D inheritance is the answer
They are specialised cells.
A closed loop system is one where the ouput of the system is at least part of the input. In a refrigerator, the output of the cooling system (the cold air inside the refrigerator) is measured, and is fed back into the system to determine whether the system needs to continue cooling.
<span>An example of a fridge that was an open loop system would be one that turns on and cools for 1 hour every 6 hours, regardless of internal temperature.</span>
The degree of saturation is the number of hydrogen molecules in a lipid. Lipids differ in their degree of saturation or unsaturation based on the number of double bonds that the lipid has; since double bonds lower the number of hydrogen molecules in the lipid.