BIOL 1108 Ch 8

Photosynthesis core concepts

Photosynthesis is the major pathway for incorporating energy and carbon into carbohydrates; the Calvin cycle uses CO2 to synthesize carbohydrates; light reactions produce ATP and NADPH for the Calvin cycle; efficiency is challenged by excess light and rubisco’s oxygenase activity; photosynthesis profoundly impacted life on Earth.

Sunlight and photosynthesis efficiency

How much of the sun’s output is usable for photosynthesis? About 40% of sunlight is in the visible range; only a maximum of 4% is converted into carbohydrates, with losses from heat, reflection, and photorespiration.

General equation for photosynthesis

What is the general equation for photosynthesis? Sunlight + CO2 + H2O → carbohydrates + O2.

Meaning of reduction in photosynthesis

What does “reduction” mean in photosynthesis? In biology/chemistry, it refers to gaining electrons, often accompanied by hydrogen addition or oxygen removal; in photosynthesis, electrons are collected and stored in carbohydrates.

Electron donor in photosynthesis

What is the electron donor in photosynthesis? Water, which is oxidized to produce electrons, protons, and O2.

Link between water oxidation and CO2 reduction

How is water oxidation linked to CO2 reduction? Oxidation of water provides electrons and protons that reduce CO2 into carbohydrates via the photosynthetic electron transport chain.

Photosynthesis as a redox reaction

Why is photosynthesis considered a redox reaction? Water is oxidized to O2, and CO2 is reduced to form carbohydrates through electron transfer.

Flow of energy and electrons in photosynthesis

What is the sequence of reactions in photosynthesis? Light reactions oxidize water to produce electrons, ATP, and NADPH, which are used in the Calvin cycle to reduce CO2 into carbohydrates.

CAM and C4 photosynthesis

What is the difference between CAM and C4 photosynthesis? CAM plants fix CO2 at night and store it as malate to use during the day, while C4 plants separate CO2 fixation and the Calvin cycle spatially, using different cell types to minimize photorespiration.

Improving photosynthesis efficiency

How could plants make photosynthesis more efficient? Plants could improve efficiency by reducing photorespiration, using alternative electron pathways, or optimizing light and carbon fixation processes.

Protection from high-energy electrons

How do plant cells protect themselves from high-energy electrons? Plants use non-photochemical quenching and alternative electron transport to safely dissipate excess energy and prevent oxidative damage.

Evolution of photosynthesis

How did photosynthesis evolve step by step? It began with light-sensitive pigments, evolved to cyclic photophosphorylation, developed into oxygenic photosynthesis with water-splitting, and ultimately led to the integration of light reactions with the Calvin cycle.

Overview of photosynthesis

What are the two main stages of photosynthesis? The light reactions, which produce ATP and NADPH using light and water, and the Calvin cycle, which uses ATP and NADPH to fix CO2 into carbohydrates.

Energy flow in photosynthesis

What molecules are produced and consumed in photosynthesis? Light reactions use water, ADP, and NADP+ to produce oxygen, ATP, and NADPH; the Calvin cycle uses ATP, NADPH, and CO2 to produce sugars.

Light properties

What are two key properties of light relevant to photosynthesis? Light travels as waves but is absorbed as particles called photons.

Quantum of light

What is a quantum of light? It is the energy of a photon, which is inversely related to its wavelength.

Visible light and photosynthesis

What portion of sunlight is used for photosynthesis? About 40% of sunlight that reaches Earth is visible light, also known as photosynthetically active radiation (PAR).

Thylakoid proton accumulation

What happens during proton accumulation? Protons build up inside the thylakoid lumen during the light reactions, creating a proton gradient used to generate ATP.

Effect of toxin on thylakoid membranes

What would happen if thylakoid membranes became permeable to hydrogen ions? The proton gradient would collapse, preventing ATP synthesis.

Effect of PSII failure

What happens if Photosystem II stops functioning? Water would not split, no oxygen would be produced, and the electron transport chain would halt.

Low light levels

What happens when light levels get very low? ATP and NADPH production decrease, slowing or stopping the Calvin cycle.

Ferredoxin and cyclic electron flow

What happens if ferredoxin stops cycling electrons? The cell cannot produce enough ATP through cyclic electron transport, leading to energy imbalance in photosynthesis.