GENERAL BIOLOGY

DIVERSITY OF LIFE

İÜ Su Ürünleri Fak.
SUUM1019
L2

Yard. Doç. Dr. Nur Eda TOPÇU ERYALÇIN

A depiction of Earth about 3 billion years ago
stromatolites
Chemical and physical processes on early Earth could have produced very
simple cells through a sequence of four main stages:

1. The abiotic (nonliving) synthesis of small organic molecules,

such as amino acids and nitrogenous bases

2. The joining of these small molecules into polymers, such

as proteins and nucleic acids

3. The packaging of these molecules into “protocells,” droplets

with membranes that maintained an internal chemistry
different from that of their surroundings

4. The origin of self-replicating molecules that eventually

made inheritance possible
Miller experiment
“Life, just like the stars, the planets and the galaxies, is
just a temporary structure on the long road from order
to disorder. But that doesn't make us insignificant,
because we are the Cosmos made conscious. Life is
the means by which the universe understands itself.
And for me, our true significance lies in our ability to
understand and explore this beautiful universe.”
― Brian Cox
Taxonomy names and classifies the diversity of life
Omurgalı, omurgasız vs
tüm hayvalar
Böcekler!
Bitkiler
Mantarlar
Algler ve diğer protistler
 Bacteria on the
point of a pin

Prokaryotic cells: 1-5 µm

Eukaryotic cells: (typically) 5-100 µm
• Several modes of nutrition
• The collective biomass of prokaryotes is at least ten times that of all eukaryotes.
• They also thrive in habitats too cold, too hot, too salty, too acidic or too alkaline for
any eukaryote.
• Scientists are JUST BEGINNING to investigate the extensive prokaryotic diversity in
the oceans
Thermus aquaticus. The thermophilic bacteria found in thermal
lakes that Taq Polymerase was isolated from.
 What are protists?

Protist is a useful term but phylogenetically

meaningless.

Eukaryotes that are not animals, plants or fungi

Eukaryotes that are not
animals, plants or fungi
Crash Course link
 Protist Diversity

•Protists are more diverse than all other

eukaryotes

•Most protists are unicellular

–And some are colonial or multi-cellular
Protist Diversity

• Organisms that range in size from single

cells to complex structures more than 100
meters long.

• They show a variety of reproductive and

nutritional strategies.
Protist Diversity
•Protists, the most nutritionally diverse of all
eukaryotes, include
–Photoautotrophs, which contain chloroplasts
(algae, another useful term but taxonomically
meaningless word)

–Heterotrophs, which absorb organic molecules

or ingest larger food particles, bateria or other
protists

–Mixotrophs, which combine photosynthesis and

heterotrophic nutrition – depending on the
conditions of light and nutrients
Protists are also diverse in habitat
•Including freshwater and marine species
(a) The freshwater ciliate Stentor,
a unicellular protozoan (LM)

100 µm

100 µm

(b) Ceratium tripos, a unicellular marine dinoflagellate (LM)

4 cm

(c) Delesseria sanguinea, a multicellular marine red alga

500 µm

(d) Spirogyra, a filamentous freshwater green alga (inset LM)

Most of them are unicellular but these cells are among the most elaborate in the world
 Protist Evolution
•The plastid-bearing lineage of protists
–Evolved into red algae and green algae

•On several occasions during eukaryotic

evolution
–Red algae and green algae underwent
secondary endosymbiosis, in which they
themselves were ingested
 Plastid

2˚ Endosymbiosis Dinoflagellates

Alveolates
Apicomplexans

Secondary
endosymbiosis

Cyanobacterium Red algae Ciliates

Primary
endosymbiosis
Stramenopiles

Heterotrophic Plastid
eukaryote

Euglenids

Secondary
endosymbiosis
Green algae

Chlorarachniophytes
Trophic Levels
Autotrophs: Heterotrophs:
· green algae · amoeboids
· brown algae · ciliates
· red algae · zooflagellates
· diatoms · sporozoans
· dinoflagellates · slime molds
· euglenoids
 A tentative phylogeny of eukaryotes includes multiple clades of protists

(Chromista)

Rhizaria

Excavata SAR
Unikonta Archaeplastida

Monophyletic lines derived from Protista, highlighted, in yellow and given a rank equivalent to
that of kingdom. Note that Fungi, Animals and Plants remained unchanged at kingdom level.
https://www.bio.fsu.edu/~stevet/pictures/Doolittle.jpg
SAR

Diatoms

Brown
algae

Apicomplexans
Ciliates
Dinoflagellates

Radiolarians Foraminiferans
 SAR
Stramenopila

•Stramenopiles have “hairy” and smooth

flagella

•The clade Stramenopila Includes:

–Water molds

–Diatoms Hairy
flagellum
–Golden algae Smooth
flagellum

–Brown algae 5 µm
Oomycetes: fungus-like eukaryotic
microorganisms
–Include water molds, white rusts, and downy
mildews

–Were once considered fungi based on

morphological studies
–Are decomposers or parasites

–Have filaments (hyphae) that facilitate nutrient

uptake

–Have cell walls

made of cellulose
 Diatoms
•Are unicellular algae
–With a unique two-part, glass-like wall of
hydrated silica

–major component of phytoplankton

 Diatoms
· Most numerous unicellular algae in the oceans
and are an important source of food and oxygen.

· Also important in freshwater environments.

· Glucose stored as polysaccharide laminarin (Same as

golden & brown algae)

· Their remains form diatomaceous earth

 Diatoms
~ 100 000 species
 25 µm

Golden Algae

•Or chrysophytes
–Are named for their color,
which results from their
yellow & brown carotenoids

– found mostly in freshwater

•The cells of golden algae

–Are typically bi-flagellated, with both flagella
attached near one end of the cell
Brown algae
•Or phaeophytes
–Are the largest and most
complex algae

–Are all multicellular, and most

are marine
–Include many of the species commonly called
seaweeds

•Seaweeds
–Have the most complex multi-cellular anatomy of
all algae
 Brown Algae
Photosynthetic & multicellular Blade
· Range in size.
Many are 50-100 m long.
· Found along rocky shores Stipe

The thalus (plant like body) contains:

Holdfast
· Holdfasts for attachment
· Blades and air bladders that function in floatation
· A stem-like structure that holds the blades is called a stipe.
Fucus
Common "seaweed" found along the rocky coast.
Brown Algae
•Kelps, or giant seaweeds
–Live in deep parts of the
ocean

–Can grow as long as 60m

Cell walls are composed of cellulose and
gel forming polysaccharides which
cushion the algae in the intertidal zone
https://bloominginthetropics.wordpress.com

Gökçeada, 2016
DIFFERENCES BETWEEN ALGAE AND PLANT
 A variety of life cycles
Have evolved among the multi-cellular algae

•The most
complex life
Sporangia

cycles include an
alternation of Sporophyte
MEIOSIS

generations
(2n)
Zoospores

Female

–The alternation
Developing
sporophyte Gametophytes

of multi-cellular
(n)
Zygote
(2n)

haploid and
Egg
FERTILIZATION Male
Mature female

diploid forms
gametophyte
(n)

Key Sperm

Haploid (n)
Diploid (2n)
 SAR
Alveolates
Members of the clade Alveolata
–Have membrane-bounded sacs (alveoli) just
under the plasma membrane

Includes:
•Dinoflagellates
•Apicomplexans
•Ciliates
 Dinoflagellates
–Are a diverse group of aquatic
photoautotrophs and heterotrophs

–Are abundant components of both marine

and freshwater phytoplankton
•Shape is reinforced by internal plates of cellulose

•Two flagella
–Make them spin as they

move through the water

 Dinoflagellates Toxins released can kill aquatic
& terrestrial animals (aerosols)
Some species are responsible for red tides that kill fish and shellfish
Zooxenthellae dinoflagellate
 SAR
Rhizaria
Foraminiferans, or forams
–Are named for their porous, generally
multichambered shells, called tests
20 µm

Pseudopodia extend through the pores in the

test
 SAR Rhizaria

Radiolarians
•Marine protists
–Whose tests are fused into one delicate piece, which is generally
made of silica

–Phagocytize microorganisms with their pseudopodia

•The pseudopodia of radiolarians, known as
axopodia
–Radiate from the central body

Axopodia

200 µm
Radiolarians

Marine plankton (float in marine environments) with

a skeleton composed of silica , and numerous needle-
like pseudopodia.
Excavata

- an “excavated” feeding groove possessed by some members of the group

- modified mitochondria that lack functional electron transport chains
- use anaerobic pathways, such as glycolysis, to extract energy

Photoautotrophs

Heterotrophic predators

Parasites

Mixotrophs
Diplomonads and Parabasalids
 Euglenozoans
Members of the clade Euglenozoa
–Very diverse clade

–Heterotrophs, photosynthetic autotrophs and

pathogenic parasites
Euglenoids move through their aquatic habitats
using two long flagella that guide them toward
light sources sensed by a primitive ocular
organ called an eyespot.

The familiar genus, Euglena, encompasses

some mixotrophic species that display a
photosynthetic capability only when light is
present. In the dark, the chloroplasts
of Euglena shrink up and temporarily cease
functioning; the cells, instead, take up organic
nutrients from their environment.
 Euglena viridis

Plant or Animal?
Or what?!

Protista
Unikonta

Protozoans
· Do not have a cell wall

· Heterotrophic

· Usually motile

· Food vacuoles

· Contractile vacuole (water elimination)

Reproduction is usually asexual but many also reproduce

sexually during some part of their life cycle.
 Amoeboids
Amoeba

Move by cytoplasmic extensions called pseudopodia .

Feed by phagocytizing (engulfing) their prey.

Most amoeboids are marine organisms;

Amoeba proteus is found in freshwater

Amoeboids
Slime molds

Dunn, Joe & Bosmani, Cristina &

Barisch, Caroline & Raykov, Lyudmil &
Lefrancois, Louise & Cardenal-Muñoz,
Elena & López-Jiménez, Ana &
Soldati, Thierry. (2018). Eat Prey, Live:
Dictyostelium discoideum As a Model
for Cell-Autonomous Defenses.
Frontiers in Immunology. 8.
Archaeplastida

The word algae refers to aquatic (freshwater or marine)

protists.

Algae photosynthesize like plants. They produce much

of the oxygen in the atmosphere.

· Algae provide food for aquatic food chains.

 Red & Green Algae

•Are the closest relatives of land plants

•Over a billion years ago, a heterotrophic protist

acquired a cyanobacterial endosymbiont

–And the photosynthetic descendants of this ancient

protist evolved into red algae and green algae
 Red Algae
• Are reddish in color
–Due to an accessory pigment called
phycoerythrin, which masks the green
of chlorophyll
Red Algae

• Red algae are found mainly in warmer,

tropical oceans.

• Accessory photosynthetic pigments are

called phycobilins which allow some
species to survive in deep waters
where blue and green light
predominates.

• Some species are filamentous but most

have a complex pattern of branching.

• Some coralline forms deposit calcium

carbonate in their cell walls, making
coral reefs.
 Green Algae
–Are named for their grass-green chloroplasts

–Are divided into two main groups: chlorophytes

and charophyceans

–Are closely related to land plants

Green Algae

Single-celled and multicellular forms.

·
Ancestors of the first plants, both have the following
characteristics in common:
They have a cell wall that contains cellulose.
They have chlorophyll
They store their food as starch inside the chloroplast.
 Chlorophytes
(green algae)
•Include:
20 µm

–Unicellular, 50 µm

colonial, and
(a)

multi-
cellular
forms

)
Ulva
• Multicellular with a leaf-
like body that is two cells
thick but up to one meter
long

• Common name: Sea lettuce

 Volvox

• Some cells are specialized to produce sperm

and eggs for sexual reproduction which is a
characteristic of multicellular organisms.

• Considered to be a colony because it appears

to be intermediate between a group of
individual cells and a multicellular organism.
 Volvox

· Colonial green algae

· They divide asexually to

produce a daughter colony.

Notice the daughter colonies

within the larger colonies.
Spirogyra Filamentous form of green
algae

Conjugation
Chlorophyte Life Cycle Harsh environmental
conditions

Flagella
1 µm −
Cell wall

Nucleus +
+ −

Zoospores
SYNGAMY
Mature cell
(n)
ASEXUAL SEXUAL
Regions REPRODUCTION REPRODUCTION
of single Zygote
chloroplast (2n)

+ −

Key + MEIOSIS

Haploid (n)
Diploid (2n)

Normal environmental
conditions
A tentative phylogeny of eukaryotes includes multiple clades of protists

(Chromista)

Rhizaria

Excavata SAR
Unikonta Archaeplastida
Choanoflagellates
- free-living unicellular and colonial flagellate

eukaryotes

- collared flagellates having a funnel shaped collar of

interconnected microvilli at the base of a flagellum

- capable of both asexual and sexual reproduction

- cell morphology characterized by an ovoid or spherical

cell body 3–10 µm in diameter with a single apical

flagellum surrounded by a collar of 30–40 microvilli

- useful model for reconstructions of the last

unicellular ancestor of animals

Poriferans: the most primitive metazoans
Multicellularity