Revision notes topic questions past papers

CIE AS Biology (9700) 2019-2021 Resources

REVISION NOTES 

 

  TOPIC QUESTIONS 

 

  PAST PAPERS

Page 37

Triglycerides: Structure & Function

Energy storage

The long hydrocarbon chains contain many carbon-hydrogen bonds with little oxygen

(triglycerides are highly reduced)

So when triglycerides are oxidised during cellular respiration this causes these bonds

to break releasing energy used to produce ATP

Triglycerides therefore store more energy per gram than carbohydrates and proteins (37kJ

compared to 17kJ)

As triglycerides are hydrophobic they do not cause osmotic water uptake in cells so more

can be stored

Plants store triglycerides, in the form of oils, in their seeds and fruits. If extracted from

seeds and fruits these are generally liquid at room temperature due to the presence

of double bonds which add kinks to the fatty acid chains altering their properties

Mammals store triglycerides as oil droplets in adipose tissue to help them survive

when food is scarce (e.g. hibernating bears)

The oxidation of the carbon-hydrogen bonds releases large numbers of water molecules

(metabolic water) during cellular respiration

Desert animals retain this water if there is no liquid water to drink

Bird and reptile embryos in their shells also use this water

Insulation

Triglycerides are part of the composition of the myelin sheath that surrounds nerve fibres

This provides insulation which increases the speed of transmission of nerve impulses

Triglycerides compose part of the adipose tissue layer below the skin which acts as insulation