8.1b Aerobic Respiration

01/12/2012 § Leave a comment

We’re coming across the final biology blogpost (or as Christina and I so lovingly call them – blosts) of the year! Afterwards, we’ll be having a test on Thursday so let’s get this post over with and start studying, please.

Our point of focus today is the vital relationship between the structure and function of organelles. A perfect example of this relationship can be found within mitochondria. The power house. We (should) know by now that the mitochondria is the structure that produces ATP for the cell, and it has the metabolism and system to do so, but a lot of it has to do with it’s structure.

We covered mitochondria briefly in a past post but now we’ll do so with more detail. Mitochondria has two membranes: the inner and outer membrane. Between these two is a narrow space that is filled with protons by chemiosmosis, a condition needed for ATP synthase to produce ATP. The inner membrane creates invaginations called cristae that has an increased surface area needed to situate electron transport chains and ATP synthase for ATP synthesis. Within the cristae is the matrix, which contains 70S ribosomes, enzymes, and a naked loop of DNA.

The relationship between an organelle’s structure and its function can be explained by natural selection and evolution, one of my favorite units. Organisms from billions of years ago must have had varied types of mitochondria and as time passed, the ones with mitochondria that produced ATP most efficiently and were basically stronger in that sense were the ones that survived. Natural selection chose them to survive through the changing environments and eventually mitochondria evolved to become better and better at producing ATP. This is adaptation, which is a change in structure so that it can execute its function more efficiently.

 

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)

 

DATA BASED QUESTIONS

Page 100, chapter 8 questions now showing «re: still faster than you»!
All questions have been checked except #5, for which the textbook provided no answers.

1.

  • a) Cell respiration is one of the characteristics of all of living organisms. Define cell respiration. Cell respiration can be aerobic or anaerobic and is “the controlled release of energy from organic compounds to form ATP”. It involves the processes of glycolysis, substrate-level phosphorylation, oxidation phosphorylation, the transfer of electrons and the movement of protons. Cellular respiration converts glucose into ATP, which is an energy rich organic molecule. 
  • b) Compare aerobic and anaerobic cell respiration. Just as their names suggest, aerobic respiration involves the use of oxygen while anaerobic respiration can occur without oxygen. Both processes start off with glycolysis but anaerobic respiration follows that by fermenting the pyruvate [that is produced by glycolysis]. Aerobic respiration, on the other hand, is followed by a series of processes that make it [aerobic respiration] an example of a metabolic pathway. It includes processes like the Krebs cycle. Anaerobic respiration happens in the cytoplasm while aerobic respiration happens in the mitochondria. Aerobic respiration involves chemiosmosis while anaerobic respiration does not. The only time CO2 is yielded in aerobic respiration is during fermentation but yielding CO2 is a large part of aerobic respiration and occurs many times. 
  • c) Distinguish between active transport and diffusion. Both active transport and diffusion are the processes of moving molecules across a permeable membrane and from one area to another. However, diffusion is the movement of molecules down a concentration gradient. Active transport is the movement of molecules AGAINST its concentration gradient. This means that diffusion is natural and molecules will naturally go from an area of higher concentration to an area of lower concentration to seek a state of equilibrium. Active transport uses pumps, like sodium-potassium pumps, to forcefully pump the molecules from an area of higher concentration to an area of lower concentration for purposes like bringing in bigger molecules, i.e. glucose. Active transport always involves a membrane but diffusion doesn’t necessarily need one (i.e. perfume in the air). 
  • d) Suggest methods that could be used to measure the rate of cell respiration in an organism. One method we already learned in our textbooks is the use of a respirometer and to measure the respiration rate. We could also measure the pH because of the production of CO2, as well as the change of mass in the organism as gas is lost (CO2). 

2. Figure 17 shows the results of an experiment in which yellow-billed magpies (Pica nuttalli) were put in a cage in which the temperature could be controlled. The birds’ rate of respiration was measured at seven different temperatures, from –10°C to +40°C. Between –10°C and 30°C the magpies contained constant body temperature, but above 30°C body temperature increased.

  • a) Describe the relationship between external temperature and respiration rate in yellow-billed magpies. Between -10°C and around 10°C, as the temperature increases, the rate of respiration decreases. From 10°C to around 30°C, the rate of respiration stays the same and remains at around 9 mWg-1. After 30°C, the rate of respiration starts to increase very rapidly.
  • b) Explain the change in respiration rate as temperature drops from +10°C to –10°C. The colder the graph gets (from 10°C to -10°C), the higher the rate of respiration gets. This means that the bird would be trying to warm itself up and slowing its breathing down to maintain temperature homeostasis. 
  • c) Suggest a reason for the change in respiration rate as temperature increased from 30°C to 40°C. Temperature affects the rate of respiration just as it affects the rate of reactions between enzymes and substrates – this is because respiration is a kind of chemical reaction for a cell’s metabolism. Therefore, when the temperature reaches a certain point, it gets hot enough that the molecules involved in the process are charged enough with a lot of energy from thermal heat that they move a lot faster, therefore, the reactions happen faster. The increase in the metabolic rate is linked to reactions that are designed to keep the bird cool.
  • d) Suggest two reasons for the variation in respiration rate between the birds at each temperature. It was probably difficult to control the size of the birds, since there can be many magpies of the same species but of different physical characteristics. It could also simply be the random/experimental of the investigation itself. Happens.

~Imagine that this is an HL ribbon.~

3.

a) State one example in aerobic cell respiration of:

  • i) a six-carbon compound: glucose
  • ii) a three-carbon compound: pyruvate
  • iii) a two-carbon compound: acetyl
  • iv) a one-carbon compound: carbon dioxide
  • v) a no-carbon compound: oxygen

b) State the stage of aerobic cell respiration that involves:

  • i) a five-carbon compound: Krebs cycle
  • ii) a four-carbon compound: Krebs cycle (substrate-level phosphorylation)

c) State the name of a compound in cell respiration that can:

  • i) accept hydrogen atoms: NAD+
  • ii) accept phosphate: ADP

4.

  • a) Distinguish between the processes of oxidation and reduction. Oxidation is the loss of electrons while reduction is the gain of electrons.
  • b) Outline the process of glycolysis. Glycolysis takes place in the cytoplasm of the cell. First, glucose is phosphorylated or reduced when 2 ATP is added to it. Then it is split, or lysed, into two 3-carbon molecules (originally 6-carbons). It then loses carbons via oxidation and is oxidized into pyruvate, at the same time while NAD+ is reduced to NADH + H+ with the addition of the proton. 2ATP is formed per 3-carbon molecule, so 4 ATP are formed. The net gain is then 2 ATP, 2 NADH + H+, and 2 pyruvate. This all happens with one glucose.
  • c) Explain the reasons for a much lower ATP yield per glucose from anaerobic cell respiration than from aerobic cell respiration. The primary reason aerobic cell respiration produces a higher yield of ATP per glucose is because of the extra strep that is required. Aerobic respiration uses oxygen at the end of the cycle to make pyruvate go through more reactions that help it to produce more ATP than in anaerobic respiration. Anaerobic respiration alone produces only 2 ATP from glycolysis. The addition of oxygen is what makes the yield of ATP in aerobic respiration far greater than the that of anaerobic respiration. In anaerobic respiration, the substrates are not fully oxidized to release energy and are left to stay as pyruvate, lactate or ethanol (in mammals or in yeast). 

5. A new technique, called electron tomography, has been used recently to obtain three-dimensional images of mitochondria. The questions below refer to the three images of the cristae of a mitochondrion on page 99. The inner and outer membranes of the mitochondrion are not shown. They would have been outside the cristae.

  • a) The diameter of the mitochondrion was 700 nm. Calculate the magnification of the image. 114286x.
  • b) Compare the cristae in Figure 18 with the cristae in Figure 17 on page 99. Figure 18 clearly has more of a globular and spherical shape than that of figure 17. The inner membrane of figure 18 looks like it’s creating holes within itself but the membrane of figure 17 has a wider surface area in that it forms plateaus and flat surfaces. Figure 18 looks more spiky and bristly than the membrane structure of figure 17. Also, one is yellow and the other is green.
  • c) Electron tomography has shown that cristae are dynamic structures and that the volume of the intracristal compartment increases when the mitochondrion is active in electron transport. Suggest how electron transport could cause an increase in the volume of fluid inside the cristae. As electron moves across the membrane from the matrix of the inner membrane to the space between the outer and inner membrane, they emit energy and pass it on (because they are just bundles of excited energy) and therefore add energy to the many substances floating within the fluid. Also, when mitochondria are active, electrons are transported (diffused) across the membrane, and it means that ATP is being produced, therefore more and more ATP being added to the fluid of the matrix will most definitely increase the volume of the fluid. 
  • d) Junctions between the cristae and boundary region of the inner mitochondrial membrane can have the shape of slots or tubes and can be narrow or wide. Suggest how narrow tubular connections could help ATP synthesis by one of the cristae in a mitochondrion. Having narrow tubular connections, I assume connections similar to microtubule spindle fibers, will help the substances of respiration get to their enzymes faster or will simply assist in accomplishing the reactions faster if there is a narrower space for the substances to move through. If the tubular connections were thicker and fatter, the substances would take more time getting to their destinations and respiration would be slower. 

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