photosynthesis Flashcards
Why is photosynthesis important for humans?
Produces the food we eat.
Provides energy sources (fossil fuels, firewood).
Supplies materials like timber and paper.
Releases oxygen, essential for aerobic life.
Cleans water, reduces flooding, and regulates soil contaminants.
How efficient is photosynthesis?
Corn: 1-2% solar energy conversion.
Sugar cane: 8% solar energy conversion.
Photorespiration reduces photosynthetic efficiency.
What is the role of Rubisco in the Calvin Cycle?
Rubisco (Ribulose-1,5-bisphosphate carboxylase/oxygenase) catalyzes CO₂ fixation by combining CO₂ with RuBP (ribulose-1,5-bisphosphate).
It can also bind oxygen, leading to photorespiration, which reduces efficiency.
What is artificial photosynthesis?
Creating devices that mimic natural photosynthesis.
Uses catalysts to convert light energy into chemical energy.
Devices can improve their efficiency over time.
What role does photosynthesis play in reducing greenhouse gases?
A:
Forests and oceans absorb CO₂.
Converts CO₂ into organic matter, reducing atmospheric CO₂ levels.
What is photorespiration?
Occurs when Rubisco fixes oxygen instead of carbon dioxide.
Leads to the production of phosphoglycolate, a waste product.
Reduces photosynthetic efficiency by wasting energy.
What are thylakoids and their function?
Flattened sac-like membranes in chloroplasts.
Contain pigments (chlorophyll, carotenoids) for light absorption.
Site of light-dependent reactions of photosynthesis.
What are the main structural components of a chloroplast?
Envelope: Outer limiting membranes.
Stroma: Unstructured matrix.
Thylakoids: Internal membrane system.
Lumen: Space inside thylakoids.
What are the environmental factors that affect Rubisco activity?
CO₂ Concentration: High CO₂ increases Rubisco’s carboxylase activity.
O₂ Concentration: High O₂ promotes photorespiration.
Temperature: Higher temperatures favor photorespiration.
What happens during the light-dependent reactions of photosynthesis?
Photosystem II (PSII): Absorbs light, splits water into oxygen, protons, and electrons.
Photosystem I (PSI): Uses light energy to excite electrons, reducing NADP+ to NADPH.
Electron Transport Chain: Creates a proton gradient across the thylakoid membrane to drive ATP production via ATP synthase.
What are the effects of increasing photorespiration in plants?
Photorespiration occurs more frequently at higher temperatures.
Reduces the efficiency of the Calvin cycle by wasting carbon and energy.
Metabolic engineering can aim to reduce photorespiration.
What are the main steps in the Calvin Cycle?
Carbon Fixation: CO₂ is attached to RuBP by Rubisco.
Reduction: ATP and NADPH reduce 3-PGA to G3P.
Regeneration of RuBP: Some G3P is used to regenerate RuBP, allowing the cycle to continue.
How do light-dependent and light-independent reactions differ?
Light-Dependent (Light): Occurs in thylakoids; uses sunlight to generate ATP and NADPH.
Light-Independent (Dark/Calvin Cycle): Occurs in stroma; uses ATP and NADPH to fix CO₂ into organic molecules.
What are the three phases of the Calvin Cycle?
Carbon Fixation: CO₂ attached to RuBP by Rubisco.
Reduction: 3-PGA is converted to G3P using ATP and NADPH.
Regeneration: G3P is used to regenerate RuBP, requiring more ATP.
What is the role of chlorophyll in photosynthesis?
Chlorophyll absorbs light, primarily in the red and blue wavelengths.
Reflects green light, making plants appear green.
Plays a key role in the light-harvesting complexes of PSII and PSI.
