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General Biology: Photosynthesis and Metabolism

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  • Overall equation for photosynthesis

    6 CO2 + 6 H2O + light energy → C6H12O6 + 6 O2. Water is oxidized, CO2 is reduced, and oxygen comes from water.

  • Is photosynthesis endergonic or exergonic?

    Photosynthesis is an endergonic reaction because it requires energy input from sunlight to produce glucose.

  • Role of stomata in photosynthesis

    Stomata regulate gas exchange by allowing CO2 to enter and O2 to exit the leaf, essential for photosynthesis.

  • How water moves from roots to leaves

    Water is absorbed by roots via osmosis and moves upward driven by transpiration, cohesion, and adhesion.

  • Chloroplast structure related to photosynthesis

    Chloroplasts have thylakoid membranes with pigments (chlorophyll) for light absorption and stroma where the Calvin cycle occurs.

  • Where do light reactions and Calvin cycle occur in cyanobacteria?

    Light reactions occur in thylakoids, carbon fixation via Rubisco in carboxysomes, and the Calvin cycle in the cytoplasm.

  • Colors and wavelengths chlorophyll absorbs

    Chlorophyll absorbs mainly blue and red light; blue light has more energy than red.

  • Why do plants look green?

    Plants look green because chlorophyll reflects green wavelengths and absorbs blue and red light.

  • Why are chlorophyll a and b nonpolar important?

    Being nonpolar helps chlorophyll embed in the hydrophobic thylakoid membranes for efficient light absorption.

  • Substrates and products of light reactions

    Substrates: light, water, ADP, NADP+. Products: ATP, NADPH, and O2.

  • Source of electrons in photosynthetic electron transport chain

    Electrons come from water, are excited twice by light in photosystems II and I, and finally reduce NADP+ to NADPH.

  • How ATP and NADPH are made in light reactions

    ATP is made by ATP synthase using a proton gradient; NADPH is made by reducing NADP+ with electrons from photosystem I.

  • Examples of active and passive transport in light reactions

    Passive: protons move down gradient through ATP synthase. Active: electron transport pumps protons into thylakoid lumen.

  • Similarities between photosynthesis and cellular respiration electron transport chains

    Both use electron transport chains to create a proton gradient that drives ATP synthesis via ATP synthase.

  • Substrates and products of the Calvin cycle

    Substrates: CO2, ATP, NADPH. Products: G3P (glyceraldehyde 3-phosphate), ADP, NADP+.

  • Location of Calvin cycle in chloroplast and bacteria

    Occurs in the stroma of chloroplasts and in the cytoplasm of bacteria.

  • Differences between Calvin cycle and Citric Acid cycle

    Calvin cycle uses ATP and NADPH to reduce CO2 to sugar; Citric Acid cycle oxidizes organic molecules to produce ATP and electron carriers.

  • First law of thermodynamics in metabolism

    Energy is transferred or transformed but not created or destroyed in metabolic reactions.

  • Second law of thermodynamics and living organisms

    Entropy increases in closed systems, but organisms are open systems that exchange energy to maintain order.

  • Why do molecules like carbohydrates have chemical potential energy?

    Because of the arrangement of atoms and their free energy state in covalent bonds.

  • Difference between exergonic and endergonic reactions

    Exergonic reactions release energy (ΔG < 0); endergonic reactions require energy input (ΔG > 0).

  • Why are endergonic and exergonic reactions often coupled?

    To drive non-spontaneous reactions by pairing them with spontaneous ones, often via ATP hydrolysis.

  • How ATP transfers energy to other molecules

    ATP transfers energy by hydrolyzing its high-energy phosphate bonds, releasing a phosphate group.

  • What fuels the ATP cycle in the body?

    Cellular respiration regenerates ATP from ADP and phosphate using energy from food molecules.

  • How enzymes lower activation energy

    By stabilizing the transition state, orienting substrates, providing a favorable microenvironment, and stressing substrate bonds.

  • Difference between competitive and noncompetitive inhibitors

    Competitive inhibitors bind the active site; noncompetitive inhibitors bind elsewhere altering enzyme shape.

  • Four modes of enzyme regulation

    Gene regulation, enzyme activation/deactivation, feedback inhibition, and localization/compartmentalization.