Cell Structure: Subcellular Components

Unit 2 · Topic 2.1 end-of-topic test

Suggested time: about 47 minutes. Answer everything, then press Submit the test to see the feedback and scoring guides.

Answer every question. For each multiple-choice question, pick one option. When you have answered every question, press Submit the test; the feedback then gives the reasoning for each. For the free-response questions, 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

A cell’s particles of RNA and protein join amino acids into a protein, in the order an mRNA sets.

What are the particles?

A. Pieces of the Golgi complex B. Pieces of rough ER C. Ribosomes D. Vesicles

Question 2

Every known kind of cell, from an archaeon in a hot spring to a cell in a whale, stores its inherited instructions in DNA. The DNA of every cell is built the same way: a double helix of the same four kinds of nucleotide.

What does a feature shared by every living thing suggest?

A. That all living things descend from shared ancestors B. That each kind of cell invented its own DNA, which happens to match the others C. That the environment forces every cell to build its DNA the same way D. That every living thing carries the same DNA

Question 3

A cell 2 μm long. X marks the region where a DNA stain collects; Y marks one of the small dots found throughout the cell.

The drawing shows a cell 2 μm long. Region X is where a DNA stain collects; no membrane separates it from the rest of the cell. The small dots marked Y are found throughout the cell. A stiff layer lies outside the plasma membrane.

What kind of cell is this, and what are X and Y?

A. Eukaryotic; X is the nucleus and Y are ribosomes B. Prokaryotic; X is the nucleoid and Y are ribosomes C. Prokaryotic; X is the nucleus and Y are vesicles D. Eukaryotic; X is a vacuole and Y are ribosomes

Question 4

A student writes: "A bacterium has no nucleus, so it has no DNA and cannot make its own proteins."

Which statement corrects the student?

A. The bacterium has DNA in a nucleus after all; the nucleus is just very small B. The bacterium has no DNA, but its ribosomes make proteins without instructions C. The bacterium has DNA, but with no nucleus it has no ribosomes either D. The bacterium has DNA in a nucleoid, and ribosomes that make its proteins

Question 5

A plant cell about 100 μm long, as seen under a microscope.

The drawing shows a plant cell about 100 μm long: one large round body that is stained dark by a dye that binds DNA, with several smaller bodies around it, each wrapped in its own membrane.

What is the dark round body, and what does it hold?

A. The nucleus, in its nuclear envelope; the cell's DNA B. The nucleoid; the cell's DNA, with no membrane around it C. The central vacuole; stored water D. A ribosome; the cell's proteins

Question 6

Four cells: Cell P, 2 μm long, has a cell wall and a nucleoid. Cell Q, 100 μm long, has a cell wall, a nucleus and chloroplasts. Cell R, a single-celled pond organism 150 μm long, has a nucleus and no cell wall. Cell S, 1 μm long, has a cell wall and a nucleoid.

Which of the cells are eukaryotic?

A. Q only B. R only C. Q and R D. P, Q, R and S

Question 7

Part of the network of branching membrane tubes that crowds the cell, one stretch of it joined to the nuclear envelope; the small dots sit on the tubes’ outer surfaces.

A cell that makes and exports a protein all day is crowded with the network of membrane tubes shown in the drawing. The network’s outer surface is studded with ribosomes, drawn as small dots.

What is this network, and what happens to a protein made by the ribosomes on it?

A. Rough ER; the protein is folded in the cytosol, on the outer surface B. Rough ER; the protein enters its interior and is folded there C. Golgi complex; the protein is made inside it and packaged D. Rough ER; the ER itself makes the protein, and the ribosomes store it

Question 8

Part of a cell's endoplasmic reticulum has no ribosomes on its surface.

What does the cell do in this part of the ER?

A. Makes proteins for export B. Digests worn-out parts of the cell C. Packages proteins into vesicles for delivery D. Makes new membrane lipids and breaks down harmful molecules

Question 9

In a gland cell, a protein for export is a plain chain of amino acids when it leaves the ribosomes on the rough ER. The same protein carries sugar chains when it leaves the cell. Between the ER and the plasma membrane, the protein passes through a stack of flattened membrane sacs.

What did the stack of flattened sacs do to the protein?

A. Added the sugar chains and packed it into vesicles B. Joined its amino acids together in order C. Stored it unchanged; the sugar chains were added at the plasma membrane D. Broke it into amino acids, which were rebuilt into a new protein

Question 10

In a patient, one digestive enzyme normally found inside lysosomes is missing. In the patient’s cells, worn-out parts of the cell that are normally broken down instead build up, whole, inside membrane-enclosed sacs.

What does this show about lysosomes?

A. They store the cell’s worn-out parts without breaking them down B. They make their own enzymes, on ribosomes inside them C. They digest the cell’s worn-out parts using the enzymes held inside them D. They carry the worn-out parts out of the cell by exocytosis

Question 11

In a developing embryo, far more nerve cells form than the body will keep. The surplus nerve cells then die in an orderly, controlled way, on schedule, as a normal part of development.

What is this process, and which organelle takes part in it?

A. Osmotic lysis; the cells swell and burst B. Apoptosis; lysosomes take part in dismantling the cells C. Endocytosis; neighboring cells engulf the surplus cells D. Exocytosis; the cells release their contents and shrink away

Question 12

A cell's endomembrane system is the set of membranes that work together to modify, package and transport proteins, lipids and polysaccharides within the cell.

Which list names only members of the endomembrane system?

A. ER, Golgi complex and mitochondria B. Ribosomes, ER and Golgi complex C. Chloroplasts, mitochondria and the nuclear envelope D. ER, Golgi complex, lysosomes and transport vesicles

Question 13

A cell in the stomach lining makes a digestive protein and exports it into the stomach.

In which order is the protein found, from where the ribosomes make it to where it leaves the cell?

A. Rough ER → vesicle → Golgi complex → vesicle → outside the cell B. Golgi complex → vesicle → rough ER → vesicle → outside the cell C. Rough ER → cytosol → plasma membrane → outside the cell D. Cytosol → straight through the plasma membrane → outside the cell

Question 14

The mitochondria in heart muscle have about 1.5 times as much folding of their inner membrane as the mitochondria in skin cells. Given the same oxygen and glucose, equal numbers of heart-muscle mitochondria make 180 units of ATP a minute; skin-cell mitochondria make 120.

Why do the heart-muscle mitochondria make ATP faster?

A. The folds store energy that is released as ATP when needed B. The folds enlarge the inner space where ATP builds up C. The folds give the inner membrane more surface on which ATP can be made D. The folds let oxygen and fuel cross the inner membrane freely

Question 15

A leaf has green patches, whose cells contain chloroplasts, and white patches, whose cells contain none. A student keeps the plant in the dark for two days to clear starch from the leaf. The student then gives the leaf water, carbon dioxide and light for 12 hours, and covers one green patch so that it stays dark. Iodine, which turns starch dark, then darkens only the uncovered green patches. The white patches and the covered green patch stay pale.

What do the results show?

A. Light makes any plant cell produce starch B. Chloroplasts make starch in the dark as well as in the light C. The white-patch cells made sugar too, but stored it as something other than starch D. Starch was made only where there were both light and chloroplasts

Question 16

A green alga is a single cell that lives in pond water. In daylight the cell gives off oxygen and builds up starch. Day and night, the cell also takes up some oxygen. The cell contains chloroplasts and mitochondria.

Which statement about this cell's organelles is right?

A. Its chloroplasts replace mitochondria, so it has no need of them B. Its chloroplasts carry out photosynthesis while its mitochondria carry out respiration C. Its chloroplasts carry out respiration and its mitochondria photosynthesis D. Its chloroplasts only store starch; its mitochondria make the oxygen

Question 17

A cook puts a limp celery stalk in pure water. An hour later the stalk is stiff again. In each of its cells the central vacuole has gained about 2,400 μm³ of water and the cytosol about 50 μm³.

What explains the stalk’s recovery?

A. The cytosol took in most of the water and swelled enough to firm the cell B. The firmness rose independently of the vacuole, which only stores materials C. The central vacuole took in most of the water and pressed the cytosol against the cell wall D. The vacuole released water into the cytosol, so both swelled

Question 18

Three cells are cut open. Cell 1 lines the gut and releases large amounts of a digestive protein into the gut. Cell 2 is a heart muscle cell that contracts about once a second, all day. Cell 3 is a white blood cell in the lung that engulfs dust particles and bacteria and destroys them.

Which organelles should each cell be full of?

A. 1: rough ER and Golgi complex; 2: mitochondria; 3: lysosomes B. 1: lysosomes; 2: rough ER and Golgi complex; 3: mitochondria C. 1: mitochondria; 2: lysosomes; 3: rough ER and Golgi complex D. 1: rough ER and Golgi complex; 2: lysosomes; 3: mitochondria

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 · 4 points

The model shows a plasma cell, a white blood cell that makes an antibody protein and releases it into the blood. Six parts are numbered. The part marked 3 is a large round body enclosed by a double membrane. The part marked 4 is a network of membrane sacs, continuous with the membrane of 3, with small dots on its outer surface. The part marked 2 is a stack of flattened membrane sacs. The cell’s outer boundary is drawn as the outer line. The part marked 5 is a small membrane sac near that boundary. The part marked 6 is a membrane sac with an acidic interior. The part marked 1 is an oval body with a smooth outer membrane and a folded inner membrane.

A plasma cell, a white blood cell that exports an antibody protein into the blood, with six parts numbered; the outer line is the cell’s boundary.

(a) Identify the parts marked 3 and 4, and describe what the dots on the part marked 4 are and what they do. (1 point)

A full-credit answer: The part marked 3 is the nucleus, enclosed by its nuclear envelope.
The part marked 4 is the rough ER.
The dots on the rough ER are ribosomes.
Ribosomes join amino acids into a protein in the order an mRNA sets.
The ribosomes on the rough ER pass each protein they make into the ER’s interior.

Check the box for each point your answer earns

3 is the nucleus (enclosed by its nuclear envelope) and 4 is the rough ER; the dots are ribosomes, which make proteins (joining amino acids in the order an mRNA sets) and pass them into the ER's interior.

Accept: "rough endoplasmic reticulum" for 4, and "ribosomes, which make protein" for the dots. Do not award the point if the dots are called vesicles or if 4 is called the Golgi complex.

Common slip: Calling the dots vesicles, or 4 the Golgi complex. The Golgi is a stack of flattened sacs; a network continuous with the nuclear envelope and studded with ribosomes is the rough ER.

(b) Explain how the parts marked 4, 2 and 5 work together to get the antibody protein out of the cell. (1 point)

A full-credit answer: Ribosomes on the rough ER make the antibody protein and pass it into the ER’s interior, where it is folded.
A vesicle buds from the ER carrying the protein and fuses with the Golgi complex.
The Golgi complex modifies the protein, for example by attaching carbohydrate chains, and packages it into a vesicle.
The vesicle moves to the plasma membrane and fuses with it.
So the protein is released outside the cell: exocytosis.

Check the box for each point your answer earns

the protein made on the rough ER is folded in the ER's interior and leaves in a vesicle that fuses with the Golgi complex, which modifies it (for example by attaching carbohydrate chains) and packages it into a vesicle that moves to the plasma membrane and fuses with it, releasing the protein outside by exocytosis.

Accept: the order ER → vesicle → Golgi → vesicle → plasma membrane with the Golgi's role given as finishing and packaging. Do not award the point if the protein is said to pass through the cytosol or straight through the plasma membrane.

Common slip: Having the protein pass through the cytosol between organelles, or straight through the plasma membrane. A protein for export travels inside membrane the whole way and leaves only when a vesicle fuses with the plasma membrane.

(c) Explain the role of the part marked 3 in making this protein. (1 point)

A full-credit answer: The part marked 3 is the nucleus.
The nucleus holds the cell’s DNA.
The DNA carries the instructions for the antibody protein.
An mRNA copy of those instructions is made in the nucleus.
The mRNA is carried out of the nucleus to the ribosomes on the rough ER.
The ribosomes join amino acids in the order the mRNA sets.
So the nucleus supplies the instructions the ribosomes follow when they build the protein.

Check the box for each point your answer earns

the nucleus holds the cell's DNA, which carries the instructions for the protein, AND an mRNA copy of those instructions is carried out to the ribosomes on the rough ER, which build the protein in the order the mRNA sets.

Accept: "the nucleus holds the instructions the ribosomes follow" with the mRNA copy named. Do not award the point for "the nucleus controls the cell" or "the nucleus makes the protein" with no mention of the instructions or their copy.

Common slip: Saying the nucleus makes the protein. Ribosomes make the protein; the nucleus holds the DNA and sends out the mRNA copy that tells the ribosomes the order of amino acids.

(d) A skin cell has far less of the parts marked 4 and 2 than this plasma cell, but the same amount of the parts marked 3, 6 and 1. Explain how this difference relates to what each cell does. (1 point)

A full-credit answer: The plasma cell makes and exports large amounts of antibody protein.
Rough ER makes and folds protein for export, and the Golgi complex finishes and packages it, so the plasma cell needs a great deal of both.
A skin cell exports little protein, so it needs little of either.
Every cell needs a nucleus for its DNA, lysosomes for digestion and mitochondria for ATP, so a skin cell and a plasma cell both keep their nucleus, lysosomes and mitochondria.

Check the box for each point your answer earns

the plasma cell's job is to make and export large amounts of protein, so it needs much rough ER (to make and fold the protein) and Golgi complex (to finish and package it); a skin cell exports little protein and so needs little of either; the parts every cell needs (a nucleus for its DNA, lysosomes for digestion, mitochondria for ATP) are the same in both.

Accept: "a cell has more of the organelles its job uses" provided the rough ER and Golgi are linked to protein export. Do not award the point for "the plasma cell is bigger" or for naming the parts with no link to the cell's job.

Common slip: Saying the plasma cell is bigger, or naming the parts with no link to the job. The point is earned by tying rough ER and Golgi to making and exporting protein.

Free-response score: 0 of 4

Free response 2 · Conceptual Analysis · 4 points

A cell in a salivary gland makes a digestive protein that breaks down starch in food, and exports it into saliva. The protein is made by ribosomes on the rough ER. The protein found in the saliva carries carbohydrate chains. The new protein at the ribosomes has none. A drug stops vesicles from budding off the ER in these cells. Everything else in the cell keeps working, including the ribosomes.

(a) Describe the route the digestive protein normally takes from the ribosomes that make it to the saliva. (1 point)

A full-credit answer: From the ribosomes on the rough ER, the protein first enters the ER’s interior.
A vesicle buds from the ER carrying the protein.
The protein then travels in that vesicle to the Golgi complex, which the vesicle fuses with.
A second vesicle buds from the Golgi complex carrying the protein.
The protein leaves the cell when the second vesicle fuses with the plasma membrane and releases the protein into the saliva: exocytosis.

Check the box for each point your answer earns

ribosomes on the rough ER → the ER's interior → a vesicle → the Golgi complex → a vesicle → the plasma membrane, where exocytosis releases it outside the cell (into the saliva).

Accept: the sequence in words without the word exocytosis, provided it ends with a vesicle fusing with the plasma membrane. Do not award the point if the protein passes through the cytosol at any stage.

Common slip: Sending the protein through the cytosol or straight across the plasma membrane. It stays inside membrane compartments and vesicles the whole way.

(b) Describe where the cell adds the carbohydrate chains to the protein, and what else happens to the protein there. (1 point)

A full-credit answer: The carbohydrate chains are added in the Golgi complex.
The Golgi complex receives the protein in vesicles from the ER.
The Golgi complex finishes the protein by attaching carbohydrate chains: glycosylation.
The Golgi complex then packages the protein into vesicles addressed to the cell surface.

Check the box for each point your answer earns

the carbohydrate chains are added in the Golgi complex, which receives the protein in vesicles from the ER, chemically modifies it (glycosylation, attaching carbohydrate chains), and packages it into vesicles addressed to its destination, here the cell surface.

Accept: the Golgi named with any two of receive / modify / package, stated for this protein. Do not award the point for the chains being added at the ribosomes or at the plasma membrane, or for "the Golgi makes the protein".

Common slip: Placing the change at the ribosomes or the plasma membrane, or saying the Golgi makes the protein. Ribosomes on the rough ER make it; the Golgi receives, modifies and packages it.

(c) Make a claim about what happens to the export of the digestive protein while the drug acts, and where the protein ends up inside the cell. (1 point)

A full-credit answer: Export stops: no digestive protein reaches the saliva.
The ribosomes still make the protein, and the ER’s interior still folds it.
But no vesicle can bud from the ER, so the protein cannot leave the ER.
So the protein builds up in the interior of the rough ER.
Therefore none reaches the Golgi complex or the plasma membrane.

Check the box for each point your answer earns

the claim that export stops (no digestive protein reaches the saliva) and that the protein builds up in the interior of the rough ER, where it is still made and folded but from which it cannot leave. No reasoning is required for this point.

Accept: "it accumulates in the ER and none is released". Do not award the point for "it leaks into the cytosol and is released anyway" or for "the ribosomes stop making it".

Common slip: Having the protein leak into the cytosol and get out anyway, or the ribosomes stop. The ribosomes keep working; the protein piles up inside the ER.

(d) Support your claim, using how a protein for export moves from one compartment to the next inside a cell. (1 point)

A full-credit answer: A protein for export travels only inside membrane compartments.
It moves from one compartment to the next only when a vesicle buds off one membrane and fuses with the next.
A protein is a large polar molecule, so it cannot cross a membrane on its own.
The drug stops vesicles budding from the ER.
Therefore the protein has no route out of the ER to the Golgi complex or the plasma membrane.

Check the box for each point your answer earns

the evidence AND the reasoning: the protein travels only inside membrane compartments (ER interior → vesicle → Golgi → vesicle), moving between them only when vesicles bud off one membrane and fuse with the next; a protein is a large polar molecule that cannot cross a membrane on its own, so with no vesicles budding from the ER it has no route out of the ER to the Golgi or the plasma membrane.

Accept: "it needs vesicles to move between compartments and cannot cross membranes by itself". Do not award the point for support based on the ribosomes stopping, which the scenario rules out.

Common slip: Justifying from the ribosomes stopping, which the scenario rules out. The block is in the vesicles, and vesicles are the only way a protein moves between compartments.

Free-response score: 0 of 4

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Multiple choice checked: 0 of 18 correct.

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