1. The History of Life on Earth

2. Why do some scientists believe that RNA, rather than DNA, was the first genetic material?
RNA has both information storage and catalytic properties.
RNA contains uracil in place of thymine.
RNA could have evolved into DNA.
RNA can replicate more accurately than DNA.
All the proto-cells on early Earth contained RNA.
Answer: A

3. Why do some scientists believe that RNA, rather than DNA, was the first genetic material?
RNA has both information storage and catalytic properties.
RNA contains uracil in place of thymine.
RNA could have evolved into DNA.
RNA can replicate more accurately than DNA.
All the proto-cells on early Earth contained RNA. 3

4. Which of the following statements concerning the evolutionary origin of mammals is most likely true?
Radiometric dating using carbon-14 shows that synapsids existed 300 million years ago.
The origin of mammals is unknown because the fossil record is incomplete.
Mammalian lower jaw bones and teeth changed gradually over time.
Modern mammals and reptiles are descendants of synapsids.
Answer C.
Radiometric dating using carbon-14 is only useful for fossils up to 75 million years in age thus this method would not be effective for dating fossils that are as old as 300 million years. The mammalian fossil record is good because anatomical features such as their lower jaw bones and teeth readily fossilize. Reptiles are from a lineage that is the sister group to synapsids therefore they are not descendants of the synapsids – only the mammals are descendants of the synapsids. 4

5. Which of the following statements concerning the evolutionary origin of mammals is most likely true?
Radiometric dating using carbon-14 shows that synapsids existed 300 million years ago.
The origin of mammals is unknown because the fossil record is incomplete.
Mammalian lower jaw bones and teeth changed gradually over time.
Modern mammals and reptiles are descendants of synapsids. 5

6. If the mitochondria and chloroplasts in eukaryotic cells resulted from endosymbiosis, what features might we expect these organelles to contain?
plasma membrane, DNA, and ribosomes
plasma membrane, nucleus, and ribosomes
nucleus, DNA, and ribosomes
plasma membrane, nucleus, and cilia
nucleus, ribosomes, and cilia
Answer: A
This question can be used to start a discussion on the evolution of eukaryotic cells and the concept of serial endosymbiosis. 6

7. If the mitochondria and chloroplasts in eukaryotic cells resulted from endosymbiosis, what features might we expect these organelles to contain?
plasma membrane, DNA, and ribosomes
plasma membrane, nucleus, and ribosomes
nucleus, DNA, and ribosomes
plasma membrane, nucleus, and cilia
nucleus, ribosomes, and cilia 7

8. Photosynthetic eukaryotes contain both mitochondria and chloroplasts
Photosynthetic eukaryotes contain both mitochondria and chloroplasts. Which sequence most likely describes the evolution of this group?
Ancestral anaerobic prokaryote engulfs heterotrophic prokaryote and then engulfs photosynthetic prokaryote.
Ancestral anaerobic prokaryote engulfs photosynthetic prokaryote and then engulfs heterotrophic prokaryote.
These sequences are equally likely.
Answer: A
This question is designed to begin the discussion of serial endosymbiosis. This could then lead to a discussion of secondary endosymbiosis. 8

9. Photosynthetic eukaryotes contain both mitochondria and chloroplasts
Photosynthetic eukaryotes contain both mitochondria and chloroplasts. Which sequence most likely describes the evolution of this group?
Ancestral anaerobic prokaryote engulfs heterotrophic prokaryote and then engulfs photosynthetic prokaryote.
Ancestral anaerobic prokaryote engulfs photosynthetic prokaryote and then engulfs heterotrophic prokaryote.
These sequences are equally likely. 9

10. Which of the following most likely arose from endosymbiosis?
nuclear membrane and Golgi apparatus
ER and chloroplasts
chloroplasts and mitochondria
mitochondria and Golgi apparatus
Answer: C
Chloroplasts and mitochondria have their own DNA. The nuclear membrane, Golgi apparatus, and ER are all thought to have evolved from infoldings of the membrane. 10

11. Which of the following most likely arose from endosymbiosis?
nuclear membrane and Golgi apparatus
ER and chloroplasts
chloroplasts and mitochondria
mitochondria and Golgi apparatus 11

12. How many mass extinction events have been documented in the fossil record over the past 500 million years?
two
three
four
five
Answer D. 12

13. How many mass extinction events have been documented in the fossil record?
two
three
four
five 13

14. According to geological evidence, which event may have triggered the Permian mass extinction?
an asteroid or comet impact off the coast of Yucatan, Mexico
global cooling caused by a series of ice ages
global cooling caused by volcanic eruptions
global warming caused by volcanic eruptions
Answer D.
The elevated atmospheric CO2 levels would, in addition to causing global warming, have caused acidification of the oceans thereby reducing the availability of calcium carbonate, which is needed by corals. 14

15. According to the geological evidence, which event may have triggered the Permian mass extinction?
an asteroid or comet impact off the coast of Yucatan, Mexico
global cooling caused by a series of ice ages
global cooling caused by volcanic eruptions
global warming caused by volcanic eruptions 15

16. A species of bird finds its way to the Galápagos Islands, where there are many ecological niches. This species evolves into many new species to fill all the unfilled niches. This is an example of
resource partitioning.
adaptive radiation.
endosymbiosis.
gradualism.
Answer: B
Adaptive radiation occurs when one species evolves into many different species as a result of the availability of several ecological niches. It could not be D because there is no mention of time frames in which this occurred. 16

17. A species of bird finds its way to the Galápagos Islands, where there are many ecological niches. This species evolves into many new species to fill all the unfilled niches. This is an example of
resource partitioning.
adaptive radiation.
endosymbiosis.
gradualism.
Answer: B
Because adaptive radiation occurs when one species evolves into many different species as a result of the availability of several ecological niches. It could not be d because there is no mention of time frames in which this occurred. 17

18. Which of the following best explains the loss of ventral spines in threespine stickleback fish?
paedomorphosis
duplication of the Pitx1 gene
changes in the Pitx1 gene sequence
changes in the regulatory sequences of the Pitx1 gene
Answer D.
Researchers showed that the Pitx1 gene in lake sticklebacks is differentially expressed depending on tissue type – this gene was switched “off” in cells relating to ventral spine production, whereas this same gene is switched “on” in other tissues (mouth). A follow-up study showed that changes to the regulatory element called the Pel enhancer causes a reduction in ventral spines in lake sticklebacks. 18

19. Which of the following best explains the loss of ventral spines in threespine stickleback fish?
paedomorphosis
duplication of the Pitx1 gene
changes in the Pitx1 gene sequence
changes in the regulatory sequences of the Pitx1 gene 19

20. Which of the following statements about evolution is most likely true?
Animal eyes evolved in a progressive sequence from simple to complex.
Horse-like animals evolved in a progressive sequence from small to large body size.
Complex animal eyes evolved independently many times.
Complicated eyes are more useful to an animal than simple eyes.
Answer C.
For example, the complex eyes of some molluscs (squids and octopuses) evolved independently of the eyes of vertebrates. 20

21. Which of the following statements about evolution is most likely true?
Animal eyes evolved in a progressive sequence from simple to complex.
Horse-like animals evolved in a progressive sequence from small to large body size.
Complex animal eyes evolved independently many times.
Complicated eyes are more useful to an animal than simple eyes. 21

22. Scientific Skills Exercise
Researchers investigated whether differing modes of dispersal could explain differences in the longevity of fossil species in one taxon of marine snails, the family Volutidae. Some volute snails had planktonic larvae that could disperse over great distances on ocean currents. Other volute snails had nonplanktonic larvae, which developed directly into adults without a swimming stage. The dispersal of snails with nonplanktonic larvae was limited by the distance they can crawl as adults. The researchers studied the distribution of volute snail fossils in outcrops of sedimentary rocks along North America’s Gulf coast. The rocks formed during the early Paleogene period, between 65 and 37 million years ago, and contain many well-preserved snail fossils. Based on features of the snail’s shell, the researchers classified each fossil species as having planktonic or nonplanktonic larvae. Each bar in the figure shows how long a snail species persisted in the fossil record.

24. How many new species of snails with nonplanktonic larvae arose between 50 and 35 million years ago?
Answer: C

25. How many new species of snails with nonplanktonic larvae arose between 50 and 35 million years ago?

26. How many new species of snails with planktonic larvae arose between 50 and 35 million years ago?
Answer: A

27. How many new species of snails with planktonic larvae arose between 50 and 35 million years ago?

28. Select a plausible hypothesis to explain the difference in mean longevity of snail species with planktonic and nonplanktonic larvae.
Snails with nonplanktonic larvae produce fewer offspring than snails with planktonic larvae.
Snails with nonplanktonic larvae have more limited distributions than snails with planktonic larvae.
Snails with nonplanktonic larvae have higher survival rates of larvae and young adults than snails with planktonic larvae.

29. Select a plausible hypothesis to explain the difference in mean longevity of snail species with planktonic and nonplanktonic larvae.
Snails with nonplanktonic larvae produce fewer offspring than snails with planktonic larvae.
Snails with nonplanktonic larvae have more limited distributions than snails with planktonic larvae.
Snails with nonplanktonic larvae have higher survival rates of larvae and young adults than snails with planktonic larvae.
Answer: B