Respiration:
4.
Anaerobic respiration in plants, bacteria and fungi
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(4) Anaerobic respiration in plants,
bacteria and fungi
Plants respire aerobically, but also
anaerobically too.
Again, as in the case of animals, if there is
a lack of oxygen ('anaerobic conditions'), you cannot oxidise the glucose sugar completely,
as in the case of aerobic respiration, but in plants and yeast cells the product isn't lactic acid, but
ethanol ('alcohol') and carbon dioxide!
An example of this in plants is fermentation
in yeast cells (a single celled organism classed as a type of fungi), the reaction being
glucose ===> ethanol ('alcohol') +
carbon dioxide + energy
C6H12O6(aq)
====> 2C2H5OH(aq) + 2CO2(g)
+ energy
The ethanol ('alcohol') is a
by-product of the respiration process.
This is how alcohol based drinks
are made - yeast + sugary liquid ==> anaerobic respiration!
Anaerobic respiration occurs in
the cytoplasm of cells.
Again, this is not as efficient as aerobic
respiration and less ATP is formed, reducing the potential energy supply,
but it does the commercial job for the alcohol drinks industry./
Notes: Fermentation in bacteria
produces lactic acid, the same as anaerobic respiration in animals.
Fermentation using yeast is
widely used in the food and drinks industry.
Yeast is used in baking
products like bread, where the evolution of the carbon dioxide
gives the 'rising' action.
Yeast fermentation of sugar
is used to make alcoholic drinks like beers and wines.
The
fermentation reaction makes the 'alcohol' (ethanol, C2H5OH)
and the dissolved carbon dioxide gas makes the 'fizz' or
'froth'.
Beer is brewed by mixing
malted barley and hops with yeast in large vats.
The yeast cells rapidly
divide and consume any oxygen present and they resort to
anaerobic respiration.
in other words yeast cells
can switch from aerobic respiration to anaerobic respiration
depending on conditions.
Anaerobic respiration in
yeast cells and other microorganisms is referred to as
fermentation.
Note that bread making uses the anaerobic respiration of yeast
to produce carbon dioxide gas to give the rising action of the
dough.
Under certain conditions plants
have to switch from aerobic respiration to anaerobic respiration
So, certain plant cells can use
'alcoholic' fermentation to produce and release chemical energy to
power all the necessary cell processes.
e.g. circumstances when there is
little oxygen in the immediate environment.
Underground, root
cells respire anaerobically, if the plants are growing in
water logged soil conditions where little oxygen can diffuse
into the soil.
Rice is grown in flooded
areas called paddy fields and there is little oxygen around
in the waterlogged soil.
Rice root cells can
respire using anaerobic respiration, but the products are
ethanol and carbon dioxide.
glucose ===> ethanol ('alcohol') +
carbon dioxide + energy
But, ethanol is a
poisonous chemical, so rice root cells must have a
high tolerance to it in order for the rice plants to grow
and ripen.
Plants that grow in marsh
lands where the soggy ground and water contain little oxygen.
Pollen grains can also use
anaerobic respiration to maintain its cells functions and
develop into a young healthy plant.
Respiration in bacteria
Bacteria use aerobic respiration when oxygen is
freely available from air, in the soil or dissolved in water.
If oxygen is not available, just like plants and
animals, they will switch to a form of anaerobic respiration
e.g. bacteria in water logged soil where little air containing
oxygen can get in..
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