Green Algae and Chlorophytes Overview

Chlorophytes

• Most chlorophytes live in fresh water, but many are marine.
• Some chlorophytes live in damp soil, as symbionts in lichens, or in snow.

Green Algae

• Green algae are named for their grass-green chloroplasts (chlorophylls a and b).
• Plants evolved from green algae.
• Chlorophytes include unicellular, colonial, and multicellular forms.
• Two main groups are chlorophytes and charophyceans.

Red Algae and Green Algae

• Red algae and green algae are the closest relatives of land plants.
• Over a billion years ago, a heterotrophic protist acquired a cyanobacterial endosymbiont.
• Photosynthetic descendants evolved into red algae/green algae and glaucophytes.
• Land plants evolved from green algae relatives that evolved from the cyanobacterial endosymbiont.
• Archaeplastida is a supergroup that includes red algae, green algae, charophytes, glaucophytes, and land plants.

Life Cycle: Porphyra

• The life cycle of Porphyra involves both haploid (n) and diploid (2n) stages.
• Alternation of generations occurs, starting with a zygote (2n).
• Meiosis creates haploid spores (n), which then form gametophytes (n).
• Fertilization occurs, restarting the cycle.

Red Algae

• Red algae are reddish due to the accessory pigment phycoerythrin, masking chlorophyll's green.
• They absorb blue light and reflect/transmit red light.
• Color varies from greenish-red in shallow water to dark red/almost black in deep water.
• Red algae are usually multicellular, with some being large seaweeds.
• Red algae are the most abundant large algae in coastal waters of the tropics.

Forams

• Foraminiferans (forams) are named for their porous, multichambered shells (tests) made of calcium carbonate.
• Pseudopodia extend through the pores in the test.
• Foram tests in marine sediments form an extensive fossil record.

Rhizarians

• 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.

Radiolarians

• Marine radiolarians have tests fused into one delicate piece, usually made of silica.
• Radiolarians use pseudopodia for engulfing microorganisms via phagocytosis.
• Radiolarian pseudopodia radiate from the central body.

Oomycetes

• Oomycetes include water molds, white rusts, and downy mildews.
• They were once considered fungi based on morphological studies.
• Most oomycetes are decomposers or parasites.
• Oomycetes have filaments (hyphae) that facilitate nutrient uptake similar to fungi.
• Phytophthora infestans, an oomycete, causes potato blight.

Alternation of Generations

• A variety of life cycles evolved among multicellular algae.
• The most complex life cycles involve alternation of generations, alternating multicellular haploid and diploid forms.
• Heteromorphic generations are structurally different, while isomorphic generations look similar.

Diatoms

• Diatoms are unicellular algae with unique two-part, glass-like walls of hydrated silica.
• Diatoms are major components of phytoplankton.
• Diatoms are highly diverse.
• Diatoms typically reproduce asexually but can occasionally reproduce sexually.

Ciliates

• Ciliates are a large group of diverse protists, named for their cilia for movement and feeding in fresh water.
• They have large macronuclei, small micronuclei, and are complex cells.
• Micronuclei function during conjugation, a sexual process that creates genetic variation.
• Conjugation is separate from reproduction, which generally occurs by binary fission within the same species.

Brown Algae

• Brown algae are the largest and most complex algae.
• Brown algae are multicellular and mostly marine.
• Brown algae include many species commonly called "seaweeds."
• The algal body (thallus) is plant-like but lacks true roots, stems, and leaves.
• Holdfasts anchor the stem-like stipe, which supports leaf-like blades.

Golden Algae

• Golden algae are named for their color from yellow and brown carotenoids.
• Golden algae cells are typically biflagellated.
• All golden algae are photosynthetic and some are heterotrophic.
• Most are unicellular but some are colonial.

Stramenopiles

• The Stramenopila clade includes several groups of heterotrophs and algae.
• Most have a "hairy" flagellum paired with a "smooth" flagellum.

Alveolata

• Alveolates (a clade: Alveolata) have membrane-bounded sacs (alveoli) beneath the plasma membrane.
• The function of the alveoli is unknown.
• Alveolata includes dinoflagellates, apicomplexans, and ciliates.

Apicomplexans

• Apicomplexans are all animal parasites, causing serious human diseases.
• One end, the apex, contains a complex of organelles specialized for penetrating hosts.
• Apicomplexans have sexual and asexual stages requiring multiple host species to complete their life cycle. Plasmodium is the parasite causing malaria
• Continuously changes surface proteins.
• Requires mosquitoes and humans for life cycle completion.
• Two million people die from Malaria each year.

Kinetoplastids

• Kinetoplastids have a single mitochondrion containing a kinetoplast (DNA mass).
• Kinetoplastids include free-living consumers of prokaryotes, particularly in freshwater, marine, or moist terrestrial ecosystems.
• This group includes Trypanosoma, causing sleeping sickness in humans.
• Frequent changes in surface proteins prevent host immunity (like in Plasmodium).

Euglenozoans

• Euglenozoa is a diverse clade including predatory heterotrophs, photosynthetic autotrophs, and pathogenic parasites.
• Distinguished by a spiral or crystalline rod of unknown function within the flagella.
• Includes kinetoplastids and euglenids. Euglenids have one or two flagella that emerge from a pocket at one end of the cell. Some species are both autotrophic and heterotrophic (mixotrophic) and contain chloroplasts..

Diplomonads and Parabasalids

• Diplomonads and parabasalids are single-celled protists.
• Diplomonads have two nuclei. Giardia intestinalis is an example.
• Parabasalids have undulating membranes. Trichomonas vaginalis is an example.

Dinoflagellates

• Dinoflagellates are a diverse group of aquatic mixotrophs and heterotrophs.
• They are abundant components of both marine and freshwater phytoplankton.
• They have a characteristic shape reinforced by internal cellulose plates; some contain chloroplasts.
• Two flagella allow them to spin through the water. Dinoflagellate blooms cause toxic red tides.

Chromalveolates

• Some data suggest that the clade Chromalveolata is monophyletic, originating in a secondary endosymbiosis event.
• The proposed endosymbiont is a red alga.
• This clade includes alveolates and stramenopiles.

This quiz explores the world of green algae and chlorophytes, highlighting their habitats, characteristics, and evolutionary significance. Delve into the relationship between green algae and land plants, including the details of their life cycles and classification. Test your knowledge on these fascinating organisms!