2002 AP® BIOLOGY FREE-RESPONSE QUESTIONS (Form B)

Copyright © 2002 by College Entrance Examination Board. All rights reserved. Advanced Placement Program and AP are registered trademarks of the College Entrance Examination Board.

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BIOLOGY SECTION II

Time—1 hour and 30 minutes

Directions: Answer all questions. Answers must be in essay form. Outline form is not acceptable. Labeled diagrams may be used to supplement discussion, but in no case will a diagram alone suffice. It is important that you read each question completely before you begin to write. Write all your answers on the pages following the questions in this booklet. 1. Bacteria were cultured in a system that allowed for the continual addition of fresh nutrients and the removal

of waste products. Bacteriophage (virus) were added at the time shown and the following population changes were observed.

(a) Describe and explain the observed results.

(b) Discuss the infection cycle of a DNA virus from attachment to lysis.

(c) Describe how the genome of a retrovirus like HIV (Human Immunodeficiency Virus) becomes incorporated into the genome of the host cell.

AP® BIOLOGY 2002 SCORING GUIDELINES (Form B)

Copyright © 2002 by College Entrance Examination Board. All rights reserved. Advanced Placement Program and AP are registered trademarks of the College Entrance Examination Board.

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Question 1

1. (a) Describe and explain the observed results. (1 point for each bullet, 4 points maximum)

• description only of relative numbers of bacteria and viruses over time; must include initial bacterial growth phase

• bacterial growth dynamics (exponential phase, carrying capacity) • infection phase (virus “attacks” bacteria, bacteria decline while virus multiplies) • recovery phase (resistant mutant/immune bacteria survive to reproduce, virus number drops) • co-existence phase (viruses multiply only in non-resistant/“sensitive” cells or lysogenic situation

develops) • exceptional description of a particular phase • population reaches an equilibrium

1. (b) Discuss the infection cycle of a DNA virus from attachment to lysis (4 points maximum)

• attachment to host cell (cell wall, membrane, etc., attachment to something) • penetration/injection of DNA/nucleic acid • synthesis of viral components (nucleic acids and/or proteins) • assembly/packaging of viruses • lysis (release, budding); needs details beyond simply cells burst/lysed

1. (c) Describe how the genome of a retrovirus like HIV (Human Immunodeficiency Virus) becomes

incorporated into the genome of the host cell. (4 points maximum)

• retrovirus = RNA virus • use of reverse transcriptase (enzyme) to create DNA “version” • single strand to double strand conversion • enzymatic incorporation into human genome, give at least one enzyme • exceptional description of mechanism

AP® BIOLOGY 2002 SCORING COMMENTARY (Form B)

Copyright © 2002 by College Entrance Examination Board. All rights reserved. Advanced Placement Program and AP are registered trademarks of the College Entrance Examination Board.

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Question 1

Sample B (Score 9) In part (a), a point was earned for the infection phase. A point was also earned for the interpretation of the populations reaching equilibrium, with an elaboration point for the description of a mutation preventing viral attachment.

Part (b) earned a point for the virus “anchoring to the bacterium,” a point for the insertion of the viral genome into the host cell, a point for the idea that viruses assemble inside the host, and a point for the elaborate description of lysis.

In part (c), a point was earned for the statement that retroviruses have an RNA genome and a point for the function of reverse transcriptase. Sample C (Score 10) In part (a), a point was earned for the description of the infection phase, a point for the dynamics of the bacterial growth, a point for the survival of resistant bacteria, and a point for dynamic equilibrium.

Part (b) earned a point for attachment and another for injection of DNA. A point is earned for the synthesis of the viral proteins, and a point for the break down of the cell membrane.

In part (c), a point was earned for stating that the genetic material of a retro virus is RNA and another for the function of reverse transcriptase. Sample D (Score 6) In part (a), a point was earned for exponential growth. In part (b), a point was earned for attachment to the host and another for injection of DNA. A point is also earned for the description of lysis.

Part (c) earned a point for RNA being the genetic material of the retrovirus and another for the function of reverse transcriptase.