Natural History

[dreamer_easy]

Questions:

1. Why have only eukaryotes - that is, organisms such as plants, animals, and fungi, whose cells have nuclei - had the ability to form multicellular creatures with different types of cells? Why can't prokaryotes such as bacteria do this?

2. All known organisms share a common ancestry. In Life: An Unauthorised Biography, which I'm currently reading, the eloquent author Richard Fortey maintains this means life only arose once on Earth. Is that necessarily the case?

3. Why green? Could the photosynthetic pigment have been another colour?

"It's going to worry me until I find out." - the Doctor

Comments

[ms-engineer.livejournal.com]

Re: Question 2...

Richard Fortey obviously knows an awful lot more about these things than I ever will (as is more than evident from this reply :)) but surely it's arguable that there have been an awful lot more species than the ones we happen to know about.

As I understand it (purely from reading popular science-y type books and not from any actual study at all) it's not all that easy to end up in the fossil record, particularly for squishy things and the beginning stages of life are generally squishy.

Personally, I think it has to be at least fairly plausible that life could have got going more than once but that the species we know now are the result of a particularly efficient life form that managed to evolve at just the right moment to not get wiped out like all of the others.

[zazuomgwtf.livejournal.com]

Have friended you, did not ask permission as I see you have many friends that you have not friended so I assume you do not mind being friended.
(someone should take that sentence out and shoot it, I am going to take a nap now so that someone will not be me)

[kateorman.livejournal.com]

Fab-o! *friends you back* If I have a Friending Policy it's apparently one of complete randomness.

[zazuomgwtf.livejournal.com]

yay for the random!

[warinbabylon.livejournal.com]

Question 3:

Photosynthetic plants absorb and utilize blue and red light. The part of the light spectrum they don't use is green. As it isn't absorbed, it's reflected back and that's what we see.

Red light is used for vegetative growth of the plant; blue light is used for reproductive growth.

Okay: Question 2: I don't believe it arose once. I believe that there was probably false steps and false starts. Evolution is a blindwatchmaker. It is simply a force; environment is what chooses the path. Therefore, I believe it is possible at the basis of that theory, that life might have arisen more than once. Even life starting flukes have a low probability of happening more than once. But Fortey is an exceptionally intelligent man so weigh my opinion very very very lightly in reference to his.

Question 1: I've had this in biology and cell biology before, but at this moment in time, I can't remember the single reason why. I'll see if I can find my notes.

[antikythera.livejournal.com]

The Sun is actually greenish-yellow. That's the maximum part of the natural light spectrum that plants get.

[the-ladylark.livejournal.com]

I'm going to try and answer these, but it's been a couple of years since my biology degree so don't take my answers as being gospel truth!

1. I think the general answer given is that the multicellular capability arose once, and then spread amongst the eukaryotes - in this sense, all multicellular eukaryotic organisms are related. However, it's possible that there are some adaptations which eukaryotes have which means they are much more suited to multicellular life. slime moulds (http://universe-review.ca/R10-18-slimemoulds.htm) give an example of how multicellular cooperation may originally have come about. Plus they're rather cool in and of themselves!

2. It's not necessarily the case, because as someone else commented I think, there could have been several different origins and life and we are all the descendants of just one of them. It's the same reasoning as 'mitochondrial eve' - you can look at the divergence of the mitochondria in all living people and trace them back to one woman who lived about 150,000 years ago (I think). But that doesn't mean she was the only woman alive at that time, it just means that all other lineages except hers have died out. However, depending on your view on the origins of life, it could be considered quite unlikely that it arose more than once, if the event itself was unusual and coincidental. It's one of those things we'll probably never get the answer to.

3. Yes, and it is in some algae, which use red or blue pigments for similar purposes. The three main classes of pigments are chlorophylls (mostly green) carotenoids (red) and the phycobilins (blue). Plants almost exclusively use chlorophylls, which is why most plants are green.

[ianmcin.livejournal.com]

Question #1: I read Bryan Sykes' "Adam's Curse" a few months back, and I think he may have gone into this particular question. Bear in mind, I'm no biologist myself, and I'm just going from memory here, but...

I think it has to do with the fact that in eukaryotic cells, there are actually two different strains of genes, each hoping to propagate itself - mitochondrial and nuclear. Eukaryotic life has developed as a way for both of the strains to potentially profit.

Man, I thought I remember more of that. But if nothing else, I can recommend the book itself!