RESPIRATION - aerobic respiration and anaerobic respiration in plants, fungi and animals
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Suitable for GCSE/IGCSE/O level Biology/Science courses or equivalent
Respiration is the process of releasing energy from digested food.
Know and understand that respiration in cells can take place aerobically or anaerobically depending on conditions and whether the cell is in an animal, plant, fungi or bacteria.
Know and understand that the energy released in respiration is used in a variety of ways.
Know that the human body needs to react to the increased demand for energy during exercise.
You should be able to use your skills, knowledge and understanding to interpret the data relating to the effects of exercise on the human body.
The substrate molecules for respiration are usually sugars like glucose, but the products of respiration depend ion conditions e.g. oxygenated environment or lack of oxygen and whether the cells are animal, plant, fungi or bacteria.
This page compares the processes of aerobic respiration and anaerobic respiration - in plants/fungi and animals and considers the different conditions, substrates, products and relative yields of ATP for the different respiration situations.
You should understand that respiration in cells can take place all the time aerobically or anaerobically.
You should know and understand that the energy released in respiration is used in a variety of ways e.g.
Aerobic respiration in animals
The sugar from digesting carbohydrates and oxygen in via air breathed in, and from the lungs carried round the body by specialised red blood cells. You need oxygen for aerobic respiration - oxygenated conditions from free dissolved oxygen gas.
Most of the reactions in aerobic respiration take place inside the mitochondria of cells.
glucose ===> carbon dioxide + water + energy
C6H12O6(aq) + 6O2(g) ===> 6CO2(g) + 6H2O(l) + energy
The actual energy release takes place through a very complex biochemistry cycle involving ADP (adenosine diphosphate) and its conversion to ATP (adenosine triphosphate) which is the molecule that actually supplies the energy to power most of the chemistry of any cell. The more ATP that is made, the greater the supply of energy available.
Aerobic respiration in plants and fungi
As above for animals. In green plants, in daylight the rate of photosynthesis will exceed that of respiration, but at night or very low light levels, the rate of respiration will exceed that of photosynthesis, otherwise the plant would die!
Anaerobic respiration in animals
If there is a lack of oxygen ('anaerobic') you cannot oxidise the glucose sugar completely, as in the case of aerobic respiration.
glucose ===> lactic acid + energy
This is not as efficient as aerobic respiration and considerably less ATP is formed, reducing the potential energy supply.
In animals, if the physical activity is intense and prolonged you get the 'cramps' due to the build up of lactic acid, which can be painful as anaerobic respiration kicks in due to lack of oxygen. With anaerobic respiration you do get the build up of lactic acid in the muscles because it is more difficult to oxidise and release energy.
Know and understand during exercise, if insufficient oxygen is reaching the muscles they use anaerobic respiration to obtain energy.
Aerobic means 'with oxygen', and anaerobic means 'without oxygen'.
Know and understand anaerobic respiration is the incomplete breakdown of glucose and produces lactic acid.
glucose ==> lactic acid + energy
This is not as efficient in energy release as the complete aerobic respiration of glucose described above, but it does enable you to keep your muscles going for longer. Anaerobic respiration produces a build up of lactic acid in the muscles which can be painful e.g. you suffer from 'cramps'. However, anaerobic respiration has the advantage of enabling the body to keep going for a limited time, even if your a bit short of oxygen!
Know and understand that as the breakdown of glucose is incomplete, much less energy is released than during aerobic respiration.
Know and understand that if muscles are subjected to long periods of vigorous activity they become fatigued, ie they stop contracting efficiently.
Anaerobic respiration in plants and fungi
Again, as in the case of animals, if there is a lack of oxygen ('anaerobic'), you cannot oxidise the glucose sugar completely, as in the case of aerobic respiration, but the product isn't lactic acid, but 'alcohol'!
An example of this in plants is fermentation in yeast cells, the reaction being
glucose ===> ethanol ('alcohol') + carbon dioxide + energyC6H12O6(aq) ====> 2C2H5OH(aq) + 2CO2(g) + energy
The ethanol/alcohol is a by-product of the respiration process.
Again, this is not as efficient as aerobic respiration and less ATP is formed, reducing the potential energy supply.
Note: Fermentation in bacteria produces lactic acid, the same as anaerobic respiration in animals.
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