Marine Biology: Nutrient Cycling and Phototrophy

A type of respiration that occurs in the absence of oxygen, using alternative electron acceptors to generate ATP.

A form of anaerobic respiration where nitrate (NO3-) is used as the terminal electron acceptor, reducing it to nitrite (NO2-).

A form of anaerobic respiration where sulfate (SO42-) is reduced to sulfide (H2S) using electrons from organic compounds.

A type of anaerobic respiration where protons (H+) are reduced to hydrogen gas (H2) to generate a sodium motive force for ATP synthesis.

The final molecule in an electron transport chain that accepts electrons, completing the process of respiration.

A diagram that shows the relative strengths of different electron acceptors based on their reduction potentials.

A series of membrane-bound proteins that transfer electrons from a donor molecule to a terminal electron acceptor, generating a proton gradient.

The potential energy stored in the form of a proton gradient across a membrane, used to drive ATP synthesis.

Organisms that use inorganic compounds as their energy source, including aerobic and anaerobic respiration.

Organisms that obtain carbon from inorganic sources, mainly CO2, through carbon fixation.

A series of biochemical reactions that convert carbon dioxide (CO2) into organic compounds, using ATP and NADH.

A key enzyme in carbon fixation, responsible for converting CO2 into organic compounds.

Specialized compartments in some autotrophs that concentrate CO2 and sequester RubisCO, preventing its inhibition by oxygen.

A biological process where methane (CH4) is produced as a byproduct of microbial respiration.

A potential energy stored in the form of a sodium ion gradient across a membrane, used to drive ATP synthesis.

Landfill pipe vents are designed to prevent the accumulation of methane gas, which can lead to explosions.

Beggiatoa bacteria oxidize sulfur in steps to sulfate (SO42-) and can store intermediate sulfur (S0) as internal granules.

Sulfolobus archaea grows attached to sulfur crystals, dissolving them and bringing sulfur into the cell for metabolism. This process releases sulfuric acid, making the environment acidic.

Sulfur-oxidizing bacteria and archaea use specialized enzymes like Sox and Dsr to obtain electrons from sulfur compounds and transfer them to the electron transport chain.

The electron flow in sulfur oxidation generates a proton motive force (PMF) that drives ATP synthesis.

In sulfur oxidation, some organisms must use reverse electron flow to generate NADH for CO2 fixation because sulfur compounds have less negative reduction potentials than NADH.

Reverse electron flow sacrifices some energy from the proton motive force, reducing the overall ATP yield in sulfur oxidation.

Ocean regions with high levels of nutrients like nitrogen and phosphorus, but low levels of chlorophyll and photosynthetic activity.

Iron is a crucial micronutrient for phytoplankton growth. Despite ample nitrogen and phosphorus, iron scarcity limits photosynthetic activity in HNLC regions.

The idea that adding iron to HNLC regions could stimulate phytoplankton growth, leading to increased CO2 absorption from the atmosphere.

Studies conducted in HNLC regions involving deliberate iron additions to test the effect on phytoplankton blooms.

Despite initial promise, iron fertilization has potential risks. Unintended consequences include harmful algal blooms, disruptions to ocean ecosystems, and unclear long-term effects on carbon sequestration.

An enzyme that breaks down hydrogen peroxide (H2O2) into water (H2O) and oxygen (O2).

Organisms that can tolerate oxygen but don't require it for growth. They have enzymes to deal with toxic oxygen byproducts.

Organisms that cannot survive in the presence of oxygen. Oxygen is toxic to them.

Three key temperatures defining an organism's growth range: minimum, optimum, and maximum.

The temperature at which an organism grows fastest.

Organisms that thrive in cold temperatures, typically below 15°C.

Organisms that thrive in hot temperatures, typically above 45°C.

The fluidity or stiffness of the cell membrane. It's affected by temperature.

The process of generating ATP (energy) using a proton gradient across a membrane.

The uptake of essential nutrients by the cell across the membrane.

A visual representation of different electron acceptors arranged by their relative reduction potentials. Higher on the tower means a stronger electron acceptor, while lower indicates a weaker one. This helps determine the direction of electron flow in redox reactions.

A coenzyme that acts as an electron carrier, carrying high-energy electrons from redox reactions in the cell. It is a good electron donor due to its high position on the electron tower.

Chemical reactions where electrons are transferred from one molecule to another. One molecule gets oxidized (loses electrons), while the other gets reduced (gains electrons).

An organism that obtains energy from breaking down organic chemical compounds. These organisms use aerobic respiration, anaerobic respiration, or fermentation to harvest electrons from these compounds.

A metabolic process that generates ATP from organic compounds, like glucose, in the absence of oxygen (anaerobic). It involves a series of reactions that transfer electrons from molecules to a product, often an organic molecule.

A metabolic process that generates ATP by oxidizing organic molecules (like sugars) in the presence of an electron acceptor. This process involves electron transport chains and proton gradients.

A series of reactions that break down glucose into pyruvate, generating ATP and NADH. It is a common pathway used by both respiration and fermentation.

In anoxygenic photosynthesis, electrons cycle within the system, starting and returning to the reaction center (RC). They travel through the electron transport chain (ETC) before returning to the RC.

A process in anoxygenic photosynthesis where light energy drives electrons in a circular flow, generating ATP through phosphorylation of ADP.

Different anoxygenic phototrophs utilize different components within their electron transport chains.

Purple bacteria require an external electron source for NADH synthesis because the electron leaving the RC is at a lower energy level than NADH on the electron tower.

Green sulfur bacteria use ferredoxin (Fd) instead of NADH and their RC produces electrons at a higher energy level than Fd on the electron tower.

Some electrons leave the photosynthetic cycle in autotrophs to reduce NADH or Fd, which are crucial for building biomass.

Photoheterotrophs use light to generate ATP but acquire organic carbon from the environment for biosynthesis, combining photosynthetic and heterotrophic traits.

Anoxygenic phototrophs often require an external source of electrons (e.g., sulfur compounds) to replenish the electron cycle for continued ATP production.