Download BI101SQ Key Ch17

General Biology BI101
Spring 2007
Answer Key Study Questions Chapter 17
1.
356.5 million years old. (3:1 ratio means that ¾ of the original uranium-235 is left, so ½ of its half-life has
passed.) Fig E17-1
2.
The boiling chamber is meant to simulate the addition of energy to the system. The electric spark
is generated in a closed chamber to simulate lightning. The condenser functions to cool the
chemical mixture after being exposed to the electric spark. The presence of oxygen would
prevent the accumulation of organic compounds by quickly oxidizing them or their precursors. All
of the successful abiotic synthesis experiments used oxygen-free “atmospheres.” Figure 17-2
3.
Miller and Urey helped to describe how the components of the early atmosphere could have given rise to
simple organic compounds, like ATP, amino acids, and so on. Section 17.1 Miller and Urey's experiment and
its variations have shown that fairly complex precursors of biological molecules could have easily formed in
conditions found on the early Earth, including simple catalysts and membranes. A very long period of time
was available from the time the Earth cooled to the time the first organisms appeared (as documented by
fossil remains), so that by a process of chemical natural selection more efficient systems of replication
and metabolism could have evolved in a stepwise manner.
4.
Chemical analyses of rocks dated to the time of the first organisms show that there was a much smaller
concentration of oxygen gas in the early atmosphere than there is now, indicating that these early
organisms must have been anaerobes. After the evolution of photosynthetic organisms, oxygen
concentrations increased as a consequence of photosynthetic activity, and aerobic metabolism evolved.
Anaerobes do not use oxygen for metabolism. Section 17.2.A
5.
Ribozymes are RNA molecules that, like protein enzymes, are capable of catalyzing chemical reactions.
This means that RNA is capable of information storage (like DNA) and catalytic activity. Some scientists
have suggested that an "RNA world" may have existed as a precursor to true life, in which the replication
of RNA molecules was catalyzed by other RNA molecules in a system that is a simpler form of the DNA
replication (catalyzed by protein enzymes) that exists in living cells.Section 17.1.C 20)
6.
RNA is capable of both information storage (as DNA is today) and catalytic activity (which today is done
by protein enzymes). RNA can also make exact copies of itself. The ability to reproduce and to
enzymatically catalyze reactions are important characteristics of cells. A primitive RNA-based
biochem
Section. 17.1
7.
Microspheres are chemical structures of protein and lipid, formed by wave action, that resemble living cell
membranes in their chemical structure. Some can pass materials, grow, and divide. In prebiotic times,
microspheres might have protected ribozymes from the surrounding environment and allowed the evolution
of protocells (nonliving cell-like structures), and eventually living cells. section 17.1.D
8.
The first photosynthesizers were probably much like the purple photosynthetic bacteria of today, using
H2S (hydrogen sulfide) as a source of hydrogen for forming more complex organic molecules from CO 2. As
H2S was depleted, they evolved to be able to use water (H2O) as a source of hydrogen, as most
photosynthesizers do today. Section 17.2.B
9.
Oxygen atoms are present in many inorganic compounds, particularly water and carbon dioxide. The action
of photosynthetic organisms of using these two chemicals along with light energy to produce organic
BI101 SQ Key Ch17
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6/29/2017
General Biology BI101
Spring 2007
Answer Key Study Questions Chapter 17
compounds produced molecular oxygen gas as a by-product. Section 17.2.C
10. The organisms at the time were strict anaerobes, not only unable to metabolically use oxygen, but actually
poisoned by it. As organisms evolved an aerobic metabolism that uses oxygen, they were able to produce
more energy from the same compounds than with anaerobic metabolism. Section 17.2.D
11. Some scientists suggest that one type of prokaryote consumed but was unable to digest certain kinds of
prokaryotes. This was a great advantage to the early cells, especially if they consumed a cell that could
produce its own energy, as a mitochondrion can. Section 17-2.
12. The bacterial sequence would be most similar to that of the plant mitochondrion, because (as the
descendant of the immediate ancestor of the mitochondrion) the bacterium shares with the mitochondrion
a more recent common ancestor than with the chloroplast or the nucleus. Figure 17-4
13. The first multicellular organisms were probably algae, as seen in the fossil record dated to about one
billion years ago. Being larger than their unicellular predators, they would have been more difficult to be
preyed upon. Also, different tissues of the the organism could evolve to specialize in their functions, such
as roots for anchorage or leaves for photosynthesis. Section 17.3.A
14. Among other things, multicellular organisms can become larger, thus making it easier to get food or acquire
other resources, such as light or water. Section 17.3
15. The fossil evidence reveals many animal body plans that are not represented in any current animal phylum.
They appear rather "suddenly" in the fossil record, suggesting that many evolutionary innovations
preceding their appearance were simply not preserved as fossils. Section 17.3.B
16. Among the possibilities are moving around without the support of water, difficulty in obtaining and
maintaining water, greater exposure to UV radiation, and reproducing without a water environment to allow
gametes to encounter each other. Section 17.4
17. Pollen represented a gamete that did not require water to survive and fertilize another gamete, so that
plants could evolve to become completely adapted to a terrestrial existence, rather than an aquatic one.
Section 17.4.A
18. Although amphibians may possess lungs for breathing oxygen gas, and legs for locomotion on land, many
still need to obtain oxygen partially through their skin, and must remain wet to do so. Also, the external
fertilization of amphibian sperm and eggs requires a water medium. Section 17.4.B
19. Although the precise causes of mass extinctions are still a matter of debate, it seems that catastrophic
climatic shifts are the major heralds of mass extinction events. Such changes may have various causes,
such as volcanic activity or the impact of a large meteor. Section 17.5
20. Some possible answers are long, grasping fingers, binocular vision, and a large brain. Section 17.6
21. Biological evolution results from genetic changes from generation to generation, so is limited by the rate
of origin of new biological features and the rate of reproduction of the population. Cultural evolution
results primarily from learning, and new cultural features can be passed from person to person almost
immediately. Section 17.6.L
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6/29/2017
General Biology BI101
Spring 2007
Answer Key Study Questions Chapter 17
22. Label A: formation of Earth
Label B: first Earth rocks Rocks appeared after the Earth was formed
Label C: first prokaryotes Prokaryotes were the first form of life and remained the only form of
life for billions of years
Label D: first eukaryotes Eukaryotes appeared after prokaryotes but still early in the
development of life
Label E: first animals From eukaryotes arose multicellular organisms and soon thereafter came
the first animals
Label F: first land plants Land plants arose after animals but relatively recently in geological time
Label G: first humans Humans are so new to the planet, their entry almost coincides with the
return to 12 midnight
23. Figure 17-4.
Label A: Anaerobic, predatory prokaryote engulfs aerobic bacterium.
Label B: Mitochondria-containing cell engulfs a photosynthetic bacterium.
Label C: Descendants of engulfed bacteria evolve into mitochondria.
Label D: Descendants of photosynthetic bacterium evolve into chloroplasts.
24. Figure 17-14
Label A: Australopithecus afarensis is the common link between the extinct Australopithecus genus and
the extant Homo genus.
Label B: Homo erectus is on an extinct branch of the genus Homo
Label C: Homo ergaster is the ancestor to modern man
Label D: Homo sapiens is modern man.
25. Figure 17-15
Label A: Homo habilis is a long extinct line of human, with no descendants leading toward modern
man.
Label B: Homo ergaster is approximately in the middle of the evolutionary tree, and his tools are
indicative of a mid-range sophistication.
Label C: Homo neanderthalensis is closest to Homo sapiens, and the tools from this species show a
great deal of sophistication.
26. Figure 17-18
Label A: multiregional hypothesis In the multiregional hypothesis, regional populations of Homo erectus
may have simultaneously evolved into Homo sapiens.
Label B: African replacement theory The African replacement theory states that Homo erectus spread
first from Africa, and Homo sapiens spread in a similar pattern many years later.
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