5.7.8 energy values of different respiratory substrates

Question 1

define respiratory substrate

Answer 1

organic substance that can be oxidised by respiration, releasing energy to make more molecules of ATP

Question 2

describe carbohydrates as a respiratory substrate

Answer 2

• mainly used = monosaccharide glucose
• animals/some bacteria store carbohydrate as glycogen, which hydrolyses into glucose for respiration
• plant cells store carbohydrate as starch, which can be hydrolysed into glucose for respiration

Question 3

describe lipids as a respiratory substrate

Answer 3

• triglycerides hydrolysed by lipase into glycerol & fatty acids
• glycerol converted into triose phosphate & respired
• fatty acids are source of protons for oxidative phosphorylation (H, C & few O)

Question 4

describe proteins as a respiratory substrate

Answer 4

• excess amino acids deaminated in liver
• deamination = removal of amino group
• keto acid enters respiratory pathway as pyruvate, acetyl CoA or krebs cycle acid

Question 5

mean energy value of each respiratory substrate (kJ g-1)

Answer 5

carbohydrate = 15.8
protein = 17.0
lipid = 39.4

Question 6

how is the respiratory quotient calculated (RQ)

Answer 6

CO2 produced divided by O2 consumed

Question 7

what does it suggest if RQ is greater than 1

Answer 7

some anaerobic respiration occurring (more carbon dioxide produced than oxygen consumed)