Cell Respiration
Define cell respiration
Definition: Cell respiration is the controlled release of energy from organic compounds in cells to form ATP.
 ATP or Adenosine triphosphate is the molecule which directly fuels the majority of biological reactions.
 Everyday each person will hydrolyze (reduce) 10 25 ATP molecules to
ADP.
 The ADP is reduced back to ATP using the free energy from the oxidation of organic molecules.
Glycolysis
 Location:
Cytoplasm
 Process:
Glycolysis
 Substrate:
Glucose
 Products: 2 Pyruvate and a small amount of ATP
 Glycolysis does not use oxygen.
Anaerobic respiration
 Anaerobic respiration is the oxidation of organic compounds without oxygen.
 It is less efficient than aerobic respiration (with oxygen).
 There are different types of anaerobic respiration. Here we will compare anaerobic respiration in yeast and humans.

Humans anaerobic respiration:
 Location: cytoplasm
 Substrate: Glucose
 Product: lactic acid
(lactate) + ATP
 Note: lactic acid 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:
 Location: cytoplasm
 Substrate:
Glucose
 Product:
Ethanol + carbon dioxide + ATP
 This is the end point for this fermentation reaction. Ethanol and CO
2 are both excreted with no further metabolism of the energy stored in the ethanol (very inefficient)
 Note: The glucose molecule has been hydrolyzed further than in human respiration. Some organisms are totally anaerobic others can switch between anaerobic and aerobic.
Exercise and anaerobic respiration:
Human lactic acid anaerobic respiration is a process that supplements the production of ATP. The lactic acid pathway is so inefficient that under normal circumstances it cannot produce enough energy to support human systems. In describing the lactic acid 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 acid pathway.
This is a misrepresentation of a complex response to the demand for ATP. It is far better to consider that anaerobic respiration in humans supplements 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 CO
2
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.
Aerobic respiration
 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 from 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. This is the 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 this stage can accompany the next stage.
(d) aerobic respiration in which pyruvate is broken down, oxidized, further in the mitochondria a lot of ATP is produced.
(e) Oxygen is required for step (d) to be completed. This is transported to the cell on the hemoglobin 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.