Week 3 — Quiz (auto-graded) · Cell Structure, Function & Membrane Transport

Course: Anatomy & Physiology I (BIOL 2301 + BIOL 2101) · Silver Oak University (fictional sample) · Prof. Navarro
Objective tested: Objective 2 — the plasma membrane & selective permeability; organelle structure→function; passive, active, and bulk transport; osmosis; tonicity (predict swell/shrink/same) and the Na⁺/K⁺ pump.
Points: 10 (1 each) · Assignment group: Quizzes (10% of grade) · Due: end of Module 3.

This is the human-readable quiz with its vetted answer key and feedback. The import-ready Classic QTI is in F-quiz-week-03-qti.xml (generated by the shared validated script — parses with 10 items, every single-answer item exactly one correct). The reusable item-bank entries and the Canvas placement block are at the bottom of this file.

Blueprint

No trick questions; distractors target the Week 3 misconceptions named in the lecture outline (hypo/hyper reversal, osmosis moves water not solute, facilitated diffusion is passive, the pump ratio, organelle job swaps).

Questions, key, and feedback

Q1 (MC). The plasma (cell) membrane is best described as —
- A. a single solid sheet of protein
- B. a phospholipid bilayer with embedded proteins ✅
- C. a double layer of DNA
- D. a rigid wall made of carbohydrate
Feedback: The membrane is a phospholipid bilayer — hydrophilic heads facing the watery inside and outside, hydrophobic tails tucked in — with proteins (channels, carriers, receptors) embedded in it (the fluid-mosaic model). It is not solid protein, DNA, or a rigid carbohydrate wall.

Q2 (Matching). Match each organelle to its main function.
| Organelle | Correct function |
|---|---|
| Mitochondrion | Produces ATP (cellular respiration) |
| Ribosome | Site of protein synthesis |
| Lysosome | Digestion / breaks down waste |
| Nucleus | Stores DNA; the cell's control center |
Feedback: The classic pairings: mitochondrion → ATP ("powerhouse"); ribosome → builds proteins (protein synthesis); lysosome → digestion (recycling crew); nucleus → DNA/control (the boss). Students most often swap the ribosome and the Golgi (which ships proteins) — anchor each organelle by what it produces or processes.

Q3 (MC). Osmosis is the movement of —
- A. solute across a membrane toward the more dilute side
- B. water across a selectively permeable membrane toward the side with more solute ✅
- C. proteins from the cytosol into the nucleus
- D. water toward the side with less solute
Feedback: Osmosis moves water, not solute, and water moves toward the side with MORE solute (higher osmolarity) — "water follows solute." D reverses the direction; A confuses osmosis with solute diffusion.

Q4 (MC). A red blood cell with an interior of about 300 mOsm is placed in a 100 mOsm solution. What happens, and why?
- A. The cell shrinks, because the solution is hypertonic
- B. The cell stays the same, because the solution is isotonic
- C. The cell swells, because the solution is hypotonic and water moves in ✅
- D. The cell swells, because solute moves into the cell
Feedback: The bath (100 mOsm) has less solute than the cell (300 mOsm), so it is hypotonic → water moves into the cell → the cell swells (and may lyse). Hook: hypO = swellO. D gets the right outcome for the wrong reason — it's water that moves in, not solute. (Pre-computed and re-verified: 100 < 300 → hypotonic → swell.)

Q5 (MC). Which statement correctly describes active transport?
- A. It moves a substance down its gradient and uses no energy
- B. It moves a substance against its gradient and requires ATP ✅
- C. It is another name for simple diffusion
- D. It only moves water across the membrane
Feedback: Active transport moves a substance against its concentration gradient (low → high), so it requires ATP. A and C describe passive transport (downhill, no ATP); D confuses it with osmosis.

Q6 (MC). For each ATP it uses, the sodium–potassium (Na⁺/K⁺) pump moves —
- A. 3 K⁺ out of the cell and 2 Na⁺ into the cell
- B. 2 Na⁺ out of the cell and 2 K⁺ into the cell
- C. 3 Na⁺ out of the cell and 2 K⁺ into the cell ✅
- D. equal amounts of Na⁺ and K⁺ in the same direction
Feedback: The pump moves 3 Na⁺ OUT and 2 K⁺ IN per ATP — leaving more Na⁺ outside and more K⁺ inside (the gradients nerves and muscles run on). A swaps the ions; B has the wrong sodium count; D ignores the opposite directions. (Verified ratio: 3 out / 2 in.)

Q7 (Multiple answer — select all that apply). Which of the following are passive transport processes (no ATP, down the gradient)?
- A. Simple diffusion ✅
- B. Facilitated diffusion ✅
- C. Osmosis ✅
- D. Active transport by the Na⁺/K⁺ pump
- E. Exocytosis
Feedback: Simple diffusion, facilitated diffusion, and osmosis are all passive — downhill, no ATP (facilitated diffusion uses a protein but is still passive). The Na⁺/K⁺ pump (active) and exocytosis (bulk transport) both require energy — those are the distractors.

Q8 (True / False). "When a cell is placed in a hypertonic solution, it takes in water and swells."
- True
- False ✅
Feedback: False. In a hypertonic solution (more solute outside than in the cell), water leaves the cell → it SHRINKS (crenates). Swelling happens in a hypotonic solution. This hypo/hyper reversal is the single most-flipped pair in the unit — anchor it with hypO = swellO.

Q9 (MC). A cell whose interior is 300 mOsm is placed in a 500 mOsm solution. Which way does water move?
- A. Into the cell, because water moves toward lower solute
- B. Out of the cell, because water moves toward the side with more solute ✅
- C. No net movement, because the solution is isotonic
- D. Into the cell, because the cell is hypertonic to the solution
Feedback: The bath (500 mOsm) has more solute than the cell (300 mOsm), so water moves OUT of the cell (toward the higher-solute side) and the cell shrinks. A and D get the direction or the label backwards; C is wrong because 500 ≠ 300 (it's hypertonic, not isotonic). (Pre-computed and re-verified: 500 > 300 → water exits.)

Q10 (MC). To say the plasma membrane is "selectively permeable" means that it —
- A. lets every substance cross freely in both directions
- B. blocks all substances from ever crossing
- C. allows some substances to cross while controlling or blocking others ✅
- D. only allows large proteins to cross
Feedback: Selectively (semi-) permeable means the membrane is a controlled border — some things cross freely (small nonpolar molecules, water slowly), while others (ions, large/polar molecules) are controlled and need proteins. It is neither a wide-open sieve (A) nor a sealed wall (B).

Answer key (quick reference)

Quality gate (self-checked): each single-answer item has exactly one correct option; the multiple-answer item (Q7) lists the three passive processes (A, B, C) and requires the two energy-using distractors (D active, E exocytosis) to be left unselected; the matching item pairs four organelles to four distinct functions, every pairing verified against standard cell biology (nucleus→DNA, ribosome→protein synthesis, lysosome→digestion, mitochondrion→ATP). Every transport classification (passive vs. active), the osmosis direction (toward higher solute), and the Na⁺/K⁺ pump ratio (3 Na⁺ out, 2 K⁺ in) are verified. Anatomy-accuracy gate: PASS. The quantitative items (Q4, Q8, Q9) were pre-computed and independently re-verified with a Python check (cell ≈ 300 mOsm: 100 mOsm → hypotonic → swell; 500 mOsm → hypertonic → shrink/water out; 300 mOsm → isotonic → no change), engineered to clean values. Quantitative gate: PASS.

Item-bank entries (for variants + the midterm/final)

All ten items are tagged course=BIOL2301 · week=3 · objective=2 · topic=cell-structure-membrane-transport and deposited in Item Bank: Week 3 — Cells & Membrane Transport. The midterm (Week 8) and the per-term variant updates draw fresh items from this bank. (Tags: q1 membrane-bilayer, q2 organelle-function-match, q3 osmosis, q4 hypotonic-swell, q5 active-vs-passive, q6 na-k-pump, q7 passive-processes, q8 hypertonic-misconception, q9 water-direction, q10 selective-permeability.)

Canvas placement block

canvas_object   = Quizzes::Quiz
title           = "Week 3 Quiz — Cell Structure, Function & Membrane Transport"
assignment_group = "Quizzes"
points_possible = 10
grading_type    = points
due_offset_days = 6        # 6 days after module start
published       = true
shuffle_answers = true
provenance      = "~ Prof. Navarro's edition · Fall 2026 · built with thecoursemaker.com"