Describe fermentation.

Fermentation is the incomplete breakdown of carbohydrates under anaerobic conditions. It is of two types:

A. Alcoholic fermentation : It occurs in fungi such as yeast, Rhizopus etc. and bacteria. It can be described in 2 steps :

Step I : Pyruvic acid is decarboxylated into acetaldehyde in the presence of enzyme pyruvate decarboxylase and CO2 is liberated.

Step II : Acetaldehyde is reduced to ethyl alcohol in the presence of enzyme alcoholic dehydrogenase and NADH2 is oxidised to NAD. There is loss of energy stored in ethyl alcohol.

Describe fermentation.


I. Alcoholic fermentation is common in yeasts which are used in industrial preparation of ethyl alcohol from molasses. It is the basic process underlying the production of beers and wines.

2. Yeasts are used in baking industry as COproduced during alcoholic fermentation raises its dough.

B. Lactic acid fermentation : Lactic acid fermentation is common in animals and certain bacteria. In vertebrates, lactic acid formed in muscles in the anaerobic conditions.

Describe fermentation.


What are the assumptions taken into account while calculating the net gain of ATP?

The calculations for the net gain of ATP is usually based on the following assumptions :

i.  All the reactions are sequential and follow a orderly pathway , with one substrate forming the next and with glycolysis, TCA cycle and ETS
pathway following one after another.

ii. The NADH synthesised in glycolysis is transferred into the mitochondria where it is subject to oxidative phosphorylation.

iii. The intermediates of the pathway are not utilised to synthesise any other compound.

iv. Only glucose is used as the respiratory substrate and no alternative r alternative substrates are used or enter the pathway at any of the intermediary stages.


What is the nature of enzymes present in Mitochondria ?

 Oxidative enzymes.

 Why does anaerobic respiration produce less energy than aerobic respiration ?

Anaerobic respiration produces less energy as compared to aerobic respiration due to the following reasons :

1. Incomplete break down. There is incomplete breakdown of repiratory substrate.

2. Incomplete oxidation. At least one of the products of anaerobic respiration is organic. It can be further oxidised to release energy.

3. Re-utilization. NADH2 produced during glycolysis is often re-utilized.

4. No A TP formation. ATP formation does not, occur during regeneration of NAD+.

5. Absence of ETC. Electron transport chain is absent.

6. No use of oxygen. Oxygen is not used for receiving electrons and protons.


Name the basic substrate for cell respiration.