"Respiration is the chemical process of releasing energy from organic compounds."
It is important that you understand the correct terms for some of the processes:
- Gas exchange - The movement of oxygen into an organism and carbon dioxide out of an organism.
- Breathing - The ventilation movements that are needed in some larger animals so that efficient gas exchange can take place. It involves ribs, intercostal muscles, the diaphragm and lungs.
- Respiration - The process by which complex organic molecules are broken down to release energy.
- Aerobic respiration - Requires oxygen to fully oxidise the organic molecule. This releases lots of energy.
- Anaerobic respiration -The breakdown of the molecule without oxygen. This releases much less energy.
At GCSE, aerobic respiration was presented in one equation:
However, this is a gross over-simplification. In reality it is a long series of enzyme-controlled reactions.
ATP (adenosine triphosphate) is the universal currency of energy. It is a small molecule with 3 phosphate groups (P) attached to an adenosine molecule i.e. Adenosine-P-P-P
During respiration, high energy C-C, C-H and C-OH bonds are broken. Lower energy bonds are formed and the difference is released and used to attach a P to Adenosine-P-P (ADP adenosine diphosphate), making ATP.
When energy is required at a later time by a cell, it can use the ATP and break a P off the end. This releases the energy needed (30.6kJ for every ATP, ADP + P). The more ATPs used, the more energy is released.
For aerobic respiration to occur, the cell needs to possess mitochondria.
Glycolysis (splitting of sugar):
What = formation of pyruvic acid from glucose.
Where = cytoplasm of a cell.
What = removal of hydrogen from pyruvic acid.
Where = matrix of the mitochondria.
Electron transport chain / oxidative phosphorylation:
What = using hydrogen to produce ATP (see chemiosmotic theory).
Where = inner mitochondrial membrane.
Many of the reactions in the stages of respiration involve oxidation by the removal of electrons or hydrogen atoms (H). These are transferred to electron/hydrogen carriers. Ultimately they are passed to oxygen to form water right at the very last stage of respiration.
Two important electron/hydrogen carriers are NAD (nicotinamide adenine dinucleotide), and FAD (flavin adenine dinucleotide).
Oxidation is the addition of oxygen, the removal of hydrogen or the loss of electrons.
Reduction is the addition of hydrogen, the removal of oxygen or the gain of electrons.
A quick way to remember this is "OILRIG":
Oxidation Is Loss, Reduction Is Gain.