Question

Describe the three pathways of glucose breakdown in living organisms.

Accepted Answer

The food material taken in during the process of nutrition is used in cells to provide energy for various life processes. Diverse organisms do this in different ways – some use oxygen to break-down glucose completely into carbon dioxide and water, some use other pathways that do not involve oxygen. In all cases, the first step is the break-down of glucose, a six-carbon molecule, into a three-carbon molecule called pyruvate.

Glucose (6 carbon molecule) $\overset{I n c y t o p l a s m}{\to}$ Pyruvate (3 carbon molecules) + Energy.

Aerobic respiration: The complete oxidation of food yielding carbon dioxide, water and energy in the presence of oxygen is called aerobic respiration. Aerobic respiration takes place inside the mitochondria. In this process glucose is oxidised into carbon dioxide and water along with energy.

Glucose (6 carbon molecule) $\overset{I n t h e p r e s e n c e o f o x y g e n (i n m i t o c h o n d r i a)}{\to}$ Carbon dioxide + water + Energy.

Anaerobic respiration: Partial oxidation of food in the absence of oxygen, resulting in the release of some amount of energy, is called anaerobic respiration. In this respiration, pyruvate is converted into lactic acid or ethyl alcohol.

In case of microorganisms like yeast and bacteria, anaerobic respiration takes place and the ethyl alcohol is formed. This is known as alcohol fermentation.

Pyruvate $\overset{a b s e n c e o f o x y g e n (i n y e a s t)}{\to}$ Ethyl alcohol + Carbon dioxide + Energy.

Lactic acid is formed in the muscle cells as well as in some microbes that lack mitochondria. This process is known as lactic acid fermentation.

Pyruvate $\overset{a b s e n c e o f o x y g e n (i n m u s c l e c e l l s)}{\to}$ Lactic acid + Energy.

Describe the three pathways of glucose breakdown in living organisms.

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