Biology Dept. / Algae Seminar

1. Algae Seminar
“Endosymbiosis & Cyanobacteria”
Peshawa Yasin

2. Contents
 Definition
 What is Endosymbiosis?
 How important is Endosymbiosis?
 Primary & Secondary endosymbiosis
 Endosymbiosis Hypothesis

3. Definition:-
 Endosymbiosis (Greek: endon= "within",
sym = "together" and biosis = "living").
 An endosymbiont is any organism that lives within
the body or cells of another organism.

4. What is Endosymbiosis?
 The endosymbiosis theory attempts to explain the
origins of organelles such as mitochondria and
chloroplasts in eukaryotic cells.
 According to Endosymbiosis theory:
modern eukaryotic cells evolved from simple,
phagotrophic cells that ingested bacteria and
cyanobacteria; the prey was not digested, and
physiological processes of the endosymbionts were
used by the host.

5. From prokaryote to eukaryote
 Mitochondria developed
from proteobacteria,
and chloroplasts
from cyanobacteria.

6. How important is endosymbiosis?
 Endosymbiosis explains the origin of mitochondria and
chloroplasts, but could it also explain other features of
the eukaryotic cell? Maybe. Endosymbiotic origins have
been suggested for many structures, including flagella,
cilia, and even the nucleus! However, scientists are still
actively debating whether or
not these structures
evolved through
endosymbiosis.

7. Mitochondria and chloroplasts (and maybe other
organelles) evolved from endosymbiotic bacteria.
Heterotrophic prokaryotes were engulfed and function as
mitochondria.
Photosynthetic prokaryotes were engulfed and function as
chloroplasts.
Eukaryotic cell is a chimera of prokaryotic ancestors [The
term chimera refers to the mixture of three prokaryotes].
a. Original contributes genome
b. One becomes mitochondrion
c. One becomes chloroplast

8. Primary & Secondary Endosymbiosis
 Primary endosymbiosis involves the engulfment of a
bacterium by another free living organism. Secondary
endosymbiosis occurs when the product of primary
endosymbiosis is itself engulfed and retained by
another free living eukaryote. Secondary
endosymbiosis has occurred several times and has
given rise to extremely diverse groups of algae and
other eukaryotes.

10. Endosymbiosis Hypothesis
A A prokaryote ingested some aerobic bacteria. The aerobes
were protected and produced energy for the prokaryote
A B C D
Cyanobacteria
Aerobic bacteria Mitochondria Chloroplasts
N
N N
Prokaryote Plant cell
N
Animal Cell

11. 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
Cyanobacteria
Aerobic bacteria Mitochondria Chloroplasts
N
N N
Prokaryote Plant cell
N
Animal Cell

12. Endosymbiosis Hypothesis
C Some primitive prokaryotes also ingested cyanobacteria,
which contain photosynthetic pigments
A B C D
Cyanobacteria
Aerobic bacteria Mitochondria Chloroplasts
N
N N
Prokaryote Plant cell
N
Animal Cell

13. Endosymbiosis Hypothesis
D Cyanobacteria became chloroplasts, unable
to live on their own
A B C D
Cyanobacteria
Aerobic bacteria Mitochondria Chloroplasts
N
N N
Prokaryote Plant cell
N
Animal Cell

14. Secondary Endosymbiosis and
Origin of Algal Diversity
Algae AB
N
N Secondary endosymbiosis
N
Heterotroph C
Algae ABC
Many membrane layers