In a microbiology laboratory, the technician uses heat to sterilise the nutrient solution that is used to grow a fungus. When the heating system broke down, he sterilised the solution by passing it (in a sterile environment) through a sterile filter with a pore size of `0.2` micrometers. when the fungs was grown on the filtered nutrient solution, it stopped growing and looked unhealthy within a few days. which statements is the most likely explanation for the observed effects on the fungus ?

Options

A. The nutrient solution contained a virus.
B. Heating makes the glucose in the nutrient solution more digestible
C. Filering removed one of the larger nutrient molecules
D. The nutrient solution contained a bacterium that was pathogenic to the fungus.

Explanation

To solve the question regarding the observed effects on the fungus when grown on a filtered nutrient solution, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Context**:
- The technician typically uses heat to sterilize the nutrient solution, which is essential for eliminating any unwanted microorganisms that could compete with or harm the fungus being cultivated.

2. **Sterilization Method Change**:
- Due to the breakdown of the heating system, the technician switched to using a sterile filter with a pore size of 0.2 micrometers to sterilize the nutrient solution. This method is effective for removing bacteria and larger contaminants.

3. **Effect of Filtration on Nutrients**:
- The pore size of 0.2 micrometers is small enough to filter out most bacteria, but it does not filter out smaller molecules such as glucose, which is a crucial nutrient for the fungus.

4. **Observation of Fungus Growth**:
- After the fungus was grown on the filtered nutrient solution, it stopped growing and appeared unhealthy within a few days. This indicates that something in the nutrient solution was not suitable for the fungus.

5. **Analyzing Possible Explanations**:
- **Statement 1**: "The nutrient solution contained a virus." - This could inhibit the growth of the fungus by affecting its cellular processes.
- **Statement 2**: "Heating makes the glucose in the nutrient solution more digestible." - Incorrect, as heating would destroy glucose, not make it more digestible.
- **Statement 3**: "Filtering removed one of the larger nutrient molecules." - Incorrect, as glucose is a small molecule and would not be filtered out.
- **Statement 4**: "The nutrient solution contained a bacterium that was pathogenic to the fungus." - Incorrect, as pathogenic bacteria would not pass through the filter.

6. **Conclusion**:
- The most likely explanation for the observed effects on the fungus is that the nutrient solution contained a virus that inhibited the fungus's growth.

### Final Answer:
The most likely explanation for the observed effects on the fungus is that the nutrient solution contained a virus that inhibited its growth.

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