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Zorluk: OrtaCause-and-Effect Relationships

Passage

In the late summer of 1928, bacteriologist Alexander Fleming left his laboratory at St. Mary's Hospital in London for a family vacation. Before departing, he stacked several petri dishes containing cultures of *Staphylococcus* bacteria on a bench in the corner of his room. During his absence, a window was left open, allowing spores of a rare mold, *Penicillium notatum*, to drift in from a laboratory downstairs. The mold spores landed on one of the exposed culture plates and began to grow. Upon returning in September, Fleming noticed a strange phenomenon: the bacterial colonies immediately adjacent to the growing mold had dissolved, leaving a distinct, clear halo of lysis. Fleming correctly hypothesized that the mold was secreting a self-defense substance that actively destroyed the *Staphylococcus* cell walls. This substance, which he named penicillin, went on to revolutionize medicine.

Based on the passage, in what chronological order did the events leading to the identification of penicillin occur?

  1. 1Fleming leaves stacked bacterial cultures unattended on a laboratory bench.
  2. 2Spores of the mold *Penicillium notatum* contaminate a stacked culture plate of *Staphylococcus* bacteria.
  3. 3The *Staphylococcus* bacterial cells near the growing mold are lysed and dissolve.
  4. 4Fleming notices a clear halo around the mold and concludes that it produces an antibacterial agent.

Cevap

The correct chronological order of the cause-and-effect chain is: Fleming leaving the bacterial cultures unattended, followed by the contamination of the plate by mold spores, which then leads to the lysis of the nearby bacterial cells, and finally culminates in Fleming observing the clear halo and concluding that an antibacterial agent is present.
The correct order follows the physical timeline of cause and effect: first, the plates are left exposed; second, the mold spores contaminate the plates; third, the mold grows and secretes a substance that lyses the nearby bacteria; and fourth, Fleming observes this lysis and draws his conclusion.

Adım Adım Çözüm

1
Identify the initial condition that allowed the subsequent events to happen.
Fleming leaving the culture plates stacked on a lab bench.
For contamination to occur, the plates had to first be left unattended in the lab.
2
Identify the immediate cause of the mold growth.
Spores of the Penicillium mold contaminating the culture plate.
The text states that the spores drifted through the window and landed on the exposed plates during Fleming's absence.
3
Determine the physical effect of the mold's growth on the bacteria.
Lysis and dissolution of the Staphylococcus bacteria surrounding the mold.
The growing mold secretes a substance that actively destroys the bacterial cell walls, which must happen before any observation can take place.
4
Identify the final observation and conclusion.
Fleming noticing the clear halo and deducing the presence of an antibacterial agent.
This observation can only happen after the bacteria have already dissolved and after Fleming returns to the laboratory.

Anahtar Kavram

Understanding chronological and causal chains of events in a scientific context.
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Konular

Cause-and-Effect Relationships

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