Overview
This lecture covers the fundamentals of cellular respiration, exploring how living organisms extract and use energy from food, the differences between aerobic and anaerobic pathways, key stages of each, experimental demonstrations, and real-world applications.
What is Cellular Respiration?
- Cellular respiration is a chemical process where cells break down molecules like glucose to release stored energy.
- It is a catabolic reaction (breaking down molecules) and part of overall metabolism.
- The released energy powers essential cell processes including growth, cell division, movement, and active transport.
Aerobic Respiration
- Requires oxygen and is highly efficient at extracting energy from glucose.
- Takes place in two main cell locations: glycolysis in the cytoplasm, Krebs cycle and oxidative phosphorylation in mitochondria.
- Glycolysis splits glucose into two smaller molecules and yields a small amount of energy and high-energy hydrogen carriers.
- Krebs cycle (in mitochondrial matrix) breaks down these molecules further, releasing more high-energy hydrogens and CO2 as waste.
- Oxidative phosphorylation (on mitochondrial inner membranes) uses hydrogen carriers, passing their electrons down a protein chain to generate lots of ATP, with oxygen accepting electrons to form water.
- The summary equation: glucose + O2 → CO2 + H2O + ATP (energy).
Anaerobic Respiration & Fermentation
- Occurs without oxygen and yields much less energy than aerobic respiration.
- Glycolysis produces a small amount of ATP, then the process diverges:
- Alcoholic fermentation (yeast, some plants): glucose → ethanol + CO2 + ATP.
- Lactic acid fermentation (animal muscles, some bacteria): glucose → lactic acid + ATP.
- Byproducts have practical uses, e.g., CO2 in bread rising, ethanol in alcohol, lactic acid in yogurt and cheese.
Comparing Aerobic and Anaerobic Respiration
- Aerobic: needs oxygen, high ATP yield, occurs in mitochondria, byproducts are CO2 and water.
- Anaerobic: no oxygen needed, low ATP yield, mainly in cytoplasm, byproducts are ethanol + CO2 or lactic acid.
Experimental Demonstrations
- Germinating beans in lime water show oxygen use and CO2 production.
- Yeast in sugar solution with lime water demonstrates anaerobic CO2 production.
- Snail and pondweed in indicator solution illustrate CO2 changes from respiration and photosynthesis.
- Controls (boiled beans, sugar solution without yeast) confirm observations are due to living activity.
Real-World Applications
- Alcoholic fermentation: used in bread making, brewing beer and wine.
- Lactic acid fermentation: key in producing yogurt and cheese via bacterial action.
Key Terms & Definitions
- Cellular respiration — process of breaking down food molecules to release energy.
- Metabolism — all chemical reactions in an organism.
- Catabolic reaction — reactions that break down molecules to release energy.
- Anabolic reaction — reactions that build up molecules using energy.
- Glycolysis — first step of respiration, splitting glucose in the cytoplasm.
- Krebs cycle — series of reactions in mitochondria releasing energy and CO2.
- Oxidative phosphorylation — stage generating most ATP using electron transport chain.
- ATP (Adenosine triphosphate) — main energy currency of the cell.
- Anaerobic respiration — respiration without oxygen.
- Fermentation — anaerobic process producing ethanol/CO2 or lactic acid.
- Lime water — indicator turning milky in presence of CO2.
Action Items / Next Steps
- Review the processes and stages of aerobic and anaerobic respiration.
- Study the summary table comparing aerobic and anaerobic respiration.
- Prepare for possible experiments or lab work on respiration (using beans, yeast, indicators).
- Reflect on how energy strategies relate to organism environments and applications in biotechnology.