Most important organelle to the existence of life on earth

[DiscoJen]

I've been given a test question by my biology professor and I could some help from some groovy bio-geeks. No offense intended...I only strive to be a bio-geek one day!

Rank the following three double membraned organelles in order of importance to the existence of life on earth and explain why each is put in that order. Mitochondria, Chloroplasts, Nuclei.

Kinda like the chicken or the egg debate but this one counts toward my grade and I need it. I have an idea of what a mildy logical answer would be, but afterall, this is chapter 3 in BIO111 at community college so I'm not educated enough on this topic to feel confident in my thoughts.

Thanks for any input!
Jen

[MrMistery]

stupid question but i would say nuclei>mitochondria>chloroplasts

[Darby]

Mitochondria would be pretty useless without chloroplasts cranking out the oxygen, but both processes occur in non-nucleated cells as well as nucleated cells.

If you think multicellularity is important, then nuclei are important.

I think that, with explanations that show that you understand the contribution each one makes, you could do almost any order and make it work. Some orders are harder to support than others, though.

[whirlboy]

i agree wtih darby.I think,the chloroplasts origin in some green bacteria. the non-nucleated cells may tell us that the nuclei are not so important for the cells on earth actually.
that's my personal opinion.

[Ultrashogun]

I agree, Id say chloro > mito > nuclei

[DiscoJen]

Cool, at least I think I am synthesizing the bit I know about biology so far in this class. I was thinking Chloroplasts, Mitochondra, Nucleus. Since the sun is really the source of all life on the planet, life could not exist without a way to synthesize the energy into oxygen so I put chloroplasts first. Especially since the question was NOT the importance to HUMAN life on earth...so prokaryotes with no nucleus can contain chloroplasts. Then the mitochondria come into play for cellular respiration.

I'll work on wording my answer more eloquently and detailed for the test.

Thanks for the insight and the confidence to think I was heading in the right direction with this.

Jen

[MrMistery]

prokaryotes do not contain chloroplasts... some can do photosynthesis by themselves, they do not need chloroplasts...

[Darby]

The prevailing theory is that chloroplasts originally were photosynthetic prokaryote cells, taken in by bigger cells (eukaryotes or cells on their way to being eukaryotes) and put to work. Changes over time made them true parts of eukaryote cells, no longer potentially independent.

Same for mitochondria - aerobic prokaryotes taken in by eukaryotes.

[RowaH]

I agree with all of Darby's theories.

Looks like we have another great scholar in the making!

[AstusAleator]

Eh, those theories were established long ago, not by Darby.

Personally, I think the most important factor to consider in this situation is what order they would have evolved in.
This wouldn't always be the case - as there are vestigial organs that have lost importance throughout the course of evolution. However, there are very rarely vestigial organelles.

In the cases of mitochondria and chloroplasts, they may have evolved (via endosymbiosis) in roughly the same time-frame, but nuclei may have actually developed as organelles BEFORE mito and chloro. If you think about it, the genetic code that dictates the division of a cell and all of its organelles is contained within the nuclei (though mito have some of their own). This would indicate to me that eukaryotic cells had already developed nuclei (also through endosymbiosis) before other organelles, otherwise there would be no mechanism to control the reproduction of organelles to coincide the reproduction of the cell.

On the other hand, it is somewhat apparent that mitochondria and chloroplasts did not originally come from cells that had nuclei. Mitochondria have genetic material, but it is not contained within its own membrane, as would be expected if they originally had nuclei. I don't believe chloroplasts have any genetic material in them.

So, my hypothesis (based on the whole 10 minutes I've spent thinking about it ) is that modern eukaryotic cells first involved nuclei, then some accepted chloroplasts, while others accepted mitochondria. So this is the order I would rank their importance.
Since chloroplasts and mitochondria may have developed around the same evolutionary time, I will rank chloroplasts as more important as mitochondria depend largely on the products of photosynthesis to function.

[sachin]

I would say "CELL WALL" or "CELL MEMBRANE" withought which cell cant be in existance..... as separation of the cell system is primarily necessary for its independant existance.....

[AstusAleator]

Silly Sachin, taking things out of context.

If you want to be like that, I'd say that ... you're probably right since proto-cells might have had a single membrane enclosing genetic material, thus the only organelle was... the membrane. But that's not what this discussion is about!