• 82 questions

AP Bio Cell Bio Practice Test

Unofficial multiple-choice practice for Unit 2 of AP Biology, Cells: organelles, cell size, membranes, transport and water balance.

What are ribosomes made of?

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Unofficial practice questions, not affiliated with the College Board. Bank checked October 11, 2026.

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All 82 questions

Topic 2.1: Organelles 22

  • A cell makes a digestive enzyme that it will secrete. Where are the ribosomes that make it? Kimball, Biology (open textbook on LibreTexts), section 3.4, "Ribosomes"; course topic 2.1
  • A cell makes an enzyme of glycolysis, which works in the cytosol. Which ribosomes make it? Kimball, Biology (open textbook on LibreTexts), section 3.4, "Ribosomes"; course topic 2.1
  • A mitochondrion that has stopped working properly is wrapped in a membrane inside the cell. Where is it sent to be broken down? Kimball, Biology (open textbook on LibreTexts), section 3.8, "Lysosomes and Peroxisomes"; course topic 2.1
  • A protein bound for secretion is made on the rough ER. Into which space does it pass as it is made? Kimball, Biology (open textbook on LibreTexts), section 3.5, "Endoplasmic Reticulum"; course topic 2.1
  • A protein is made for secretion. Which path does it take through the cell? Kimball, Biology (open textbook on LibreTexts), section 3.4, "Ribosomes"; course topic 2.1
  • Among other jobs, what does the large central vacuole of a plant cell help maintain? Kimball, Biology (open textbook on LibreTexts), section 3.16, "Plant Cells"; course topic 2.1
Show all 82 questions (76 more)

Topic 2.1: Organelles, continued

  • Cells of the adrenal cortex secrete steroid hormones. Which organelle is especially prominent in them? Kimball, Biology (open textbook on LibreTexts), section 3.5, "Endoplasmic Reticulum"; course topic 2.1
  • How do the vacuoles of animal cells and plant cells differ? National Human Genome Research Institute, Talking Glossary, "Vacuole"; course topic 2.1
  • How many types of membrane make up a chloroplast, by the textbook? Kimball, Biology (open textbook on LibreTexts), section 3.17, "Chloroplasts"; course topic 2.1
  • In an electron micrograph, what does the Golgi apparatus look like? Scitable by Nature Education, "Endoplasmic Reticulum, Golgi Apparatus, and Lysosomes"; course topic 2.1
  • The inside of a lysosome is kept near pH 5, far more acid than the cytosol. What does the acid suit? Kimball, Biology (open textbook on LibreTexts), section 3.8, "Lysosomes and Peroxisomes"; course topic 2.1
  • Lysosomal enzymes work best near pH 5, and the cytosol is near pH 7.2. How does this difference protect the cell? Kimball, Biology (open textbook on LibreTexts), section 3.8, "Lysosomes and Peroxisomes"; course topic 2.1
  • The membranes of the endoplasmic reticulum are continuous with which other membrane? Kimball, Biology (open textbook on LibreTexts), section 3.5, "Endoplasmic Reticulum"; course topic 2.1
  • Ribosomes are found in the cells of every form of life. What does the course description say this reflects? College Board, AP Biology Course and Exam Description, essential knowledge 2.1.A.1; course topic 2.1
  • Vesicles budding from the ER carry new proteins to the Golgi. Where do they fuse? Scitable by Nature Education, "Endoplasmic Reticulum, Golgi Apparatus, and Lysosomes"; course topic 2.1
  • What are ribosomes made of? National Human Genome Research Institute, Talking Glossary, "Ribosome"; course topic 2.1
  • What is one fold of the inner mitochondrial membrane called? Wikipedia, "Crista"; course topic 2.1
  • What is the major processing activity of the Golgi apparatus? Kimball, Biology (open textbook on LibreTexts), section 3.6, "Golgi Apparatus"; course topic 2.1
  • Which cell would you expect to have the most rough ER? Kimball, Biology (open textbook on LibreTexts), section 3.5, "Endoplasmic Reticulum"; course topic 2.1
  • Which of these is NOT part of the endomembrane system as the course description lists it? College Board, AP Biology Course and Exam Description, essential knowledge 2.1.A.2; course topic 2.1
  • Which organelle manufactures lysosomes? Kimball, Biology (open textbook on LibreTexts), section 3.8, "Lysosomes and Peroxisomes"; course topic 2.1
  • Why is a mitochondrion's inner membrane folded? Wikipedia, "Mitochondrion"; course topic 2.1

Topic 2.2: Cell size 8

  • A cell is a cube with edges of 2 micrometers. Work out its surface area divided by its volume. College Board, AP Biology Course and Exam Description, essential knowledge 2.2.A.1; course topic 2.2
  • A mouse and an elephant stand in the same cold air. Which loses heat faster for each gram of body, and why? College Board, AP Biology Course and Exam Description, essential knowledge 2.2.A.2; course topic 2.2
  • The cells that line the gut have a plasma membrane thrown into many folds. What do the folds do? College Board, AP Biology Course and Exam Description, essential knowledge 2.2.A.2; course topic 2.2
  • Eight cube-shaped cells, each with edges of 1 micrometer, hold the same total volume as one cube with edges of 2 micrometers. How do the total surface areas compare? College Board, AP Biology Course and Exam Description, essential knowledge 2.2.A.2; course topic 2.2
  • How does metabolic rate for each unit of body mass usually change with the size of an organism? College Board, AP Biology Course and Exam Description, essential knowledge 2.2.A.2; course topic 2.2
  • Two cells each hold 1,000 cubic micrometers. One is a cube 10 micrometers on a side; the other is a flat slab of 100 by 10 by 1 micrometers. Which has more surface, and how much? College Board, AP Biology Course and Exam Description, essential knowledge 2.2.A.1; course topic 2.2
  • Two spherical cells have radii of 1 micrometer and 3 micrometers. How do their ratios of surface area to volume compare? College Board, AP Biology Course and Exam Description, essential knowledge 2.2.A.1; course topic 2.2
  • Why are most cells small, in terms of exchange with their surroundings? College Board, AP Biology Course and Exam Description, essential knowledge 2.2.A.2; course topic 2.2

Topics 2.3 and 2.4: Membranes and permeability 13

  • A membrane protein stays in one region of the cell surface and does not drift through the bilayer. Which reason does the textbook give for such limits? Kimball, Biology (open textbook on LibreTexts), section 3.2, "Cell Membranes"; course topic 2.3
  • A phospholipid has a hydrophobic hydrocarbon tail and a hydrophilic polar head. What is such a molecule called? Kimball, Biology (open textbook on LibreTexts), section 3.2, "Cell Membranes"; course topic 2.3
  • A transmembrane protein crosses the lipid bilayer. Which amino acids make up the part that lies within the bilayer? Kimball, Biology (open textbook on LibreTexts), section 3.2, "Cell Membranes"; course topic 2.3
  • By the course description, which parts of the plasma membrane can move around within it? College Board, AP Biology Course and Exam Description, essential knowledge 2.3.B.1; course topic 2.3
  • In the fluid mosaic model of the membrane, what is embedded in the lipid bilayer? Wikipedia, "Fluid mosaic model"; course topic 2.3
  • Parts of membrane proteins that project into the watery surroundings of the cell usually carry sugar residues. What are such proteins called? Kimball, Biology (open textbook on LibreTexts), section 3.2, "Cell Membranes"; course topic 2.3
  • The plasma membrane has water on both of its sides. How do its phospholipids arrange themselves? Kimball, Biology (open textbook on LibreTexts), section 3.2, "Cell Membranes"; course topic 2.3
  • What makes the plasma membrane selectively permeable, by the course description? College Board, AP Biology Course and Exam Description, essential knowledge 2.4.A.1; course topic 2.4
  • Which groups of organisms have cell walls, according to the course description? College Board, AP Biology Course and Exam Description, essential knowledge 2.4.B.1; course topic 2.4
  • Which material forms the stiff fibrils of a plant's cell wall, and what surrounds them? Kimball, Biology (open textbook on LibreTexts), section 3.16, "Plant Cells"; course topic 2.4
  • Which membrane proteins are loosely associated with the membrane, usually bound to the protruding parts of other proteins? Kimball, Biology (open textbook on LibreTexts), section 3.2, "Cell Membranes"; course topic 2.3
  • Which membranes contain no cholesterol, according to the Scitable article? Scitable by Nature Education, "Cell Membranes"; course topic 2.3
  • Which of these crosses a lipid bilayer freely, with no help from a protein? Kimball, Biology (open textbook on LibreTexts), section 3.23, "Diffusion, Active Transport and Membrane Channels"; course topic 2.4

Topics 2.5, 2.6 and 2.8: Transport 16

  • A chloride channel needs ATP to open, yet the textbook says ions passing through it are not actively transported. Why? Kimball, Biology (open textbook on LibreTexts), section 3.23, "Diffusion, Active Transport and Membrane Channels"; course topic 2.6
  • A transporter in the gut carries glucose into a cell against its gradient but does not split ATP itself. Where does the energy come from? Kimball, Biology (open textbook on LibreTexts), section 3.23, "Diffusion, Active Transport and Membrane Channels"; course topic 2.8
  • A vesicle carrying membrane proteins on its inner surface fuses with the plasma membrane. Where are those proteins afterward? Kimball, Biology (open textbook on LibreTexts), section 3.25, "Exocytosis"; course topic 2.5
  • A white blood cell engulfs a bacterium whole. What is this form of endocytosis called, and where does the bacterium end up? Kimball, Biology (open textbook on LibreTexts), section 3.24, "Endocytosis"; course topic 2.5
  • About how much of the energy made by the mitochondria of an animal cell goes to running the sodium-potassium pump, by the textbook? Kimball, Biology (open textbook on LibreTexts), section 3.23, "Diffusion, Active Transport and Membrane Channels"; course topic 2.8
  • An active cell can take in, by endocytosis, an amount of membrane equal to its whole plasma membrane in 30 minutes. What restores the membrane? Kimball, Biology (open textbook on LibreTexts), section 3.25, "Exocytosis"; course topic 2.5
  • An ion channel opens when a small signaling molecule binds to it. What kind of channel is it? Kimball, Biology (open textbook on LibreTexts), section 3.23, "Diffusion, Active Transport and Membrane Channels"; course topic 2.6
  • As an impulse passes down a neuron, a change in charge across the membrane opens sodium channels just ahead of it. What kind of channels are these? Kimball, Biology (open textbook on LibreTexts), section 3.23, "Diffusion, Active Transport and Membrane Channels"; course topic 2.6
  • Compared with the fluid outside it, how much potassium and sodium does the cytosol of an animal cell hold? Kimball, Biology (open textbook on LibreTexts), section 3.23, "Diffusion, Active Transport and Membrane Channels"; course topic 2.8
  • Endocytosis and exocytosis move material in opposite directions. What do both need, by the course description? College Board, AP Biology Course and Exam Description, essential knowledge 2.5.B.1; course topic 2.5
  • Glucose enters a red blood cell through a membrane protein, moving from the blood, where there is more of it, into the cell. No ATP is used. What is this? Kimball, Biology (open textbook on LibreTexts), section 3.23, "Diffusion, Active Transport and Membrane Channels"; course topic 2.6
  • How does the sodium-potassium pump help make the inside of a cell negative relative to the outside? Wikipedia, "Sodium-potassium pump"; course topic 2.8
  • In a symport pump, how do the driving ion and the pumped molecule move? Kimball, Biology (open textbook on LibreTexts), section 3.23, "Diffusion, Active Transport and Membrane Channels"; course topic 2.8
  • In endocytosis, what happens to the plasma membrane? Kimball, Biology (open textbook on LibreTexts), section 3.24, "Endocytosis"; course topic 2.5
  • What defines active transport? Kimball, Biology (open textbook on LibreTexts), section 3.23, "Diffusion, Active Transport and Membrane Channels"; course topic 2.5
  • What do aquaporins do? Wikipedia, "Aquaporin"; course topic 2.6

Topic 2.7: Tonicity and osmoregulation 13

  • A freshwater plant is put into sea water. Its cells shrink, and the plasma membrane pulls away from the cell wall. What is this called? Kimball, Biology (open textbook on LibreTexts), section 3.16, "Plant Cells"; course topic 2.7
  • A plant cell with a water potential of -6 bars sits in a solution whose water potential is -2 bars. Which way is the net movement of water? College Board, AP Biology Course and Exam Description, essential knowledge 2.7.A.1; course topic 2.7
  • A red blood cell bursts in pure water, and a plant cell in the same water does not. Why? Kimball, Biology (open textbook on LibreTexts), section 3.23, "Diffusion, Active Transport and Membrane Channels"; course topic 2.7
  • A single-celled protist lives in fresh water and gains water constantly by osmosis. Which organelle is involved in its osmoregulation? Wikipedia, "Contractile vacuole"; course topic 2.7
  • By the course description, in which direction does water move in terms of solute concentration? College Board, AP Biology Course and Exam Description, essential knowledge 2.7.B.2; course topic 2.7
  • The cytosol of an animal cell holds many dissolved organic molecules that are absent outside it. What keeps the cell from swelling with water? Kimball, Biology (open textbook on LibreTexts), section 3.23, "Diffusion, Active Transport and Membrane Channels"; course topic 2.7
  • How do dissolved solutes and added pressure each change the water potential of a solution? Wikipedia, "Water potential"; course topic 2.7
  • In terms of water potential, which way does water move when nothing restricts its flow? Wikipedia, "Water potential"; course topic 2.7
  • Red blood cells are put into sea water, which is about 3% salt. What happens to them? Kimball, Biology (open textbook on LibreTexts), section 3.23, "Diffusion, Active Transport and Membrane Channels"; course topic 2.7
  • Red blood cells placed in a 0.9% salt solution neither gain nor lose water. What is such a solution called? Kimball, Biology (open textbook on LibreTexts), section 3.23, "Diffusion, Active Transport and Membrane Channels"; course topic 2.7
  • Sea water is hypertonic to the body fluids of a bony fish such as the cod. How does the fish avoid fatal dehydration? Kimball, Biology (open textbook on LibreTexts), section 3.23, "Diffusion, Active Transport and Membrane Channels"; course topic 2.7
  • Sodium chloride separates into two ions in water, so its ionization constant is 2. How does the solute potential of 0.10 molar sodium chloride compare with that of 0.10 molar sucrose at the same temperature? College Board, AP Biology Course and Exam Description, essential knowledge 2.7.B.2; course topic 2.7
  • Using the solute potential equation, what is the solute potential of a 0.10 molar sucrose solution at 27 degrees Celsius? Sucrose does not ionize, so i is 1, and R is 0.0831 liter bars per mole kelvin. College Board, AP Biology Course and Exam Description, essential knowledge 2.7.B.2; course topic 2.7

Topics 2.9 and 2.10: Compartments and their origin 10

  • A chloroplast carries its own DNA. Does that DNA encode everything the chloroplast needs? Kimball, Biology (open textbook on LibreTexts), section 3.17, "Chloroplasts"; course topic 2.10
  • About how long ago did mitochondria arise by endosymbiosis, according to the Scitable article on their origin? Scitable by Nature Education, "The Origin of Mitochondria"; course topic 2.10
  • From which kind of organism do chloroplasts probably descend? Kimball, Biology (open textbook on LibreTexts), section 3.16, "Plant Cells"; course topic 2.10
  • How did mitochondria and chloroplasts originate, according to the course description? College Board, AP Biology Course and Exam Description, essential knowledge 2.10.A.1; course topic 2.10
  • How do internal membranes help a eukaryotic cell, by the course description? College Board, AP Biology Course and Exam Description, essential knowledge 2.9.B.1; course topic 2.9
  • Mitochondria have two membranes and their own genome, and they divide independently of the cell. What does Scitable say of such features? Scitable by Nature Education, "Mitochondria"; course topic 2.10
  • Prokaryotes lack membrane-bound organelles. What do bacteria have in their place for some tasks? Wikipedia, "Prokaryote"; course topic 2.10
  • Scientists sort cells into two categories by how they package genetic material. Which cell is a prokaryote? Scitable by Nature Education, "What Is a Cell?"; course topic 2.10
  • What are the specialized compartments called in which eukaryotic cells partition off different functions? Scitable by Nature Education, "Eukaryotic Cells"; course topic 2.9
  • Which pair of observations is among the evidence for the endosymbiotic origin of mitochondria and plastids? Wikipedia, "Symbiogenesis"; course topic 2.10

How this list was compiled: Our own questions, written to Unit 2 (Cells; topic 2.1 is Cell Structure and Function) of the College Board's AP Biology Course and Exam Description, effective fall 2025, https://apcentral.collegeboard.org/media/pdf/ap-biology-course-and-exam-description.pdf, read 2026-10-11. Each fact was read on 2026-10-11 in the public page named under its question: John W. Kimball's Biology (an open textbook on LibreTexts), Scitable by Nature Education, the Talking Glossary of the National Human Genome Research Institute, the essential knowledge statements of the course description, and Wikipedia. Licence: Own work. Short quotations from the public documents named under each question.

How it works

This AP Bio cell bio practice test has 82 questions of our own on Unit 2 of AP Biology: cell structure and function, cell size, membranes and transport. It is unofficial practice, and the College Board, which owns AP, has no part in it.

Read the full guide

What Unit 2 covers

The College Board's course description, effective fall 2025 and read October 11, 2026, names Unit 2 Cells; Cell Structure and Function is its topic 2.1. The bank follows all ten topics: organelles (22 questions), cell size (8), the plasma membrane and its permeability (13), transport across membranes (16), tonicity and osmoregulation (13), and compartments and their origin (10). How many questions a topic gets was our decision, since the description gives the topics no weights.

Sources you can open

Each answer links to the page it was checked on: John W. Kimball's open textbook Biology, a Scitable article from Nature Education, the glossary of the National Human Genome Research Institute, the course description, or a Wikipedia article.

  • For any organelle, name the structure, then what the structure lets it do: folds add surface, membranes keep reactions apart.
  • In a surface area and volume question, work out both numbers before you compare. Volume grows faster than surface.
  • Water moves toward the lower water potential. Solutes lower it, and pressure raises it.

Questions and answers

What is Unit 2 in AP Bio?

The course description in force calls it Cells. Its ten topics run from cell structure and function and cell size through membranes, transport and tonicity to the origins of cell compartments, in about 14 to 16 class periods.

How much of the AP Bio exam is Unit 2?

Between 10 and 13%, by the exam weighting in the College Board's course description. Unit 1, Chemistry of Life, carries 8 to 11%.

Is there an AP Biology practice test on cell organelles alone?

Yes, within this page. The first set, topic 2.1, has 22 questions: ribosomes, rough and smooth ER, the Golgi, mitochondria, lysosomes, vacuoles and chloroplasts, each asked by what its structure lets it do.

Is this an AP Bio cells and membranes practice test?

Yes. Forty-two of the questions are on membranes: the phospholipid bilayer and its proteins, what crosses it unaided, channels and pumps, endocytosis and exocytosis, tonicity and water potential.

Are these real AP Biology exam questions?

No. The College Board owns the real questions, and none appears here even in other words. Every question of this AP Biology practice test on cells was written for the page from the Unit 2 topic list.

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