Overview of Respiration (College Board AP® Biology)

Respiration & Fermentation

• Respiration is a chemical process that involves the breakdown of biological macromolecules (specifically glucose) in order to release the energy stored within the bonds of these molecules

  • Respiration in eukaryotes involves a series of enzyme-controlled reactions

• Respiration can take place with oxygen (aerobically) or without oxygen (anaerobically).

  • Much less energy is released for each glucose molecule broken down anaerobically compared to the energy released when it is broken down aerobically

• Respiration occurs in all living cells; most of the chemical reactions in aerobic respiration take place in the mitochondria

• Humans need the energy released during respiration to carry out many processes

  • Muscle contraction

  • Protein synthesis

  • Cell division (to make new cells)

  • Growth

  • Active transport across cell membranes

  • Generation of nerve impulses

  • Maintaining a constant internal body temperature

The energy released during respiration is used to fuel many processes in the human body

Aerobic Respiration

• Aerobic respiration requires oxygen and is defined as the chemical reactions in cells that use oxygen to break down nutrient molecules to release energy

• It is the complete breakdown of glucose to release a relatively large amount of energy for use in cell processes

• It produces carbon dioxide and water as well as releasing useful cellular energy

 Word Equation for Aerobic Respiration

In aerobic respiration, glucose is the main respiratory substrate from which energy is released (as ATP) in the presence of oxygen. Carbon dioxide and water are the waste products

Fermentation

• Fermentation does not require oxygen and is defined as the chemical reactions in cells that break down nutrient molecules to release energy without using oxygen

• It is the incomplete breakdown of glucose and releases a relatively small amount of energy (compared to aerobic respiration) for use in cell processes

• It produces different breakdown products depending on the type of organism it is taking place in

  • Fermentation in humans (animals) produces different products compared to fermentation in the microorganism yeast

Lactic Acid Fermentation

• Lactic acid fermentation (a type of anaerobic respiration) mainly takes place in muscle cells during vigorous exercise

• When we exercise vigorously, our muscles have a higher demand for energy than when we are resting or exercising normally. Our bodies can only deliver so much oxygen to our muscle cells for aerobic respiration

• In this instance, as much glucose as possible is broken down with oxygen, and some glucose is broken down without it, producing lactic acid instead

• There is still energy stored within the bonds of lactic acid molecules that the cell could use; for this reason, less energy is released when glucose is broken down anaerobically

In lactic acid fermentation (also called anaerobic respiration) in muscle cells, glucose is broken down in the absence of oxygen to release energy whilst producing lactic acid

Alcohol Fermentation

• Alcohol fermentation is the name given to anaerobic respiration in yeast which produces alcohol and carbon dioxide

• We use the products of fermentation...

  • In bread making, where

    • The carbon dioxide produced causes the dough to rise

  • And in brewing, where

    • The ethanol produced gives the beer its alcoholic nature

    • The carbon dioxide produced gives beer its fizz

 Word Equation for Alcohol Fermentation

In alcohol fermentation (also called anaerobic respiration) in yeast, glucose is broken down in the absence of oxygen to release energy whilst producing alcohol and carbon dioxide