Origin of Life, Endosymbiosis, and Biodiversity in BIOL 205

Why do scientists think early life began deep in the ocean?

Many scientists hypothesize that life began near hydrothermal vents due to harsh conditions on early Earth's surface, including intense UV radiation and volcanic activity. Deep-sea vents provided a stable, protected environment rich in essential chemicals and energy sources.

What evidence shows the interconnectedness of life?

Genetic similarities across all life forms—bacteria, archaea, and eukarya—suggest a common ancestry, with shared genes indicating that modern organisms inherited traits from a single ancestral life form (LUCA).

What do shared genes between archaea, bacteria, and eukarya tell us about LUCA?

The presence of common genes suggests LUCA was a heat-loving, anaerobic organism thriving in environments without oxygen and obtaining energy from chemical gradients, similar to those found at hydrothermal vents.

What are the two types of hydrothermal vents?

They are categorized into black smokers and white smokers, which differ in chemical composition and temperature.

What is the difference between black smokers and white smokers?

Black smokers emit superheated, acidic water full of metals like sulfur, iron, and copper, reaching temperatures of several hundred degrees Celsius. White smokers release alkaline, methane-rich water at more moderate temperatures.

Why do scientists believe white smokers are more likely the location of early life?

Black smokers were likely too hot for LUCA to survive, while white smokers provided necessary chemistry at milder temperatures, making them more hospitable to early life.

What hydrothermal field is considered a leading candidate for life's first home?

The Lost City hydrothermal field.

What type of organisms are the ancestors of eukaryotes likely to be?

Archaea, specifically Asgard archaea.

Why is Earth's distance from the Sun crucial for the origin of life?

Earth is in the habitable zone where liquid water can exist, essential for life.

What are the three stages of the chemical-biological theory?

1. Formation of simple organic molecules 2. Formation of macromolecules 3. Formation of protocells.

What was the outcome of the Urey and Miller experiment?

It produced amino acids and fatty acids, supporting the idea that life's building blocks could form naturally.

Why were the results of the Urey and Miller experiment significant?

They provided experimental support for the Chemical-Biological Theory by showing that organic molecules can form from simple gases and energy.

How does today's atmosphere differ from that of early Earth?

Early Earth's atmosphere lacked oxygen and was rich in methane, ammonia, and hydrogen; today's atmosphere is 78% nitrogen and 21% oxygen.

What are stromatolites and what are the oldest known stromatolites?

Stromatolites are layered rocks formed by cyanobacteria trapping sediments; the oldest are 3.5 billion years old.

Why were stromatolites and cyanobacteria important for early Earth's atmosphere?

They performed photosynthesis, releasing oxygen and reducing CO2, initiating the Great Oxygenation Event.

How do we know that oxygen produced by cyanobacteria was first used in the oceans?

Oxygen reacted with dissolved iron to form rust, indicating it was absorbed in oceans before entering the atmosphere.

What major changes occurred as atmospheric oxygen levels rose to 10%, 15%, and 21%?

10%: Great Oxygenation Event; 15%: emergence of multicellular ocean life; 21%: supported land animals and complex ecosystems.

What is the significance of the Great Oxygenation Event?

It enabled aerobic respiration and complex life while causing extinctions of many anaerobic species.

What are the main differences between prokaryotic and eukaryotic cells?

Prokaryotes: no nucleus, smaller, simpler; Eukaryotes: nucleus, organelles, larger, complex structure.

Why are most bacteria very small compared to eukaryotic cells?

They rely on diffusion and need high surface area-to-volume ratios for efficient material exchange.

What do endocytosis and exocytosis mean?

Endocytosis: cell engulfs materials into vesicles; Exocytosis: cell expels materials via vesicle fusion with the membrane.

What hallmarks of multicellular life do some bacteria display?

Cell communication, differentiation, cooperation, and coordinated reproduction.

Why was the unintentional infection of Dr. Jeon's amoeba cultures significant?

It demonstrated how bacteria can evolve into endosymbionts, supporting the idea of endosymbiosis.

What are the three kinds of symbiosis?

Mutualism, commensalism, parasitism.

Why are mitochondria important for eukaryotic cells?

They generate ATP, the energy needed for cellular processes.

Why are mitochondria important for understanding the evolution of eukaryotic cells?

They evolved from bacteria, providing evidence for endosymbiosis.

What is endosymbiosis in simple terms?

When one organism lives inside another and both benefit.

What lines of evidence support the theory of endosymbiosis?

Mitochondria and chloroplasts have their own DNA, replicate independently, and resemble bacteria.

What do mitochondria and chloroplasts have in common regarding their DNA?

They have their own DNA and replicate independently.

Can mitochondria and chloroplasts live independently?

No, they rely on the host cell.

How many times did mitochondria arise in evolutionary history?

Only once.

How are eukaryotes related to bacteria and archaea?

Eukaryotes are hybrids of archaeal hosts and bacterial symbionts.

What is biogeography?

The study of the geographic distribution of species and how it's shaped by environmental and historical factors.

How does continental drift influence species assemblage on Earth?

It causes physical separation of species, leading to allopatric speciation and unique biodiversity across continents.

Why are dispersal and vicariance important for biogeography?

They explain how species spread or are separated: dispersal by movement, vicariance by barriers.

How do selective pressures contribute to the evolution of flightless birds?

On predator-free islands, flight is unnecessary and energy is better spent on survival traits.

What is the importance of continental drift to species evolution?

It causes isolation, new environments, and extinction, all key drivers of evolution.

What is a random walk in evolutionary terms?

A pattern of evolution with no consistent direction.

How does stabilizing selection produce stasis?

It maintains the status quo by favoring average traits.

What is the difference between punctuated equilibrium and gradualism?

Punctuated equilibrium involves sudden changes after stasis; gradualism is slow, continuous evolution.

Why does separation into small populations increase extinction rates?

Smaller populations are more vulnerable to genetic drift and environmental events.

What are the hypotheses for why the tropics have lower extinction rates?

More stable climates and greater energy support longer species survival.

What is adaptive radiation?

Rapid evolution of new species to fill various ecological roles.

What triggers adaptive radiation?

New environments, lack of competitors, and evolutionary innovations.

Why are insects considered more diverse?

They fly, reproduce quickly, and often feed on plants, all increasing speciation.

How does figure 10.11 illustrate Cambrian rapid speciation?

It shows a phylogram with a burst of lineages, indicating rapid adaptive radiation.

What are the hypotheses for Cambrian radiation?

Oxygen rise, genetic tools like Hox genes, and ecological interactions.

How did specialized structures influence Cambrian diversification?

They enabled animals to exploit new ecological niches.

What was the relationship between predators and prey during the Cambrian?

They co-evolved in an arms race, driving complexity.

What is the proposed connection between temperature and species diversity?

Warmer regions support more speciation and lower extinction.

What are the two major extinction pulses in China?

End-Permian (~252 MYA) and End-Cretaceous (~66 MYA).

Why is Alvarez's discovery of iridium significant?

It supports the asteroid impact theory of dinosaur extinction.

What are other extinction theories besides Alvarez's?

Volcanism, climate change, and sea-level shifts.

Why is it unusual that reptiles like snakes survived the dinosaur extinction?

They're reptiles too, but survived likely due to burrowing and smaller size.

What was the state of animal populations after the Permian extinction?

Most marine and terrestrial life died; survivors were few and simple.

What happened to animal populations after the Cretaceous extinction?

Mammals and birds diversified rapidly into vacant niches.

What are background extinction rates?

Natural extinction rates: ~1 species/million/year.

How do current extinction rates compare to background rates?

They're 100-1000× higher due to human impact.

What are two effects of increased carbon levels?

Global warming and ocean acidification.

Why is the collapse of coral reefs a concern?

They support 25% of marine biodiversity.

Why is rising global temperature concerning for biodiversity?

It shifts habitats, stresses species, and accelerates extinctions.

Why should we be concerned about today's extinctions?

Losing species weakens ecosystems and endangers humans too.