Practice questions · Topic 2.1

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

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 tells you what a wrong choice assumed. 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 your answer in full sentences as you would in the test, 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. A: stiff outer layer; B: thin layer inside it; C: region where a DNA stain collects; D: one of the small dots throughout the cell.

The drawing shows a cell 3 μm long from a pond. Four parts are lettered. A is a stiff layer at the very outside; B is a thin layer just inside it; C is a region where a DNA stain collects, with no membrane around it; D marks one of the many small dots throughout the cell. A student labels C "the nucleus".

Which statement corrects the student's label?

A. C is a vacuole, a membrane sac of stored water, and the cell is a plant cell B. C is the nucleus after all, a very small one with a very thin envelope C. C is a ribosome, the largest one in the cell, holding the cell's proteins D. C is the nucleoid, so the cell is prokaryotic

Question 4

A photograph of a liver cell 25 μm across, taken through a microscope, shows many structures scattered through the cytosol, each wrapped in its own membrane. The largest, 6 μm across, is bounded by a double membrane and stains for DNA.

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 largest is the nucleoid C. Membrane-bound organelles; the largest is the nucleus, in its nuclear envelope, holding the cell's DNA D. Vacuoles storing water; the largest is a vacuole full of DNA

Question 5

Two single-celled organisms are taken from the same pond water. Organism 1 is 60 μm long and has a nucleus, mitochondria and no cell wall. Organism 2 is 3 μm long and has a cell wall, ribosomes and its DNA in a region with no membrane around it.

How should the two be classified?

A. 1 is eukaryotic, a protist; 2 is prokaryotic B. Both are prokaryotic, since both are single cells C. Both are eukaryotic, since both have DNA D. 1 is prokaryotic, since it has no wall; 2 is eukaryotic, since it has one

Question 6

Rats are given a drug that their liver cells must break down. Within days, 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 the sugar chains it normally carries, 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.

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

A labeled phospholipid is made in the membrane of a cell's ER. Over the next 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 lettered. Part N is a large round body enclosed by a double membrane. Part R is a network of membrane sacs continuous with the membrane of N, with small dots on its outer surface. Part G is a stack of flattened membrane sacs. Part V is a small membrane sac near the plasma membrane. Part M 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 lettered.

(a) Identify part N and part R, and identify the dots on R. (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: N is the nucleus, enclosed by its nuclear envelope, a double membrane. R is the rough ER, a network of membrane sacs continuous with the nuclear envelope. The dots on R are ribosomes.

Check the box for each point your answer earns

N is the nucleus (in its nuclear envelope); R 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 R is called the Golgi complex.

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

(b) Describe what the dots on R do, and where the milk protein goes the moment it is made. (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 ribosomes join amino acids into the milk protein in the order set by a messenger RNA, a copy of the instructions carried from the DNA in N. As each protein is made it passes straight into the interior of the ER, a compartment separate from the cytosol, where it is folded.

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 never spends time in the cytosol; the ribosome passes it into the ER's interior.

(c) Describe what G does to the protein when it arrives from R. (1 point)

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

A full-credit answer: G, the Golgi complex, receives the protein in vesicles that bud from the ER. It finishes the protein and modifies it chemically, for example by attaching carbohydrate chains, and then packages it 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 "G makes the protein".

Common slip: Saying G makes the protein. Ribosomes on R make it; G receives, modifies and packages it.

(d) Explain how the protein gets from V 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 V and the plasma membrane for the protein to end up outside the cell?

A full-credit answer: V moves to the plasma membrane and fuses with it, its membrane becoming part of the plasma membrane, so the milk protein inside it 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.

Check the box for each point your answer earns

vesicle V 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 the same part M. Predict which lettered 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 R and G, and fewer vesicles like V, because those are the parts a cell uses to make, finish, package and ship protein for export, and this cell exports very little. It keeps M, the mitochondria, because every cell needs ATP whatever its job, and it keeps N because every cell needs its DNA.

Check the box for each point your answer earns

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

Accept: R and G named with the link to protein export, with or without V. 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 M. The point is earned by tying R and G to protein export and M 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. A cell from the growing tip of a root, which divides often and builds new protein quickly, 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 a double membrane: a smooth outer membrane and a highly folded inner membrane that divide the inside into compartments where aerobic cellular respiration, the oxygen-using breakdown of glucose, takes place. The folds give the inner membrane a large surface, so the reactions that make ATP have more membrane to run on and ATP is made more efficiently.

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 runs; 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 run 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 the site of photosynthesis, the light-driven making of sugar from carbon dioxide and water. A leaf cell is in the light and makes sugar, so it has chloroplasts; a root cell is underground with no light, so it has none and lives on sugar sent from the leaves. Both cells need ATP, made by aerobic cellular respiration in mitochondria, so both 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 runs 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) Predict which of the two cells has more rough ER and Golgi complex, and justify your prediction. (1 point)

A full-credit answer: The root-tip cell has more rough ER and Golgi complex. It divides often and builds new protein quickly; ribosomes on the rough ER make that protein and pass it into the ER to be folded, and the Golgi complex finishes and packages it. A cell that makes a great deal of protein is full of the organelles that make and ship it.

Check the box for each point your answer earns

the root-tip cell, because it builds new protein quickly for division and growth; rough ER makes and folds protein and the Golgi complex finishes and packages it, so a cell that makes much protein has much of both.

Accept: the root-tip cell with rough ER and Golgi linked to protein-making. Do not award the point for "the root cell is more active" with no link to protein.

Common slip: Choosing the leaf cell because it is doing photosynthesis. Photosynthesis is the chloroplast's work; rough ER and Golgi go with making protein.

(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 it fills, it presses the cytosol against the cell wall, and that push against the wall, turgor pressure, is what keeps the mature cell firm; a plant cell has one large central vacuole where an animal cell has many small ones.

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 wall keeps the cell firm".

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

Free-response score: 0 of 4

Multiple choice checked: 0 of 10 correct.

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