Question

repel most polar molecules.
complete the paragraph to describe the phospholipid bilayer.
both the intracellular and extracellular environments contain water. the water attracts the phosphate - containing heads and repels the fatty acid tails of the phospholipids. so the heads of the phospholipids face inward, and the tails face outward in the lipid bilayer.

Explanation:

To solve this, we analyze the properties of phospholipids and water:

Step 1: Understand Hydrophilic/Hydrophobic Interactions

Phosphate - containing heads of phospholipids are hydrophilic (water - attracting), and fatty acid tails are hydrophobic (water - repelling). Water is polar, so it interacts with hydrophilic heads and repels hydrophobic tails.

Step 2: Determine Orientation in Bilayer

Since intracellular and extracellular environments have water, hydrophilic heads (attracted by water) face outward (towards the water - containing environments: extracellular and intracellular). Hydrophobic tails (repelled by water) face inward (away from water, towards the interior of the bilayer).

For the blanks (correcting the wrong "inward" for heads and wrong "outward" for tails in the original):

• The water $\boldsymbol{\text{attracts}}$ the phosphate - containing heads (hydrophilic interaction).
• The water $\boldsymbol{\text{repels}}$ the fatty acid tails (hydrophobic interaction).
• Heads face $\boldsymbol{\text{outward}}$ (towards water - filled environments: extracellular and intracellular).
• Tails face $\boldsymbol{\text{inward}}$ (away from water, between the two layers of heads).

If we assume the task is to correct the dropdowns:

• First dropdown (water - head interaction): $\boldsymbol{\text{attracts}}$ (correct as is, since heads are hydrophilic).
• Second dropdown (water - tail interaction): $\boldsymbol{\text{repels}}$ (correct as is, since tails are hydrophobic).
• Third dropdown (head orientation): $\boldsymbol{\text{outward}}$ (corrected from "inward" in the original, as heads face water - containing environments).
• Fourth dropdown (tail orientation): $\boldsymbol{\text{inward}}$ (corrected from "outward" in the original, as tails face away from water).

Answer:

• Water - head interaction: attracts
• Water - tail interaction: repels
• Head orientation: outward
• Tail orientation: inward