Final answer:
Newly synthesized phospholipids are inserted into the cytosolic leaflet of the cell membrane and organized with hydrophilic heads facing the aqueous environments and hydrophobic tails facing each other. The correct answer is option 1.
Step-by-step explanation:
When phospholipids are newly synthesized, they are initially inserted into the cytoplasmic leaflet of the cell membrane, which is the layer facing the cytosol. The process of incorporating phospholipids into the membrane is tightly regulated by enzymes, such as flippases, which help maintain the asymmetric distribution of phospholipids between the two leaflets of the bilayer. Each phospholipid molecule consists of a hydrophilic (water-attracting) 'head' and two hydrophobic (water-repelling) 'tails'. When assembling into a bilayer, the phospholipids orient in such a way that the heads point toward the aqueous environments both inside and outside of the cell, while the tails face each other away from water, forming the interior of the membrane.
Given the structure of a phospholipid bilayer, when new phospholipids are synthesized, they are not inserted randomly nor are they inserted into both the cytosolic and extracellular-facing leaflets simultaneously. Over time, certain phospholipids may be transferred from the cytosolic leaflet to the outer leaflet facing the extracellular space by the action of specific enzymes.
The correct option that describes how newly synthesized phospholipids are inserted into the bilayer leaflet is: 1) They are inserted into the bilayer leaflet facing the cytosol.