Chapter 12: Respiration
- Internal respiration is the enzyme-controlled release of energy from food
- External respiration is the exchange of gases with environment
Aerobic versus anaerobic:
- Aerobic respiration is the enzyme-controlled release of energy from food using oxygen
- Anaerobic respiration is the enzyme-controlled release of energy from food without the use of oxygen
Aerobic respiration occurs in the mitochondrion.
Structure of the mitochondrion
Two stage process:
- Krebs cycle & Electron Transport Chain
Stage 1: Glycolysis
- Oxygen-independent (can occur in presence or absence of oxygen)
- Occurs in cytosol
- Glucose (a 6-carbon molecule) is changed into 2 three-carbon molecules (pyruvate)
- This breaking down of glucose releases high energy electrons and protons – they are captured by NAD+ to become NADH
- Glycolysis also produces two molecules of ATP directly
- Oxygen-dependent (can only occur in the presence of oxygen).
- Occurs in the lumen of the mitochondrion (matrix).
- Pyruvate enters the mitochondrion and is converted to two-carbon molecule (acetyl-coA) with release of NADH and carbon dioxide.
- The acetyl-coA then joins with four-carbon molecule from the previous Krebs cycle to form six-carbon molecule.
- The six-carbon molecule is then broken down into five-carbon molecule with release of carbon dioxide and NADH.
- The five-carbon molecule is then broken down into four-carbon molecule with release of ATP, carbon dioxide, and 2NADH.
- The four-carbon molecule goes into the next Krebs cycle.
- The ATP goes to power metabolism (chemical reaction in cells).
- The NADH is an energy carrier that goes to the electron transport chain where its energy is used to power the production of three ATP molecules.
- The electron transport chain is located in the inner membranes of the mitochondrion (cristae).
Anaerobic respiration occurs when no oxygen or limited oxygen is present.
- Lactic acid fermentation/Alcohol fermentation
- Deionised water
- Conical flasks
- Vegetable oil
- Fermentation lock
- Filter paper
- Potassium iodide
- Sodium hypochlorite
- Water bath
- Dissolve 50 g glucose in 500 ml deionised water and bring to the boil (to exclude oxygen).
- Separate into two conical flasks (250 ml glucose solution in each).
- Once cooled add 5 g yeast to one of the conical flasks and label this “TEST’ – the other flask remains as the control (without yeast).
- Slowly pour a layer of vegetable oil on top of each glucose solution (keeps the oxygen out).
- Place a stopper in each and attach fermentation locks each containing limewater.
- Leave in a 25˚C incubator for 2 days.
Test for alcohol (Iodoform test):
- Filter the solutions obtained from each conical flask.
- Place 3 ml of each in two separate test tubes.
- Add 3 ml of a potassium iodide solution and 5 ml of a sodium hypochlorite solution to each test tube.
- Warm the test tubes in a hot water bath and observe any changes.
- Appearance of pale yellow crystals in the ‘TEST’.
- No appearance of pale yellow crystals in the control.
- Yeast produced alcohol by anaerobic respiration in the ‘TEST’.