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Biology asks two things of you: how a process works, and how we know. These habits serve both, and each is shown on Chapter 14. They need only a pen and paper; where Hemle saves you time, we point to what it made.

Every card on three more concepts

Flashcards Hemle wrote on the chapter, each set whole: the question, the answer behind it, and the pages it cites. Try each one before you open it.

Made in Hemle on 28 October 2026: every card on 3 concepts, word for word, of the 5 sets we asked for (another is in the window above). The set on “Enzymatic Roles in Replication” isn’t shown: one of its cards came back with “{cloze}” where its blank should be. From Chapter 14 of Biology, first edition (2013), by OpenStax, under a CC BY 4.0 licence. Download for free at openstax.org/details/books/biology. The cards, quiz and answers were made by Hemle’s AI; OpenStax doesn’t endorse Hemle.

A whole quiz on Hershey and Chase

Hemle’s five questions on Hershey-Chase Isotopic Labeling, as they came: two on why each label works, two that ask what the experiment found, and one that corrects a student’s claim. Each answer quotes the chapter’s sentence it rests on.

1. Question 1 of 5

   In the Hershey-Chase experiments, why was ³⁵S used specifically to label the viral protein coat rather than nucleic acids?

   • ASulfur binds directly to deoxyribose sugar backbones.
   • BSulfur forms the core nitrogenous base linkages in viral capsids.
   • CSulfur is present in proteins but is absent from DNA.
   • DSulfur is abundant in both nucleic acids and proteins but decays faster.
   Show answerHide answer

   Answer C: Sulfur is present in proteins but is absent from DNA.

   Page 4 explains that sulfur is found in protein but not in nucleic acids such as DNA. Radioactive sulfur (³⁵S) therefore selectively tags the viral protein coat. Ask yourself: Which chemical element is distinct to proteins compared to nucleic acids in viral structures?

   “Hershey and Chase labeled one batch of phage with radioactive sulfur, 35S, to label the protein coat.”

   SourcePage 4p.4

2. Question 2 of 5

   Which statement correctly describes why Alfred Hershey and Martha Chase used radioactive ³²P in their bacteriophage cultures?

   • APhosphorus is an integral element of DNA but is not found in protein.
   • BPhosphorus integrates into the amino acid chains forming the viral capsid.
   • CPhosphorus prevents the detachment of phage coats during blending.
   • DPhosphorus allows the phage to replicate inside bacteria without host enzymes.
   Show answerHide answer

   Answer A: Phosphorus is an integral element of DNA but is not found in protein.

   As stated on page 4, phosphorus is found in DNA but not in protein. This chemical distinction allowed Hershey and Chase to selectively tag phage DNA with radioactive phosphorus. Ask yourself: What molecular component of bacteriophages contains phosphorus atoms?

   “Because phosphorous is found in DNA, but not protein, the DNA and not the protein would be tagged with radioactive phosphorus.”

   SourcePage 4p.4

3. Question 3 of 5

   A researcher repeats the Hershey-Chase protocol using bacteriophages labeled with ³⁵S. After allowing bacterial infection, agitating the mixture in a blender, and centrifuging the suspension, where will the majority of the radioactivity be detected?

   • AIn the supernatant containing the detached viral coats
   • BIn the bacterial pellet at the bottom of the tube
   • CEvenly distributed between the pellet and supernatant
   • DInside the newly assembled intracellular bacteriophages
   Show answerHide answer

   Answer A: In the supernatant containing the detached viral coats

   According to page 4, the blender detaches phage coats from the bacterial cell surface, and centrifugation pellets the heavier bacterial cells. In the ³⁵S batch, the empty viral protein coats remain in the lighter supernatant where the radioactivity is detected. Ask yourself: Where do the detached, lighter viral protein coats remain after centrifugation?

   “In the tube that contained phage labeled with 35S, the supernatant contained the radioactively labeled phage, whereas no radioactivity was detected in the pellet.”

   SourcePage 4p.4

4. Question 4 of 5

   How did the post-centrifugation distribution of ³²P differ from that of ³⁵S in the Hershey-Chase experiment?

   • A³²P was detected in the bacterial pellet, whereas ³⁵S was found in the supernatant.
   • BNeither isotope appeared in the pellet because both remained attached to detached phage heads.
   • C³²P was recovered entirely in the supernatant, whereas ³⁵S was localized to the pellet.
   • DBoth ³²P and ³⁵S remained trapped exclusively inside the bacterial pellet.
   Show answerHide answer

   Answer A: ³²P was detected in the bacterial pellet, whereas ³⁵S was found in the supernatant.

   Page 4 highlights that in the tube with ³²P-labeled phage, radioactivity was detected in the pellet containing the heavier bacterial cells. Conversely, in the tube with ³⁵S, radioactivity was present only in the supernatant with no radioactivity detected in the pellet. Ask yourself: Which isotope was carried into the heavy bacterial pellet at the bottom of the centrifuge tube?

   “In the tube that contained the phage labeled with 32P, the radioactivity was detected in the pellet that contained the heavier bacterial cells, and no radioactivity was detected in the supernatant.”

   SourcePage 4p.4

5. Question 5 of 5

   A student claims: 'In the Hershey-Chase experiment, both the protein capsid and the viral DNA enter the bacterial host, but only DNA directs replication.' What is incorrect about this statement?

   • AThe viral capsid enters the host cell while phage DNA stays in the supernatant.
   • BThe protein capsid does not enter the host cell; it remains attached outside and is detached.
   • CDNA remains outside the bacterial cell while injecting viral regulatory proteins.
   • DThe entire virus enters the bacterial cell through endocytosis before uncoating inside.
   Show answerHide answer

   Answer B: The protein capsid does not enter the host cell; it remains attached outside and is detached.

   Page 4 notes that bacteriophages attach to the cell surface and inject only their nucleic acids inside the cell. The empty protein coats remain outside and can be sheared off in a blender, leaving the supernatant radioactive in ³⁵S trials. Ask yourself: Does any part of the bacteriophage protein coat actually enter the bacterial cytoplasm?

   “The bacteriophage infects the host bacterial cell by attaching to its surface, and then it injects its nucleic acids inside the cell.”

   SourcePage 4p.4

Made in Hemle on 28 October 2026: the whole quiz, word for word. Question 1’s explanation says page 4 explains that sulfur is in protein but not in nucleic acids; page 4 says only that sulfur labelled the protein coat. From Chapter 14 of Biology, first edition (2013), by OpenStax, under a CC BY 4.0 licence. Download for free at openstax.org/details/books/biology. The cards, quiz and answers were made by Hemle’s AI; OpenStax doesn’t endorse Hemle.

One more question, word for word

The leading and lagging strands are the chapter’s most often confused pair, so we asked Chat for the difference. Here is Hemle’s answer in full, with the pages it cites in brackets.

1. What's the difference between the leading strand and the lagging strand?

   Show Hemle’s answerHide Hemle’s answer

   The leading strand is made continuously toward the replication fork, while the lagging strand is made away from the fork in short pieces called Okazaki fragments. Both differences arise because DNA polymerase can extend DNA only in the 5′ to 3′ direction, while the two parental DNA strands run in opposite directions (p. 15).

   Feature	Leading strand	Lagging strand
   Direction relative to the replication fork	Synthesized toward the fork	Synthesized away from the fork
   Pattern of synthesis	Continuous	In short Okazaki fragments
   Primers needed	One primer can start its synthesis	A new primer is needed for each fragment

   At the origin of replication, helicase separates the DNA strands and forms a replication fork. Because the parental strands are antiparallel, DNA polymerase can follow one template toward the fork while extending the new strand 5′ to 3′. That is the leading strand. On the other template, synthesis must proceed away from the fork in separate stretches, producing the lagging strand (pp. 15, 24).

   The distinction is useful because it explains why replication proceeds differently on the two sides of the fork and why the lagging strand needs extra steps. The RNA primers are replaced with DNA, and DNA ligase seals the gaps between Okazaki fragments to make a continuous strand (p. 15). Figure 14.14 illustrates this arrangement: helicase opens the DNA, DNA polymerase makes the leading strand continuously and the lagging strand in fragments, and ligase joins those fragments (p. 15).

Asked in Hemle’s Chat on 28 October 2026, each question in a new chat; the answer is word for word. One of the questions we asked isn’t shown: “How did Meselson and Stahl show that DNA replication is semi-conservative?” Its answer missed information that’s on page 13: the two bands after the second generation. From Chapter 14 of Biology, first edition (2013), by OpenStax, under a CC BY 4.0 licence. Download for free at openstax.org/details/books/biology. The cards, quiz and answers were made by Hemle’s AI; OpenStax doesn’t endorse Hemle.