447 - week 2

What are the other major components of bacterial cells by mass

~70 % water. carbon, oxygen, nitrogen, hydrogen and phosphorus

what is the great oxidation event

After microbes evolve the ability to do oxygenic photosynthesis. Earth’s atmosphere was primarily made of N2 , CO2, CH4, CO and H2 and GOE increased oxygen

What started GOE

cyanobacterual photosynthesis

What is an iron sink

any process or reservoir that removes free oxygen (O₂) from the environment by reacting it with reduced iron. Eventually, the iron sinks depleted. Less O2 was absorbed, and more was released into the atmosphere, eventually bringing the amount of O2 in the atmosphere to the 21% that we know today

Why is atmospheric O₂ so important for organisms?

allows organisms to perform aerobic cellular respiration, which yields far more ATP than glycolysis alone, supporting growth, biosynthesis, motility, and active transport.

Why is NAD⁺ required in glycolysis?

acts as an electron acceptor, becoming NADH; without recycling NADH back to NAD⁺, glycolysis would stop.

If fermentation produces no extra ATP, why do cells perform it?

recycles NADH back to NAD⁺ so glycolysis can continue when no external electron acceptor (like O₂) is available; it produces waste products such as ethanol or lactic acid.

What makes cellular respiration different from fermentation?

uses the citric acid cycle and an electron transport chain to recycle NADH to NAD⁺ and generates much more ATP, whereas fermentation only regenerates NAD⁺ without producing additional ATP.

Why do organisms that can perform both pathways prefer cellular respiration?

yields far more ATP, so organisms use it whenever an appropriate electron acceptor is available.

What electron acceptor is commonly used in the electron transport chain for aerobic respiration?

O₂, which allows aerobic cellular respiration in animals, plants, fungi, and many microorganisms.

How are the oxygen (O) and carbon (C) nutrient cycles interconnected?

take O from water and release it as O₂, while fixing C from CO₂ into organic molecules; during cellular respiration they use O₂ and organic molecules and release CO₂ and water, linking both cycles.

What are the major reservoirs in the carbon cycle?

Biomass, soil organic matter, atmospheric CO₂, dissolved CO₂ in oceans and shells, and long-term stores like sedimentary rock and fossil fuels.

What does an atom’s oxidation state represent?

The charge an atom would have if all bonds were ionic, determined by which atom in a bond “gets” the electrons based on electronegativity.

How does the oxidation state of carbon change in photosynthesis and respiration?

In photosynthesis carbon is reduced (gains electrons), while in respiration and fermentation carbon is oxidized (loses electrons).

What are the two stages of photosynthesis and their roles?

Light reactions store energy in ATP and NADPH; dark reactions use ATP and NADPH to fix carbon from CO₂ into organic molecules.

How is water involved in the light reactions of photosynthesis?

Water donates electrons to replace those lost by pigments, releasing O₂ and H⁺; in this process oxygen is oxidized from –2 in H₂O to 0 in O₂.

What does nutritional classification describe for organisms?

How organisms obtain energy (light vs. molecules), electrons (organic vs. inorganic), and carbon (organic vs. CO₂).

What are the major nutritional categories used to classify organisms?

Phototroph/chemotroph (energy source), organotroph/lithotroph (electron source), heterotroph/autotroph (carbon source).

Give an example of each: cyanobacteria, humans, anammox bacteria.

Cyanobacteria = photolithoautotrophs; humans = chemoorganoheterotrophs; anammox bacteria = chemolithoautotrophs.

What is a chemotroph?

An organism that obtains energy from molecules rather than light, using chemical reactions to generate ATP.

What do methanotrophs use as their energy and carbon source?

Methanotrophs use methane (CH₄) as their main source of carbon and energy.

Where are aerobic methanotrophs typically found?

At the oxic–anoxic boundary—areas where oxygen is present but methane is also available.

What distinguishes anaerobic methanotrophs from aerobic ones?

Anaerobic methanotrophs oxidize methane without oxygen, often using sulfate or other electron acceptors in anoxic environments.

How do symbiotic algae benefit coral cells?

Algae use sunlight and CO₂ to produce carbohydrates that feed both themselves and the coral; they are the coral’s primary food source and give corals their colors.

What happens during coral bleaching?

Corals expel their symbiotic algae in response to stress (e.g., heat, light changes, nutrient shifts), losing their major food source and color.

According to one hypothesis, how does stress lead to coral bleaching?

Stress damages algal cells, causing them to produce ROS that leak into coral tissue; corals expel algae to prevent further damage.

Why are bleached corals more vulnerable?

Without algae, corals lose their main energy source and become more susceptible to starvation and disease

What ecosystem services do coral reefs provide?

They protect coastlines from flooding and erosion, create calm waters for recreation, and provide habitat for fish and other marine life, supporting fishing and tourism industries.