Lecture 02: Life Origins: Potential Exam Questions

Potential exam question #1

Give a brief explanation of one of the theories on the origin of life discussed in class?

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Primordial Soup Hypothesis:
In early Earth's strongly reducing atmosphere (ammonia and methane), simple organic molecules were able to form in the presence of energy (i.e. lightning, intense UV rays).

Deep Sea Vent Hypothesis:
Reducing conditions in the Earth's atmosphere were not strong enough for molecule formation (perhaps not enough ammonia or methane), however reducing conditions near deep sea vents where volcanic activity occurred may have been suitable.

Seeding Hypothesis (also called Panspermia):
Carbon-rich meteorites that land on Earth, called chondrites, are thought of as evidence of the extra-terrestrial origin of amino acids. In the presence of an equal mix of D and L isomers these chondrites are considered "seeds" of life on Earth that have or can be delivered to other inhabitable bodies as well. This theory, while plausible, does not go so far as to explain where the amino acids originated from or how they were formed.

Potential exam question #2

What are the major distinctions between prokaryotes and eukaryotes?

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Prokaryotic cells lack internal membranes and have little internal organization. Prokaryotes include bacteria and blue-green algae. In contrast, eukaryotic cells have a nucleus (internal membrane) and sub-cellular organelles (such as mitochondria, chromosomes, and chloroplasts) representing superior internal organization. Prokaryotes are smaller because they can only transport materials via diffusion across their cytoplasm. This smaller size allows for a faster metabolism and reproductive rate, but constrains their ability to become large because nutrients are not able to travel through the cytoplasm fast enough. Eukaryotic cells are the foundation for plants, animals, protozoans, and fungi.

Potential exam question #3

Describe how biodiversity can be considered a dynamic model.

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A dynamic model is one that accounts for the element of time. Biodiversity changes over time according to (on a global scale) the relative rates of speciation and extinction, and therefore can be considered a dynamic model.

Potential exam question #4

Describe two important consequences of continental drift for ecological systems

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Continental drift, the movement of landmass across the surface of the earth, has two important consequences for ecological systems. First, the positions of continents and major ocean basins profoundly influence climatic patterns. Second, continental drift creates and breaks down barriers to dispersal, alternately connecting and separating evolving biotas in different regions of the earth.

Potential exam question #5

List three causes of the geographically isolation of a species.

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Dispersal, continental drift, climate fluctuations (including glaciation).

Potential exam question #6

Describe in detail the iterative process of crisis and innovation that drove the development of aerobic respiration from the earliest autotrophs

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The earliest autotrophs likely derived their H from H2 or H2S (akin to chemosynthesis by bacteria of deep sea vents). This in itself (producing organic compounds from inorganic materials) was an innovation from the heterotrophic life forms that almost certainly evolved beforehand. Then, as the H source became exhausted (crisis), photosynthesis developed to cleave H from H2O (innovation). As the resulting O2 poisoned the atmosphere (crisis), the development of aerobic respiration enabled life to continue in this environment (innovation).

Potential exam question #7

Explain the concept of "evolutionary convergence"

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Unrelated lineages living under similar conditions may evolve to resemble one another more than their ancestors did. In essence, the evolutionary process tends to converge on a particular structure and function of an organism given a particular set of ecological conditions and opportunities.

Potential exam question #8

What is a species?

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Two definitions exist morphological and biological, and yet neither fully answers the question. Morphologically speaking, species resemble one another. In the 18th century this morphology was the foundation for taxonomy. Critics of this approach cite it's arbitrary nature and the inability to precisely handle mimicry. The biological definition determines that species are groups of interbreeding (or potentially interbreeding) individuals reproductively isolated from other individuals. This definition offers a concrete test of whether or not individuals are in the same species. However it is only applicable to organisms alive now and is no help in understanding the fossil record, spatially separated organisms (lions and tigers - horses and donkeys, can mate but are different species), and hybridization.

Potential exam question #9

Define "molecular clock"

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Molecular evolution happens at a constant rate. If you plot molecular changes in a particular lineage of organisms against time they seem to accumulate, these changes occur at a constant rate.