Which molecule forms cell membranes and is typically drawn as a sphere with two “tails” attached to it?

The molecules with head and two tails found on the surface of cell membrane are referred to as phospholipids. phospholipids have only two fatty acids attached to glycerol and are joined to phosphate group that gives them a negative charge. the phosphate head could be attached to another group such as choline. the positive end of the this molecule is hydrophilic whereas the tail end is hydrophobic. this property leads to creation of bi-layer plasma membrane.  

Reduction in overall biodiversity