Week 4 — Quiz (auto-graded) · Cell Structure & Function

Course: Introduction to Biology — General Biology I (BIOL 101) · Silver Oak University (fictional sample) · Prof. Castellano
Objective tested: Objective 3 — prokaryotic vs. eukaryotic cells; organelle functions; the plasma membrane & transport (diffusion, osmosis, passive vs. active); tonicity; surface-area-to-volume.
Points: 10 (1 each) · Assignment group: Quizzes (10% of grade) · Due: end of Module 4.

This is the human-readable quiz with its vetted answer key and feedback. The import-ready Classic QTI is in F-quiz-week-04-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 4 misconceptions named in the lecture outline (plant-cell mitochondria, osmosis-moves-solute, reversed tonicity, passive/active confusion, un-simplified SA:V).

Questions, key, and feedback

Q1 (MC). What is the single feature that distinguishes a eukaryotic cell from a prokaryotic cell?
- A. A plasma membrane
- B. Ribosomes
- C. A true, membrane-bound nucleus ✅
- D. DNA
Feedback: The dividing line is the nucleus. Eukaryotes wrap their DNA inside a membrane-bound nucleus; prokaryotes leave it loose in the nucleoid. (A, B, and D are found in both kinds of cell, so none can be the distinguishing feature.)

Q2 (Multiple answer — select all that apply). Which of the following are found in ALL cells — both prokaryotic and eukaryotic?
- A. A plasma membrane ✅
- B. A membrane-bound nucleus
- C. Ribosomes ✅
- D. DNA ✅
- E. Chloroplasts
Feedback: Every cell shares a plasma membrane, cytoplasm, DNA, and ribosomes (A, C, D). A nucleus (B) is eukaryote-only, and chloroplasts (E) are found only in plants and some protists — not in all cells.

Q3 (Matching). Match each organelle to its primary function.
| Organelle | Correct function |
|---|---|
| Nucleus | Holds the DNA and directs protein synthesis (control center) |
| Mitochondrion | Makes ATP through cellular respiration (power plant) |
| Ribosome | Builds proteins |
| Lysosome | Digests waste and worn-out cell parts |
Feedback: Structure → function: the nucleus directs, the mitochondrion powers (ATP), the ribosome builds proteins, and the lysosome is the recycling/garbage crew. (Don't confuse the ribosome — which builds proteins — with the mitochondrion, which supplies the energy.)

Q4 (True / False). "Plant cells do NOT contain mitochondria, because they carry out photosynthesis in chloroplasts instead."
- True
- False ✅
Feedback: False. Plant cells have both. Chloroplasts capture light to make sugar; mitochondria still burn that sugar for ATP, day and night. Photosynthesis and cellular respiration are different jobs, and plants do both.

Q5 (MC). Osmosis is best defined as the movement of —
- A. dissolved salt across a membrane, toward the side with less salt
- B. water across a membrane, toward the side with more dissolved solute ✅
- C. any molecule against its concentration gradient, using ATP
- D. proteins from the ribosome to the Golgi apparatus
Feedback: Osmosis moves WATER, not the solute — water crosses the membrane toward the saltier (higher-solute) side. (A describes solute movement; C describes active transport; D is the protein-secretion pathway.)

Q6 (MC). A red blood cell is placed in a HYPERTONIC solution (more dissolved solute outside the cell than inside). What happens?
- A. Water moves into the cell and it swells (may burst)
- B. Water moves out of the cell and it shrinks (shrivels) ✅
- C. Salt moves into the cell and its size does not change
- D. There is no net movement of anything
Feedback: In a hypertonic environment there's more solute outside, so by osmosis water leaves the cell and it shrinks — the same reason salt wilts lettuce and dehydrates a slug. (Option A is what happens in a hypotonic solution; the reference point is always inside the cell.)

Q7 (MC). Which statement correctly describes active transport?
- A. It moves substances down their concentration gradient and requires no energy
- B. It moves substances against their concentration gradient and requires ATP ✅
- C. It only moves water across the membrane
- D. It is another name for simple diffusion
Feedback: Active transport goes "uphill" — against the gradient (low → high) — so it costs ATP and uses a pump protein. Passive transport (A, D) is downhill and free; only osmosis is water-specific (C).

Q8 (MC). Model a cell as a cube with side length 2. Its surface area is 6 × 2² = 24 and its volume is 2³ = 8. What is its surface-area-to-volume ratio, simplified?
- A. 6:1
- B. 3:1 ✅
- C. 1:3
- D. 2:1
Feedback: 24 ÷ 8 = 3, so the ratio is 3:1. (6:1 is the ratio for a side-1 cube; 1:3 flips surface area and volume; 2:1 is the side-3 cube. Always keep surface area on top and simplify.)

Q9 (MC). As a cell grows larger (its volume increases), what happens to its surface-area-to-volume ratio?
- A. It increases
- B. It decreases ✅
- C. It stays exactly the same
- D. It first decreases, then increases
Feedback: It decreases. Volume grows faster than surface area, so SA:V falls (6.0 → 3.0 → 2.0 → 1.5 as a cube grows from side 1 to 4). That's the squeeze that forces cells to stay small, divide, or add folds/microvilli.

Q10 (MC). Four model cube-shaped cells have side lengths of 1, 2, 3, and 4. Which one has the HIGHEST surface-area-to-volume ratio?
- A. The cube with side 1 (ratio 6:1) ✅
- B. The cube with side 2 (ratio 3:1)
- C. The cube with side 3 (ratio 2:1)
- D. The cube with side 4 (ratio 1.5:1)
Feedback: The smallest cube has the highest SA:V. Using ratio = 6 ÷ s: side 1 → 6:1, side 2 → 3:1, side 3 → 2:1, side 4 → 1.5:1. Smaller cells service their volume most efficiently.

Answer key (quick reference)

Quality gate (self-checked): each single-answer item has exactly one correct option; the multiple-answer item lists all three shared features (A, C, D) and requires B and E to be left unselected; the matching item pairs four organelles to four distinct functions; no item asserts a fact outside the Week 4 course definitions. Quantitative gate: PASS — every numeric answer was independently re-derived in the scratchpad (cube side s: SA = 6s², V = s³, ratio = 6/s → side 1 = 6:1, side 2 = 3:1, side 3 = 2:1, side 4 = 1.5; SA:V strictly decreases as s grows; highest ratio = side 1 at 6:1). Q8 (3:1), Q9 (decreases), and Q10 (side 1 = 6:1) match the pre-computed values in week-specs.md exactly.

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

All ten items are tagged course=BIOL101 · week=4 · objective=3 · topic=cell-structure-function and deposited in Item Bank: Week 4 — Cell Structure & Function. The final (Week 16) and the per-term variant updates draw fresh items from this bank. (Tags: q1 prokaryote-eukaryote, q2 all-cells-share, q3 organelle-function-match, q4 plant-mitochondria, q5 osmosis-is-water, q6 tonicity-hypertonic, q7 active-transport, q8 sa-to-v-cube, q9 sa-v-decreases, q10 highest-sa-v.)

Canvas placement block

canvas_object   = Quizzes::Quiz
title           = "Week 4 Quiz — Cell Structure & Function"
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. Castellano's edition · Fall 2026 · built with thecoursemaker.com"