Introduction to Protists

Eukaryotic Evolution and Diversity

Learning Goals

• Understand theory of endosymbiosis in the

evolution of eukaryotes

• Provide evidence for the theory of

endosymbiosis

• Distinguish between the 3 groups of

protists (animal; fungus; plant-like)

Origin of Eukaryotes

• First eukaryotic organism thought to have evolved about 1.5 billion years ago. Prokaryotes are as old as 4 billion years

• Protozoans (protists) possibly evolved from the 1st eukaryotes by Endosymbiosis

• Endosymbiosis –theory that explains how eukaryotic cells evolved from the symbiotic relationship between two or more prokaryotic cells; often one prokaryote lives inside another becoming dependent upon each other

Endosymbiotic Theory

• First postulated by Lynn Margulis in 1967

• Although now accepted as a well-supported theory, both she and the theory were ridiculed by mainstream biologists for a number of years. Thanks to her persistence, and the large volumes of data that support this hypothesis gathered by her and many other scientists over the last 30 years, biology can now offer a plausible explanation for the evolution of eukaryotes.

Endosymbiosis wha???

• Endo = "within“

• Endocytosis = (cyto = cell) a process of 'cell

eating' - cells are engulfed, but then usually

digested as food....

• Endosymbiosis = cells are engulfed, but not

digested...cells live together in a mutually

benefiting relationship, or symbiosis

Origin of Eukaryotes

• Eukaryotic cells more complex than

prokaryotic cells:

– Membrane-bound nucleus and organelles

– Many chromosomes that occur in pairs.

– Protists, fungi, plants & animals are

composed of eukaryotic cells.

Typical Animal Cell

Eukaryotic Animal Cell

Typical Plant Cell

Eukaryotic Plant Cell

Infolding of membrane

system forming nucleus

and ER

Origin of Eukaryotes

Endomembrane infolding

Origin of Eukaryotes: Cholorplasts and

Mitochondria• Mitochondria and chloroplasts

(endosymbionts) were prokaryotes that invaded larger cells (host cell)

• Mitochondria provided energy for the host cell and chloroplasts converted solar energy into molecular energy

• Endosymbiont, ancestral mitochondria:– Aerobic, heterotrophic & prokaryotic

• Endosymbiont ancestral chloroplasts:– Anaerobic, autotrophic and prokaryotic

Origin of Eukaryotes

• Ancestral chloroplasts were photosynthetic, prokaryotes that became endosymbionts (cyanobacteria)

• Relationship began as parasitic or undigested prey

• Assumed here that endomembrane infolding evolved first, i.e., cell already evolved nucleus, ER, …

Endosymbiosis Hypothesis

A

A prokaryote ingested some aerobic bacteria. The

aerobes were protected and produced energy for

the prokaryote

ChloroplastsAerobic bacteria MitochondriaCyanobacteria

Prokaryote

Animal Cell

Plant cell

B C D

A

N

NN

N

Endosymbiosis Hypothesis

B Over a long period of time the aerobes

became mitochondria, no longer able to

live on their own

A B C D

ChloroplastsAerobic bacteria MitochondriaCyanobacteria

Prokaryote

Animal Cell

Plant cell

N

NN

N

Endosymbiosis Hypothesis

C Some primitive prokaryotes also

ingested cyanobacteria, which contain

photosynthetic pigments

A B C D

ChloroplastsAerobic bacteria MitochondriaCyanobacteria

Prokaryote

Animal Cell

Plant cell

N

NN

N

Endosymbiosis Hypothesis

D Cyanobacteria became chloroplasts,

unable to live on their own

A B C D

ChloroplastsAerobic bacteria MitochondriaCyanobacteria

Prokaryote

Animal Cell

Plant cell

N

NN

N

Scientific Evidence for Theory of

Endosymbiosis • Membranes of chloroplasts and mitochondria are similar

to those of living prokaryotes

• The ribosomes found in these organelles are more similar to prokaryotic ribosomes than to ribosomes found in eukaryotes

• These organelles reproduces by binary fission within the cell

• Each organelle contains a circular chromosome and gene sequences match those of living prokaryotes

Multicellularity

• Endosymbiosis does not

explain multicellularity,

another eukaryotic

advance

• First multicellular

organisms existed 1.2 to

1.5 billion years ago (or

half as long as unicellular

organisms) Red Algae

• Large complex eukaryotes

fist developed 550 million

years ago

Red Algae fossils

Life Cycles and Reproduction• Eukaryotes also have more diverse life cycles than

prokaryotes

• In prokaryotes cell division and reproduction are the same thing: Asexual

• In multicellular eukaryotes cell division ≠ reproduction

• In sexual reproduction, two individuals make eggs and sperm knows as gametes

• Gametes are haploid (one set of chormosomes, ha=half) compared to cells of the rest of the organism; diploid (both sets of chromosomes, di=2)

Asexual Life Cycle

• All prokaryotes

• Some eukaryotes

(yeast)

Gametic Sexual Life Cycle

• Organism is diploid

• Produces haploid gametes which are fertilized (zygote)

• Zyogote undergoes mitosis (cell division) to become organism– Humans

Zygotic Sexual Life Cycle

• Organism is haploid

• Produces haploid gametes that

upon fertilization form diploid

zygote

• Zygote undergoes meiosis to

produce haploid spores that

develop into organism

• Most fungi

• Some protists (malaria parasite

Sporic Sexual Life Cycle

• Organism lives in 2 stages: diploid and haploid

• Haploid organism produces haploid gamete

• Zygote undergoes mitosis to become diploid organism

• Diploid organism produces haploid spores

• Haploid spores become haploid organism

Protists: The Unicellular Eukaryotes

General Characteristics• All are eukaryotic, mostly single-celled microscopic

organisms

• Come in all shapes, sizes and colours

• Some have cell walls, some are motile

• Classified together because they do not fit into other kingdoms, rather than because they are similar or closely related to one another

• Most diverse group of eukaryotes, but not as diverse as the bacteria or archaea

• 3 main groups of protists, characterized by how they get their nutrients.

Three groups of protists

• Animal-like protists

• Fungus-like protists

• Plant-like protist

Animal-like Protists

• (Protozoa) – e.g. Amoebas

– Consume other organisms for food

– Some species are parasites

Protozoa

• Means first animals

• Scavengers or predators

• Some are parasites.

• Vary in shape and size.

• Most live as single cells

but others form colonies

The Cercozoans: Phylum Cercozoa

• Amoebas

• Cell membrane w/o cell wall, so can change

shape

• Can form cytoplasmic extensions called

pseudopods (false feet) for feeding and

movement

• http://www.youtube.com/watch?v=7pR7TNzJ_pA

The Ciliates: Phylum Ciliophora

• Paramecia

• Have many short hair-like projections called cilia (singular cilium)

• move by cilia beating in a coordinated rhythm, they also help move food into the paramecium’s gullet, which leads to a food vacuole.

• http://www.youtube.com/watch?v=fh_yjLppNAg&

feature=fvwrel

Flagellates: Phylum Zoomastigina

• Have one or more flagella which whip from side to side to move them about

• some are mutualistic: Trichonympha live in digestive systems of termites and help break down cellulose.

• some are parasitic: Trypanosomia causes African sleeping Sickness

• http://www.youtube.com/watch?v=9duvzqvVflw

The Sporozoans: Phylum Sporozoa

• Parasites

• they have spores at some point in their

lifecycle

• they contain a number of complex organelles

at one end of their bodies to help them invade

their victim. Plasmodium vivax causes one

type of malaria in humans

Life Cycle of Malaria-causing Plasmodium

http://highered.mcgraw-hill.com/olc/dl/120090/bio44.swf

Fungus-like Protists

• – e.g. Slime moulds, water moulds

– Absorb nutrients from other organisms (living

or dead)

– Some consume other organisms, some are

parasites

Slime and Water Moulds

• Have the characteristics of

fungi, protozoa and plants.

• They glide from place to place

and ingest food like protozoa.

• They have cellulose in their

cell walls like plants. They

also absorb nutrients from

their environment like fungi.

• Visible to the naked eye as tiny slug like

organisms that creep over damp, decaying

plant material in forests and fields.

• This blob, called a plasmodium, contains many nuclei. Feed in a similar manner to amoebae.

• http://www.youtube.com/watch?v=khEAZabMtOk&feature=related

Plasmodial Slime Moulds (Myxomycotes)

Cellular Slime Moulds (Acrasiomycota):

• exist as individual amoeboid like cells with one nucleus each.

• Feed by ingesting tiny bacteria or yeast cells.

• When food becomes scarce, the cells release a chemical that causes them to gather together to form a pseudoplasmodium. This is a jelly-like mass, which produces a sporangia that releases spores.

Water Moulds (Oomycota):

• includes water moulds, white rusts and downy mildews

• Filamentous organisms that resemble fungi. Most live as saprotrophs (dead organic matter)

• some are parasitic on plants, insects and fish. They extend fungus like threads into their host where they release digestive enzymes and absorb the nutrients.

• Cause of the Irish Potato Famine.

Plant-like Protists

• e.g. Diatoms and dinoflagellates

– Make their own food by photosynthesis

– Some can consume other organisms when

light is unavailable

Diatoms: Phylum Chrysophyta

• most abundant unicellular algae in the oceans. They are

one of the biggest components of plankton.

• Can reproduce asexually. Sexual reproduction is less

common

• As photosynthetic organisms they are also a major source

of atmospheric oxygen. They have rigid cell walls that

contain silica, a common ingredient in sand and glass.

• The remains of diatoms stick around for a long time and

they are used in filters, sound proofers, insulation and as a

gentle abrasive in metal polishes and toothpastes.

Diatoms

Dinoflagellates: Phylum Pyrophyta

• Unicellular, photosynthetic and mostly marine.

• They have protective coats made of stiff cellulose

plates. They all have two distinct flagellae

• They are extremely numerous and form an important

base for marine food chains. Form red tides which

cause toxins to built up in shellfish that eat them.

Red Tide

Some bioluminescence

http://www.youtube.com/watch?v=

Py-J1ZazHDM&feature=fvwrel

Euglenoids

• Unicellular freshwater organisms with two

flagellae, one usually much longer than the

other.

• They contain chloroplasts but if there is no

sunlight then they lose their chloroplasts and

ingest and eat food.

• Have a light receptor and allows them to move

towards light

Homework

• Pg 69, Q 13-18

• Pg 76, Q 19-24

2.3 and 2.4 of the textbook