Cell Structure: Subcellular Components

Unit 2 · Topic 2.1 end-of-topic 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 two free-response questions, write your answer in full sentences, then open the scoring guide and mark your own work against it.

Question 1

Particles taken from a cell are found to be built of RNA and protein. Given a supply of amino acids and an mRNA, the particles produce a protein whose amino acids are in the order the mRNA sets.

What are the particles?

A. Pieces of the Golgi complex, which make proteins B. Pieces of rough ER, which make proteins on their surface C. Ribosomes, which join amino acids into proteins D. Vesicles, which carry each new protein to the Golgi complex

Question 2

The ribosomes of a bacterium and the ribosomes of a human cell are both built from ribosomal RNA and protein, and look alike under the electron microscope. Every known kind of cell has ribosomes of this same basic build.

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 ribosomes, which happen to match C. That ribosomes pass from one kind of cell to another D. That every living thing has 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. It has DNA in a nucleus after all; the nucleus is just very small B. It has no DNA, but its ribosomes make proteins without instructions C. It has DNA, but with no nucleus it has no ribosomes either D. It has DNA in a nucleoid, and ribosomes that make its proteins

Question 5

Under a microscope, an onion skin cell about 100 μm long shows one large dark round body, 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

A cell in the pancreas that makes and exports a protein all day is crowded with a network of folded membrane whose outer surface is studded with ribosomes.

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

A gland cell is fed labeled amino acids for a short time. The label appears first in a protein at ribosomes on the ER, then inside a stack of flattened membrane sacs, and finally outside the cell. The protein at the ribosomes was a plain chain of amino acids; the protein found outside the cell carries sugar chains.

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

White blood cells from a patient engulf bacteria as fast as healthy cells do. Hours later, many engulfed bacteria are still intact inside the patient's cells. Tests show that one digestive enzyme normally found in lysosomes is missing.

What does this show about lysosomes?

A. They hold engulfed bacteria as waste without breaking them down B. They make their own enzymes, on ribosomes inside them C. They digest engulfed material using the enzymes held inside them D. They engulf the bacteria in the first place

Question 11

In a developing human embryo, the hand begins as a paddle. The cells of the webbing between the fingers then die in an orderly, controlled way, as a normal part of development, and separate fingers form.

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 webbing 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 gland cell is given labeled amino acids for one minute, then unlabeled ones. The labeled protein it makes for export is tracked over the next hour.

In what order does the label appear?

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

Equal numbers of mitochondria are taken from an endurance athlete's muscle and from an untrained person's muscle and given the same oxygen and fuel. The athlete's mitochondria have 1.5 times as much folding of their inner membrane and make 180 units of ATP a minute; the others make 120.

Why do the athlete's 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 plant is kept in the dark for two days to clear starch from its leaves. Two kinds of cell are then taken from one leaf: inner leaf cells, which contain chloroplasts, and cells from the leaf's surface layer, which do not. Given water, carbon dioxide and light for 12 hours, the inner cells stain dark with iodine (starch present); the surface cells stay pale. Inner cells kept in the dark stay pale too.

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 surface 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 leaf cell in the light gives off oxygen and builds up starch. The same cell also contains working 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

Wilted plant cells are put in water. In 30 minutes the central vacuole grows from 4,800 μm³ to 7,200 μm³, the cytosol from 2,000 μm³ to 2,050 μm³, and the firmness of the cells rises from 2 to 8 on a relative scale.

What explains the cells' 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 wall D. The vacuole released water into the cytosol, so both swelled

Question 18

Three cells are cut open. Cell 1 releases large amounts of a protein into the blood. Cell 2 contracts a thousand times a day. Cell 3 engulfs 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 cell from the pancreas that makes a digestive protein and releases it into a duct leading to the gut. Six parts are numbered. Part 1 is a large round body enclosed by a double membrane. Part 2 is a network of membrane sacs, continuous with the membrane of part 1, with small dots on its outer surface. Part 3 is a stack of flattened membrane sacs. Part 4 is a small membrane sac near the plasma membrane. Part 5 is a membrane sac with an acidic interior. Part 6 is an oval body with a smooth outer membrane and a folded inner membrane.

A pancreas cell that exports a digestive protein, with six parts numbered.

(a) Identify parts 1 and 2, and describe what the dots on part 2 are and what they do. (1 point)

A full-credit answer: Part 1 is the nucleus, enclosed by its nuclear envelope, and part 2 is the rough ER. The dots are ribosomes: they join amino acids into proteins in the order an mRNA sets and pass the protein into the ER’s interior.

Check the box for each point your answer earns

part 1 is the nucleus (enclosed by its nuclear envelope) and part 2 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 part 2, and "ribosomes, which make protein" for the dots. Do not award the point if the dots are called vesicles or if part 2 is called the Golgi complex.

Common slip: Calling the dots vesicles, or part 2 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 parts 2, 3 and 4 work together to get the digestive protein out of the cell. (1 point)

A full-credit answer: The protein made on the rough ER (2) is folded in the ER’s interior and leaves in a vesicle that fuses with the Golgi complex (3). The Golgi modifies it, for example by attaching carbohydrate chains, and packages it into a vesicle (4), which moves to the plasma membrane and fuses with it, releasing the protein outside by exocytosis.

Check the box for each point your answer earns

the protein made on the rough ER (2) is folded in the ER's interior and leaves in a vesicle that fuses with the Golgi complex (3), which modifies it (for example by attaching carbohydrate chains) and packages it into a vesicle (4) 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) On a sketch of the model, or in words, trace the route the protein takes from part 2 to the outside of the cell with arrows, and mark the point where it leaves the cell. (1 point)

A full-credit answer: 2 → vesicle → 3 → 4 → plasma membrane. The protein leaves the cell where vesicle 4 fuses with the plasma membrane: exocytosis.

Check the box for each point your answer earns

arrows (or a written sequence) 2 → vesicle → 3 → 4 → plasma membrane, with the exit marked at the plasma membrane where vesicle 4 fuses with it (exocytosis).

Accept: a written sequence "rough ER → Golgi complex → vesicle → plasma membrane → outside". Do not award the point for a route through part 5 or part 6, or for one that skips the Golgi complex.

Common slip: Routing the protein through the lysosome (5) or the mitochondrion (6), or skipping the Golgi. The export route runs rough ER, Golgi, vesicle, plasma membrane.

(d) A skin cell has far less of parts 2 and 3 than this pancreas cell but the same parts 1, 5 and 6. Explain how this difference relates to what each cell does. (1 point)

A full-credit answer: The pancreas cell makes and exports large amounts of protein, so it needs a great deal of rough ER to make and fold the protein and a large Golgi complex to finish and package it. A skin cell exports little protein and so needs little of either. Both cells need a nucleus for their DNA, lysosomes for digestion and mitochondria for ATP, so parts 1, 5 and 6 are the same.

Check the box for each point your answer earns

the pancreas 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 (5) for digestion, mitochondria (6) 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 pancreas cell is bigger" or for naming the parts with no link to the cell's job.

Common slip: Saying the pancreas 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. Researchers treat the cells with a drug that stops vesicles from budding off the ER. 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: Ribosomes on the rough ER make the protein and pass it into the ER’s interior. A vesicle buds from the ER and fuses with the Golgi complex; a second vesicle buds from the Golgi, moves to the plasma membrane and fuses with it, releasing the protein into the saliva by 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 what the Golgi complex does to the protein on the way. (1 point)

A full-credit answer: The Golgi complex receives the protein in vesicles from the ER, finishes it, for example by attaching carbohydrate chains (glycosylation), and packages it into vesicles addressed to the cell surface.

Check the box for each point your answer earns

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

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

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

(c) Predict what happens to the export of the digestive protein after the drug is added, and where the protein ends up inside the cell. (1 point)

A full-credit answer: Export stops: no digestive protein reaches the saliva. The protein is still made and folded, but it builds up in the interior of the rough ER, because it cannot leave; none reaches the Golgi complex or the plasma membrane.

Check the box for each point your answer earns

export stops (no digestive protein reaches the saliva); the protein builds up in the interior of the rough ER, where it is still made and folded but from which it cannot leave; none reaches the Golgi complex or the plasma membrane.

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) Justify your prediction, 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, moving from one to the next when a vesicle buds off one membrane and fuses 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.

Check the box for each point your answer earns

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 a justification 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

Multiple choice checked: 0 of 18 correct.

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