Antibiotics — return questions key

1. AR1 · Return

Model answer. A drug is any substance taken into the body that modifies or affects chemical reactions in the body.

A full answer includes

• I wrote that a drug is a substance taken into the body.
• I wrote that it modifies or affects chemical reactions in the body.

Also accept

• any substance taken into the body that modifies or affects chemical reactions in the body

Watch for

• “A drug is a medicine.” — Medicines are drugs, but so are substances such as alcohol that are not medicines.
• “A drug is a substance that kills germs.” — Some drugs do, but a disinfectant kills germs without being a drug. The definition is about reactions in the body.

2. AR2 · Return

Model answer. Diameter = 41 − 22 = 19 mm. It includes the disc.

Checked automatically

• Diameter of the zone: 19 mm (exact value)
  • Common wrong answer 13 : That leaves out the disc. The zone is measured from edge to edge and includes the disc.
  • Common wrong answer 63 : That adds the readings. The diameter is the larger reading minus the smaller.

A full answer includes

• I subtracted the smaller reading from the larger: 41 − 22.
• I wrote 19 mm.

Also accept

• 19 mm

Watch for

• “Subtract the disc as well.” — The diameter of a clear zone includes the disc, so nothing more is subtracted.

3. BR1 · Return

Model answer. A cold is caused by a virus, and antibiotics kill bacteria but do not affect viruses.

A full answer includes

• I wrote that a cold is caused by a virus.
• I wrote that antibiotics kill bacteria but do not affect viruses.

Also accept

• a cold is caused by a virus; antibiotics do not affect viruses

Watch for

• “The cold virus is resistant to antibiotics.” — Resistance is a property of some bacteria. Antibiotics never affected viruses in the first place.

4. BR2 · Return

Model answer. K will not kill these bacteria or stop them growing, so it will not treat this infection; a different antibiotic that still stops them is needed. Resistance belongs to the bacteria, so the patient is not resistant, and other kinds of bacteria are not made resistant.

A full answer includes

• I chose: K will not kill these bacteria or stop them growing, so it will not treat the infection.

Also accept

• K will not kill these bacteria or stop them growing, so it will not treat the infection

Watch for

• “The patient has become resistant to every antibiotic.” — The patient is not resistant to anything. These bacteria are resistant to K.
• “Every other kind of bacterium in the body is now resistant to K.” — Resistance belongs to particular bacteria. Other kinds in the body are not resistant just because these are.
• “K will work once the bacteria have stopped growing.” — Resistant bacteria keep growing in K. That is what resistance means.

5. BR3 · Return

Model answer. Each use of an antibiotic kills the bacteria that are not resistant, while resistant ones survive and multiply. Using antibiotics only when essential means fewer uses, so resistant bacteria get that advantage less often and become common more slowly.

A full answer includes

• I wrote that each use kills the bacteria that are not resistant.
• I wrote that the resistant bacteria survive and multiply.
• I wrote that fewer uses give resistant bacteria fewer chances, so they become common more slowly.
• I did not write that the bacteria get used to the antibiotic.

Also accept

• each use selects resistant bacteria; fewer uses, fewer chances, slower development

Watch for

• “Bacteria get used to an antibiotic if they meet it often.” — Bacteria do not get used to an antibiotic. The resistant ones were already there and survive while the others are killed.