3.7b Aerobic Respiration

27/11/2012 § Leave a comment

Glycolysis is the basis of anaerobic cell respiration, which requires no oxygen. If there is no oxygen, glycolysis will take pyruvate and produce ethanol and carbon dioxide, or lactate. If there is oxygen available in a cell, the pyruvate can then be oxidized in the mitochondrion to release more energy. The energy released from this oxidation is used to produce ATP – and more than ten times as much ATP than is produced during anaerobic cell respiration.

In the process of oxidizing pyruvate, carbon dioxide and water is also produced. The carbon dioxide is waste and is excreted but the water is kept for use. For example, desert animals are supplied with almost all of their water through cellular respiration.

Oxidation and reduction are two chemical processes that come hand in hand. Oxidation is the loss of electrons while reduction is the gain of electrons. The substances that help in oxidation and reduction are electron carriers, which are substances that can accept and give up electrons. The main carrier in cellular respiration is nicotinamide adenine dinucleotide (or NAD). Starting with reduction (a substance’s gain of electrons), the reaction can be described with the following basic equation:

(NAD+) + (2H+) + 2 electrons (2e-) –––––> NADH + (H+)
(NAD+) + (2H) –––––> NADH + (H+)

What happens is that NAD, which originally has a positive charge (shown by the +) accepts two electrons by removing two hydrogen atoms from the substance that is being reduced. One of those hydrogen atoms splits into a proton and electron and the NAD+ accepts the electron of that hydrogen atom, and accepts the electron and proton of the other hydrogen atom. Oxidation would be the opposite of gaining hydrogen atoms and would instead involve losing hydrogen atoms.

I’m sorry if that didn’t make any sense and here is an image to help you out.

Oxidation and reduction can also happen with the loss and gain (respectively) of oxygen atoms, but there are fewer examples of this because, when oxidation and reduction began, almost 3.5 billion years ago, there was no trace of oxygen in the atmosphere. However, similarly to with hydrogen atoms, adding oxygen atoms is oxidation (because oxygen tends to draw electrons away from other substances, therefore it would lose electrons) and losing oxygen atoms is reduction.


Essay Questions

  1. Outline the process of glycylosis. (5)
  2. Draw the structure of a mitochondrion as seen in an electron microscope. (5)
  3. Explain how the structure of the mitochondrion allows it to carry out its function efficiently. (8)
  4. Explain the reactions that occur in the matrix of the mitochondrion that are part of aerobic respiration. (8)
  5. Explain the process of aerobic respiration. (8)
  6. Outline the role of oxygen in providing cells with energy. (6)
  7. Explain how chemiosmosis assists in ATP production during oxidative phosphorylation. (9)
  8. Explain the similarities and differences in anaerobic and aerobic cellular respiration. (8)
  9. Describe the central role of acetyl (ethanoyl) CoA in carbohydrate and fat metabolism. (5)



Page 92, respirometers and respiration rates

1. Explain the need for a base inside the respirometer.

A base, like potassium hydroxide, is needed inside the respirometer so that the carbon dioxide (waste product) of respiration can be absorbed and does not disturb the process.

2. Deduce, with a reason, which direction the fluid will move in on the right hand side of the capillary tube.

For aerobic cellular respiration to happen, oxygen is needed. Since there is no oxygen in the contraption, the fluid in the capillary tube will move in a left to right direction towards the container holding the organism. This will allow space for oxygen to enter the tube towards the solution for respiration to happen. 

3. Predict, with a reason, the change in nitrogen concentration inside the test tube during the experiment.

Since the oxygen is the substance being consumed during respiration and not specifically nitrogen, alone, the actual concentration of nitrogen won’t change. As a ratio compared to the concentration of oxygen, however, the concentration of nitrogen will naturally rise against the concentration of oxygen, surpassing it as more and more oxygen is consumed for respiration.

4. Explain how the following changes would improve the reliability of results from the experiment:

  • a) Placing the test tube in a thermostatically controlled water bath. Temperature, similarly to how it affects the rate of enzymatic reactions, affects the rate of respiration in an organism, which is understandable because respiration involves some enzymes and is part of the organism’s metabolism. As the temperature increases, the rate of respiration will increase as well, and the same goes for when the temperature decreases (the rate of respiration will decrease). To improve the reliability of the results, the temperature should become a controlled variable so that all samples will have had the same temperature and will be controlled at least in that variable.
  • b) Attaching the left-hand side of the capillary tube to another test tube, identical to the right-hand tube except that it has no respiring tissue inside. Attaching a second test tube that has no respiring tissue inside will block the point of entrance that oxygen can go through to get to the tube that DOES have respiring tissue within it. Cellular respiration won’t be able to happen because no oxygen will be entering the tube and nothing will be happening in the second tube where there is simply nothing (specifically no respiring tissue). For more reliable results, there should only be one test tube attached to the capillary tube so that cellular respiration can actually happen.

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