Biological membranes are present in all cells, and in eukaryotic
cells they also form the endomembrane system. They act as
gatekeepers that selectively move certain ions and compounds into
and out of the cell or cell
organelles.             (a)
Which of the following best describes a biological membrane?

a bilayer containing lipids with hydrophilic head groups facing
the extracellular fluid and cytoplasm, and hydrophobic tail groups
extending inward…OR… a bilayer containing lipids with
hydrophobic head groups facing the extracellular fluid and
cytoplasm, and hydrophilic tail groups extending inward…OR… a
bilayer containing lipids with hydrophilic head groups facing
inward and hydrophobic tail groups extending toward the
extracellular fluid and cytoplasm.

(b) Which of the following are components of biological
membranes? select all that apply…… nucleic
acids…OR…lipids…OR…protiens