HL 1 Biology

3.7b Aerobic Respiration

<<Aerobic Cell Respiration>>

Aerobic Cell Respiration: cell respiration with oxygen, uses end product of glycolysis (pyruvate)  to produce more energy  in the form of ATP  

  • when oxygen is available = pyruvate produced by glycolysis can be oxidized to release more energy
  • inside mitochondrion
  • Energy released form pyruvate oxidation used to produce ATP
  • Oxidation of pyruvate: produce carbon dioxide and water

<<Oxidation and Reduction>>

Oxidation and reduction are chemical processes that always occur together due to the involvement of transferring electrons from one substance to another.

  • Oxidation involves the loss of electrons (energy) from an element;  frequently gaining oxygen or losing hydrogen
  • Reduction involves gain in electrons; and that oxidation; frequently involves losing oxygen/gaining hydrogen.
Catabolic Reactions (Oxidation)
  • digesting food
  • breaking down stored fats
Anabolic Reactions (Reduction)
  • synthesizing protein
  • replicating DNA
Electron Carriers: substances that can accept + give up electrons as required; often bond oxidations and reductions in cells

  • Main e.g. in respiration: NAD (nicotinamide adenine dinucleotide)
  • e.g. in photosynthesis: NADP (nicotinamide adenine dinucleotide phosphate)
    • Basic reaction: NAD + 2 electrons –> reduced NAD
  • Reduction can be achieved by getting atoms of hydrogen since they have an electron, oxidation achieved by losing hydrogen atoms.
  • In both mitochondria + chloroplasts: chains of electron carriers are located in membranes; pairs of electrons passed along chains by carriers first being oxidized and then reduced

<<The Krebs Cycle>>

The Krebs Cycle: a series of chemical reactions used by aerobic organisms to produce energy through oxidization (from carbohydrates,fats and proteins) into carbon dioxide
  • First reaction of cycle: an acetyl group transferred form acetyl CoA to a four-carbon compound (oxaloacetate) to form a six-carbon compound (citrate)
  • Citrate converted back to oxaloacetate through three types of reactions:
    • Decarboxylations: carbon dioxide removed in two of reactions, CO2 is waste product & excreted together with carbon dioxide from the link reaction
    • Oxidations: reactions where hydrogen is removed. In three oxidations, hydrogen accepted by NAD+; the other oxidation FAD accepts it. Energy released in oxidation reaction stored, later used to make ATP as its released by electron transport chain
    • Substrate-level phosphorylation: ATP produced directly in one of reactions


Monitoring Anaerobic Cell Respiration in Yeast (p. 91)
1) Total loss of mass: 560g-544g = 16g
Mean daily loss: 16g/13days = 1.2g per day
2) The loss of mass is apparent due to the process of fermentation through the alcohol, during the brewing of the wine. Since the CO2 is the waste product, it has to be excreted out. Thus, the excretion of the CO2 enables a loss in the mass of the yeast.
3) The increasing rate of the mass loss may be apparent from the start of the experiment until Day 6 because more yeast is going through the process of respiration as there is an increase in the population of the yeast. Also, the increasing rate of the carbon dioxide from a higher population provides a lower solubility, thus having a increasing rate of the mass loss as the carbon dioxide is released faster.
4) The mass may be remaining constant from Day 11 onwards due to the decrease in the substrates and is close to running out inside the yeast. The high exposure to the wine may have caused the yeast to die, thus causing the mass to stay constant.

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