pepperlandgirl

I'm a freshman in college, and part of our GE requirements is a lab science. This interterm I chose to take Biology 101. It's a pretty quick overview of Biology, we cover what happens, but we don't really have time to go indepth. We cover about 2-3 chapters a day. The class is only 3 weeks long.
Anywho, I love biology, and I'm very interested, but we don't really have time to ask questions and form discussions. So, I thought I would ask here. Note, I am not a creationist/christian/theist. But these questions do pertain to evolution, and I have formed some hypothesis...whatever the plural for that is. So, here we go.
I know these may seem like dumb questions, but this is the first biology class I've had. I've done some independent reading on evolution, but not enough to answer these questions yet.
Question 1: Why haven't our bodies evolved in some way in order to better break down cellulose? Wouldn't that be a great way to get energy? Or why haven't we gone the way of the cow, with methogens in our digestive track?
Hypothesis: We don't really need to evolve a method to break down cellulose, or evolve a way to make the enzyme cellulase (sp?) because there are plenty of other energy sources. If there weren't plenty of other energy sources, we would have found away to break down cellulose or we would have died.

Question 2a: Are viruses alive?
Question 2b: Are they similiar to cell organelles, like mitochondria?
Hypothesis a: Uh...well, I don't have one, since I don't know enough about viruses. And besides, if scientists who study and work hard and devote their lives to answering this are still unsure, I'm pretty sure I can't figure it out.
Hypothesis b: I read somewhere that some scientists believe that mitochondria were smaller bacteria cells floating along and kind of got sucked into a cell. The mitochondira liked it there, and the cell got energy from it, so a long and happy symbiotic relationship was born. This makes sense to me because during mitosis the organelles divide up on their own and have their own DNA. Problem solved. Only, I'm not confident enough in my own knowledge to accept that just yet.

Question 3: It's kind of convenient that plants give off oxygen and we give off CO2. How did that happen?
Hypothesis: Well, if plants gave off nitrogen (say, just to pull a gas out of the air, so to speak) then all oxygen breathing animals would die or evolve a way to live off of nitrogen. For all I know there was once nitrogen breathing animals and they since died because there wasn't enough air for them to breath. (Work with me here, I know that nitrogen is abundant in the atmosphere, this was just the first thing I thought of.) Therefore the relationship between plants and animals is not a big surprise.

Anyway, this is a good start. Thanks for your time, I appreciate it.

ecco

What’s to say we haven’t? Perhaps our ancestor’s bodies had even less ability to break down cellulose. On the other hand perhaps we are now ingesting more/different foods that contribute to the building of more cellulose and evolution just hasn’t caught up yet (this would be my guess).
Don’t forget that for a loooong time there were ONLY plants and only (or predominately) CO2. Once the atmophere, thanks to all the plants) became rich in oxygen, evolution had a new empty niche to fill and along came oxygen breathers. Alternatively, aquatic life breathed oxygen from the water. As the atmosphere became richer in oxygen, they migrated from sea to land.

theyeti

Short answer: it's a terribly inefficient way to obtain energy. It requires lots of eating, a huge digestive tract, and lots of extra mechanical digestion (like chewing the cud). Basically, you've got to be a specialist to eat that stuff. Since we have meat and high protein vegetables available, it would make no sense for us to eat grass. Afterall, we can just eat the animals that eat the grass.

Yes and no. It depends on how you define "alive". They occupy a rather strange grey area between life and non-life. The biggest difference is that they don't metabolize energy and they don't keep themselves far from thermodynamic equilibrium, which is considered a key component of most living systems. I prefer to think of them as renegade nulceic acids with some cool adaptations.

Not at all. Cellular organelles are similar to and most certainly derived from prokaryotes (i.e. bacteria) which are orders of magnitude larger and far more complex than viruses. What viruses are similar to is transposable elements and retrotransposons in your genome (i.e. "selfish" DNA).

All photosynthetic organisms use CO2 and give off O2. This includes a great many bacteria that were here long before plants and animals. The primitive Earth atmosphere had no free oxygen in it, and only after it began to build up to decent levels did organisms (still bacteria) evolve to utilize it for metabolism. In fact, modern plants use O2 as well; they use it to get energy from the sugars that they created with sunlight and CO2. There are still anerobic bacteria that do not use O2 -- in fact, it's poisonous to them. This was likely the situation on the primordial Earth. O2 levels climbed slowly and some bacteria evolved a resistance to it, eventually utilizing it.

This has to do with the chemistry of the respective compounds. There are organisms that use N2 as an energy source, and it's a good thing too, because that's where natural fertilizer comes from (nitrate and nitrite, eventually from ammonia -- this is where all the nitrogen in your amino acids ultimately comes from). These organisms are all bacteria, and they are all anerobic by chemical necessity -- oxygen is poisonous to them. And it takes an awful lot of energy to break the bonds in N2. The reason why it's abundant is that it's very stable, unlike O2, which reacts readily with lots of things. This is why it's not used much for respiration. I'll try looking up the chemistry issue sometime later.

Legumes (beans, peas, etc.) have these little root nodules in which these guys live, and it's currently the Holy Grail of plant genetic engineering to find out how to put them on other plants. It's very hard because the nodules have to bind any free oxygen and transport it away. Then there are bacteria that use nitrate and nitrite to get energy in the reverse reaction, though I forget the details.

theyeti

P.S. On the last part, be sure to check out the "Nitrogen Cycle" in your biology text. More sophisticated texts will explain the thermodynamics.

[ January 23, 2002: Message edited by: theyeti ]</p>

tronvillain

Question 2a: Are viruses alive?
Question 2b: Are they similiar to cell organelles, like mitochondria?

A) If by "life" you mean "a replicator" then yes, but if you consider metabolism to be an important component of life then no. Since we don't seem to consider an individual chromosome or gene to be alive, I'd say that viruses shouldn't be considered alive either. It's not something that requires additional research to answer.

B) In some respects they are similar, in that mitochondria depend the the cell to replicate themselves, but they have a metabolism. As to where mitochondria came from, it seems fairly apparent that they originated as independent bacteria, though whether they were parasite or prey doesn't seem certain (I'd go with parasite).

Oolon Colluphid

Hi pepperlandgirl!

I'm short of time, so hope these will suffice.

Hypotheses.

Maybe I've just spent too long round creationists, but they're some of the smartest questions I've seen for a long time!

That's a good one to ask creationists, who believe in a designer. You could just as easily ask why we can't photosynthesise. The simple answer is that with evolution, the 'design is constrained by history. Natural selection can only preserve those mutations that turn up in pre-existing systems. Not that it can't build new stuff, but there's got to be the options.

More or less, the final sentence especially. Note that about 99.9% of species that have existed became extinct. Not that we don't need to, but that our ancestors managed to get by without, plus the relevant mutations not turning up, (or maybe they did, but those first steps might not have been short-term (the only sort evolution knows) advantageous).


That's about the size of it. IMO they are, since they are replicators -- they actively get themselves copied.

Nope. Viruses are just packets of DNA (or RNA), surrounded by proteins and sometimes lipids (fats). They are generally far smaller than organelles... which as you say, are most likely derived from bacteria. Note that organelles have their own DNA: that in the nucleus makes all the tissues in a body, yet these intracellular things keep theirs apart.

Yep, it's called 'endosymbiosis, and Lynn Margulis is the name to look up. It's pretty certain that mitochondria, at least are related to bacteria, specifically to Rickettsia prowazekii. See these two links:

<a href="http://www.the-scientist.com/yr2000/oct/hot1_001016.html" target="_blank">http://www.the-scientist.com/yr2000/oct/hot1_001016.html</a>

<a href="http://www.nature.com/genomics/papers/r_prowazekii.html" target="_blank">http://www.nature.com/genomics/papers/r_prowazekii.html</a>

I like your thinking..., but the gas in question was oxygen. Without looking it up I'll have to leave it to others to explain in depth, but it's basically that oxygen is a waste product of photosynthesis. Oxygen is a reducing gas, basically pretty nasty toxic stuff. The earth was animal-less for at least 500 million years, yet stromatolites show there were photosynthesising bacteria. The atmosphere got so clogged up with the oxygen pollution that there was strong selection pressure for things that could use it rather than be broken down by it.

You're welcome. If I had more time I could suggest some more links. As it is, the best thing you could do is track down any book by Richard Dawkins. From what you say, you really would appreciate that his writings!

Cheers, Oolon

[ January 23, 2002: Message edited by: Oolon Colluphid ]</p>

Queen of Swords

pepperlandgirl,

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theyeti

&lt;nitpick&gt; Oxygen is an oxidating gas, hence the name. It is being reduced in a redox reaction by a reducing agent. To keep it straight, think of the transfer of charge -- the oxygen has it's charge "reduced" by one when it reacts. In other words, it grabs an electron because it's so electronegative. Only flourine is stronger in this regard. &lt;/nitpick&gt;

theyeti

tronvillain

Huh. You say oxidating rather than oxidizing?

theyeti

Hey, I'm a biochem person. Everything is "oxidative" to us, as in "oxidative phosphorylation". Come to think of it, oxydizing is probably correct.

theyeti

Peez

&lt;nitpick&gt; There are photosynthetic organisms that do not produce oxygen (certain "purple sulphur bacteria"). They release sulphur instead. &lt;/nitpick&gt;


Peez