Cellular Respiration

Big Picture

Cellular respiration is the process cells use to convert glucose into ATP (energy). It occurs in both plants and animals and involves the cytoplasm and mitochondria.

• Overall Equation:

Example:

Autotrophs vs Heterotrophs

Organisms differ in how they obtain energy:

• Autotrophs: Make their own food (using photosynthesis)

• Heterotrophs: Must obtain energy from other organisms (animals, humans)

Energy Flow: Sun → Plants → Animals (only autotrophs convert solar energy)

ATP (Adenosine Triphosphate)

ATP is the main energy molecule of the cell.

• Stores energy in phosphate bonds

• Used in muscle contraction, active transport, and biosynthesis

Types of Cellular Respiration

Aerobic Respiration

• Requires oxygen

• Produces more ATP (≈ 34-36 ATP)

Anaerobic Respiration (Fermentation)

• Occurs in the absence of oxygen

• Produces less ATP

Steps of Cellular Respiration

Step 1: Glycolysis

Location: Cytoplasm Oxygen needed? No

• Glucose → 2 Pyruvate (3C)

• Energy Investment Phase: Uses 2 ATP

• Energy Payoff Phase: Produces 4 ATP and 2 NADH

• Net Gain: 2 ATP, 2 NADH, 2 pyruvate

Pyruvate Oxidation (Link Reaction)

• Pyruvate enters mitochondria (not part of Krebs Cycle directly)

• Converted into Acetyl-CoA (2C)

• Produces CO2 and NADH per pyruvate

Step 2: Krebs Cycle (Citric Acid Cycle)

Location: Mitochondrial matrix Oxygen needed? Yes

• Acetyl-CoA combines with Oxaloacetate → Citrate (6C)

• Cycle produces: 2 ATP, 6 NADH, 2 FADH2, 4 CO2 per glucose

Electron Carriers

• NADH and FADH2 carry high-energy electrons to the ETC

Step 3: Electron Transport Chain (ETC)

Location: Inner mitochondrial membrane (cristae)

• Series of proteins use electrons from NADH/FADH2

• Oxygen is the final electron acceptor → forms water

• Produces most ATP

Chemiosmosis

• Proton (H+) buildup creates a proton motive force

• Protons flow through ATP synthase

• Produces ≈ 34 ATP

Oxidative Phosphorylation

• ATP production using chemiosmosis and ETC

• Most efficient and productive stage of respiration

Fermentation

Occurs when oxygen is unavailable.

Lactic Acid Fermentation

• Pyruvate → Lactate

• No CO2 released

• Occurs in muscle cells

Alcohol Fermentation

• Pyruvate → Ethanol + CO2

• Occurs in yeast and some bacteria

• Purpose: Regenerates NAD+ so glycolysis can continue

Key Vocabulary (Simplified)

• Oxidation: Loss of electrons

• Reduction: Gain of electrons

• Substrate-level phosphorylation: Direct ATP formation

• Oxidative phosphorylation: ATP formation using oxygen

• Aerobic: Requires oxygen

• Anaerobic: Occurs without oxygen

ATP Totals (Per Glucose)

Study Tips

• Memorize steps and locations of respiration in mitochondria

• Understand electron carriers (NADH & FADH2)

• Practice with diagrams and flowcharts

• Review differences between aerobic and anaerobic respiration

Additional info: For exam prep, create quiz questions, one-page cheat sheets, and diagram walkthroughs to reinforce understanding.