Week 2 Flashcards
What is carbon fixation, and why is it crucial?
Carbon fixation incorporates CO₂ into organic molecules, forming the foundation of all organic carbon on Earth. The Calvin-Benson-Bassam (CBB) cycle, utilized by phytoplankton, is the most significant pathway globally for carbon fixation.
What is oxygenic photosynthesis, and who performs it?
Oxygenic photosynthesis uses water as an electron source and releases oxygen as a byproduct. It is performed by organisms such as cyanobacteria, algae, plants, and prochlorophytes.
What is anoxygenic photosynthesis?
Anoxygenic photosynthesis, performed by certain bacteria (e.g., purple sulfur bacteria), uses substances like H₂ or H₂S instead of water as an electron source and does not produce oxygen.
What are the two main stages of photosynthesis?
Light reactions: Convert solar energy into ATP and NADPH while splitting water to release oxygen.
Dark reactions: Use ATP and NADPH to fix CO₂ into carbohydrates via the Calvin cycle.
What are chemoautotrophs, and where are they found?
Chemoautotrophs obtain energy by oxidizing inorganic substances like sulfides. They thrive in extreme environments, such as hydrothermal vents, supporting ecosystems without sunlight.
What is the role of RuBisCO in photosynthesis?
RuBisCO catalyzes the reaction between CO₂ and RuBP during carbon fixation in the Calvin cycle. It is the most abundant enzyme on Earth but is inefficient, requiring mechanisms to concentrate CO₂ at its active site.
What are ATP and NADPH, and why are they important?
ATP: The primary energy carrier, transferring energy for cellular processes.
NADPH: An electron carrier, providing high-energy electrons for biosynthesis in the Calvin cycle.
What are the six known pathways of carbon fixation?
Calvin-Benson-Bassam (CBB) cycle.
Reductive TCA cycle.
Reductive acetyl-CoA pathway.
3-hydroxypropionate (3-HP) cycle.
3-HP/4-hydroxybutyrate (3-HP/4-HB) cycle.
Dicarboxylate/4-hydroxybutyrate (DC/4-HB) cycle.
What is the role of photosystems in photosynthesis?
Photosystem II (PSII) initiates electron flow by splitting water, while Photosystem I (PSI) reduces NADP⁺ to NADPH. Together, they provide energy and reducing power for the Calvin cycle.
What are the phases of the Calvin cycle?
Carboxylation: CO₂ is fixed to RuBP by RuBisCO.
Reduction: ATP and NADPH convert intermediates into G3P.
Regeneration: RuBP is regenerated for continued CO₂ fixation.
Why is photosynthesis considered inefficient?
Photosynthesis converts only ~0.13% of solar energy into chemical energy. Despite this, the vast energy production drives Earth’s biogeochemical cycles and supports life.
What is photolysis, and why is it significant?
Photolysis is the splitting of water molecules during light reactions, providing electrons for the electron transport chain, releasing oxygen, and producing protons for ATP synthesis.
Where do light-dependent reactions occur, and what do they produce?
Light-dependent reactions occur in the thylakoid membranes. They produce ATP and NADPH for the Calvin cycle, along with oxygen as a byproduct.
What are extremophiles, and what roles do they play?
Extremophiles are organisms that thrive in harsh environments. Chemoautotrophic extremophiles contribute to nitrogen cycling and support unique ecosystems, such as those at hydrothermal vents.
How do hydrothermal vent ecosystems sustain life?
Chemoautotrophic bacteria fix CO₂ using energy from chemical reactions, forming the base of the food chain. These bacteria support heterotrophic organisms, creating a self-sustained ecosystem.
What limits photosynthesis as light intensity increases?
Photosynthesis increases with light intensity up to a saturation point. Beyond this, the rate plateaus because the photosynthetic apparatus cannot process additional energy, and excessive light may cause photoinhibition.
How do phytoplankton contribute to nutrient cycles?
Phytoplankton absorb nutrients like nitrogen, phosphorus, and iron, which are incorporated into their biomass. These nutrients are recycled back into the ecosystem when phytoplankton die or are consumed.
Why does chlorophyll concentration peak during certain seasons?
Chlorophyll concentration peaks in spring and summer due to increased sunlight and nutrient availability, fueling phytoplankton growth. In winter, reduced light and nutrient limitation suppress growth, lowering chlorophyll levels.
What causes changes in ocean color during phytoplankton blooms?
The chlorophyll in phytoplankton absorbs light, altering the ocean’s color. High chlorophyll concentrations during blooms make the water appear greener, indicating elevated phytoplankton biomass.
How do primary producers influence nutrient cycling?
Primary producers absorb CO₂ for photosynthesis, releasing oxygen and forming organic compounds. They drive the cycling of nutrients like nitrogen and phosphorus, essential for sustaining ecosystems.
What role do phytoplankton play in the marine food web?
Phytoplankton are the base of the marine food web, providing energy to zooplankton, which feed fish and higher predators. They transfer solar energy into the ecosystem through their biomass.
How do hydrothermal vent ecosystems survive without sunlight?
Chemoautotrophic bacteria at hydrothermal vents use chemical energy from sulfides or methane to fix CO₂. These bacteria support other organisms, creating an ecosystem independent of sunlight.
Why are accessory pigments important for photosynthesis?
Accessory pigments absorb additional light wavelengths beyond those captured by chlorophyll, maximizing the use of available sunlight and enhancing photosynthetic efficiency.
How do photosystems contribute to photosynthesis?
Photosystem II splits water to release electrons, which flow through an electron transport chain to Photosystem I. Photosystem I uses these electrons to produce NADPH, a key molecule for carbon fixation.
