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General Biology: Cellular Respiration and Photosynthesis

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  • Photosynthesis overall equation

    Energy (sunlight) + CO2 + H2O → Organic molecules (sugar) + O2

  • Cellular respiration overall equation

    Organic molecules (sugar) + O2 → CO2 + H2O + Energy (ATP)

  • Difference between respiration and cellular respiration

    Respiration is gas exchange (breathing). Cellular respiration is aerobic harvesting of energy from organic molecules.

  • What is a redox reaction?

    Transfer of electrons between reactants; oxidation is loss of electrons, reduction is gain of electrons.

  • Role of NAD+ in cellular respiration

    NAD+ is a coenzyme that accepts electrons to become NADH, shuttling electrons in redox reactions.

  • Three main stages of cellular respiration

    1. Glycolysis, 2. Pyruvate oxidation and citric acid cycle, 3. Oxidative phosphorylation.

  • Location of glycolysis

    Occurs in the cytosol, breaking glucose into two pyruvate molecules.

  • Substrate-level phosphorylation

    ATP production by transferring a phosphate group directly from a substrate to ADP during glycolysis and citric acid cycle.

  • Energy investment and payoff in glycolysis

    Uses 2 ATP to energize glucose; produces 4 ATP and 2 NADH; net gain of 2 ATP.

  • Why is glycolysis considered an ancient process?

    It occurs in the cytosol, does not require oxygen, and is universal among life, suggesting early evolution.

  • Pyruvate oxidation steps

    1. CO2 removed from pyruvate, 2. NAD+ reduced to NADH, 3. Coenzyme A added to form Acetyl CoA.

  • Citric acid cycle outputs per Acetyl CoA

    2 CO2, 3 NADH, 1 FADH2, and 1 ATP; doubled per glucose molecule.

  • Role of NADH and FADH2 in cellular respiration

    Carry high-energy electrons to the electron transport chain for ATP production.

  • Oxidative phosphorylation components

    Electron transport chain and chemiosmosis in mitochondria produce ~90% of ATP.

  • Chemiosmosis in mitochondria

    H+ gradient drives ATP synthase to phosphorylate ADP to ATP.

  • Fermentation purpose

    Harvests energy anaerobically by regenerating NAD+ to allow glycolysis to continue without oxygen.

  • Lactic acid fermentation

    Pyruvate reduced to lactate; NADH oxidized to NAD+; occurs in muscle cells and some bacteria.

  • Alcohol fermentation

    Pyruvate reduced to ethanol and CO2; NADH oxidized to NAD+; used by yeasts in brewing and baking.

  • Difference between obligate and facultative anaerobes

    Obligate anaerobes require no oxygen and are poisoned by it; facultative anaerobes can use oxygen or fermentation.

  • Photosynthesis light reactions location and function

    Occur in thylakoid membranes; convert light energy to ATP and NADPH, split water to release O2.

  • Calvin cycle function and location

    Occurs in stroma; fixes CO2 into organic molecules using ATP and NADPH to produce G3P.

  • Role of rubisco in Calvin cycle

    Enzyme that attaches CO2 to RuBP, initiating carbon fixation.

  • Difference between C3, C4, and CAM plants

    C3 fix CO2 directly; C4 fix CO2 into 4-carbon compounds in separate cells; CAM fix CO2 at night to conserve water.

  • Photorespiration problem

    Rubisco adds O2 instead of CO2, producing no sugar and wasting ATP and NADPH.

  • Chlorophyll function

    Light-absorbing pigment in chloroplasts that captures light energy for photosynthesis.

  • Structure of chloroplast

    Contains thylakoid membranes (site of light reactions) and stroma (site of Calvin cycle).

  • Function of stomata in leaves

    Pores that allow CO2 to enter and O2 to exit the leaf.

  • Photoprotection in plants

    Carotenoids dissipate excess light energy to protect chlorophyll and cells from damage.