AP Biology Practice Quiz: Plasma Membrane
Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026
Test your understanding with short quizzes. This quiz has 14 questions to check your progress.
Question 1 of 14
All Questions (14)
A) The hydrophobic nonpolar tail
B) The hydrophilic polar head
C) The embedded steroid molecule
D) The fatty acid chain
Correct Answer: B
According to the provided content, phospholipids have hydrophilic polar heads that are oriented toward the aqueous environments (both inside and outside the cell), while the hydrophobic tails face inward.
A) The constant passage of water across the membrane.
B) The ability of phospholipids and embedded proteins to move laterally.
C) The liquid state of the cytoplasm and extracellular fluid.
D) The fixed, rigid arrangement of membrane components.
Correct Answer: B
The content states that the fluid mosaic model illustrates plasma membranes as a dynamic structure where phospholipids and proteins can move laterally. This movement is the 'fluid' characteristic of the membrane.
A) Its attachment to carbohydrate chains on the cell surface.
B) The random chance of its insertion during synthesis.
C) The arrangement of its hydrophilic and hydrophobic regions.
D) The concentration of steroid molecules within the membrane.
Correct Answer: C
The provided content specifies that embedded proteins have hydrophilic and hydrophobic regions that determine their orientation and interaction within the phospholipid bilayer. Hydrophobic regions will associate with the nonpolar tails, while hydrophilic regions will face the aqueous environments.
A) The hydrophilic polar heads of phospholipids
B) The hydrophobic nonpolar tails of phospholipids
C) The carbohydrate chains attached to proteins
D) The aqueous environment inside and outside the cell
Correct Answer: B
The content explicitly states that the hydrophobic nonpolar tails of phospholipids face inward, forming the core of the membrane. This nonpolar core repels polar molecules.
A) The uniform and repeating pattern of phospholipids.
B) The rigid and static nature of the membrane structure.
C) The mixture of different components like proteins and steroids embedded in the phospholipid bilayer.
D) The single layer of phospholipid molecules.
Correct Answer: C
The content describes the membrane as a structure of phospholipid molecules embedded with proteins, steroids, and carbohydrates. This patchwork or 'mosaic' of different types of molecules gives the model its name.
A) Tightly embedded and spanning the hydrophobic core of the membrane.
B) Loosely associated with the polar heads on the surface of the membrane.
C) Dissolved within the nonpolar tails of the phospholipids.
D) Uniformly distributed both on the surface and within the core.
Correct Answer: B
A protein's orientation is determined by its hydrophilic and hydrophobic regions. A protein that is almost entirely hydrophilic would interact favorably with the aqueous environment and the hydrophilic polar heads of the phospholipids but would be repelled by the hydrophobic core.
A) By allowing all substances to pass freely into the cell.
B) By creating a nonpolar barrier that separates the internal and external aqueous environments.
C) By forming a rigid, impermeable wall around the cell.
D) By using its polar heads to actively transport ions across the membrane.
Correct Answer: B
The hydrophobic tails of the phospholipids form a continuous nonpolar core. This core acts as a barrier that separates the aqueous environment inside the cell from the aqueous environment outside, which is a primary function in maintaining the distinct internal environment.
A) Ribosomes
B) Proteins
C) Mitochondria
D) Nucleic acids
Correct Answer: B
The content explicitly lists proteins, steroids, and carbohydrates as components embedded within the phospholipid molecules that make up the plasma membrane.
A) covalently bonded to each other in a rigid lattice.
B) amphipathic, having both hydrophilic and hydrophobic regions.
C) entirely nonpolar molecules.
D) attracted to the nonpolar tails of other phospholipids more than to water.
Correct Answer: B
Phospholipids are amphipathic, meaning they have a hydrophilic head and a hydrophobic tail. In an aqueous environment, they arrange themselves to shield the hydrophobic tails from water, resulting in the formation of a bilayer, as described in the content.
A) Only hydrophilic regions on its surface.
B) Only hydrophobic regions on its surface.
C) Hydrophobic regions in contact with the phospholipid tails and hydrophilic regions facing the aqueous environments.
D) A completely random arrangement of hydrophilic and hydrophobic regions.
Correct Answer: C
The content states that a protein's orientation is determined by its hydrophilic and hydrophobic regions. To span the membrane, a protein must have hydrophobic regions to interact with the nonpolar core (tails) and hydrophilic regions to interact with the aqueous environments on both sides.
A) A rigid, static layer of phospholipids with fixed proteins.
B) A semi-permeable barrier composed solely of proteins and carbohydrates.
C) A dynamic structure where phospholipids, proteins, and other components can move laterally.
D) A solid wall made of steroids that protects the cell.
Correct Answer: C
The provided content describes the fluid mosaic model as a dynamic structure of phospholipid molecules embedded with proteins, steroids, and carbohydrates that can move laterally. This captures both the 'fluid' (movement) and 'mosaic' (mixture of components) aspects.
A) Embedded proteins
B) Carbohydrates
C) Phospholipids
D) Steroids
Correct Answer: C
The content describes how phospholipids, with their hydrophilic heads and hydrophobic tails, form the bilayer. This bilayer is the basic structure that separates the two aqueous environments, fulfilling a key role in maintaining the internal environment.
A) held together by strong, permanent covalent bonds that allow for flexing.
B) held in place by non-covalent interactions, such as hydrophobic interactions, which allow them to shift.
C) all identical in structure, allowing for easy substitution.
D) anchored firmly to the cytoskeleton, preventing any movement.
Correct Answer: B
The 'fluid' nature described in the content implies that the forces holding the membrane together are not rigid. The hydrophobic interactions between the nonpolar tails are non-covalent, allowing individual phospholipid and protein molecules to move past one another.
A) Phospholipids provide a rigid structure while proteins allow for flexibility and movement.
B) Phospholipids form a general barrier, while proteins provide specific functions like transport.
C) Both phospholipids and proteins are primarily involved in providing structural support and shape to the cell.
D) Proteins form the main barrier, while phospholipids are responsible for cell-to-cell recognition.
Correct Answer: B
This question requires synthesizing multiple points. Phospholipids (with their hydrophilic/hydrophobic nature) form the basic, semi-permeable barrier. Embedded proteins, with their specific structures, are positioned within this barrier to carry out specific roles (like transport, signaling, etc.) that are essential for maintaining the internal environment.