The plasma membrane is an essential part of the cell. It surrounds the cell and has a unique chemical combination that allows for the transport of molecules into and out of the cell.Figure 2. The eukaryotic plasma membrane is a phospholipid bilayer with proteins and cholesterol embedded in it. by OpenStax (CC BY-SA 4.0)Which of the following statements describes the chemical composition of the plasma membrane and the permeability of the membrane?Elimination ToolSelect one answerAThe plasma membrane is hydrophilic on the outside layers and hydrophobic in the inside layers. The plasma membrane is permeable.BThe plasma membrane is hydrophobic on the outside layers and hydrophilic in the inside layers. The plasma membrane is permeable.CThe plasma membrane is hydrophobic on the outside layers and hydrophilic in the inside layers. The plasma membrane is semi-permeable.DThe plasma membrane is hydrophilic on the outside layers and hydrophobic in the inside layers. The plasma membrane is semi-permeable.
Question
The plasma membrane is an essential part of the cell. It surrounds the cell and has a unique chemical combination that allows for the transport of molecules into and out of the cell.Figure 2. The eukaryotic plasma membrane is a phospholipid bilayer with proteins and cholesterol embedded in it. by OpenStax (CC BY-SA 4.0)Which of the following statements describes the chemical composition of the plasma membrane and the permeability of the membrane?Elimination ToolSelect one answerAThe plasma membrane is hydrophilic on the outside layers and hydrophobic in the inside layers. The plasma membrane is permeable.BThe plasma membrane is hydrophobic on the outside layers and hydrophilic in the inside layers. The plasma membrane is permeable.CThe plasma membrane is hydrophobic on the outside layers and hydrophilic in the inside layers. The plasma membrane is semi-permeable.DThe plasma membrane is hydrophilic on the outside layers and hydrophobic in the inside layers. The plasma membrane is semi-permeable.
Solution
The correct answer is D. The plasma membrane is hydrophilic on the outside layers and hydrophobic in the inside layers. The plasma membrane is semi-permeable.
This is because the plasma membrane is made up of a phospholipid bilayer. Each phospholipid molecule has a hydrophilic (water-loving) head and two hydrophobic (water-fearing) tails. The hydrophilic heads are attracted to water, so they line up on the outside of the membrane, in contact with the watery cytosol and extracellular fluid. The hydrophobic tails are repelled by water, so they line up in the middle of the membrane, away from the water.
The semi-permeability of the plasma membrane means that it allows some substances to pass through, but not others. Small, non-polar molecules can pass directly through the phospholipid bilayer, but ions and larger, polar molecules cannot. Instead, these substances must be transported across the membrane by proteins.
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