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Pre AP Biology -CELLS 3.1 Cell Membrane Structure- FRQ Exam Style Questions -New Syllabus

Pre AP Biology -CELLS 3.1 Cell Membrane Structure- FRQ Exam Style Questions – New Syllabus 2025-2026

Pre AP Biology -CELLS 3.1 Cell Membrane Structure- FRQ Exam Style Questions – Pre AP Biology – per latest Pre AP Biology Syllabus.

Pre AP Biology – FRQ Exam Style Questions- All Topics

Question

The diagram below shows a cross section of part of a cell membrane.

a. Describe the basic structure of the cell membrane. In other words:

  • What molecules make up the cell membrane?
  • Which part of the cell membrane is hydrophobic and the part that is hydrophilic.
b. Explain the function of the cell membrane.
c. Explain in detail what happens when a cell is placed in a hypertonic solution. Give a reason for your answer.
d. Define “passive transport” and explain an example.
e. Define “active transport” and explain an example.

Most-appropriate topic codes (Pre-AP Biology):

• TOPIC: CELLS 3.1 — Cell Membrane Structure: Phospholipid bilayer, polar heads, and nonpolar tails — part (a)
• TOPIC: CELLS 3.1 — Cell Membrane Structure: Selective permeability and function in maintaining homeostasis — part (b)
• TOPIC: CELLS 3.2 — Cell Transport: Movement of solutes and solvents across membranes and effects of tonicity — part (c)
• TOPIC: CELLS 3.2 — Cell Transport: Passive transport and movement along the concentration gradient — part (d)
• TOPIC: CELLS 3.2 — Cell Transport: Active transport, movement against the gradient, and bulk transport (endocytosis) — part (e)
• Science Area of Focus — Attention to Modeling: Using representations to explain patterns and relationships in biological systems — context of diagram
▶️ Answer/Explanation
Detailed solution

(a) Structure of the Cell Membrane
The cell membrane is primarily a phospholipid bilayer[cite: 653]. It is made up of polar heads (hydrophilic) and nonpolar tails (hydrophobic)[cite: 653].
The arrangement is specific due to interactions with water:

  • The heads are hydrophilic and face the external and internal aqueous environments[cite: 653].
  • The tails are hydrophobic and face inward, away from water[cite: 653].

(b) Function of the Cell Membrane
The cell membrane acts as a selectively permeable barrier that separates the cell from its environment and maintains dynamic homeostasis[cite: 653].

(c) Hypertonic Solution Effect
When placed in a hypertonic solution (higher solute concentration outside), the cell will shrivel.
Reason: Water moves out of the cell along the concentration gradient via osmosis to balance the environment[cite: 653].

(d) Passive Transport
Definition: Movement of solutes across the membrane along the concentration gradient without the use of additional energy [cite: 653].
Example: Facilitated diffusion through transport proteins[cite: 653].

(e) Active Transport
Definition: Movement of solutes against their concentration gradients with the use of additional energy [cite: 653].
Example: Endocytosis, a form of bulk transport where the membrane encloses particles to bring them into the cell[cite: 653].

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