1.6Unit 1 — Cell Biology

Respiration

5 min read 4 parts Lesson 22 of 28 Virtual lab

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Part 1 of 2Cellular respiration and ATP

Active transport: movement against concentration gradient (ATP)

Respiration

Respiration is a series of enzyme-controlled chemical reactions that breakdown glucose to release chemical energy stored in the form of ATP (Adenosine Triphosphate):

ADP + Inorganic Phosphate (Pi) + Energy ⇌ ATP

Cellular processes requiring ATP energy

Muscle cell contraction and movement.
Cell division (mitosis).
Protein synthesis at ribosomes.
Active transport of ions against concentration gradients.
Transmission of electrical nerve impulses.

Part 2 of 2Aerobic respiration vs Fermentation

Aerobic respiration in mitochondria with ATP

Table of ATP molecules made per glucose in aerobic respiration

Anaerobic Respiration in Yeast — products

Lactic Acid Fermentation — Interactive Teaching Console

Aerobic vs anaerobic respiration comparison table

Anaerobic respiration in yeast (ethanol and CO2)

Anaerobic respiration in animal muscle (lactic acid)

Feature	Aerobic Respiration	Fermentation in Animal Cells	Fermentation in Plant & Yeast Cells
Oxygen requirement	Requires oxygen	Absence of oxygen	Absence of oxygen
Stage 1: Glycolysis	Occurs in cytoplasm: Glucose broken into 2 pyruvate molecules, yielding 2 ATP	Occurs in cytoplasm: Glucose broken into 2 pyruvate molecules, yielding 2 ATP	Occurs in cytoplasm: Glucose broken into 2 pyruvate molecules, yielding 2 ATP
Stage 2: Fate of Pyruvate	Occurs in mitochondria: Pyruvate completely broken down to CO₂ and H₂O, yielding many ATP (approx. 36 ATP)	Occurs in cytoplasm: Pyruvate is converted to lactate (lactic acid); no further ATP produced	Occurs in cytoplasm: Pyruvate is converted to ethanol and CO₂; no further ATP produced
Total ATP yield per glucose	Large yield (~38 ATP)	Small yield (2 ATP only)	Small yield (2 ATP only)
Reversibility	Irreversible overall	Reversible (when oxygen returns, lactate converts back to pyruvate)	Irreversible (CO₂ gas diffuses away)

Key terms

Term	Meaning
Aerobic respiration	The complete enzymatic breakdown of glucose in the presence of oxygen yielding large amounts of ATP.
Fermentation	The incomplete breakdown of glucose in the absence of oxygen producing limited ATP.
Glycolysis	The first stage of cellular respiration occurring in cytoplasm converting glucose to pyruvate.
Lactate	The metabolic product of anaerobic fermentation in animal muscle cells causing muscle fatigue.

Avoid these mistakes

Stating fermentation produces no ATP — stage 1 (glycolysis) produces 2 molecules of ATP per glucose molecule even without oxygen.

Thinking stage 2 of fermentation takes place in mitochondria — fermentation occurs entirely in the cytoplasm.

Try it in the virtual labYeast respiration \n