Practice questions · Topic 2.1

Unit 2 · Practice for the Topic 2.1 end-of-topic test

You’ve gone through everything in this topic. The summary video below recaps it all, so you’re ready for the questions.

Watch first: Topic 2.1 summary, part 1: two kinds of cell, and the network inside one

A bacterium and an onion skin cell to one scale: what every cell has, where the DNA sits, and the ER running out from the nuclear envelope.

Watch next: Topic 2.1 summary, part 2: what the organelles do

One protein’s route through the pancreas cell, the Golgi complex, lysosomes and the seven members of the endomembrane system; the mitochondrion and the chloroplast cut open; each cell full of the organelle that does its job.

These are practice questions in the shape of the topic test. Work through them before you take the test; every question tells you what it wanted.

These practice questions have the shape of the Topic 2.1 test. Answer every question. For each multiple-choice question, pick one option and press Check; the feedback gives the reasoning. For the first free-response question, you work through one scenario in small steps, and each step offers a hint if you want one. For the second, write one short sentence for each step of your reasoning, each on its own line, and make every link clear (so, because, therefore). That is what the exam’s ‘paragraph form’ means for you: linked sentences, not bullet points. Then open the scoring guide and mark your own work against it.

Question 1

An antibiotic binds to the ribosomes of a bacterium. Within minutes the bacterium stops making new proteins, although its DNA and its mRNA molecules are intact and its supply of amino acids is normal.

Why does protein-making stop?

A. Ribosomes make the mRNA, so no instructions reach the rest of the cell B. Ribosomes join amino acids into proteins in the order an mRNA sets, and that is blocked C. Ribosomes store the amino acids, which are now locked away inside them D. Ribosomes hold the cell's DNA, so the instructions for every protein are lost

Question 2

Cells from a mushroom, a fern, a trout and a soil bacterium are examined. Every one of them contains ribosomes built from rRNA and protein, with the same basic shape and the same job.

What is this shared feature evidence of?

A. Common ancestry: the four kinds of organism descend from shared ancestors B. Ribosomes spreading from one kind of organism to another by infection C. Each kind of organism building the same particle by chance D. The four kinds of organism having identical DNA

Question 3

A pond cell 3 μm long. W: stiff outer layer; X: thin layer inside it; Y: region where a DNA stain collects; Z: one of the small dots throughout the cell.

The drawing shows a cell 3 μm long from a pond. Y is a region where a DNA stain collects, with no membrane around it. A student labels Y “the nucleus”.

Which statement corrects the student's label?

A. Y is a vacuole, a membrane sac of stored water, and the cell is a plant cell B. Y is the nucleus after all, a very small one with a very thin envelope C. Y is a nucleus whose envelope the stain has dissolved D. Y is the nucleoid, so the cell is prokaryotic

Question 4

A liver cell 25 μm across, as seen through a microscope; the shading in the largest structure is where a DNA stain collects.

The drawing shows a liver cell 25 μm across: many structures scattered through the cytosol, each wrapped in its own membrane. The largest, 6 μm across, is bounded by a double membrane and is shaded where a DNA stain collects.

What are the wrapped structures, and what is the largest one?

A. Prokaryotic cells living inside the liver cell; the largest is their host's nucleoid B. Ribosomes, the particles that make protein; the largest is the nucleoid C. Membrane-bound organelles; the largest is the nucleus, holding the cell's DNA D. Vacuoles storing water; the largest is a vacuole that has filled with DNA

Question 5

Two single-celled organisms come from the same pond water. Cell A is 60 μm long and has a nucleus, mitochondria and no cell wall. Cell B is 3 μm long and has a cell wall, ribosomes and its DNA in a region with no membrane around it.

Which of the following classifies the two cells, and why?

A. Cell A is eukaryotic and cell B is prokaryotic, since only cell A keeps its DNA inside a nucleus B. Both cells are prokaryotic, since both are single cells C. Both cells are eukaryotic, since both have DNA D. Cell A is prokaryotic and cell B is eukaryotic, since only cell B has a cell wall

Question 6

Scientists give rats a drug that the rats’ liver cells must break down. Within days, the part of the liver cells’ endoplasmic reticulum that carries no ribosomes has doubled in area, and the drug disappears from the rats’ blood twice as fast.

What is this part of the ER, and what does its growth do for the cell?

A. Rough ER; more of it makes more protein for export B. Smooth ER; more of it breaks down harmful molecules faster C. Rough ER; more of it breaks down harmful molecules faster D. Smooth ER; more of it makes more protein for export

Question 7

A drug destroys the stack of flattened membrane sacs in a gland cell. The cell's ribosomes on the rough ER keep making a protein for export, and the protein still folds in the ER's interior. But the protein that reaches the outside now lacks sugar chains that are normally added to it after it leaves the ER, and much of it is delivered to the wrong places in the cell.

What does this show the stack of sacs normally does?

A. Makes the protein, joining its amino acids in order on the sacs' surfaces B. Folds the protein for the first time, before it reaches the ER C. Digests the protein once the cell has finished using it D. Attaches the sugar chains and packages the protein into addressed vesicles

Question 8

A cell at the back of the eye takes in worn-out fragments shed by its neighbors every day and normally digests them. In a patient, the fragments pile up undigested inside membrane-enclosed sacs in these cells, and the interior of those sacs is found to be far less acidic than normal. The cell still takes the fragments in.

What has gone wrong?

A. The cell has stopped taking the fragments in from its neighbors B. The Golgi complex has stopped making the proteins the cell needs C. The lysosomes are too weakly acidic, so their digestive enzymes work slowly D. The mitochondria have stopped supplying the sacs with the ATP they need

Question 9

As a caterpillar changes into a moth inside its case, most of its larval muscle cells shrink, dismantle themselves and are cleared away on a fixed schedule. The cells are healthy and uninfected when this begins.

What is happening to the muscle cells, and which organelle takes part?

A. Osmotic lysis; the cells burst as water enters B. Apoptosis, programmed cell death; lysosomes take part in dismantling the cells C. Endocytosis; neighboring cells swallow the muscle cells whole D. Exocytosis; the cells release their contents and empty out

Question 10

Scientists label a phospholipid in the membrane of a cell’s ER and follow the label for an hour. The label appears in the membranes of the Golgi complex, then in the membranes of small sacs near the cell surface, and finally in the plasma membrane itself.

What carried the labeled lipid from one membrane to the next, and what does the result show about these membranes?

A. Vesicles that budded from one membrane and fused with the next; one endomembrane system B. The cytosol, through which the lipid diffused on its own; separate, unconnected membranes C. Ribosomes, which carried the lipid along with them; the membranes are all rough ER D. Mitochondria, which absorbed and released the lipid; the membranes are all mitochondrial

How to tackle the free-response questions. Read the verb first: describe asks what you see or know; explain asks why or how, so name the mechanism; predict asks what will happen and why; justify asks for the evidence that supports a claim. Each point is earned by one idea, stated in a sentence that names the thing and the mechanism. Extra words earn nothing; a wrong extra can lose the point. If there is a figure or table, use what it shows. When you finish, check the box for each point your answer earns and compare your sentences with the full-credit answer.

Free response 1 · Analyze Model or Visual Representation · 5 points

The model shows a cell from a mammary gland that makes a milk protein and releases it into the milk duct. Five parts are numbered. The part marked 1 is a large round body enclosed by a double membrane. The part marked 2 is a network of membrane sacs continuous with the membrane of 1, with small dots on its outer surface. The part marked 3 is a stack of flattened membrane sacs. The part marked 4 is a small membrane sac near the plasma membrane. The part marked 5 is an oval body with a smooth outer membrane and a highly folded inner membrane.

A mammary gland cell that exports a milk protein, with five parts numbered.

(a) Identify the parts marked 1 and 2, and identify the dots on the part marked 2. (1 point)

Hint: A double membrane around a large round body, and a network continuous with it carrying particles on its surface, are two of the parts every cell that exports protein is full of.

A full-credit answer: The part marked 1 is the nucleus, enclosed by its nuclear envelope, a double membrane.
The part marked 2 is the rough ER, a network of membrane sacs continuous with the nuclear envelope.
The dots on the rough ER are ribosomes.

Check the box for each point your answer earns

1 is the nucleus (in its nuclear envelope); 2 is the rough ER (rough endoplasmic reticulum); the dots are ribosomes. All three identifications are needed for the point.

Accept: "nucleus" without naming the envelope. Do not award the point for two of the three, or if the dots are called vesicles or 2 is called the Golgi complex.

Common slip: Naming 1 and 2 but leaving the dots unnamed, or calling 2 the Golgi complex. All three identifications are needed; the Golgi is a separate stack of flattened sacs (3), and a network continuous with the nuclear envelope and studded with ribosomes is the rough ER.

(b) Describe what the dots on the part marked 2 do, and where the milk protein goes the moment a dot finishes making it. (1 point)

Hint: What do the dots build, and from which building blocks? Look at where the dots sit in the model: what lies directly beneath them?

A full-credit answer: The dots are ribosomes.
The ribosomes join amino acids into the milk protein in the order set by a messenger RNA.
The messenger RNA is a copy of instructions carried from the DNA in the nucleus.
As each protein is made, the ribosome passes it straight into the interior of the ER.
The ER’s interior is a compartment separate from the cytosol.
The protein is folded there.

Check the box for each point your answer earns

the ribosomes join amino acids into the protein in the order an mRNA sets, and the protein passes straight into the interior of the ER, a compartment separate from the cytosol, where it is folded.

Accept: "ribosomes make the protein and pass it into the ER". Do not award the point if the protein is placed in the cytosol.

Common slip: Sending the finished protein into the cytosol. A protein for export is never loose in the cytosol. The ribosome passes the protein into the ER’s interior.

(c) Describe what the part marked 3 does to the protein when it arrives from the part marked 2. (1 point)

Hint: Three verbs: what 3 takes in, what it changes, and what it sends out, and in what.

A full-credit answer: The part marked 3 is the Golgi complex.
The Golgi complex receives the protein in vesicles that bud from the ER.
The Golgi complex then finishes the protein and changes it chemically, for example by attaching carbohydrate chains.
Finally the Golgi complex packages the protein into vesicles addressed to the plasma membrane.

Check the box for each point your answer earns

the Golgi complex receives the protein in vesicles from the ER, finishes and chemically modifies it (for example by glycosylation, attaching carbohydrate chains), and packages it into vesicles addressed to its destination, here the plasma membrane.

Accept: any two of receive / modify / package, stated for this protein. Do not award the point for "3 makes the protein".

Common slip: Saying the Golgi complex makes the protein. Ribosomes on the rough ER make it; the Golgi complex receives, modifies and packages it.

(d) Explain how the protein gets from the part marked 4 to the milk duct, naming the process. (1 point)

Hint: Can a large polar protein cross a membrane on its own? If not, what has to happen between the part marked 4 and the plasma membrane for the protein to end up outside the cell?

A full-credit answer: The part marked 4 is a vesicle.
The vesicle moves to the plasma membrane.
The vesicle fuses with the plasma membrane, and the vesicle’s membrane becomes part of the plasma membrane.
So the milk protein inside the vesicle is released outside the cell, into the duct.
This is exocytosis.
A protein is far too large and polar to cross the membrane on its own, so the protein can leave only this way.

Check the box for each point your answer earns

the part marked 4, a vesicle, moves to the plasma membrane and fuses with it, so its contents are released outside the cell into the duct; this is exocytosis (and the vesicle's membrane becomes part of the plasma membrane).

Accept: the fusion and release described without the word exocytosis. Do not award the point for the protein passing through the plasma membrane on its own.

Common slip: Having the protein pass through the plasma membrane by itself. It leaves only when the vesicle fuses with the membrane and opens outward.

(e) A cell lining a blood vessel exports very little protein but has just as many of the part marked 5. Predict which numbered parts it has far less of than the mammary cell, and justify your prediction. (1 point)

Hint: Ask what each part does for a cell whose job is exporting protein, and what every cell needs whatever its job.

A full-credit answer: The blood-vessel cell has far less rough ER and far less Golgi complex, and fewer vesicles.
Those parts make, finish, package and ship protein for export.
The blood-vessel cell exports very little protein, so it needs little of them.
It keeps its mitochondria, because every cell needs ATP whatever its job.
It keeps its nucleus, because every cell needs its DNA.

Check the box for each point your answer earns

far less rough ER (which makes and folds protein for export) and Golgi complex (which finishes and packages it), and fewer vesicles, because it exports little protein; it keeps its mitochondria because every cell needs ATP.

Accept: the numbers 2, 3 and 4 in place of the names; the rough ER and the Golgi complex with the link to protein export, with or without the vesicles. Do not award the point for parts named with no link to the cell's job.

Common slip: Naming parts with no link to the job, or dropping the mitochondria. The point is earned by tying the rough ER and the Golgi complex to protein export and the mitochondria to a need every cell has.

Free-response score: 0 of 5

Free response 2 · Conceptual Analysis · 4 points

Two cells from one plant are compared. A leaf cell contains chloroplasts, mitochondria and one large central vacuole. The leaf cell is fully grown and no longer divides. The leaf cell exports almost no protein. A cell from the growing tip of a root divides about once a day. The root-tip cell contains mitochondria but no chloroplasts, and holds many small vacuoles that later fuse into one large central vacuole as the cell matures.

(a) Describe the structure of a mitochondrion and what its folded inner membrane does for the cell. (1 point)

A full-credit answer: A mitochondrion has two membranes.
The outer membrane is smooth.
The inner membrane is folded again and again.
The two membranes divide the inside into compartments.
Aerobic cellular respiration, the oxygen-using breakdown of glucose, happens in those compartments.
The folds give the inner membrane a large surface.
So more of the reactions that make ATP happen at once, and ATP is made faster.

Check the box for each point your answer earns

a double membrane, a smooth outer membrane and a highly folded inner membrane, dividing the inside into compartments where aerobic cellular respiration happens; the folds give the inner membrane a large surface, so ATP can be made more efficiently.

Accept: "two membranes, the inner one folded; more surface for the reactions that make ATP".

Common slip: Saying mitochondria 'make energy'. They transfer energy from glucose into ATP; the folds matter because those reactions happen on the inner membrane's surface.

(b) Explain why the leaf cell has both chloroplasts and mitochondria while the root cell has mitochondria only. (1 point)

A full-credit answer: Chloroplasts are where photosynthesis happens: the light-driven making of sugar from carbon dioxide and water.
A leaf cell is in the light, so it makes sugar, so it has chloroplasts.
A root cell is underground with no light, so it cannot make sugar, so it has no chloroplasts.
The root cell lives on sugar sent from the leaves.
Both cells need ATP.
Aerobic cellular respiration in mitochondria makes ATP.
So both cells have mitochondria.

Check the box for each point your answer earns

chloroplasts are the site of photosynthesis, the light-driven making of sugar from carbon dioxide and water, which a leaf cell in the light can do and a root cell underground cannot; every cell, leaf or root, needs ATP from aerobic cellular respiration, which happens in mitochondria, so both cells have them.

Accept: "the leaf catches light and makes sugar; both cells break sugar down for ATP".

Common slip: Saying plant cells have chloroplasts instead of mitochondria. The leaf cell has both; chloroplasts make the sugar, mitochondria break it down for ATP.

(c) Make a claim about which of the two cells has more rough ER and Golgi complex, and support your claim with evidence from the descriptions of the two cells. (1 point)

Hint: Ask what rough ER and Golgi complex do for a cell. Then ask which of the two cells needs more of that done.

A full-credit answer: The root-tip cell has more rough ER and more Golgi complex.
The root-tip cell divides about once a day.
So it must build new proteins and new membrane for each daughter cell.
Rough ER makes and folds those proteins.
The Golgi complex finishes and packages them.
Therefore the cell that builds new parts every day is full of both.

Check the box for each point your answer earns

the claim that the root-tip cell has more rough ER and Golgi complex, supported by evidence AND reasoning: it divides about once a day (evidence), so it must build new proteins and new membrane for each daughter cell, and rough ER makes and folds protein while the Golgi complex finishes and packages it (reasoning).

Do not award the point for the claim alone, or for the leaf cell: the stimulus says it exports almost no protein and no longer divides.

Do not award the point for "the root cell is more active" or "the leaf cell does photosynthesis" with no link to protein for new cell parts.

Common slip: Making the claim without the evidence, or naming the evidence (daily division) without linking it to protein for new cell parts. The point needs the claim, the evidence and the link.

(d) The root cell's small vacuoles fuse into one large central vacuole as the cell matures. Explain what that central vacuole does for the mature cell. (1 point)

A full-credit answer: The central vacuole stores water and nutrients.
As the vacuole fills, it presses the cytosol against the cell wall.
That push against the cell wall is turgor pressure.
Turgor pressure keeps the mature cell firm.
A plant cell has one large central vacuole; an animal cell has many small vacuoles.

Check the box for each point your answer earns

the central vacuole stores water and nutrients and, as it fills, presses the cytosol against the cell wall, maintaining turgor pressure so the cell is firm.

Accept: "stores water; its pressure against the cell wall keeps the cell firm".

Common slip: Describing the vacuole as a store only. Its filling is what presses the cytosol against the cell wall and gives the cell its firmness.

Free-response score: 0 of 4

Multiple choice checked: 0 of 10 correct.

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