Respiration
3.7.1 Define cell respiration
3.7.2 Glycolysis
3.7.3 Anaerobic respiration
3.7.4 Aerobic respiration
3.7.1 Define cell respiration. (1)
Define means to give a the precise meaning of a word, phrase or physical quantity.
Syllabus definition: Cell respiration is the controlled release of energy from organic compounds in cells to form ATP.
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ATP or Adenosine triphosphates is the molecule which directly fuels the majority of biological reactions.
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Everyday each person will hydrolyse (reduce) 1025 ATP molecules to ADP.
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The ADP is reduced back to ATP using the free energy from the oxidation of organic molecules.
3.7.2 State that, in cell respiration, glucose in the cytoplasm is broken down by glycolysis into pyruvate, with a small yield of ATP.(1)
State means to give a specific name, value or other brief answer without explanation or calculation.
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Location: Cytoplasm
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Process: Glycolysis
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Substrate: Glucose
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Products: 2 Pyruvate and a small amount of ATP
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Glycolysis does not use oxygen.
3.7.3 Explain that, during anaerobic cell respiration, pyruvate can be converted in the cytoplasm into lactate, or ethanol and carbon dioxide, with no further yield of ATP.(3)
Explain means to give a detailed account of causes, reasons or mechanisms.
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Anaerobic respiration is the oxidation of organic compounds without oxygen.
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It is less efficient than aerobic respiration (with oxygen).
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There are different types of anaerobic respiration. Here we will compare anaerobic respiration in yeast and humans.
Humans anaerobic respiration:
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Location: cytoplasm
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Substrate: Glucose
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Product: lactic acid (lactate) + ATP
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Note: lactic anaerobic respiration supplements aerobic respiration in the production of ATP. Both aerobic and anaerobic respiration can take place in the human cell at the same time.
Yeast anaerobic respiration:
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Location: cytoplasm
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Substrate: Glucose
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Product: Ethanol + carbon dioxide + ATP
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This is the end point for this fermentation reaction. Ethanol and CO2are both excreted with no further metabolism of the energy stored in the ethanol (very inefficient)
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Note: The glucose molecule has been hydrolysed further than in human respiration. Some organisms are totally anaerobic others can switch between anaerobic and aerobic.
Exercise and anaerobic respiration :
Human lactic anaerobic respiration is a process that supplements the production of ATP. The lactic pathway is so inefficient that under normal circumstances it cannot produce enough energy to support human systems. In describing the lactic pathway it is often suggested that sprinters 'do not breath during the 100m sprint' (they do, just watch any video) and they only produce ATP for running from the lactic pathway. This is a ms-representation of a complex response to the demand for ATP. It is far better to consider that anaerobic respiration in humans supplements (adds to) the aerobic production of ATP.
Anaerobic respiration:
Fermentation respiration in yeast yields two useful products from a human perspective. The carbon dioxide can be used in a variety industrial processes the best known of which is to raise bread. Many Brewers of alcohol will bottle the CO2 for use in the 'carbonation' of other drink products.
The alcohol itself is of course the basis of many industries such as beer brewing. In more recent time the use of fermentation products is being used as an alternative source of fuel such as is the case in fuel for automobiles.
3.7.4 Explain that, during aerobic cell respiration, pyruvate can be broken down in the mitochondrion into carbon dioxide and water with a large yield of ATP. (3)
Explain means to give a detailed account of causes, reasons or mechanisms.
Location: Mitochondria
Substrate: Pyruvate
Products: ATP, Carbon dioxide, water and heat.
The production of ATP in the aerobic pathway is much greater than in either glycolysis or the anaerobic alternatives. The oxygen breathed in during ventilation is sent form the lung into the blood and then transported to the cell. The oxygen diffuses into the cell and then into the mitochondria for aerobic respiration.
Cellular respiration:
This diagram is a summary of the complete aerobic pathway.
The by-product carbon dioxide is excreted and of course the heat produced is important in thermoregulation.
Summary of human cellular respiration :
(a) Glucose transported to the cell diffuses into the cytoplasm. Glucose is the initial substrate for respiration.
(b) Glycolysis in which glucose with six carbons is broken down into two Pyruvate each with 3 carbons. This yields a small amount of ATP.
(c) Anaerobic respiration in which lactic acid is produced, oxidation from glucose yields a small amount of ATP.
Remember that anaerobic respiration will occur at the same time as aerobic respiration to provided more energy.
(d) Aerobic respiration in which pyruvate is broken down, oxidised, further in the mitochondria where a lot of ATP is produced.
(e) Oxygen is required for step (d)to be completed. This is transported to the cell on the haemoglobin found inside red blood cells.
(f) carbon dioxide is produced as waste from aerobic respiration it diffuses into the blood and is transported to the lungs where it is excreted in exhaled air.