Protists

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4

Isomorphic generations look similar.

Slide 27

Brown Algae Alternation of Generations

10 cm

Haploid (n)

Diploid (2n)

Key

Sporangia

Sporophyte

(2n)

Zoospore

MEIOSIS

Female

Gametophytes

(n)

Egg

Male

Sperm

FERTILIZATION

Zygote

(2n)

Developing

sporophyte

Mature female

gametophyte

(n)

Slide 28

Oomycetes (Water Molds and Their Relatives)

Oomycetes include water molds, white rusts, and downy mildews… Fungus-like.

They were once considered fungi based on morphological studies.

Most oomycetes are decomposers or parasites

They have filaments (hyphae) that facilitate nutrient uptake.

Their ecological impact can be great, as in Phytophthora infestans causing potato blight.

Slide 29

Life Cycle of Oomycetes = Water Mold

Germ tube

Cyst

Hyphae

ASEXUAL

REPRODUCTION

Zoospore

(2n)

Zoosporangium

(2n)

Haploid (n)

Diploid (2n)

Key

Oogonium

Egg nucleus (n)

Antheridial hypha with sperm nuclei (n)

MEIOSIS

Zygote

germination

SEXUAL

REPRODUCTION

Zygotes

(oospores)

(2n)

FERTILIZATION

Slide 30

Concept 28.4: Rhizarians are a diverse group of protists defined by DNA similarities

DNA evidence supports Rhizaria as a monophyletic clade.

Amoebas move and feed by pseudopodia; some but not all belong to the clade Rhizaria.

Rhizarians include forams and radiolarians.

Slide 31

Protists: Forams and Radiolarians

Foraminiferans, or forams, are named for porous, generally multichambered shells, called tests. Pseudopodia extend through the pores in the test.

Foram tests in marine sediments form an extensive fossil record.

Radiolarians have tests fused into one delicate piece, made of silica.

Radiolarians use their pseudopodia to engulf microorganisms by phagocytosis.

Slide 32

Radiolarian Protist

Pseudopodia

200 µm

Slide 33

Concept 28.5: Red algae and green algae are the closest relatives of land plants

Over a billion years ago, a heterotrophic protist acquired a cyanobacterial endosymbiont.

The photosynthetic descendants of this ancient protist evolved into red algae and green algae.

Land plants are descended from the green algae.

Archaeplastida is a supergroup used by some scientists and includes red algae, green algae, and land plants.