Question

the cell membrane consists of two layers of phospholipids. the head of each phospholipid is made of a phosphate group, a molecule that is negatively charged and polar. this makes the head hydrophilic, or water loving, so it is attracted to other polar molecules like water. the tails are uncharged, nonpolar fatty acid chains. they are hydrophobic, or water fearing, so they repel most polar molecules. complete the paragraph to describe the phospholipid bilayer. both the intracellular and extracellular environments contain water. the water the phosphate - containing heads and the fatty acid tails of the phospholipids. so the heads of the phospholipids face, and the tails face in the lipid bilayer.

Explanation:

1. For the first blank: The heads are hydrophilic (water - loving), so water "attracts" the phosphate - containing heads.
2. For the second blank: The tails are hydrophobic (water - fearing), so water "repels" the fatty acid tails.
3. For the third blank: Since the heads are attracted to water and both intracellular and extracellular environments have water, the heads face "the water - containing environments (intracellular and extracellular)".
4. For the fourth blank: The tails are repelled by water, so they face "each other (the interior of the bilayer, away from water)".

Let's fill in the blanks step by step:

• First blank: The head of the phospholipid is hydrophilic (water - loving), and water is a polar molecule. So the water "attracts" the phosphate - containing heads.
• Second blank: The tails are hydrophobic (water - fearing), so water "repels" the fatty acid tails.
• Third blank: Both intracellular and extracellular environments have water. The hydrophilic heads are attracted to water, so the heads of the phospholipids face "the intracellular and extracellular environments (or the water - rich areas inside and outside the cell)".
• Fourth blank: The hydrophobic tails are repelled by water, so the tails face "each other (the middle of the bilayer, away from the water - containing regions)".

Answer:

• First blank: attracts
• Second blank: repels
• Third blank: the intracellular and extracellular environments (or the water - rich areas inside and outside the cell)
• Fourth blank: each other (the middle of the bilayer, away from the water - containing regions)

(Note: For the third and fourth blanks, more precise answers based on biological knowledge: Third blank - "the inside and outside of the cell (or the aqueous environments)" ; Fourth blank - "the interior of the bilayer (or each other)")