Understanding Paramecium

About microscopic forms of life, including Bacteria, Archea, protozoans, algae and fungi. Topics relating to viruses, viroids and prions also belong here.

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Poison
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Post by Poison » Sun Mar 12, 2006 8:56 pm

Is this ok? :)
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Post by bionewbie » Sun Mar 12, 2006 9:06 pm

Yes, it's fascinating! :D
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Post by Ken Ramos » Sun Mar 12, 2006 9:17 pm

Poison asked:
Is this ok? :D


Yes it is, a good image of the Vorticella. The blur of the cilia is quite distinct while in motion. Did you know that they spin counter-clockwise. :o We were discussing rotation in ciliates while swimming. I forgot to mention that the Vorticella does rotate also while swimming and it too is in a counter-clockwise motion.

bionewbe asked:

You wouldn't happen to have a picture of a Vorticella, do you? :D


Yes, I have tons of them! :lol:

Click on images for a larger view! :o
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Post by bionewbie » Mon Mar 13, 2006 1:10 am

Khaiy wrote:It's about adaptation. Asexual reproduction means that a paramecium that is already well adapted to its environment will be able to produce more well-suited individuals, without risking taking on new alleles for less well adapted traits.

However, conjugation allows for one paramecium to take on a plasmid (genetic segment) from another paramecium. This way, if one has a beneficial trait, that trait can move through the population more quickly, as well as combining with paramecia that may have another well adapted trait.

This is seen in bacteria once antibiotics have been introduced. If one bacterium is resistant, then conjugation can allow for more resistant organisms to be produced quickly, allowing for a resistant colony to be established.


My apologies for refering back to an earlier statement, but I was just wondering if there are certain situations where a zygote won't undergo meiosis immediately?

Also, why is fission not considered as a sexual process?

Ken Ramos wrote: I forgot to mention that the Vorticella does rotate also while swimming and it too is in a counter-clockwise motion.


Is this before or after undergoing the "telotroch" stage that you mentioned earlier?
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Post by Ken Ramos » Mon Mar 13, 2006 2:51 am

bionewbe asks:

I was just wondering if there are certain situations where a zygote won't undergo meiosis immediately?


You have me on that question there. :roll: :lol: Maybe Khaiy or some of the others can answer that, it is a little out of my territory at present. :D


Also, why is fission not considered as a sexual process?


To the best of my knowledge, I would say that because fission is the process of splitting or dividing of ones self to reproduce, where as conjugation is the coupling, joining or mating of two organisms in order to reproduce. You must also keep in mind that we are talking about single celled micro organisms here also or unicellular forms of life. :D

Ken Ramos wrote:
I forgot to mention that the Vorticella does rotate also while swimming and it too is in a counter-clockwise motion.


Is this before or after undergoing the "telotroch" stage that you mentioned earlier?


This is after becoming free-swimming or in the telotroch stage. :D
Last edited by Ken Ramos on Mon Mar 13, 2006 10:27 am, edited 1 time in total.
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Post by Khaiy » Mon Mar 13, 2006 3:38 am

bionewbie wrote:My apologies for refering back to an earlier statement, but I was just wondering if there are certain situations where a zygote won't undergo meiosis immediately?

Also, why is fission not considered as a sexual process?


Well, as for the zygote, it's important to point out that we'd only be talking about multicellular life, not unicellular anymore. A zygote will not undergo meiosis, but rather mitosis. Meiosis only occurs to produce gametes, which combine to create an individual with the correct number of chromosomes for its species (for example, in humans the necessary number of chromosomes is 46. When the gametes are being produced, sperm for males and eggs for females, meiosis occurs to produce cells that have one half that number, or 23 chromosomes. When the gametes combine during sexual reproduction, the zygote formed would have 46 chromosomes, in 23 pairs).

Therefore, if the zygote underwent meiosis it would produce cells with 23 chromosomes once more, and not be able to produce a functional individual. But undergoing mitosis allows for more cells to develop, leading to a functional individual without disrupting the chromosome number.

I can't think of any situation in which a zygote would not undergo mitosis right away (since there wouldn't be much point to delaying the mechanism that allows the individual to develop), but I suppose that there could be. Nature has done stranger things.

As for why fission is not considered a sexual process, ken got it right. It's only considered a sexual process when the genetic material of two organisms is combined to create offspring that have some combination of the genes of its parents. Since fission is an asexual process, only genes from one individual are present in the offspring, and no combinations with other organisms take place. And ken is also right that fission is for unicellular organisms.

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Post by bionewbie » Mon Mar 13, 2006 12:26 pm

Khaiy wrote:
bionewbie wrote:My apologies for refering back to an earlier statement, but I was just wondering if there are certain situations where a zygote won't undergo meiosis immediately?


Well, as for the zygote, it's important to point out that we'd only be talking about multicellular life, not unicellular anymore. A zygote will not undergo meiosis, but rather mitosis. Meiosis only occurs to produce gametes, which combine to create an individual with the correct number of chromosomes for its species (for example, in humans the necessary number of chromosomes is 46. When the gametes are being produced, sperm for males and eggs for females, meiosis occurs to produce cells that have one half that number, or 23 chromosomes. When the gametes combine during sexual reproduction, the zygote formed would have 46 chromosomes, in 23 pairs).

Therefore, if the zygote underwent meiosis it would produce cells with 23 chromosomes once more, and not be able to produce a functional individual. But undergoing mitosis allows for more cells to develop, leading to a functional individual without disrupting the chromosome number.

I can't think of any situation in which a zygote would not undergo mitosis right away (since there wouldn't be much point to delaying the mechanism that allows the individual to develop), but I suppose that there could be. Nature has done stranger things.


Are you referring to just eukaryotes while zygotes will just undergo mitosis or prokaryotes as well? The reason why I wanted to clarify is because some prokaryotes like Chlamydomonas will just have fusion of its gametes to form a zygote. Then when the conditions are ideal, it will just splite the zygote into haploid to and develop into mature cells. (Is that correct? :?)
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Post by Khaiy » Mon Mar 13, 2006 3:08 pm

It's possible, some organisms are haploid. I just have never heard of an organism that behaves like the Chlamydomonas you described before. In that light, I would only be describing diploid individuals, and specifically eukaryotes (because prokaryotes don't need to divide to develop). Thanks for pointing that out!

EDIT: A bit of research yielded the information that Chlamydomonas can grow as either haploid or diploid, so they don't have to undergo meiosis.

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Post by bionewbie » Tue Mar 14, 2006 2:55 am

Ok then, would you mind explaining to me, the concept of "alternation of generation?"
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Post by Khaiy » Tue Mar 14, 2006 4:59 am

bionewbie wrote:Ok then, would you mind explaining to me, the concept of "alternation of generation?"


Sure. Alternation of generations just means that there is a mitotic phase and a meiotic phase necessary for sexual reproduction. I'll use humans again as an example. If there were no meiosis, then gametes would each be diploid cells (2n, or 46 chromosomes). When these combine, they would create an individual with 92 chromosomes. This process would continually produce individuals with progressively higher and higher numbers of chromosomes. This would be bad for the organism. However, if there were no mitosis, then the number of chromosomes would decrease with each successive division of cells. This would mean that your life would be very short, as your cells could only divide so many times before your cells would all be haploid.

It's the balance of these two that allow animals to live the way that they do; your cells reproduce mitotically to preserve the number of chromosomes, and then meiotically to create gametes capable of producing a new individual with the appropriate number of chromosomes. When the gametes fuse you have a zygote, the cells of which will reproduce mitotically until it is ready to produce gametes itself.

In plants, the process is a bit different. There is a generation that is diploid, called the sporophyte generation, which will produce haploid cells by meiosis (these are called spores). These give rise to haploid individuals (because those haploid cells reproduce by mitosis), which is called the gametophyte generation. These haploid individuals cannot undergo meiosis (because they are already haploid). They produce gametes (reproductive cells that are haploid) by mitosis, and then these gametes fuse together, which produces a diploid organism. When the gametes first fuse, the structure formed is called a zygote.

I'm glad you pointed this out, because I was wrong above. When I said that a haploid organism could not function, I was responding too quickly. Had I stopped to think a moment longer, I would have realized that I was only describing animals. As I said above, plants obviously have functional haploid individuals, and as you pointed out there are other organisms as well that can function as haploids, like the Chlamydomonas.

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Post by Ken Ramos » Tue Mar 14, 2006 11:12 am

You know I remember studying this many years ago in school but it never really sank in, so it has always been a gray area in my studies, in trying to understand the reproductive nature of life in some species of both plants and animals. Some good stuff both of you have brought forward in this discussion here. Continue on. :wink:
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Post by bionewbie » Tue Mar 14, 2006 8:55 pm

Khaiy wrote:In plants, the process is a bit different. There is a generation that is diploid, called the sporophyte generation, which will produce haploid cells by meiosis (these are called spores). These give rise to haploid individuals (because those haploid cells reproduce by mitosis), which is called the gametophyte generation. These haploid individuals cannot undergo meiosis (because they are already haploid). They produce gametes (reproductive cells that are haploid) by mitosis, and then these gametes fuse together, which produces a diploid organism. When the gametes first fuse, the structure formed is called a zygote.


In plants, there is also a differentiate between male and female gametes right? so how does alternation of generation fit in?
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