Question

why proteins and fats are not used as respiratory substrates

Answer 1

HEYA--

Proteins and fats have to undergo a series of chemical reactions to form simple compound and then only they can enter Krebs Cycle( it is a cycle where our cells during aerobic respiration generate energy). After forming simple compounds only then they can enter the cycle and help to produce energy which takes a lot of time. Glucose on the other hand can be easily oxidised without any complex or time consuming reactions and also it present in a quite large quantity. Due to above reasons fats and proteins are not used as respiratory substrate and glucose is used.
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Answer 2

Proteins and fats have to undergo a series of chemical reactions to form simple compound and then only they can enter Krebs Cycle( it is a cycle where our cells during aerobic respiration generate energy). After forming simple compounds only then they can enter the cycle and help to produce energy which takes a lot of time. Glucose on the other hand can be easily oxidised without any complex or time consuming reactions and also it present in a quite large quantity. Due to above reasons fats and proteins are not used as respiratory substrate and glucose is used.

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