Photosynthesis & Cellular Respiration - Quick Notes

Photosynthesis

• Autotrophs: organisms that use light energy to produce food (auto = self); examples: plants, some bacteria and protists.
• Essential inputs: $\text{H}<em>2\text{O}, \text{CO}</em>2, \text{Light energy}$
• Location: chloroplasts; pigment: chlorophyll (green pigment)
• Key structures: Outer membrane, Inner membrane, Stroma, Thylakoids, Granum (grana), Lumen
• Overall equation: $\text{CO}<em>2 + \text{H}</em>2\text{O} + \text{Light energy} \rightarrow \text{C}<em>6\text{H}</em>{12}\text{O}<em>6 + \text{O}</em>2$
• Two stages of photosynthesis:
  • Light Reactions (location: thylakoid membranes): Reactants = light energy; Products = ATP, NADPH, O₂
  • Calvin Cycle / Light-independent reactions (location: stroma): Reactants = CO₂, ATP, NADPH; Products = Glucose, ADP, NADP⁺
• What happens: chlorophyll absorbs light; water split to supply electrons; energy stored in glucose
• What happens in leaves:
  • CO₂ enters via stomata
  • Sugar produced is transported to other plant parts and used for energy, stored as starch, or built into tissue
• Importance to life:
  • Produces oxygen
  • Base of food chain; stores energy as sugar

Chloroplast structure

• Outer membrane and Inner membrane
• Stroma: fluid interior
• Thylakoids: flattened sacs; area for light reactions
• Granum: stacks of thylakoids
• Lumen: internal space of thylakoids
• Chlorophyll sits in thylakoid membranes to capture light

Photosynthesis in detail

• Light reactions: Occur in the thylakoid membrane; produce ATP and NADPH; release O₂ from water
• Calvin Cycle: Occurs in the stroma; uses ATP and NADPH to convert CO₂ into glucose

What is cellular respiration?

• The release of chemical energy for cellular use (ATP)
• Process of extracting energy from glucose in the food you eat
• Occurs in all living organisms (autotrophs and heterotrophs)

Cellular respiration equation

• Overall equation (a common representation):
  $\text{C}<em>6\text{H}</em>{12}\text{O}<em>6 + 6\,\text{O}</em>2 \rightarrow 6\,\text{CO}<em>2 + 6\,\text{H}</em>2\text{O} + \text{ATP}$

Where respiration occurs

• Glycolysis: cytoplasm; does not require oxygen
• Krebs Cycle: mitochondrial matrix
• Electron Transport Chain (ETC): inner mitochondrial membrane

Three stages of aerobic cellular respiration

• Glycolysis: glucose is split into two pyruvate molecules; nets 2 ATP and 2 NADH; occurs in cytoplasm
• Krebs Cycle: pyruvate is converted to acetyl-CoA; acetyl-CoA enters cycle to produce CO₂, NADH, FADH₂, and ATP; two turns per glucose
• Electron Transport Chain: NADH and FADH₂ donate electrons through a chain of proteins; energy used to synthesize ATP via oxidative phosphorylation; occurs in the inner membrane

Glycolysis (key points)

• Meaning: splitting of sugar
• Reactants: glucose
• Products: 2 pyruvate, 2 ATP (net), 2 NADH
• Location: cytoplasm; can proceed with or without O₂

Mitochondria structure (why it matters)

• Outer membrane contains porins for ion movement
• Intermembrane space between outer and inner membranes
• Inner membrane contains enzymes essential for respiration; contains cristae
• Matrix: inner compartment; contains enzymes, mitochondrial DNA, ribosomes
• Cristae: folds increasing surface area for energy production
• ATP synthase located on inner membrane; synthesizes ATP

Krebs Cycle details (quick recap)

• Occurs in mitochondrial matrix
• Pyruvate → acetyl-CoA (CO₂ released)
• Citric acid cycle turns twice per glucose; generates NADH, FADH₂, ATP, and CO₂ as waste

Electron Transport Chain (ETC) recap

• Final stage of aerobic respiration
• Located on inner mitochondrial membrane
• Electrons pass through complexes I-IV; energy used to make ATP (oxidative phosphorylation)

Connect: Photosynthesis and respiration

• Photosynthesis captures and stores energy as glucose; respiration releases that energy to power cell activities
• By-products: photosynthesis releases O₂ and organic molecules; respiration releases CO₂ and H₂O

Why this matters to us

• We rely on plants for food (glucose) and oxygen
• Plants are the entry point of most food chains
• Oxygen produced by photosynthesis is essential for aerobic life

Quick reference formulas

• Photosynthesis: $\text{CO}<em>2 + \text{H}</em>2\text{O} + \text{Light energy} \rightarrow \text{C}<em>6\text{H}</em>{12}\text{O}<em>6 + \text{O}</em>2$
• Cellular respiration: $\text{C}<em>6\text{H}</em>{12}\text{O}<em>6 + 6\,\text{O}</em>2 \rightarrow 6\,\text{CO}<em>2 + 6\,\text{H}</em>2\text{O} + \text{ATP}$