasites and predators

Radiolarians Foraminiferans Cercozoans

Rhizaria

Excavata Chromalveolata

Archaeplastida Unikonta

Pseudopodia

200 µm

Fig. 28.18

Chromatophore

5 µm

Fig. 28.19

ArchaeplastidaLand plants are descended from the green algae

Includes red algae, green algae, and land plants

Red algae - most abundant large algae in tropics

Green algae - paraphyletic group that gave rise to land plants

Chlorophytes Charophytes

Archaeplastida

Excavata Chromalveolata Rhizaria

Unikonta

Red algae

Green algae

Land plants

20 cm

8 mm

Bonnemaisonia hamifera

Dulse (Palmaria palmata)

Nori

Fig. 28.20(a) Ulva, or sea lettuce

(b) Caulerpa, an intertidal chlorophyte

2 cm

Fig. 28.21

Flagella

Cell wall

Nucleus

Cross section of cup-shaped chloroplast

1 µm

(TEM)

Zoospore

ASEXUAL REPRODUCTION SEXUAL

REPRODUCTION

Gamete (n)

Mature cell (n)

Zygote (2n)

FERTILIZATION

MEIOSIS Key

Haploid (n) Diploid (2n)

-

-

-

- +

+

+

+

Fig. 28.22

10

11

12

Cercozoans and RadiolariansCercozonans (type of amoebas) - move by thread-like pseudopodia

Foraminiferans - named for porous, multichambered shells called tests (pseudopods extend through pores in tests)

Radiolarians (marine protists)

Tests fused into one delicate piece made of silica

Pesudopodia known as axopodia

Figure 28.22

20 µm

Figure 28.23 200 µm

Axopodia

Unikonts

Group that contains animals, fungi, and some protists

Amoebozoans - amoeba that include slime molds

Choanoflagellates Animals

Unikonta

Excavata Chromalveolata Rhizaria Archaeplastida

Amoebozoans

Nucleariids Fungi

Stalk

Zygote (2n)

FERTILIZATION

MEIOSIS

Amoeboid cells (n)

Germinating spore

Spores (n)

Flagellated cells (n)

Mature sporangium

Young sporangium

Feeding plasmodium

Mature plasmodium (preparing to fruit)

4 cm

1 mm

Key

Haploid (n) Diploid (2n)

Fig. 28.24

Spores (n)

600 µm

200 µm

Solitary amoebas (n)

Emerging amoeba (n)

Fruiting bodies (n)

Aggregated amoebas

Amoebas (n) ASEXUAL REPRODUCTION

SEXUAL REPRODUCTION

Zygote (2n)

Migrating aggregate

Key

Haploid (n) Diploid (2n)

FERTILIZATION

MEIOSIS

Fig. 28.25Plasmodial Slime Mold

Cellular Slime Mold

Role in EnvironmentSymbiotic protists

Dinoflagellates nourish coral polyps that build reefs, wood-digesting protists digest cellulose in the gut of termites

Parasites

Plasmodium causes malaria, Phytophthora ramorum causes sudden oak death

Producers

Photosynthetic protists and prokaryotes are the main producers in aquatic environments

Populations will explode when limiting nutrients are added

Biomass has declined as sea surface temperature increases

Herbivorous plankton

Other consumers

Carnivorous plankton

Protistan producers

Prokaryotic producers

Fig. 28.27

Higher Lower

SST SST

Growth Growth In regions between the black lines, a layer of warm water rests on top of colder waters.

In the yellow regions, high SSTs increase the temperature differences between warm and cold waters, which reduces upwelling.

Fig. 28.28

13

14

15