Chapter 28: Eukaryotes

protists

a microscopic living thing with a cell nucleus that is not an animal, a plant, or a fungus

characteristics:

• Eukaryotic: Their cells have a true nucleus and special inner parts called organelles.

• Mostly Single-Celled: Most protists are made of only one cell. A few grow into large, multi-celled forms like giant kelp.

  • Unicellular protists carry out the same essential functions, but they do so using subcellular organelles, not multicellular organs.

• Diverse: They do not share a single common ancestral group. They form a "catch-all" category for organisms that do not fit elsewhere

• they are structurally and functionally diverse and have a wide variety of life cycles.

• they have a cytoskeleton

• protists include photo- autotrophs, heterotrophs, and mixotrophs.

Protists form mutualistic and parasitic relationships that affect their symbiotic partners and many other members of the community

cytoskeleton

enables them to have asymmetric forms and to change shape as they feed, move, or grow.

allowed eukaryotes to engulf alpha proteobacterium and lea dto teh mitochondria

Photoautotrophs

Organisms that make their own food using light.

hey use sunlight, water, and carbon dioxide to create sugars through a process called photosynthesis.

the most important producers in aquatic communities. Because they are at the base of the food

web, factors that affect photosynthetic protists affect many other species in the community.

Heterotrophs

Organisms that cannot make their own food and must consume other living things.

They get their energy by engulfing smaller microbes, absorbing decaying organic matter, or living as parasites inside a host.

Mixotrophs

Organisms that can switch between making their own food and eating other things

• If there is plenty of sunlight, they act like plants and photosynthesize. If it gets dark or nutrients run low, they switch to hunting and eating bacteria or other small cells.

endosymbiosis

the evolution of eukaryote form a symbiotic relationshoi beetn arcahe and alpha-proteobacterium

an archaeal host (or a host closely related to the archaea) engulfed an alpha proteobacterium that would evolve into an organelle found in all eukaryotes, the mitochondrion.

Plastids

double-membrane organelles found in the cells of plants, algae, and certain other protists

• crucial for producing and storing food.

plastids evolved from a cyanobacterium that was engulfed by an ancestral heterotrophic eukaryote (primary endosymbiosis).

• That ancestor then diversified into red algae and green

cyanobacteria

n ancient group of photosynthetic bacteria that live primarily in water

cyanobacteria are prokaryotes, meaning they are true bacteria and completely lack a cell nucleus.

seen as green

red algae

an ancient group of eukaryotic organisms

evolved through primary endosymbiosis and later became the evolutionary source of chloroplasts for many other complex protists via secondary endosymbiosis.

Red algae and green algae are the closest relatives of plants

characteristic:

• Phycoerythrin (photosyn-thetic pigment), phycocyanin, and allophycocyanin

• multicellular

• reproduce sexually and have diverse life cycles in which alternation of generations is common.

• do not have flagellated gametes, so they depend on water currents to bring gametes together for fertilization.

green algae

Green algae are photosynthetic eukaryotic organisms that arose from primary endosymbiosis and are the direct evolutionary ancestors of all modern land plants.

Red algae and green algae are the closest relatives of plants

characteristic:

• Plant-type chloroplasts

• LHC bind to the chlorophylls a and b in their pigment molecules

Green algae can be divided into two main groups, the charophytes and the chlorophytes. The charophytes include the algae most closely related to plants

how did otehr protist group evolve

through secondary endosymbiotic events in which red algae or green algae were themselves engulfed.

unikonta

had a single flagellum ("uni-konta").

Animals and Fungi belong here

• humans evolve form here

• Excavata, SAR, and Archaeplastida share a more recent common ancestor than any of them does with Unikonta

archaeplastida

Meaning "ancient plastids," this group is unified by primary endosymbiosis—their shared ancestor was the very first eukaryote to swallow a cyanobacterium. Group includes: red algae, green algae, and plants

a monophyletic group that descended from the ancient protist that engulfed a cyanobacterium

SAR

An acronym for three massive sub-branches: Stramenopiles, Alveolates, and Rhizarians. This group includes everything from massive kelp forests to the parasites that cause malaria

Major groups:

• Stramenopiles

  • Diatoms

  • Oomycetes

  • Brown algae

• Alveolates

  • Dinoflagellates

  • Apicomplexans

  • Ciliates

• Rhizarians

  • Radiolarians

  • Forams

  • Cercozoan

Excavata

Excavates include protists with modified mitochondria and protists with unique flagella

major groups:

• Diplomonads

• parabasalids

• Euglenozoans

  • Kinetoplastids

  • Euglenids

the modern scientific blueprint of the Eukaryotic Tree of Life, four massive evolutionary branches called "supergroups"

Excavata, SAR, Archaeplastida, and Unikonta

the evolution of the mitochondria

mitochondria and plastids are derived from bacteria that were engulfed by the ancestors of early eukaryotic cells.

mitochondria evolved before plastids. Thus, important in eukaryotes evolution when a host cell engulfed a bacterium that would later become an organelle found in all eukaryotes—the mitochondrion.

mitochondria arose from an alpha proteobacterium

the mitochondria of protists, animals, fungi, and plants descended from a single common ancestor, thus suggesting that mitochondria arose only once over the course of evolution

the eovlution of plastids

mitochondria and plastids are derived from bacteria that were engulfed by the ancestors of early eukaryotic cells.

mitochondria evolved before plastids.

plastids descended from a single com- mon ancestor—a cyanobacterium that was engulfed by a eukaryotic host cell.

evolution of algae

secondary endosymbiosis: a heterotrophic eukaryote ungulfed an additional endosymbiont, a photosynthetic cyanobacterium, that then evolved into plastids.

this plastid-bearing lineage the photosynthetic protists, or algae: red algae and green algae.

cynobacteria

Cyanobacteria ; they are prokaryotic bacteria that evolved into the chloroplasts found inside eukaryotic plants and algae

cyanobacteria are gram-negative and that gram-negative bacteria have two cell membranes, an inner plasma membrane and an outer membrane that is part of the cell wal
pirmary endosymbiosis, The engulfment of a cyanobacteium by a pimitive eukayote, protozoan

nucleomorph

the engulfed cell contains tiny vestigial nucleus called nucleonorph. evidence for secondary endosymbiosis

Diplomonads

Diplomonads have reduced mitochondria called mitosomes. Many diplomonads are parasites

Euglenozoans

Autotrophic Green algae as symbiont

freshwater, free-living flagellate

Diatom

unicellular algae that have glass-like wall made of silicon dioxide

their photosynthetic activity affects global carbon dioxide (CO2) lev- els.

Diatom effect on carbon levels

uneaten diatoms die, their bodies sink to the ocean floor. It takes decades, or even centuries, for dead diatoms that sink to the ocean floor to be broken down by bacteria and other decomposers. As a result, the carbon in their bodies remains there for some time, rather than being released immediately as CO2 as the decomposers respire. The overall effect of these events is that CO2 absorbed by diatoms during photosynthesis is transported, or “pumped,” to the ocean floor.

e protists are 0.15 mm of less. Their skeletons are fotified by transparant silica mateials ('glass houses')

brown algae

a group of stramenopiles which is a subgroup of SAR whcih is a protist

All are multicellular, and most are marine.

brown or olive color to the carotenoids in their plastids.

• these simialirties between plants and algae occured independently in the algal and plant lineages and are thus analogous, not homologous.

brown algae lack true tissues and organs

brown algae have adaptations that enable their main photosynthetic surfaces (the leaflike blades) to be near the water surface

• Some brown algae accomplish this task with gas- filled, bubble-shaped floats.

diploid and haplod conditions

diploid: Contains two complete sets of chromosomes, with one set inherited from each biological parent.

haploid:Contains only a single, complete set of unpaired chromosomes, representing half the genetic material of a diploid cell.

alternation of generation

a specialized biological life cycle found in all plants and some algae where an organism alternates between a multicellular haploid form and a multicellular diploid form within its lifetime.

applies only to life cycles in which both haploid and diploid stages are multicellular

eg borwn algae

the alveolates

subgroup of SAR

alveolate clades: a group of flagellates (the dinoflagellates), a group of parasites (the apicomplexans), and a group of protists that move using cilia (the ciliates).

Dinoflagellates

a sub group of the alveolates, a sub group of SAR,

two whip liek flagellates

• heterotrophic

• many photosynthetic dinoflagellates are mixotrophic

photosynthesis pathogens

seen in bioluminescen andred tide

red tide

Periods of explosive population growth (blooms) in dino flagellates cause a “red tide”

The blooms make coastal waters appear brownish red or pink because of the presence of carotenoids, the most common pigments in dinoflagellate plastids.

when blooms occur, toxins produced by certain dinoflagellates have caused massive kills of invertebrates and fishes. Humans who eat molluscs that have accumulated the toxins are affected as well, sometimes fatally

rhizarians

subgroup of SAR

Many species in this group are amoebas

Radiolarians

silica (SiO2) skeleton

Radiolarians are primarily heterotrophic and feed on smaller organisms

After radiolarians die, their skeletons settle to the seafloor, where they have accumulated as an ooze that is hundreds of meters thick in some locations.

Forams

protists also called foraminiferans or forams

CaCO3 exoskeleton

Many forams also derive nourishment from the photosynthesis of symbiotic algae that live within the tests.

the color of reed algae

due to the photosynthetic pigment phycoerythrin, which masks the green of chlorophyll.

However, other species (those adapted to shallow water) have less phycoerythrin. As a result, red algal species may be greenish red in very shallow water, bright red at moderate depths, and almost black in deep water. Some species lack pigmentation altogether and live as heteroptrophic parasites on other red algae.

how has green algae evolved

1. The formation of colonies of individual cells and other species that contribute to the stringy masses known as pond scum.

2. The formation of true multicellular bodies by cell divi- sion and differentiation

3. The repeated division of nuclei with no cytoplasmic division

producers

many protists are producers: organisms that use energy from light (or in some prokaryotes, inorganic chemicals) to convert CO2 to organic compounds. Producers form the base of ecological food webs.

consumers

All other organisms in the com- munity are consumers that depend on producers for food, either directly (by eating them) or indirectly (by eating an organism that ate a producer).

primary endosymbiosis

The engulfment of a cyanobacteium by a pimitive eukayote, protozoan, leading to chloroplast

led to Photosynthesis in eukayotic cells

secondary endosymiosis

Secondary endosymbiosis is the engulfment of a photosynthetic eukaryotic cell (such as a red or green alga) by another non-photosynthetic eukaryotic cell

secondary vs primary endosymbiosis

In primary endosymbiosis, a primitive eukaryote, protozoan engulfs a prokaryote (a cyanobacterium).

• leading to chloroplast

• led to Photosynthesis in eukayotic cells

In secondary endosymbiosis, a eukaryote engulfs another eukaryote that already contains a plastid from primary endosymbiosis.

photosystems and eukaryotic evolution

Eukaryotic cells did not evolve the mechanism of oxygenic photosynthesis (which relies on both PSI and PSII) on their own. Instead, they acquired it by absorbing it from prokaryotes

Because cyanobacteria were the only organisms to have evolved both PSII and PSI working together, the new eukaryotic lineage suddenly inherited the ability to perform oxygenic photosynthesis. This lineage gave rise to all modern red algae, green algae, and land plants

multi-protein complexes in the thylakoid membrane that work together to harvest light energy during the light-dependent reactions of photosynthesis: Water molecules first supply electrons to PSII, which then pass through an electron transport chain to PSI.

• PSII splits water molecules to release oxygen, protons, and electrons

What event is widely recognized as leading to the availability of oxygen for the development of complex life foms, including eukayotes?

Neoproterozoic Oxidation Event NOE

The last eukayotic common ancestor LECA acquired many complex traits, including

Endomembrane system and nucleus

Which photosystem in red algae and cyanobacteia do phycobilisomes pimaily transfer energy to?

Photosystem II

What light-havesting stucture is absent in most green algae but present in red algae and cyanobacteia?

Phycobilisomes

What citical evolutionay step was enabled by the oxidation of water through photosystems in cyanobacteia?

The fomation of the ozone layer and the success of aerobic respiration

Which plastid-beaing organisms obtained their chloroplasts via seconday endosymbiosis with a green alga?

Chlorarachniophytes

What is the main advantage of oxygenic photosynthesis compared to other metabolic processes?

It produces unsurpassed amounts of metabolic energy by using oxygen as a major oxidant

Which core protein pigment is most closely associated with the ability of cyanobacteia to pefom oxygenic photosynthesis?

Chlorophyll a

The nucleomorph found in some eukayotes is evidence of

Endosymbiosis involving a green algal ancestor

Which group of archaea is thought to have played a cucial role in the oigin of eukayotes by engaging in symbiosis with an ancestral alpha-proteobacteium?

Lokiarchaeota

What bacteria is responsible for the formation of banded ion formation and how?

Cyanobacteia by releasing oxygen and oxidizing iron in ocean water

How do LHC proteins in green algae differ from phycobilisomes in red algae?

LHC proteins bind chlorophyll, while phycobilisomes use phycobiliproteins.

What is the pimay function of phycobilisomes in red algae and cyanobacteia?

Capture and transfer light energy to Photosystem II

What evolutionay change occured in green algae duing the transition from red algae in tems of light-havesting systems?

Loss of phycobilisomes and adoption of chlorophyll-binding LHC proteins.

Which major biological innovation occured after the Great Oxidation Event according to the timeline in the source?

The radiation of major cyanobacteial clades into diverse foms

How many membranes are present in the chloroplasts of red and green algae?

2

What was lost in the ancestral plastid in the evolution towards both red and green algae?

Peptidoglycan

What is shown in the illustration?

The engulfment and subsequent endosymbiosis of an alga

what importnat function do Carotenoids have in the Archaeplastida.

Improving efficiency of photosynthesis, Acting as a sunblock, Acting as an anti-oxidant

. Haptophytes are pat of the Archaeplastida supergroup of eukayotes. Haptophyte protists have a CaCO3 based skeleton. What are they famous for?

They are coccolitophores

Which of the following Archaeplastida share a common ancestor with land plants?

Charophytes

Siliceous rock (chet, SiO2) is a type of organic sedimentay rock. The tem 'organic' is misleading as these rocks do not contain any organic mateials. Rather it is a reference to the organisms that are responsible for the fomation of these rocks. In which supergroup of eukayotes are these organisms placed?

SAR clade

In which supergroup of eukayotes did the human species evolve?

Unikonts

The flagellated protist Bigellowiella natans is a typical chlorarchniophyte. The result of seconday endosymbiosis. An electron micrograph is shown. The chloroplast caies a number of stuctures including a prominent pyrenoid that is continous with a plastid. In front of the plastid lies a spheical stucture that has an envelope. It is labeled with a questionmark. What is the identity of that stucture?

Nucleomorph

What happened to the red secondary endosymbiosis?

Most ended up in the SAR clade

Gold Algae

siliceous scales and bristles that form their cell covering

unicellular and solitary

oxygenic photosynthesis

• Pigment:

  • fucoxanthin

Silicification

chemical weathering of silicate rocks on land

difference ebtween eukaryotic cells and prokaryotic cells

They have membrane-bound organelles, including a nucleus.