4. Cholesterol is a lipid which forms part of the structure of membranes of animal cells. It is
absorbed from food and can also be synthesised by liver cells.
Cholesterol is transported by the blood with the help of specific transport proteins to which
cholesterol molecules become reversibly attached. These complexes of lipid and protein
are known as lipoproteins. There are three different types of lipoprotein transporting
cholesterol in the blood. The concentration of cholesterol in blood can be measured, either
as the total cholesterol, or as the amount carried by each of the different types of
lipoprotein.
Explain why cholesterol must be carried in the blood by proteins while glucose does not
need any transport protein.