BSC1005-Disc4

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This is a graded discussion: 30 points possible

due -

Discussion 4 - Endosymbiosis 40 48

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Directions: The mitochondria and chloroplast are thought to have once

been free-living prokaryotes that were engulfed by an early eukaryote and

incorporated into the functioning of that cell. For this discussion, describe

the theory of endosymbiosis in your own words and discuss some of the

evidence for this theory. You can use your textbook as a reference and

research this theory online as well. For full credit, I will be looking for unique

thoughts (compared to other classmate submissions) on the evidence for

the theory of endosymbiosis and your interaction with classmates.

Submission: After you have posted your initial post, read and respond to

two or more of your classmates' posts. Be sure to make substantive and

constructive comments (just posting “nice post” doesn’t count). For

example, add something from your own experience, something you’ve read

or seen. If the situation calls for it, feel free to state an opinion, but be sure

to state any points with which you agree and/or those with which you

disagree, as well as your reasons for agreeing or disagreeing.

Grading: This discussion is worth 30 points and will be graded using

the Discussion Rubric. Pease use it as a guide toward successful completion

of this assignment. 

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6/30/23, 2:54 AM Page 1 of 40

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Harun Vatres (https://canvas.fscj.edu/courses/71848/users/106498)

Jun 4, 2023

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The theory of endosymbiosis suggests that mitochondria and

chloroplasts, two important organelles found in eukaryotic cells, were

once independent prokaryotic organisms that became incorporated into

the functioning of a host cell through a process of engulfment. According

to this theory, an ancestral eukaryotic cell engulfed a free-living

prokaryote, forming a symbiotic relationship where both the host cell and

the engulfed prokaryote benefited.

There are several lines of evidence supporting the theory of

endosymbiosis:

1. Structural Similarities: Mitochondria and chloroplasts have their own

distinct structures resembling those of free-living prokaryotes.

2. DNA Evidence: The DNA of mitochondria and chloroplasts is similar to

that of prokaryotes rather than the nuclear DNA of eukaryotic cells.

3. Replication: Mitochondria and chloroplasts replicate independently

within the eukaryotic cell, similar to the way prokaryotes replicate. They

have their own machinery for DNA replication, transcription, and

translation, which is distinct from the host cell's machinery.

6/30/23, 2:54 AM Page 2 of 40

(https://canvas.fscj.edu/courses/71848/users/26650)

Jomer Ibarreta (https://canvas.fscj.edu/courses/71848/users/26650)

Jun 12, 2023

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Great information Harun! Mitochondria and chloroplasts are about

the same size as free-living bacteria, and they both divide in two to

make more of themselves, just like bacterial cells do. The cell splits

into two equal parts during this process of binary fission.

Mitochondria and chloroplasts are important parts of living things.

Without them, there would be no life as we know it. "The

Endosymbiotic Theory" says that these organelles are thought to have

come from free-living bacteria that were eaten by bigger cells billions

of years ago. This idea explains how mitochondria and chloroplasts

work inside cells and how they are similar to free-living bacteria.

Reference:

"The Endosymbiotic Theory." Encyclopædia Britannica, Encyclopædia

Britannica, Inc., 11 June 2019,

www.britannica.com/science/endosymbiotic-theory

(http://www.britannica.com/science/endosymbiotic-theory)

(https://canvas.fscj.edu/courses/71848/users/129249)

Beyonce Miranda-Gomez (She/Her) (https://canvas.fscj.edu/courses/71848/users/129249)

Jun 15, 2023

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6/30/23, 2:54 AM Page 3 of 40

Hello Harun! I appreciate the information given in your post. I also

wrote about the contribution replication does to this theory. I learned

that the mitochondria replicates in a "pinch." Basically, it pinches

apart and forms two. It was quite fascinating to learn!

(https://canvas.fscj.edu/courses/71848/users/148561)

Eliana Curry (https://canvas.fscj.edu/courses/71848/users/148561)

Jun 19, 2023

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Great information Harun! 

Also, a cool fact about the theory of endosymbiosis is that it explains

how eukaryotic cells obtained the ability to perform aerobic

respiration, which is the process by which cells convert glucose into

energy using oxygen. This allowed eukaryotes to become much more

metabolically efficient than prokaryotes, and paved the way for the

evolution of complex multicellular organisms.

(https://canvas.fscj.edu/courses/71848/users/122748)

Onix Crespo (https://canvas.fscj.edu/courses/71848/users/122748)

Jun 20, 2023

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6/30/23, 2:54 AM Page 4 of 40

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  Short and precise explication with in depth and irrefutable evidence.

Found it interesting that the engulfed prokaryotes also enjoy benefits

from this symbiosis, beforehand I only saw it as a “parasitic” type of

relationship between the phagosome and the phagocyte. 

(https://canvas.fscj.edu/courses/71848/users/137133)

Claudia Huerta (https://canvas.fscj.edu/courses/71848/users/137133)

Jun 5, 2023

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6/30/23, 2:54 AM Page 5 of 40

The theory of endosymbiosis suggests that eukaryotic cells evolved from

the merging of two or more free-living prokaryotic cells. Specifically, it

proposes that mitochondria and chloroplasts found in eukaryotic cells

were once free-living bacteria that were engulfed by a larger host cell,

forming a mutually beneficial relationship.

There is compelling evidence in support of this theory. One of the most

convincing pieces of evidence is the fact that mitochondria and

chloroplasts have their own circular DNA, which is similar to that of

prokaryotic cells, rather than linear like that of eukaryotic cells.

Additionally, the DNA sequences of mitochondria and chloroplasts are

more similar to those of free-living bacteria than to the nuclear DNA of

eukaryotic cells.

Another piece of evidence is the fact that the membranes of mitochondria

and chloroplasts are similar in structure and composition to the

membranes of prokaryotic cells. Specifically, they contain lipids that are

not found in the membranes of eukaryotic cells, and they have their own

unique set of membrane proteins.

Furthermore, the size of mitochondria and chloroplasts is similar to that

of free-living bacteria, and they both reproduce by binary fission, just like

prokaryotic cells do.

Taken together, these lines of evidence strongly suggest that the

mitochondria and chloroplasts found in eukaryotic cells today were once

free-living bacteria that were incorporated into the functioning of the host

cell through endosymbiosis.

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6/30/23, 2:54 AM Page 6 of 40

Tiara Taylor (https://canvas.fscj.edu/courses/71848/users/13719)

Jun 8, 2023

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Hi Claudia, 

 

I enjoyed reading your post. I like how you broke it down when you

stated that mitochondria and chloroplasts have their own circular

DNA, which is similar to that of prokaryotic cells, rather than linear

like that of eukaryotic cells. It's interesting to learn all of this

material. Especially   for me seeing how I never knew about a lot of

these different cells and how they play off of one another. I never

knew about lipids. I never knew that mitochondria and chloroplasts

are found in eukaryotic cells. It's quite fascinating to learn about all

of these cells and how they benefit so many different things in us,

animals and plants. 

(https://canvas.fscj.edu/courses/71848/users/54253)

Corbin Miller (https://canvas.fscj.edu/courses/71848/users/54253)

Jun 8, 2023

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6/30/23, 2:54 AM Page 7 of 40

Hello Claudia,

You did a good job of clarifying the definition of endosymbiosis. I

also agree that one of the biggest pieces of evidence proving this

theory is the similar style DNA that is found in both the organelles

and prokaryotic cells. I did not know that they also split in a similar

way to the prokaryotic cells.

Great discussion!

(https://canvas.fscj.edu/courses/71848/users/107427)

Bonni Haber (She/Her) (https://canvas.fscj.edu/courses/71848/users/107427)

Jun 11, 2023

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Claudia, this was by far the best explanation I've read thus far.

Sometimes I have a harder time following explanations of things like

this and your post helped me more than about ten different websites!

Great post. 

(https://canvas.fscj.edu/courses/71848/users/26650)

Jomer Ibarreta (https://canvas.fscj.edu/courses/71848/users/26650)

Jun 12, 2023

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6/30/23, 2:54 AM Page 8 of 40

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Wonderful post, Claudia! Both mitochondria and chloroplasts are very

small, about the same size as bacteria that live on their own. This is

because they both divide in two, the same way that bacterial cells do.

Binary fission is a type of asexual reproduction that happens when a

single cell splits into two cells that are exactly the same. Because of

this, mitochondria and chloroplasts stay about the same size because

they can't get bigger before splitting. This is also why they are both

about the same size as germs that live on their own. So, mitochondria

and chloroplasts are about the same size as free-living bacteria, and

they both divide into two parts to make more of themselves, just like

bacterial cells do.

 

"Binary Fission." Khan Academy, Khan Academy, 22 Oct. 2020,

https://www.khanacademy.org/science/biology/cellular-respiration-

and-fermentation/cellular-respiration-in-depth/a/binary-fission

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Onix Crespo (https://canvas.fscj.edu/courses/71848/users/122748)

Jun 20, 2023

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  Hello Claudia, found it very interesting and thought stimulating that

you brought up the unique set of membrane proteins that differ on

both organisms.

6/30/23, 2:54 AM Page 9 of 40

(https://canvas.fscj.edu/courses/71848/users/13719)Tiara Taylor (https://canvas.fscj.edu/courses/71848/users/13719)

Jun 6, 2023

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The theory of endosymbiosis is one of the most important theories in cell

biology. It helps us to understand how eukaryotic cells evolved and how

they function. Thus, allowing us to be able to continue learning. 

The theory of endosymbiosis states that some of the organelles in

eukaryotic cells were once free-living prokaryotic cells. Over time, these

prokaryotic cells were engulfed by other prokaryotic cells and evolved to

live in a symbiotic relationship. The engulfed cell provided the host cell

with new capabilities, like the ability to produce energy or to perform

photosynthesis. The host cell provided the engulfed cell with a safe

environment and a source of nutrients. 

One piece of evidence is the fact that mitochondria and chloroplasts, two

of the most important organelles in eukaryotic cells, have their own DNA.

This DNA is different from the DNA of the nucleus, which is the control

center of the cell. Meaning that mitochondria and chloroplasts were once

free-living cells. 

Another piece of evidence for endosymbiosis is that mitochondria and

chloroplasts have their own ribosomes (ribosomes are the structures that

make proteins). The ribosomes in mitochondria and chloroplasts are

different from the ribosomes in the cytoplasm of the cell. The

mitochondria and chloroplasts were once free-living cells that had their

own protein-making machinery. 

https://www.albert.io/blog/endosymbiosis-ap-biology-crash-course/

(https://www.albert.io/blog/endosymbiosis-ap-biology-crash-course/)  

 

https://www.biologyonline.com/dictionary/endosymbiotic-theory

6/30/23, 2:54 AM Page 10 of 40

https://www.biologyonline.com/dictionary/endosymbiotic-theory

(https://www.biologyonline.com/dictionary/endosymbiotic-theory)  

 

https://www.khanacademy.org/science/ap-biology/cell-structure-

and-function/cell-compartmentalization-and-its-

origins/a/chloroplasts-and-mitochondria

(https://www.khanacademy.org/science/ap-biology/cell-structure-and-

function/cell-compartmentalization-and-its-origins/a/chloroplasts-and-

mitochondria)

(https://canvas.fscj.edu/courses/71848/users/54253)

Corbin Miller (https://canvas.fscj.edu/courses/71848/users/54253)

Jun 8, 2023

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Hello Tiara,

I agree with you that this is one of the most important theories as

this is where the life of the eukaryotic cell is formed. With out it there

would be no human life. Also your evidence of ribosomes, I did not

know that, is also convincing towards this theory.

Great discussion!

(https://canvas.fscj.edu/courses/71848/users/113155)

Cori Perry (https://canvas.fscj.edu/courses/71848/users/113155)

Jun 12, 2023

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6/30/23, 2:54 AM Page 11 of 40

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Tiara,

This theory is so important, I concur with what Corbin said, without it

there would be no life. Thank you for your post, it was a great read.

(https://canvas.fscj.edu/courses/71848/users/54253)

Corbin Miller (https://canvas.fscj.edu/courses/71848/users/54253)

Jun 8, 2023

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The endosymbiotic theory shows that the ancestorial history of the

eukaryotic cell was derived through one larger prokaryotic cell absorbing

other prokaryotic cells (early mitochondria and chloroplast which would

be aerobic bacteria at the time). The cell than would then divide into

more. This would help explain the presence of mitochondria and

chloroplast in the eukaryotic cells versus not in the prokaryotic cells.

Breaking the word endosymbiosis down it translates to one organism

that is living "within" another with organism. There is multiple pieces of

evidence that proves this theory. One big piece of evidence to this theory

is the evidence of circular DNA inside of mitochondria and chloroplast

just like how prokaryotic cells have circular DNA. This alone is a big clue

to the origin of the existence of these organelles in eukaryotic cells.

These organelles also have double membranes which is evidence of

being engulfed by other prokaryotic cells.

Fowler, S., Roush, R., & Wise, J. (2017). Chapter 3.3 & Chapter 13.2. In

Concepts of Biology. essay, OpenStax.

6/30/23, 2:54 AM Page 12 of 40

THE ORIGIN OF MITOCHONDRIA. The brain from top to bottom. (n.d.).

https://thebrain.mcgill.ca/flash/a/a_05/a_05_cl/a_05_cl_her/a_05_cl

_her.html#:~:text=The%20double%20membrane%20found%20in,fr

om%20the%20host%20cell%20itself

(https://thebrain.mcgill.ca/flash/a/a_05/a_05_cl/a_05_cl_her/a_05_cl_her.ht

ml#:~:text=The%20double%20membrane%20found%20in,from%20the%20

host%20cell%20itself) .

Understand endosymbiotic theory - AP biology. Private Tutoring. (n.d.).

https://www.varsitytutors.com/ap_biology-help/understand-

endosymbiotic-

theory#:~:text=a%20single%20membrane-,Explanation%3A,the%2

0origin%20of%20eukaryotic%20cells

(https://www.varsitytutors.com/ap_biology-help/understand-endosymbiotic-

theory#:~:text=a%20single%20membrane-,Explanation%3A,the%20origin

%20of%20eukaryotic%20cells) .

 

 

(https://canvas.fscj.edu/courses/71848/users/13719)

Tiara Taylor (https://canvas.fscj.edu/courses/71848/users/13719)

Jun 10, 2023

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6/30/23, 2:54 AM Page 13 of 40

Hi Corbin, 

 

I like how you broke down endosymbios. It's crazy to me to be

learning all of these new things and how they all function with one

another. This is something that I did not learn in school and really

wish I did. Like how did so many cells come bout, as well as how they

know to mix with other cells in order to function the way that they do.

Or what would happen if they were to ever stop functioning altogether

or with certain ones. Does this cause like a domino effect for the

worse or will this cause something new to be discovered and learned

about. Nice post.

 

 

(https://canvas.fscj.edu/courses/71848/users/107427)

Bonni Haber (She/Her) (https://canvas.fscj.edu/courses/71848/users/107427)

Jun 11, 2023

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Corbin, great detail in you post and so easy to follow! "This alone is a

big clue to the origin of the existence of these organelles in

eukaryotic cells. These organelles also have double membranes

which is evidence of being engulfed by other prokaryotic cells." was a

great way to sum up that information and make it clear and precise.

Great discussion! 

6/30/23, 2:54 AM Page 14 of 40

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Cori Perry (https://canvas.fscj.edu/courses/71848/users/113155)

Jun 12, 2023

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Corbin,

Great way to break it down and make it easier to understand!

(https://canvas.fscj.edu/courses/71848/users/107427)

Bonni Haber (She/Her) (https://canvas.fscj.edu/courses/71848/users/107427)

Jun 11, 2023

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6/30/23, 2:54 AM Page 15 of 40

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The Endosymbiotic Theory states that the mitochondria and chloroplast

in eukaryotic cells were once aerobic bacteria (prokaryote) that were

ingested by a large anaerobic bacteria (prokaryote). This theory explains

the origin of eukaryotic cells. Endosymbiosis can best be described as

one organism living completely inside another. The evidence backing this

theory comes from a few different views, some of them are

that Mitochondria (and chloroplasts) aren’t free-living bacteria anymore.

The first eukaryotic cell evolved more than a billion years ago. Since

then, these organelles have become completely dependent on their host

cells. For example, many of the key proteins needed by the

mitochondrion are imported from the rest of the cell. Sometime during

their long-standing relationship, the genes that code for these proteins

were transferred from the mitochondrion to its host’s genome. Scientists

consider this mixing of genomes to be the irreversible step at which the

two independent organisms become a single individual. 

(https://canvas.fscj.edu/courses/71848/users/24335)

Brooklyn Rossi (https://canvas.fscj.edu/courses/71848/users/24335)

Jun 16, 2023

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It is interesting that the proteins transferred from one to the other.

An interesting question that would like to look at further is what

would have happened had this not occurred so long ago. It is

possible the cell structure we see today would be very different. That

being said, it seems unavoidable when one is engulfed in the other

for as long as it was. 

6/30/23, 2:54 AM Page 16 of 40

(https://canvas.fscj.edu/courses/71848/users/113155)Cori Perry (https://canvas.fscj.edu/courses/71848/users/113155)

Jun 12, 2023

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6/30/23, 2:54 AM Page 17 of 40

The theory of endosymbiosis is the theory of how organelles like

mitochondria and chloroplasts arose in eukaryotic cells from symbiotic

relationships between ancestral prokaryotic cells. According to this

theory, a larger cell engulfed a smaller cell by endocytosis or

phagocytosis and did not digest it, but rather kept it in its cytoplasm. The

smaller cell then survived and provided benefits to the host cell, such as

energy or photosynthesis. The smaller cell also replicated in sync with the

host cell, so that the offspring of the host cell inherited the symbiotic

cell. This theory is widely accepted and explains the origin of different

organelles in eukaryotes. 

Some of the evidence that proves this theory:

1.) The presence of DNA - Mitochondria and Chloroplast DNA exists in

closed circular form as it does in a prokaryotic cell. This DNA of the

chloroplast is very similar to photosynthetic blue-green bacteria, while

the mitochondrion DNA is very similar to the aerobic bacteria. Both

organelles lack histones and introns like bacteria.

2.) Inhibition by antibiotics - Several antibiotics kill or inhibit bacteria

by disrupting their 70s ribosomal function. The same antibiotics also

inhibit ribosomal function in mitochondria and chloroplast. Like bacteria,

mitochondria and chloroplast are sensitive to chloramphenicol,

streptomycin, etc.

3.) Same Size - Mitochondria and chloroplast are the same in size as

bacteria. The size of bacteria is commonly 0.1-10 micrometers, while the

size of mitochondria and chloroplast is 0.5-10 micrometers and 1- 10

micrometers respectively.

These are just a few of the ways to prove the theory of endosymbiosis.

6/30/23, 2:54 AM Page 18 of 40

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Beyonce Miranda-Gomez (She/Her) (https://canvas.fscj.edu/courses/71848/users/129249)

Jun 15, 2023

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Hello Corey! 

I appreciate the format of your response and how it was generally

written. It makes it easier to understand the similarities between the

chloroplast and mitochondria and prokaryotes. One similarity that I

did not mention was the presence of DNA, I was actually surprised by

the contribution of DNA. Thanks for your response!

 

(https://canvas.fscj.edu/courses/71848/users/148561)

Eliana Curry (https://canvas.fscj.edu/courses/71848/users/148561)

Jun 19, 2023

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Hello Cori! I love that you added the different types of evidence that

proves the theory of endosymbiosisz! 

Some evidence that supports the theory of endosymbiosis includes

the fact that mitochondria and chloroplasts have their own DNA (which

you mentioned) , which is circular like that of prokaryotes, and that

they replicate through binary fission, like prokaryotes. Additionally,

both organelles have a double membrane, which is consistent with the

idea that they were engulfed by a host cell.

6/30/23, 2:54 AM Page 19 of 40

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Jomer Ibarreta (https://canvas.fscj.edu/courses/71848/users/26650)

Jun 12, 2023

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6/30/23, 2:54 AM Page 20 of 40

DNA data shows that the DNA of mitochondria and chloroplasts is more

like the DNA of prokaryotes than the nuclear DNA of eukaryotic cells.

This shows that mitochondria and chloroplasts were once free-living

prokaryotes that were eaten by the ancestor of eukaryotic cells in a

process called endosymbiosis. This endosymbiosis theory explains why

the DNA of mitochondria and chloroplasts is more like the DNA of

prokaryotes than the nuclear DNA of eukaryotes. This idea has been

accepted as a way to explain how eukaryotic cells came to be because

DNA evidence backs it up.

The idea that coral and dinoflagellates live together is an interesting one.

It says that these two organisms have a symbiotic connection in which

the coral gives the dinoflagellates food and shelter, and the

dinoflagellates give the coral energy through photosynthesis. This link is

important for coral reefs to stay healthy and helps them do well in their

environments. We know a lot about coral reefs and how they interact with

their environment because of the idea of endosymbiosis between coral

and dinoflagellates.

 

References:

"Endosymbiosis." Encyclopædia Britannica, Encyclopædia Britannica,

Inc., 2 May 2020, www.britannica.com/science/endosymbiosis

(http://www.britannica.com/science/endosymbiosis)

 

Glynn, Peter W. "The Symbiotic Relationship between Corals and

Dinoflagellates." The Smithsonian Institution, The Smithsonian

Institution, 11 Apr. 2019, www.si.edu/spotlight/coral-reefs/symbiosis

(http://www.si.edu/spotlight/coral-reefs/symbiosis)

6/30/23, 2:54 AM Page 21 of 40

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Brooklyn Rossi (https://canvas.fscj.edu/courses/71848/users/24335)

Jun 16, 2023

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I believe that the proof that we see the same thing occur in nature

like the coral you mentioned is a great argument for the theory of

endosymbiosis. We have examples of this occurring in ecosystems,

communities, populations, and organisms. It is good reasoning to

believe it caries down even to the cells. 

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Brianna Neeley (https://canvas.fscj.edu/courses/71848/users/139670)

Jun 17, 2023

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Awesome post, Your Coral analogy is a great example of how this

theory of an exchange of energy can take place in many sectors of

life. 

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Beyonce Miranda-Gomez (She/Her) (https://canvas.fscj.edu/courses/71848/users/129249)

6/30/23, 2:54 AM Page 22 of 40

Jun 15, 2023



I would describe the theory of endosymbiosis as the idea that the

mitochondria and chloroplast were once able to survive with no oxygen.

Also, the theory states that they were able to be ingested by larger cells,

like plant or animals cells, which helped the functioning of the cell. 

According to an article titled, "Understanding Evolution," there is a lot of

evidence backing up this idea and theory. The evidence is mainly

focused on the mitochondria. First, the topic of membrane. The

mitochondria has it's own cell membranes, which is similar to prokaryote

cells. Next, reproduction, Mitochondria pinches apart in replication, this

is how the mitochondria reproduces. Similarly, bacteria also reproduces. 

Other evidence leads towards the chloroplast. The main claim is that

chloroplasts are very similar to the mitochondria. Hence, chloroplasts are

similar to mitochondria, mitochondria's are similar to prokaryotes, which

means it comes full circle, Chloroplasts are also similar to Prokaryote. 

6/30/23, 2:54 AM Page 23 of 40

 

 

 

https://evolution.berkeley.edu/it-takes-teamwork-how-

endosymbiosis-changed-life-on-earth/evidence-for-endosymbiosis/

(https://evolution.berkeley.edu/it-takes-teamwork-how-endosymbiosis-

changed-life-on-earth/evidence-for-endosymbiosis/)  

(https://canvas.fscj.edu/courses/71848/users/148704)

Robin Patterson (https://canvas.fscj.edu/courses/71848/users/148704)

Jun 18, 2023

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Hi Beyonce,

The explanation that chloroplasts are very similar to the

mitochondria, chloroplasts are similar to mitochondria, mitochondria

are similar to prokaryotes, really brings all of the together. The

relationship for these organelles is beneficial and the use of the

diagram was a nice touch. 

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Ashley Burris (https://canvas.fscj.edu/courses/71848/users/142506)

Jun 19, 2023

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6/30/23, 2:54 AM Page 24 of 40

Hi Beyonce!

Thanks for adding the visual, I am a visual learner and love to review

diagrams! I am learning that mitochondria are a very complex cell, I

wrote about how it has its own DNA, and you have included here that

it has its own membrane. Fun fact about mitochondria, it produces

90% of the energy in our bodies! My mitochondria must be running

low today… mom joke! 

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Heidi Street (She/Her) (https://canvas.fscj.edu/courses/71848/users/136481)

Jun 19, 2023



Beyonce,

Awesome visual! I think the evidence strongly supports

Endosymbiosis and evolution. Additionally, mitochondria contains a

double membrane, similar to prokaryotic cells. So cool!

Best wishes, Brooke

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Alexis Clements (https://canvas.fscj.edu/courses/71848/users/137316)

Jun 19, 2023

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6/30/23, 2:54 AM Page 25 of 40

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Hello Beyonce,

Thank you for your response to this discussion board. I first want to

thank you for adding a visual for those of us who are visual learners. I

did my own research on the topic and still learned from your

response. I also appreciated you giving supporting evidence outside

of DNA evidence. Great response to the discussion board and very

detailed.

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Claudia Pena (https://canvas.fscj.edu/courses/71848/users/70051)

Sunday



Hello Beyonce,

I loved you use a picture to your post, this caught my attention, and

your explanation help me to understand better this topic. It is very

creative you state the mitochondria pinches apart in replication

because for me it is a creative way to explain binary fission process.

Thank you for sharing. Great job!

Claudia. 

(https://canvas.fscj.edu/courses/71848/users/24335)

6/30/23, 2:54 AM Page 26 of 40

Brooklyn Rossi (https://canvas.fscj.edu/courses/71848/users/24335)

Jun 16, 2023



The theory of Endosymbiosis is that mitochondria and chloroplast started

as a possible bacteria that got into a another prokaryote. After the

mitochondria/chloroplast entered the prokaryote, they benefited each

other and continued to regenerate together. Eventually they became

completely reliant on each other. The primary evidence for this is that

mitochondria/chloroplast contain DNA, their membranes, and their

reproduction. Mitochondria/chloroplast both contain DNA which makes

them unique as they are not the nucleus of the cell. They both have their

own membranes within the cell membrane. Cells are incapable of

building their own mitochondria/chloroplast on their own. They have to

replicate by splitting. This is the same way the prokaryotes replicate. This

theory makes sense in ways. If you look at nature, we as living things

often could function in many different situation, but once we become

reliant on it after a while. There are many examples of ecosystems where

a new organism is introduced and it becomes a symbiotic relationship. It

would be a stretch to believe that this didn't occur in the very cells that

build us.  

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Brooklyn Rossi (https://canvas.fscj.edu/courses/71848/users/24335)

Jun 16, 2023



6/30/23, 2:54 AM Page 27 of 40

My apologies here is my citation 

(2021). Retrieved from https://evolution.berkeley.edu/it-takes-

teamwork-how-endosymbiosis-changed-life-on-earth/evidence-for-

endosymbiosis/

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Brianna Neeley (https://canvas.fscj.edu/courses/71848/users/139670)

Jun 17, 2023



Good job Brooklyn! This is a beautiful way to describe The

Endosymbiotic Theory. I agree that it is true that this kind of

relationship can reflect to other situations here on earth where

different substances choose to conjoin due to good chemistry.

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Heidi Street (She/Her) (https://canvas.fscj.edu/courses/71848/users/136481)

Jun 19, 2023



6/30/23, 2:54 AM Page 28 of 40

 Reply

Hi Brooklyn,

I agree that is is hard to deny the theory as a fact with the amount of

supporting evidence. We see similar instances in nature often when

new organisms are created. I believe the evidence not only supports

the theory of endosymbiosis but it supports evolution as well.

Best wishes,

Brooke

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Brianna Neeley (https://canvas.fscj.edu/courses/71848/users/139670)

Jun 17, 2023



6/30/23, 2:54 AM Page 29 of 40

 Reply

The Endosymbiotic theory states that some of the organelles in

eukaryotic cells were once prokaryotic microbes.

Evidence: Mitochondria and Chloroplasts have circular single stranded

DNA. This is found exclusively in Prokaryotes. This supports the theory of

endosymbiosis because these characteristics suggest that mitochondria

and chloroplast's can survive on their own.  They are also the same size

and can divide by binary fission. 

 

Endosymbiotic theory - Definition and Examples - Biology Online

Dictionary (https://www.biologyonline.com/dictionary/endosymbiotic-

theory)

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Robin Patterson (https://canvas.fscj.edu/courses/71848/users/148704)

Jun 18, 2023



6/30/23, 2:54 AM Page 30 of 40

The theory of endosymbiosis is the theory that eukaryotic cells may have

evolved when multiple cells joined together. This is a mutually beneficial

relationship in which one organism lives within another. Some organelles

in today's eukaryotic cells were previously prokaryotic microbes. The first

eukaryotic cells were thought to be amoeba-like cells that received their

nutrients by phagocytosis and had a nucleus that was formed when it was

pinched off and surrounded by the chromosomes. Specifically, the

mitochondria formed bacteria that had aerobic respiration were ingested

and chloroplasts were formed when photosynthetic bacteria were

ingested. Some proof is that mitochondria and chloroplasts have their

own circular DNA like bacteria. They also have their own ribosomes that

are like bacterial ribosomes. Lastly, the mitochondria and chloroplasts

are the same size as prokaryotic cells and divide by binary fission. 

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Ashley Burris (https://canvas.fscj.edu/courses/71848/users/142506)

Jun 19, 2023



Hi Robin!

I also found it intriguing that mitochondria and chloroplasts have

their own DNA. I found it very insightful how you elaborated further

and included ribosomes. Fun fact about ribosomes, they are known as

the protein factory of the cell! I always found this easy to remember

due to "rib" which is clearly a protein that most of us eat on occasion,

it just seems perfectly fitting. 

 

6/30/23, 2:54 AM Page 31 of 40

 Reply

 Reply

(https://canvas.fscj.edu/courses/71848/users/142506)

Ashley Burris (https://canvas.fscj.edu/courses/71848/users/142506)

Jun 19, 2023



In ∼900 Mya endosymbiosis was discovered. It is defined as one

organism living within another organism. The name is derived from two

Greek root words: endo, meaning within, and symbios, meaning living

together. Without endosymbiosis, many life forms would not exist, such

as plants, fungi, and animals. I found the most intriguing evidence to be

mitochondria and chloroplast having their own DNA. Mitochondrial DNA

can resist degrading and is an expert at duplicating/copying itself.

Chloroplasts also play a major part in our world as they produce energy

through photosynthesis. Without photosynthesis, there would be no

oxygen, lack of oxygen means almost no living thing could survive. It is

so intriguing how things are intertwined, working together, to supply the

only life that we know.

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6/30/23, 2:54 AM Page 32 of 40

Heidi Street (She/Her) (https://canvas.fscj.edu/courses/71848/users/136481)

Jun 19, 2023



The theory of endosymbiosis proposes that mitochondria and

chloroplasts were once independent prokaryotic organisms that were

engulfed by another ancestral cell. It is believed that hosts cells ingested

aerobic bacteria. Rather than being destroyed, these prokaryotes formed

a mutually beneficial relationship with the host cell, eventually becoming

essential components of the eukaryotic cell's functioning.

through evolution,  the aerobic bacteria becoming mitochondria and the

photosynthetic bacteria becoming chloroplasts.

The similarities between mitochondria and chloroplasts when compared

to bacteria supports the theory of endosymbiosis. Both contain double

membranes similar to prokaryotic cells and are the same size.

Additionally, mitochondria and chloroplasts have DNA, like bacteria.

Mitochondria and chloroplasts also reproduce through a process called

binary fission, which is similar to the way bacteria replicate.

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Alexis Clements (https://canvas.fscj.edu/courses/71848/users/137316)

Jun 19, 2023



6/30/23, 2:54 AM Page 33 of 40

 Reply

Hello Heidi,

Thanks for your response to the discussion board. This was a great

response and great supporting evidence. I appreciate the fact that

you  mentioned evidence outside of DNA. I also find the evidence

provided about the double membranes very useful. Thank you for your

detailed response, I enjoyed reading it.

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Alexis Clements (https://canvas.fscj.edu/courses/71848/users/137316)

Jun 19, 2023



6/30/23, 2:54 AM Page 34 of 40

The theory of endosymbiosis explains the origin of certain organelles

within eukaryotic cells, such as mitochondria and chloroplasts. Some

evidence supporting this theory, includes DNA, similarities in structure,

membranes, and reproduction. Mitochondria have their own cell

membranes, just like a prokaryotic cell does. The DNA of mitochondria

and chloroplasts is more closely related to bacterial DNA than to nuclear

DNA. Mitochondria and chloroplasts exhibit striking similarities to free-

living bacteria. They have their own circular DNA, similar to bacterial

DNA, and possess ribosomes that resemble bacterial ribosomes.

https://evolution.berkeley.edu/it-takes-teamwork-how-

endosymbiosis-changed-life-on-earth/evidence-for-endosymbiosis/

(https://evolution.berkeley.edu/it-takes-teamwork-how-endosymbiosis-

changed-life-on-earth/evidence-for-endosymbiosis/)

https://biologydictionary.net/endosymbiotic-theory/

(https://biologydictionary.net/endosymbiotic-theory/)

 

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Robin Patterson (https://canvas.fscj.edu/courses/71848/users/148704)

Jun 19, 2023



Hi Alexis,

I did not realize before this assignment that there were different

types of DNA. As you pointed out in your discussion there is circular

DNA which is found in bacterial DNA. These discussions truly are

helping me understand how all of this relates.

6/30/23, 2:54 AM Page 35 of 40

 Reply

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Eliana Curry (https://canvas.fscj.edu/courses/71848/users/148561)

Jun 19, 2023



Endosymbiosis is a theory that explains how eukaryotic cells evolved from

prokaryotic cells. The theory suggests that mitochondria and chloroplasts,

the organelles that produce energy in eukaryotic cells, were once free-

living prokaryotic cells that were engulfed and then evolved a symbiotic

relationship with their host cell. Evidence for this theory includes the fact

that mitochondria and chloroplasts have their own DNA, which is circular

like that of prokaryotes, and that they replicate through binary fission, like

prokaryotes. Additionally, both organelles have a double membrane, which

is consistent with the idea that they were engulfed by a host cell.

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Claudia Pena (https://canvas.fscj.edu/courses/71848/users/70051)

Sunday



6/30/23, 2:54 AM Page 36 of 40

 Reply

Hello Eliana,

I like your clear and concise post. In addition, form my research I

found out that this theory is not from the past, it can also be present

in organisms like termites, which can have prokaryotes that live in

their duct and help to digest wood, without them they could not

digest it. 

Claudia.

 

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Onix Crespo (https://canvas.fscj.edu/courses/71848/users/122748)

Jun 20, 2023



The theory of Endosymbiosis is based on the premise that chloroplasts and mitochondria arise from Prokaryotic cells. According to this theory, the first Eukaryotic cell was likely a amoeba-like organism that received nutrients by phagocytosis (its the process by which a organism uses its plasma membrane to engulf a particle, after, it compartmentalizes inside the organism. The engulfed particle is called a phagosome while the organism that partakes in phagocytosis is called a phagocyte.) Some of these Amoeba-like organisms ingested prokaryotic cells who survived inside them and developed a symbiotic relationship. A common use of phagocytosis in the human body is our immune system, its a major mechanism used to remove cell debris / pathogens by digesting them in the phagosome. 

6/30/23, 2:54 AM Page 37 of 40

 Reply

Evidence:  Prokaryotic cells and chloroplasts are the same size, they also divide by binary fission.  Mitochondria and Chloroplasts have their own DNA that is circular, not linear.  Several primitive eukaryotic microbes, such as Giardia and Trichomanas have a nuclear membrane but no mitochondria. 

Evidence against:  Although less convincing, it is possible that flagella and cilia may have come from spirochetes. 

(https://bio.libretexts.org/Bookshelves/Microbiology/Microbiology_(Kaiser)/U

nit_4%3A_Eukaryotic_Microorganisms_and_Viruses/07%3A_The_Eukaryotic

_Cell/7.8%3A_The_Endosymbiotic_Theory)

References; https://bio.libretexts.org/Bookshelves/Microbiology/Microbiology_(Kais er)/Unit_4%3A_Eukaryotic_Microorganisms_and_Viruses/07%3A_The _Eukaryotic_Cell/7.8%3A_The_Endosymbiotic_Theory (https://bio.libretexts.org/Bookshelves/Microbiology/Microbiology_(Kaiser)/U

nit_4%3A_Eukaryotic_Microorganisms_and_Viruses/07%3A_The_Eukaryotic

_Cell/7.8%3A_The_Endosymbiotic_Theory)

https://askabiologist.asu.edu/explore/cells-living-in-cells (https://askabiologist.asu.edu/explore/cells-living-in-cells)

https://ib.bioninja.com.au/standard-level/topic-1-cell-biology/15-the- origin-of-cells/endosymbiosis.html (https://ib.bioninja.com.au/standard-level/topic-1-cell-biology/15-the-origin-

of-cells/endosymbiosis.html)

6/30/23, 2:54 AM Page 38 of 40

 Reply

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Claudia Pena (https://canvas.fscj.edu/courses/71848/users/70051)

Sunday



Before I start to write about the endosymbiosis theory, I have to recap

prokaryotes and eukaryotes. Then, prokaryotes have not nucleus and

membrane - bound organelles, but eukaryotes do. However, they have

common like cell membrane, cytoplasm, ribosomes, genetic material, and

finally mutualism is equal a symbiosis where both are benefit. 

Therefore, the endosymbiosis theory consists with the general

evolutionary one that all organisms come from another ancestor. It could

be prokaryote or bacteria with a single DNA caused by plasma

membrane. Evidence of this theory is showed in the same bacteria which

uses oxygen to produce their own energy to evolve to mitochondria, and

also uses some energy to produce their own food considered to evolve to

chloroplast. In addition, mitochondria and chloroplasts contain their own

DNA and ribosomes, and have similar size as bacteria's do.

Overall, this theory is not just for the past, nowadays the clear example of

this are the termites that can have prokaryotes that live in their duct to

help to digest wood, otherwise, without them they could not ingest wood

again. 

 

 

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