WARM UP #11: The Three Domains of Life
With selected student responses

QUESTION 1: The Archaea are thought to be the most ancient group of organisms, first appearing on Earth about 3.3
billion years ago. The Archaea include organisms that grow at extremes - very high (or low) temperature, highly acidic or
salty environments, needing neither light or oxygen to grow. What does this suggest about the environment on the Early
Earth?

From BT: Q1 = It suggests that Earth probably had little light and no oxygen and was very unsable in it's ability to maintain a stable temperature.

From Jenn: Q1 = This suggests that there was very little light or oxygen on the earth in early times. The temperature on earth would very and there was a high count of acid on the surface.

From RV: Q1 = That the earth was very different than it is today. It was able to sustain life of a different form like archaea but may not have been able to sustain life as we know it today because of a lack of light from the sun and oxygen in the air. The lack of oxygen would suggest that there was little plant life at one time on earth. The lack of sun light would explain the extreme temperatures and possibly the acidic or salty environments as well.

From Jennay: Q1 = I think that that could mean that the Earth was dark and desolate. It could also mean that it was covered mostly by water and the Earth was just a deep, dark ocean.

From RW Q1 = This suggests that the "Early Earth" was probably mostly under water where it is very salty and the light and oxygen is limited or non-existent.

From EC: Q1 = This suggests that the environment on Early Earth was an extreme one. If these organisms were some of the only ones around during that early time it suggests that the environment was either very hot or very cold and that there were highly salty, acidic environments and that there was not necesarily always light and an atmosphere made of oxygen on the planet.

QUESTION 2: In the figure in your notes that shows the three domains in different colors, what do the lines between the
different domains and different groups within domains represent? Why are some lines short and some lines long?

From Emer: Q2 = okay...am i messed up or what!? i am looking in my notes and all i see are sheep...where is this diagram!?! am i seeing this wrong?

From NW: Q2 = They represent the life span of certain organisms and the span the lived, and that is why some of the lines are longer than the others and some are shorter.

From Bill: Q2 = I think it stands for time periods and species. The longer the lines either means more species or that they lived longer and theshorter lines mean the opposite.

From NP: Q2 = They share some features and also have unique characteristics of their own. The lines that are long are what connects them or what they share and the short lines represent features that are unique to the domains or the different groups within the domain.

From Lily: O2 = I think the three colors represent the three domains of life, and within each domain we find the main divisions within
each group. The lines may represent branches within each group and the length the length of their known existence.

From Dr. Marrs: (Sorry to those of you who weren't able to see the figure.) These lines are based on the Evolutionary Distance between organisms, based on rRNA sequences. The rRNA sequences of all known living organisms fall into three major groups (the 3 Domains).

QUESTION 3: If there was once a "Common Universal Ancestor"that gave rise to the life forms we see on Earth today,
what do you think would have been some of the characteristics of this organism? What types of events would have led this
Common Ancestor to branch off into the Three domains we see today?

From AD: Q3 = If there was a "Common Universal Ancestor" it would have to share the same basic characteristics as all living things and it would evolve due to the changes in the environment and to survive.

From Just Some Guy: Q3 = I would think it would more closely resemble that of a bacteria or archaea. What would probably cause it to branch off is whateverthe environement presented to different "Common Universal Ancestors" (heh, I'm not quite sure what to call it). If different "CUAs" adapted better to what the environment demanded, they'd be what future life would be based off of.

From DJ: Q3 = Some of the characteristics would be that the organism would not have been a single organism, but a community of organisms. They would also have inaccurate DNA replication, and lots of genetic diversity. The fact that this organism has so much genetic diversity might have caused it to branch off into other organisms or domains.

From ND: Q3 = The "Common Universal Ancestor" would of had to been a small form of bacteria that developed into a single cell organism thatwould of been able to survive in extremely cold temperatures. Environment changes (earth heating, oxygen allowed in, more sunlight,polar caps melting) would of allowed this organism to develop into the three domains that we see today. It would of needed to adapt in order to survive.

From Dr. Marrs: a "Last Common Universal Ancestor" of all life would have had properties that are now to common to all life, ie: the very simplest forms of life. We know that the very simplest forms of life (Archea and Bacteria) today all have

(1) Nucleic acids as genetic material (DNA or RNA)
(2) Ribosomes and tRNAs for making proteins
(3) The universal genetic code (AUG = Met)
(4) Amino acids for making proteins

So, at the minimum, the "Last Common Universal Ancestor" would be cells that had all of these characteristics but had not yet changed enough from each other to differentiate into Domains.
Note: Viruses, not considered life, have a hereditary systems based on DNA/RNA, but use the ribosomes, tRNAs, and amino acids of other cells to make their proteins!

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