End-of-topic test: Biotechnology

Unit 6 · Topic 6.8 end-of-topic test

Suggested time: about 44 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 technician loads a mixture of DNA fragments into one well of a gel, switches on the voltage for a set time, and adds a dye. The lane shows three dark bands at three heights.

Which of the following does the lane show about the fragments that were loaded?

A. Exactly three DNA molecules were loaded, one for each band B. Fragments of one size were loaded, and the mesh split them into three groups C. Fragments of at least three different sizes were loaded D. Exactly three fragments were loaded, each of a different size

Question 2

A mixture of DNA fragments of 550 and 2,650 base pairs is loaded into one well, and the voltage is switched on. In the gel, after the run, the two kinds lie in two bands, the 550-base-pair band lower.

Which of the following explains why the two kinds of fragment separate in the gel?

A. The mesh of the gel slows the 2,650-base-pair fragments more than the 550-base-pair fragments B. The 2,650-base-pair fragments carry more negative charge, so the positive electrode pulls them farther C. The 550-base-pair fragments carry more negative charge per base pair, so they move faster D. The dye sticks to the 550-base-pair fragments first and drags them down the gel

Question 3

The ladder and lane 2, after the run.

In the drawing below, the small boxes along the top edge are the wells, and each dark bar is a band. The first lane is the ladder. Lane 2 holds one band.

About how long are the fragments in lane 2’s band?

A. About 1,600 base pairs B. About 2,300 base pairs C. About 2,800 base pairs D. About 3,300 base pairs

Question 4

The skin sample beside the same stretch from three species of snake.

In the drawings below, the small boxes along the top edge are the wells, and each dark bar is a band. The first lane is the ladder. Suppose a customs officer seizes a handbag made of snakeskin. One enzyme cuts the same stretch of DNA from the skin and from three species of snake, and the fragments are loaded beside the ladder.

Which species has the same band pattern as the skin sample?

A. The tree snake B. The sand snake C. The water snake D. None of the three

Question 5

The plasmid before the substitution: two cut sites, 2,150 base pairs apart.

In the drawing below, the circle is the plasmid, drawn as one closed line. A short line across the circle marks a place where the enzyme cuts: a cut site. Suppose a 5,700-base-pair plasmid carries an enzyme’s six-letter cut sequence at two places, 2,150 base pairs apart. Inside the larger piece, 1,450 base pairs from one site, a third place carries five of the six letters. A substitution changes the sixth letter to the one the cut sequence needs.

Which list gives the sizes of the pieces, in base pairs, after the enzyme cuts the changed plasmid?

A. 3,550 and 2,150 B. 4,250 and 1,450 C. 2,150, 2,100 and 1,450 D. 3,550, 2,150 and 1,450

Question 6

The four drawings, numbered 1 to 4.

In the drawings below, a dark strand is the sample’s DNA, and a light strand is a primer or a new strand grown from one. A short light strand paired against a dark strand is a primer. The four drawings below show the events of one cycle of PCR and the cycle’s end, in a mixed order. A rounded box is a DNA polymerase.

Which drawing shows annealing?

A. Drawing 1 B. Drawing 2 C. Drawing 3 D. Drawing 4

Question 7

Suppose a tube holds 5 copies of a target at the start, with both primers, free nucleotides and the heat-stable DNA polymerase. The machine heats and cools the tube for 11 cycles.

How many copies of the target does the tube hold after the 11 cycles?

A. 16 B. 110 C. 2,048 D. 10,240

Question 8

Suppose a vet pulls a tick from a dog and tests it for the DNA of a bacterium that ticks can carry, with primers that match a stretch found only in that bacterium. The tick’s cells hold far more of the tick’s own DNA than of the bacterium’s. After 30 cycles the tick’s lane on the gel shows one band, at the bacterium’s stretch’s size, and nothing else.

Which of the following explains why the tick’s own DNA shows as no band?

A. The primers pair only where their bases match the bacterium’s stretch, so the tick’s own DNA is never copied B. The tick’s own DNA molecules are too long to enter the gel’s mesh C. The heat of about 95 °C in every cycle breaks the tick’s own DNA into pieces too small to see D. The tick’s own DNA was copied, and its bands lie at the same height as the bacterium’s band

Question 9

The five tubes and their lanes after the run.

Suppose a laboratory tests three batches of animal feed for the DNA of one kind of bacterium, with primers that match a stretch found only in that bacterium. Beside the three feed tubes it sets up a tube with water in place of a sample and a tube with a little of the bacterium’s own DNA. The table gives each tube’s lane after the run.

Which feed batches held the bacterium’s DNA?

A. Feed batch 1 only B. Feed batch 2 only C. Feed batch 1 and feed batch 3 D. Feed batch 1, feed batch 2 and feed batch 3

Question 10

Suppose a technician seals a sea anemone’s gene for a venom protein into one plasmid, and a gene for resistance to an antibiotic into a second, separate plasmid. She mixes both kinds of plasmid with treated cells of a bacterium and spreads the cells on jelly that contains the antibiotic.

Which cells grow into colonies on the plate?

A. Only the cells that took up both plasmids B. The cells that took up the resistance plasmid, whether or not they also took up the venom-gene plasmid C. The cells that took up the venom-gene plasmid, whether or not they also took up the resistance plasmid D. Every treated cell, whether or not it took up a plasmid

Question 11

Suppose a plasmid carries a saffron crocus’s gene for a scent-making enzyme and two resistance genes, one against each of two antibiotics. A technician mixes the plasmid with treated cells of a bacterium and spreads the cells on jelly that contains both antibiotics.

What grows on the plate?

A. No growth B. A few colonies C. A lawn covering the plate D. About twice as many colonies as on jelly holding one of the two antibiotics

Question 12

The bases of each species’ stretch that match the caterpillar’s read.

Suppose a caterpillar is found eating a farmer’s cabbages. A biologist reads a 30-base stretch of its DNA and sets the read against the same stretch from three moth species whose caterpillars look alike. The table gives the count of matching bases for each species.

What can the biologist conclude the caterpillar is?

A. A moth of species S B. A moth of species U C. A moth of a species other than S and U D. A moth of either species, S or U

Question 13

Suppose a biologist seals a stretch of a brittle star’s DNA into a plasmid and puts the plasmid into bacteria. She grows the bacteria for a day, until the flask holds enough copies of the stretch for a machine to read its sequence.

Which of the four jobs is this?

A. Forensic identification B. Identifying species or relatives C. A transgenic organism D. Gene cloning

Question 14

A biologist uses one enzyme to cut the same stretch of DNA from a sample and from a reference, and loads the fragments in two lanes of one gel. The sample’s band pattern matches the reference’s exactly.

Which of the following does the matching pattern show?

A. The sample and the reference carry the enzyme’s cut sequence at the same places along that stretch B. The sample and the reference hold the same amount of DNA C. The sample and the reference came from the same individual D. The sample and the reference carry the same number of genes along that stretch

Question 15

Oysters in a bay are dying. Suppose a laboratory tests a sample of oyster tissue for a virus that carries RNA, using PCR with primers that match a stretch of the virus’s sequence.

What must the laboratory do to the sample’s RNA before PCR can copy the virus’s stretch?

A. Copy the RNA into DNA B. Heat the RNA to about 95 °C so that its bases pair with the primers C. Cut the RNA at the primers’ sites with an enzyme D. Sort the RNA by size on a gel

Question 16

Suppose a poplar tree carries a gene from a soil bacterium for an enzyme that breaks a pollutant down, and the tree’s roots break the pollutant down in the soil around them.

Which of the four jobs is this?

A. Forensic identification B. Identifying species or relatives C. A transgenic organism D. Gene cloning

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 · Conceptual Analysis · 4 points

Suppose a biologist seals a daffodil’s gene for an enzyme into a vector and puts the vector into cells of a rice plant. In the daffodil, the enzyme builds an orange pigment in the petals. Rice grains are white and hold none of that pigment. The biologist grows transgenic rice plants from the cells that took up the gene, beside ordinary rice plants of the same kind. A test for the daffodil enzyme detects it in the transgenic plants’ developing grains and none in the ordinary plants’ grains.

(a) Describe what the detected enzyme shows about the daffodil gene in the transgenic plants’ grain cells. (1 point)

A full-credit answer: The grain cells carry the daffodil gene, and they transcribed it and translated its mRNA.
A protein is built only from its mRNA, so the detected enzyme shows the gene is expressed there.

Check the box for each point your answer earns

the gene is expressed in the grain cells (transcribed and translated) — the enzyme is there because the cells built it from the gene. Accept: the gene is present and expressed; the cells built the enzyme from the gene’s mRNA.

Common slip: Saying only that the cells carry the gene. A protein detected shows the gene was transcribed and translated, not only that it is present.

(b) Explain why the enzyme the rice cells build from the daffodil gene is the same enzyme a daffodil cell builds. (1 point)

A full-credit answer: The rice cells’ RNA polymerase transcribes the daffodil gene into mRNA, and their ribosomes translate it.
The genetic code is universal, so the rice cells read each codon as the same amino acid a daffodil cell reads it as.
So the ribosomes join the same amino acids in the same order, and the protein is the daffodil’s enzyme.

Check the box for each point your answer earns

the genetic code is universal (each codon means the same amino acid in rice as in the daffodil), so the rice cells’ RNA polymerase and ribosomes build the same amino acid chain from the gene. Accept with or without: transcription and translation named.

(c) Predict the most likely difference in phenotype of the transgenic rice plants compared with the ordinary rice plants. (1 point)

A full-credit answer: The transgenic plants’ grains are orange or yellow, and the ordinary plants’ grains are white.

Check the box for each point your answer earns

the transgenic plants’ grains are colored (orange / yellow) while the ordinary plants’ grains stay white. Accept: the transgenic grains hold the pigment.

Common slip: Restating that the transgenic grains hold the daffodil enzyme. The stimulus says so; the point is the visible difference the enzyme makes: colored grains against white.

(d) Justify your prediction in part (c). (1 point)

A full-credit answer: The daffodil enzyme builds the orange pigment, and the transgenic grain cells hold that enzyme.
So the enzyme builds the pigment in those grains, and the grains are colored.
The ordinary plants’ grain cells have no daffodil enzyme, so they build none of the pigment and stay white.

Check the box for each point your answer earns

the daffodil enzyme in the transgenic grain cells builds the orange pigment there, so the grains are colored. Accept, for the point, either link on its own: the transgenic grains hold the enzyme that builds the pigment; or the ordinary grains lack the enzyme, so they build no pigment and stay white. Accept reasoning consistent with the prediction in part (c).

Common slip: Stopping at ‘the transgenic plants have the enzyme’. The point needs the link from the enzyme to the pigment it builds.

Free-response score: 0 of 4

Free response 2 · Scientific Investigation · 4 points

Suppose a technician seals a lobster’s gene for a shell protein into a plasmid that also carries a gene for resistance to an antibiotic. She chills cells of a bacterium from a cave pool in a salt solution and warms them for a moment, so that they can take up DNA, and mixes them with the plasmid. Four plates are lettered I to IV, and she spreads treated cells on jelly with the antibiotic (I) and on plain jelly (II), and untreated cells on jelly with the antibiotic (III) and on plain jelly (IV). In every plate drawing, a plate is a round dish of agar jelly seen from above: a dot is one colony, light shading over the whole dish is a lawn, and a blank dish is a plate where nothing grew. The plates after a day are drawn below.

The four plates after a day. Plate I: 19 colonies.

(a) Identify the plate on which only cells that took up the plasmid grew. (1 point)

A full-credit answer: Plate I.

Check the box for each point your answer earns

plate I (treated cells, antibiotic in the jelly). Accept with or without: the antibiotic kills the cells that carry no resistance gene, so only cells with the plasmid grow.

(b) The technician includes plate III as a control. Justify including plate III. (1 point)

A full-credit answer: Plate III shows that the antibiotic kills these cells when they carry no resistance gene: untreated cells on the antibiotic grew nothing.
Without plate III, some of the cells might have been resistant before the plasmid was added, and the colonies on the antibiotic might have grown from those cells.
Because plate III grew nothing, colonies on the antibiotic can be credited to the plasmid.

Check the box for each point your answer earns

plate III shows the antibiotic kills these cells when they carry no resistance gene (nothing grew), so colonies on the antibiotic cannot be cells that were resistant before the plasmid was added (the control lacks only the treatment). Accept: to justify a control, say what it shows.

(c) A fifth plate is spread with treated cells that were mixed with no plasmid, on jelly with the antibiotic. Predict what grows on the fifth plate. (1 point)

A full-credit answer: Nothing grows on the fifth plate.

Check the box for each point your answer earns

no growth (nothing grows / no colonies). Accept with or without: the treatment alone gives a cell no resistance gene, so the antibiotic kills every cell.

(d) A student claims that the cells in a colony on plate I build the lobster shell protein. Evaluate the claim using the plates. (1 point)

A full-credit answer: The claim is not supported by the plates.
A colony on plate I shows that its cells took up the plasmid and built the resistance protein, because the antibiotic tests for that protein only.
The shell-protein gene rode on the same circle, so the cells carry it, but a gene present is not a gene expressed.
Whether the cells build the shell protein needs a test for that protein itself.

Check the box for each point your answer earns

not supported — the colony shows the resistance gene was taken up and expressed (the cells carry the plasmid and so the shell-protein gene), but a gene present is not a gene expressed; a test for the shell protein itself is needed.

Common slip: Saying the colony proves the cells build the shell protein because both genes ride on one circle. The circle shows the gene is present; only a test for the protein shows it is expressed.

Free-response score: 0 of 4

Feedback and scoring guides appear after you submit.

Multiple choice checked: 0 of 16 correct.

Next: One field of dandelions