Question

Why are the tails of lipids in the membrane towards the inner part?
A. The tails are nonpolar hydrocarbons, so they are protected with an aqueous environment.
B. The tail is polar hydrocarbon and so protected from the aqueous environment.
C. The non-polar or hydrophobic hydrocarbon trails of lipids, being on the inner side, ensure their protection from aqueous environments.
D. The tail is hydrophilic so it tends to be located in the aqueous inner side of the membrane.

Answer 1

Hint: First of all, before going into the discussion of this question, we should clear the concept of hydrophilic substances and hydrophobic substances.
The hydrophilic substances are the ones which are readily soluble in water and readily associate with the water molecules forming bonds in it. Hydrophilic means ‘water loving’.
The hydrophobic substances are the ones which are not soluble in water and are not attracted to it. Hydrophobic means ‘water hating’.

Complete answer:
Option-C) The non-polar or hydrophobic hydrocarbon trails of lipids, being on the inner side, ensure their protection from aqueous environments.
The cell membrane is a P-L-P structure, a lipid layer sandwiched between two protein layers. The lipid layer is the hydrophobic part of the cell membrane and the protein layer is the hydrophilic part. Thus, being immiscible in water, the lipid tails, which are basically hydrocarbon parts, arrange themselves in the inner side, to ensure that they do not come in contact with the surrounding aqueous environment.
The protein moiety, being the polar and hydrophilic part, interact with the outer environment.

Thus, the correct answer is option C.

Note:
Most of the compounds except a few ones like steroidal hormones are insoluble in lipids. The protein parts of the cell membrane bear receptors with the help of which the cell interacts with the outer world. The protein compounds also form channel pathways which allow entry of selective ions/molecules into the cell. Thus, the protein is the main part that has the major roles and lipids just provide fluidity and flexibility to the membrane.