Which statement best explains how the loop dilution/pour plate technique results in the isolation of individual colonies?

• A. Serial dilution of the sample reduces the number of cells, so when the diluted sample is mixed with molten agar and poured into a plate, individual cells are separated and form isolated colonies.
• B. The sample is streaked across the surface of the agar, physically separating cells to form isolated colonies.
• C. The technique uses selective media that only allows certain bacteria to grow, resulting in isolated colonies.
• D. Heat is applied to the plate to kill excess bacteria, leaving only a few to form isolated colonies.

Answer: (A)

Verified step by step guidance

1. Understand the purpose of the loop dilution/pour plate technique: it is designed to separate individual bacterial cells so that each can grow into a distinct colony.
2. Recognize that the key to isolating individual colonies is reducing the concentration of cells in the sample, which is achieved through serial dilution. This means repeatedly diluting the original sample to decrease the number of cells per unit volume.
3. After dilution, the sample is mixed with molten agar and poured into a petri dish. Because the cells are now fewer and more spread out, they are physically separated within the solidifying agar.
4. Each separated cell then grows independently into a visible colony, allowing for isolation and further study of individual bacterial types.
5. Contrast this with other methods mentioned: streaking physically separates cells on the surface, selective media restricts growth to certain bacteria, and heat treatment kills cells rather than diluting them. The loop dilution/pour plate technique relies specifically on dilution to achieve isolation.