2.8 Cellular Respiration
Essential idea: Cell respiration supplies energy for the functions of life.
Energy in cells is all about the molecule above, Adenosine Triphosphate (ATP). The energy is held in the bonds between atoms, in particular the high energy bond that joins the second and third phosphates. ATP is the energy currency of the cell. Hence the efficiency of respiration is measured by the yield of ATP.
Understandings
2.8.U1 Cell respiration is the controlled release of energy from organic compounds to produce ATP.
2.8.U2 ATP from cell respiration is immediately available as a source of energy in the cell.
2.8.U3 Anaerobic cell respiration gives a small yield of ATP from glucose.
2.8.U4 Aerobic cell respiration requires oxygen and gives a large yield of ATP from glucose.
Applications
2.8.A1 Use of anaerobic cell respiration in yeasts to produce ethanol and carbon dioxide in baking.
2.8.A2 Lactate production in humans when anaerobic respiration is used to maximize the power of muscle contractions.
Skills
2.8.S1 Analysis of results from experiments involving measurement of respiration rates in germinating seeds or invertebrates using a respirometer. [There are many simple respirometers which could be used. Students are expected to know that an alkali is used to absorb CO2, so reductions in volume are due to oxygen use. Temperature should be kept constant to avoid volume changes due to temperature fluctuations.]
Essential idea: Cell respiration supplies energy for the functions of life.
Energy in cells is all about the molecule above, Adenosine Triphosphate (ATP). The energy is held in the bonds between atoms, in particular the high energy bond that joins the second and third phosphates. ATP is the energy currency of the cell. Hence the efficiency of respiration is measured by the yield of ATP.
Understandings
2.8.U1 Cell respiration is the controlled release of energy from organic compounds to produce ATP.
2.8.U2 ATP from cell respiration is immediately available as a source of energy in the cell.
2.8.U3 Anaerobic cell respiration gives a small yield of ATP from glucose.
2.8.U4 Aerobic cell respiration requires oxygen and gives a large yield of ATP from glucose.
Applications
2.8.A1 Use of anaerobic cell respiration in yeasts to produce ethanol and carbon dioxide in baking.
2.8.A2 Lactate production in humans when anaerobic respiration is used to maximize the power of muscle contractions.
Skills
2.8.S1 Analysis of results from experiments involving measurement of respiration rates in germinating seeds or invertebrates using a respirometer. [There are many simple respirometers which could be used. Students are expected to know that an alkali is used to absorb CO2, so reductions in volume are due to oxygen use. Temperature should be kept constant to avoid volume changes due to temperature fluctuations.]
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2.8.U1 Cell respiration is the controlled release of energy from organic compounds to produce ATP.
Cell Respiration Equation (Complete Breakdown)
- The main organic compound used for this process is carbohydrates (glucose), although lipids and proteins can also be digested
- Anaerobic respiration involves the partial breakdown of glucose in the cytosol for a small yield of ATP
- Aerobic respiration utilises oxygen to completely break down glucose in the mitochondria for a larger ATP yield
Cell Respiration Equation (Complete Breakdown)
2.8.U2 ATP from cell respiration is immediately available as a source of energy in the cell.
ATP (adenosine triphosphate) is a high energy molecule that functions as an immediate source of power for cell processes
Relationship between ATP and ADP
ATP (adenosine triphosphate) is a high energy molecule that functions as an immediate source of power for cell processes
- One molecule of ATP contains three covalently linked phosphate groups – which store potential energy in their bonds
- When ATP is hydrolysed (to form ADP + Pi) the energy stored in the phophate bond is released to be used by the cell
- Cell respiration uses energy stored in organic molecules to regenerate ATP from ADP + Pi (via oxidation)
Relationship between ATP and ADP
2.8.U3 Anaerobic cell respiration gives a small yield of ATP from glucose.
Both anaerobic and aerobic respiration pathways begin with the anaerobic breakdown of glucose in the cytosol by glycolysis
Glycolysis breaks down glucose (6-C) into two molecules of pyruvate (3C), and also produces:
Overview of Glycolysis
Both anaerobic and aerobic respiration pathways begin with the anaerobic breakdown of glucose in the cytosol by glycolysis
Glycolysis breaks down glucose (6-C) into two molecules of pyruvate (3C), and also produces:
- Hydrogen carriers (NADH) from an oxidised precursor (NAD+)
- A small yield of ATP (net gain of 2 molecules)
Overview of Glycolysis
Anaerobic Respiration
Anaerobic respiration proceeds in the absence of oxygen and does not result in the production of any further ATP molecules
Anaerobic respiration proceeds in the absence of oxygen and does not result in the production of any further ATP molecules
- In animals, the pyruvate is converted into lactic acid (or lactate)
- In plants and yeasts, the pyruvate is converted into ethanol and carbon dioxide
- By restoring stocks of NAD+ via anaerobic pathways, the organism can continue to produce ATP via glycolysis
- Hence, pyruvate levels can be restored once oxygen is present and a greater yield of ATP may be produced aerobically
2.8.A1 Use of anaerobic cell respiration in yeasts to produce ethanol and carbon dioxide in baking.
Muscle contractions require the expenditure of high amounts of energy and thus require high levels of ATP
When exercising at high intensity, the cells’ energy demands will exceed what the available levels of O2 can supply aerobically
The Effect of Exercise Intensity on Carbohydrate Consumption (and Lactate Production)
Muscle contractions require the expenditure of high amounts of energy and thus require high levels of ATP
When exercising at high intensity, the cells’ energy demands will exceed what the available levels of O2 can supply aerobically
- Hence the body will begin breaking down glucose anaerobically to maximise ATP production
- When the individual stops exercising, oxygen levels will increase and lactate will be converted back to pyruvate
The Effect of Exercise Intensity on Carbohydrate Consumption (and Lactate Production)
The above graph demonstrates how the conditions of cell respiration change with increasing energy demand
- At high intensities, the aerobic consumption of fats is decreased while the anaerobic consumption of sugars increases
- Consequently, lactate levels will increase at higher levels of exercise intensity
2.8.U4 Aerobic cell respiration requires oxygen and gives a large yield of ATP from glucose.
Aerobic cell respiration requires the presence of oxygen and takes place within the mitochondrion
Pyruvate is broken down into carbon dioxide and water, and a large amount of ATP is produced (~34 – 36 molecules)
Although aerobic respiration typically begins with glycolysis in carbohydrates, glycolysis itself is an anaerobic process
Overview of Aerobic Respiration
Aerobic cell respiration requires the presence of oxygen and takes place within the mitochondrion
Pyruvate is broken down into carbon dioxide and water, and a large amount of ATP is produced (~34 – 36 molecules)
Although aerobic respiration typically begins with glycolysis in carbohydrates, glycolysis itself is an anaerobic process
- Aerobic respiration consists of the link reaction, citric acid cycle (or Krebs cycle) and the electron transport chain
Overview of Aerobic Respiration
2.8.A1 Use of anaerobic cell respiration in yeasts to produce ethanol and carbon dioxide in baking.
Anaerobic respiration (fermentation) involves the breakdown of carbohydrates in the absence of oxygen
In yeasts, fermentation results in the production of ethanol and carbon dioxide – which can be used in food processing:
Production of Fermented Foods by Bacteria and Yeast (Saccharomyces)
Anaerobic respiration (fermentation) involves the breakdown of carbohydrates in the absence of oxygen
In yeasts, fermentation results in the production of ethanol and carbon dioxide – which can be used in food processing:
- Bread – Carbon dioxide causes dough to rise (leavening), the ethanol evaporates during baking
- Alcohol – Ethanol is the intoxicating agent in alcoholic beverages (concentrations above ~14% damage the yeast)
- Yogurt / Cheese – Bacteria produce lactic acid anaerobically, which modifies milk proteins to generate yogurts and cheeses
Production of Fermented Foods by Bacteria and Yeast (Saccharomyces)
2.8.S1 Analysis of results from experiments involving measurement of respiration rates in germinating seeds or invertebrates using a respirometer.
A respirometer is a device that determines an organism’s respiration rate by measuring the rate of exchange of O2 and CO2
Factors which may affect respiration rates include temperature, hydration, light (plants), age and activity levels
Schematic of a Simple Respirometer Designed to Measure Oxygen Uptake
A respirometer is a device that determines an organism’s respiration rate by measuring the rate of exchange of O2 and CO2
- The living specimen (e.g. germinating seeds or invertebrate organism) is enclosed in a sealed container
- Carbon dioxide production can be measured with a data logger or by pH changes if the specimen is immersed in water
- When an alkali is included to absorb CO2, oxygen consumption can be measured as a change in pressure within the system
- The pressure change can be detected with a data logger or via use of a U-tube manometer
Factors which may affect respiration rates include temperature, hydration, light (plants), age and activity levels
- An increase in carbon dioxide levels will indicate an increase in respiration (CO2 is a product of aerobic respiration)
- A decrease in oxygen levels will indicate an increase in respiration (O2 is a requirement for aerobic respiration)
Schematic of a Simple Respirometer Designed to Measure Oxygen Uptake