Question

1. what is a phospholipid made of? which part is hydrophilic, and which is hydrophobic? 4. why do phospholipids form a bilayer? sketch a phospholipid bilayer with 6 total phospholipids. 5. what is the role of cholesterol in a membrane? what does cholesterol touch in the membrane?

Explanation:

1. A phospholipid is made of a glycerol molecule, two fatty - acid tails, and a phosphate - containing head group. The phosphate - containing head group is hydrophilic due to its polar nature, while the fatty - acid tails are hydrophobic as they are non - polar.
2. Phospholipids form a bilayer because the hydrophilic heads are attracted to water (both inside and outside the cell), while the hydrophobic tails repel water and face each other in the interior of the bilayer to avoid contact with water. (Sketching requires drawing which is not possible in this text - based format, but it would show 3 phospholipids in one layer with heads out and tails in, and 3 in the opposite layer with the same orientation).
3. The role of cholesterol in a membrane is to maintain membrane fluidity. At high temperatures, it restricts movement of phospholipids to prevent excessive fluidity, and at low temperatures, it prevents the membrane from becoming too rigid. Cholesterol touches the fatty - acid tails of the phospholipids in the membrane.

Answer:

1. Made of glycerol, two fatty - acid tails, and a phosphate - containing head group. Head group is hydrophilic, fatty - acid tails are hydrophobic.
2. Form bilayer due to hydrophilic heads and hydrophobic tails' interaction with water. Sketch not provided.
3. Role is to maintain membrane fluidity. Touches fatty - acid tails of phospholipids.