Question 5
(5) Chromobacterium violaceum is a species of bacteria that is used in different biological tests. C. violaceum is able to sense the presence of other cells by releasing and detecting some signaling molecules. When C. violaceum multiplies and reaches a certain population called the quorum population, it begins to release a purple-colored compound called violacein. This mechanism is called quorum-sensing.
A scientist is investigating whether a seaweed extract inhibits the quorum sensing of C. violaceum. She grows C. violaceum together with the seaweed extract in a liquid broth for 24 hours, and then measured the concentration of violacein and the number of cells. In the experiment, methanol is used as negative control, while cinnamaldehyde is used as a positive control. Below is the result that she obtained.
| | Methanol | Cinnamaldehyde | Seaweed extract |
| --- | --- | --- | --- |
| Concentration of violacein (mg/L) | 80 | 40 | 20 |
| Number of cells (×1,000) | 110 | 110 | 110 |
Based on the results, what is the possible effect of the seaweed extract on C. violaceum? [1.5 marks]
A. The seaweed extract is an antibiotic as it does not allow the number of cells to exceed 110,000.
B. The seaweed extract is an antibiotic as it reduces the number of cells producing violacein.
C. The seaweed extract is a quorum-sensing inhibitor as it stops the cells from producing violacein, preventing them to multiply.
D. The seaweed extract is a quorum-sensing inhibitor as it prevents cells to communicate with each other without killing them.
A scientist is investigating whether a seaweed extract inhibits the quorum sensing of C. violaceum. She grows C. violaceum together with the seaweed extract in a liquid broth for 24 hours, and then measured the concentration of violacein and the number of cells. In the experiment, methanol is used as negative control, while cinnamaldehyde is used as a positive control. Below is the result that she obtained.
| | Methanol | Cinnamaldehyde | Seaweed extract |
| --- | --- | --- | --- |
| Concentration of violacein (mg/L) | 80 | 40 | 20 |
| Number of cells (×1,000) | 110 | 110 | 110 |
Based on the results, what is the possible effect of the seaweed extract on C. violaceum? [1.5 marks]
A. The seaweed extract is an antibiotic as it does not allow the number of cells to exceed 110,000.
B. The seaweed extract is an antibiotic as it reduces the number of cells producing violacein.
C. The seaweed extract is a quorum-sensing inhibitor as it stops the cells from producing violacein, preventing them to multiply.
D. The seaweed extract is a quorum-sensing inhibitor as it prevents cells to communicate with each other without killing them.