UK GCSE level age ~14-16, ~US grades 9-10 Biology revision notes re-edit 22/05/2023 [SEARCH]

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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