Triglycerides
Triglycerides are fats and oils
Fatty acid and glycerol molecules are the components that make up triglycerides
Fats and oils have a number of important functions in organisms: energy storage, insulation, buoyancy, and protection
Energy storage
The long hydrocarbon chains in triglycerides 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