Cellular Respiration: Comprehensive Study Guide

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:

$\text{Glucose} + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O} + \text{ATP}$

Example: $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{ATP}$

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)

Stage	ATP Produced
Glycolysis	2 ATP
Krebs Cycle	2 ATP
ETC	≈ 34 ATP
Total	≈ 38 ATP

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.