Unit 6 Lecture 1

The lecture states that after the Great Oxidation Event, oxygen levels reached about 10% of modern levels. Why was this important for cellular respiration?

It was high enough for a new form of respiration using oxygen (aerobic respiration) to evolve

How did increasing oxygen levels make many mineral nutrients more available to organisms?

Oxidation promoted chemical weathering of rocks, releasing minerals into rivers and oceans

What does the lecture suggest about the evolutionary reason oxygenic photosynthesis first spread in microbial lineages?

It was selected because mutations allowed microbes to produce glucose, a more energy-rich carbon source, not because of any benefit of oxygen itself at that time

Which comparison between formaldehyde and glucose is most accurate based on the lecture?

Formaldehyde has a single carbon and no carbon–carbon bonds, whereas glucose has many carbon–carbon bonds and is higher energy

Which sequence best matches the order of events described in the lecture?

Evolution of anoxygenic photosynthesis → evolution of oxygenic photosynthesis in cyanobacteria → Great Oxidation Event

Which statement best captures the interaction between nitrogen fixation and changing oxygen levels on early Earth?

Nitrogen fixation evolved long before oxygen accumulated, but later oxygen-driven weathering increased minerals that boosted nitrogen fixation rates

What is the main significance of stromatolites in the context of this lecture?

They are layered sedimentary formations built by ancient microbes, including cyanobacteria

Which shift in matter and energy sources is emphasized as a consequence of oxygenic photosynthesis?

Many organisms shifted from relying on inorganic carbon sources like formaldehyde to using organic molecules such as sugars for matter and energy

How does the lecture connect patterns and processes when explaining oxygenation of the Earth?

By using processes (mutations, photosynthesis, respiration, nitrogen fixation) to explain patterns of oxygen and nutrient change over Earth's history

What modern-day consequence of human activity is contrasted with early nitrogen limitation in the lecture?

Humans have added so much biologically available nitrogen that some organisms overgrow at the expense of others

Why did rising oxygen levels initially reduce the diversity of many microbial taxa?

Oxygen was toxic to many early anaerobic lineages, causing extinctions

Which statement about the timing of nitrogen fixation relative to photosynthesis is supported by the lecture?

Nitrogen fixation predates both land plants and photosynthesis by billions of years

According to the lecture, why did oxygenic photosynthesis persist and spread, even though oxygen was toxic to most early life?

Organisms gained access to a new, higher-energy carbon source (glucose) compared to earlier inorganic carbon sources

Which relationship among the three domains of life is highlighted in the lecture?

Archaea share genes and metabolic pathways that are more closely related to eukaryotes than to bacteria

Which description of early Earth compared to modern Earth best reflects the lecture?

Early Earth lacked plants and animals, had intense volcanic activity and strong UV radiation, unlike the modern Earth

Which statement about the origins of metabolic diversity is most consistent with the lecture?

All forms of metabolism in the tree of life were initially invented and evolved in microbes

What role do cyanobacteria play in explaining large-scale changes in Earth’s biosphere?

They evolved oxygenic photosynthesis, producing oxygen and organic carbon that helped oxygenate the biosphere

Why did aerobic respiration become so successful relative to anaerobic respiration?

It produced much more ATP from food molecules, increasing survival and reproduction.