Bio Exam 2 Study Questions

1. What is an adaptive radiation? What conditions often lead to adaptive radiation? Why?

Adaptive radiation is the process by which a lineage rapidly diversifies into multiple species. Conditions that often lead to adaptive radiation include mass extinctions that leave openings for survivors, especially those that were previously competitors or prey. More niches are available and less competetive pressures allow for niches to be taken up and also previously less likely survivors to survive.

2. Describe some of the ways we try to define “species". Why do these definitions not work in some cases?

Some of the ways that we try to define species are

• groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such groups

• a phyletic lineage evolving independently of others, with its own separate evolutionary role and tendencies

• phenomena formally viewed as necessary and sufficient defining criteria for specieshood are instead understood to bear on whether two lineages are evolving separately. Things don’t define species, but instead help us discover them.

• Organisms that look similar are grouped into species

These definitions do not work in some cases because there is always an exception, or there is just information that we will never be able to know, so we can’t say for sure.

3. Why is it important to care about what a species is, even if the definition is difficult or if species isn’t a “real” thing?

It is important to care about what a species is because

• we need some way to group, categorize, and organize organisms.

• important for figuring out things in the past

• helps when studying them without leading to mass confusion

• good for understanding evolutionary processes and adaptations

• Categorization is helpful for survival

• helps with policy decisions and conservation in regards to what is an endangered species and such.

4. What is a clade?

A clade is an ancestral taxon in addition to all of its decendents; it is a complete evolutionary story.

5. How do we find clades?

Clades are found by identifying shared traits that unite all organisms in a clade but also make them different from organisms in other clades.

6. List and explain the three main ways we can find homologies while avoiding accidentally finding analogies.

1. see if the feautres are similar on the inside too, not just the outside

2. look for shared traits that are complex (they are less likely to be random)

3. compare gene sequences-homologies will likely be built on nearly identical genes.

7. What is parsimony? Why is it an important idea for building clades?

Parsimony is the simplest evolutionary explanation. It is an important idea for building clades because it acts as a rule to follow and evolution is likely to take a path that is more simpler than complex.

8. Explain why it is accurate to say that all humans are fish, that all whales are hoofed mammals, and that all birds are dinosaurs.

It is accurate to say that all humans are fish because we evolved from lobe-finned fish, which gave rise to tetrapods.

It is accurate to say that all whales are hoofed mammals because, since whales are mammals (have pelvic hip girlies), they had to evolve to live on land as tetrapods, specifically mammals, and then retreat to the water; the organisms that did this were, in fact, hoofed(had astragalus bones)!

It is accurate to say that all birds are dinosaurs because they evolved from little, feathered theropod dinosaurs. They are a part of the dinosauria clade!

9. Explain why the left laryngeal recurrent neuron is much longer than it ought to be.

The left recurrent laryngeal nerve is so much longer than it should be because it shoots down the neck and loops under the aortic arch, then comes up to meet the larynx. This happened because we evolved from fish that had hearts located right next to their brains, so there wasn’t much of an actual detour. (Fish don’t really have necks… I guess….)

10. Why do so many humans have vision issues?

So many humans have vision issues because, AGAIN, we evolved from fish that live underwater, and we, in fact, do not live underwater, and that affects our eyes. Our eyes were made to drive vision underwater, and when light hits water, it bends. Our eyes are filled with fluid, which makes light bend.

11. What are the 4 main eons in the history of the world? Briefly describe each one.

The four main eons in the history of the world are

• Hadean Eon (hellish, no atmosphere, 4.6- 4.0 billion years ago)

• Archean Eon (somewhat livable, 4.0-2.5 billion years ago, no O2 in the air, HOT)

• Proterozoic Eon (Eukaryotes & Multicellularity!, 2.5 billion to 541 million years ago, almost entirely aquatic

• Phanerozoic Eon (541 million years ago to present, contains 3 eras, colonization of land, origin of plants, modern animals)

12. Why did oxygen first start accumulating in the Earth’s atmosphere? Which eon did this happen in?

Oxygen first started to accumulate in Earth’s atmosphere because of cyanobacteria that were able to do photosynthesis, allowing the release of oxygen into the atmosphere. This took place in the Proterozoic Eon.

13. Pulling the following major events in chronological order

a. Origin of photosynthesis

b. First flowering plants

c. Formation of the atmosphere

d. First 4-limbed animals

e. First life forms

c. e. a. d. b.

14. What does the term “the background extrinction rate” mean?

The term background extinction rate refers to the normal, baseline rate of species disappearance that occurs naturally over time without human influence. OR the rate of extinction of species under normal conditions throughout Earth’s history.

15. What is rarefaction and how does it help us estimate the number of species on Earth?

It is estimating how many species have yet to be discovered based on how regularly we encounter new species during surveys.

16. What are the 5 mass extinction events?

The five mass extinction events are

• End Ordovician

• End Devonian

• End Permian

• End Triassic

• End Cretaceous

17. What caused the end-Ordovician extinction? What were some of the challenges life faced during this time?

The thing that caused the end-Ordovician extinction was from 2 pulses: first, 1st there was the Late Ordovician glaciation, which dropped global temps and covered land with ice. Then the glaciation receded and warm conditions returned with caused global anoxia and euxinia.

Some of the challenges of life faced during this time was a loss of 40-60% of marine genera and 85 % of marine species

18. What caused the end- Devonian extinction? What were some of the challenges life faced during this time?

The thing that caused the End- Devonian extinction is a little unknown, but the likely causes could be ocean anoxia, changes in sea level, global cooling, oceanic volcanic activity, meteorite/comet impact, or reduced speciation/increased invasion of some species.

Roughly 50% of marine species died out, and it mostly affected marine life like coral and trilobites. Continents were starting to converge into Pangea.

19. What caused the end-Permian extinction? What were some of the challenges life faced during this time?

The thing that caused the end-Permian extinction was volcanic activity in the Siberian Traps that began a 100,000-year-long eruption cycle that caused sharp increases in crazy CO2 because of the ignition of coal beds. There was a 14°F increase in global average temperature and a 2,000 PPM increase in atmospheric CO2

There was acid rain, local cooling, reductions in photosynthesis, ocean acidification, and hypoxia.

Earth almost lost all multicellular life. 96% of it

20. What caused the volcanic activity during the Triassic-Jurassic mass extinction?

The thing that caused the volcanic activity during the Triassic-Jurassic mass extinction was similar to the end-Permian extinction but less severe because there were not as many coal beds. A rift that broke up the supercontinent of pangea which resulted in bleeding lava across the continent.

21. What caused the K-PG extinction? What were some of the challenges life faced during this time?

The thing that caused the K-Pg extinction was an asteroid strike off the coast of the Yucatan Peninsula.

Animals that were within a 1000 mile radius were immediately vaporized, and there were megatsunamis about 300 ft tall, and there were impact winters that were continuous for 2 years.

22. What evidence do we have to show the cause of the K-Pg extinction? Explain how this evidence supports the theory.

Evidence that we have to show the cause of the K-Pg extinction is looking at the levels of iridium. They found a clay layer that can be seen all across the Earth that contains 30x more iridium than normal, which indicates that one large but short event caused this extinction. Iridium comes from meteors, so if there was suddenly a crazy increase in iridium a giant meteor looks like a pretty good answer to me.

23. Briefly explain how fossils form.

There are body fossils and trace fossils.

Fossils form through several processes

Unaltered body fossils can form when frozen, preserved in tar pits, or mummified; there are also cases where amber traps an organism

Carbonization transforms soft tissues into thin black films of carbon (coal)

permineralization when minerals from ground or water enter pores of dead plant or animal material, the minterals attache to the cell wall and build crystalline netwrok in those empty cavaties, the mineralization hardens the bone turning it into stone

24. How does unstable isotope dating work?

over a certain period of time the isotope will decay to half its amount (half-life) while the amount of the stable atom will be the same. we can compare these two numbers to see many years it has been since the animal has died.