Photosynthesis and Cellular Respiration Quiz

Photosynthesis and Cellular Respiration

• Photosynthesis and cellular respiration are complementary biological reactions
• Photosynthesis uses carbon dioxide and water to create glucose and oxygen as outputs
• Cellular respiration uses oxygen and glucose as inputs and generates water, carbon dioxide, and energy (ATP) as outputs

Photosynthesis and Cellular Respiration

• Photosynthesis and cellular respiration are complementary processes.
• Photosynthesis uses carbon dioxide and water to generate glucose (sugar) and oxygen as a by-product.
• Cellular respiration uses oxygen and glucose to generate ATP (energy), carbon dioxide, and water.

Photosynthesis and Cellular Respiration

• Photosynthesis produces glucose and oxygen using carbon dioxide and water.
• Cellular respiration uses oxygen and glucose to produce carbon dioxide, water, and ATP, an energy-carrying molecule.
• Both reactions complement each other in the environment.
• Photosynthesis is how plants obtain energy from the sun, using light as the energy source.
• Cellular respiration is how animals and humans obtain energy from food, using food as the energy source.

Photosynthesis

• Light-dependent Reactions
  • Occur within the thylakoid membrane of chloroplasts
  • Capture light energy and convert it into chemical energy
  • Key steps include:
    • Light excites electrons in chlorophyll
    • Water is split (photolysis), releasing oxygen
    • Excited electrons move through an electron transport chain, generating ATP and NADPH
    • Outputs include ATP, NADPH, and oxygen

Cellular Respiration

• Glycolysis

  • Occurs within the cytoplasm
  • Breaks down glucose to extract energy
  • Key steps include:
    • Glucose is phosphorylated and cleaved into two pyruvate molecules
    • Energy investment phase utilizes ATP, while the energy payoff generates ATP and NADH
    • Outputs include two pyruvate, two ATP (net), and two NADH per glucose molecule
  • Anaerobic process that can feed into the Krebs Cycle if oxygen is present

• Krebs Cycle (Citric Acid Cycle)

  • Occurs within the mitochondria
  • Oxidizes acetyl-CoA to produce energy carriers
  • Key steps include:
    • Acetyl-CoA combines with oxaloacetate to form citrate
    • Citrate undergoes a series of oxidative reactions, releasing CO2 and regenerating oxaloacetate
    • Outputs include three NADH, one FADH2, one ATP/GTP per cycle, and two CO2
  • Provides electron carriers (NADH and FADH2) for the electron transport chain

• Electron Transport Chain (ETC)

  • Occurs within the inner mitochondrial membrane
  • Produces ATP through oxidative phosphorylation
  • Key steps include:
    • Electrons from NADH and FADH2 pass through a series of protein complexes
    • Energy from electron transfer pumps protons (H+) into the intermembrane space, generating a proton gradient
    • ATP synthase utilizes this gradient to produce ATP when protons flow back into the matrix
    • Outputs include approximately 32-34 ATP per glucose molecule and water as electrons reduce oxygen

Calvin Cycle (Light-independent Reactions)

• Occurs within the stroma of chloroplasts
• Fixes carbon dioxide into organic molecules (glucose)
• Key steps include:
  • CO2 is incorporated into ribulose bisphosphate (RuBP) by the enzyme Rubisco
  • The resulting 3-phosphoglycerate (3-PGA) is reduced to glyceraldehyde-3-phosphate (G3P) using ATP and NADPH
  • Some G3P exits to form glucose, while others are recycled to regenerate RuBP
  • Outputs include one G3P per three CO2 molecules fixed
  • Requires ATP and NADPH generated during the light-dependent reactions
  • Essential for synthesizing carbohydrates using atmospheric CO2

Light-dependent Reactions

• Occur in the thylakoid membranes of chloroplasts.
• Convert light energy into chemical energy (ATP and NADPH).
• Photolysis splits water molecules into oxygen, protons, and electrons using light energy.
• Electron Transport Chain (ETC) uses light energy to excite electrons, which move through a series of proteins, releasing energy to pump protons into the thylakoid lumen.
• ATP Production occurs as protons flow back into the stroma through ATP synthase, generating ATP via chemiosmosis.
• NADPH Formation occurs at the end of the ETC when electrons reduce NADP+ to NADPH.

Electron Transport Chain (ETC)

• A key process in both cellular respiration (inner mitochondrial membrane) and photosynthesis (thylakoid membrane).
• Transfers electrons through a series of proteins, generating a proton gradient across the membrane.
• This proton gradient drives ATP synthesis via ATP synthase.
• In cellular respiration, oxygen accepts electrons at the end of the ETC, forming water.
• Produces a substantial amount of ATP through oxidative phosphorylation (cellular respiration) and photophosphorylation (photosynthesis).

Krebs Cycle (Citric Acid Cycle)

• Takes place in the mitochondrial matrix.
• Oxidizes acetyl-CoA (derived from carbohydrates, fats, and proteins) to generate electron carriers (NADH and FADH2) and ATP.
• Acetyl-CoA combines with oxaloacetate to form citrate.
• A series of reactions involving decarboxylation (removal of CO2) and oxidation regenerates oxaloacetate.
• Outputs include: 3 NADH, 1 FADH2, 1 ATP (or GTP), and 2 CO2 (waste product).
• Plays a central role in connecting carbohydrate, fat, and protein metabolism, providing substrates for aerobic respiration.