Plant-like Protist Diversity

Protist

• Eukaryotes — diverse structurally and functionally

• Have organelles

• Most are unicellular

  • Some live in groups and multicellular species

SAR clade

• Protist

  • Diverse

• Defined by DNA similarities — evolutionary relationship

• Consists of:

  • Stramenopiles

  • Alveolates

  • Rhizarians

Stramenopiles

• SAR clade

• Diatoms

  • Unicellular algae with a unique two-part glass-like wall of silicon dioxide (glass)

  • Major component of phytoplankton

  • Fossilized walls compose of diatomaceous earth (sediment)

Golden Algae

• Yellow and brown carotenoids

• Simple structure

• Mostly groups of unicellular organisms

Brown Algae

• Large complex multicellular structures

  • Kelps, giant seaweed

• Close to surface to capture more sunlight

Plant-like Structures

• Holdfast

  • Anchors the algae to a substrate — like roots

• Stipe

  • Supports upper structures — like stem

• Blade

  • Structures for photosynthesis — like leaves

• Analogous structures to plants

Alternation of Generations

• Most complex lifestyle

• Alternation of multicellular haploid and diploid forms

Heteromorphic generations

• Structurally different

Isomorphic generations

• Look similar

Dinoflagellates

• Made of cellulose — polymer of simple sugars, tough

• Phytoplankton

• Blooms (explosive growth) results in ‘red tide’

Red Tide

• Occurs in shallow water (easier to photosynthesize)

• Warm

• Toxins produced by dinoflagellates causes massive kills of invertebrates and fishes

Archaeplastida

• Red algae and Green algae

  • Diverse habitats

    • Freshwater, marine, terrestial

• Unicellular

• Generally grouped together

• Multicellular

• Closest relatives of land plants

Red Algae

• Reddish in colour due to phycoeythrin

• Mostly multicellular

• No flagellate structures in the life cycles

• Paper thin glossy sheets of nori — for sushi

Algal cell structure

• Cell wall — similar to plants

  • Cellulose, some carbohydrates, proteins

  • Rigid when mature

  • Permeable to water, gases, minerals (nutrition)

• Vacuole

  • Regulate the water content of the cell

  • Water moving in exerts outward pressure — turgor pressure

• Pyrenoids — only in algae

  • Within chlorplasts

  • Site of starch synthesis — source of energy

Isogamy

• Gametes of different mating types (+/-) are morphologically identical

Mature cells of algae develop into gametes

• Due to environmental stress (nitrogen stress)

Haplontic life cycle

• Main form is haploid