In 2012, the Curiosity rover Island on Mars. Curiosity was designed to assess wh

ID: 69240 • Letter: I

Question

In 2012, the Curiosity rover Island on Mars. Curiosity was designed to assess whether the Martian environment was ever capable of supporting microorganisms. Using the newer technology available on Curiosity, NASA scientists repeated their experiments on the specimen discovered over two decades earlier (Viking landers never returned specimens to earth). The results contradicted earlier findings. Scientists no longer believe the earlier claim that the specimen has been alive. In your lab group, fill out the chart below based on Table 2 findings. Conclude whether the results of each experiment support, or contradict the hypothesis that the specimens are biotic. Which experimental findings above do you find most compelling? Do they support or contradict the hypothesis? Then formulate an argument to support your conclusion.

Explanation / Answer

Experiment

Conclusion

Supports/contradicts

Specimen culture

White film on the surface of the culture is generated. This supports the presence of microorganisms in the culture.

White film resembles bacterial growth, but it takes three weeks to grow. The time period seems very long. Further analysis of the culture becomes necessary .

Gamma radiation

Exposure of the specimen to gamma radiation prevents the formation of white film. This observation supports presence of some biotic factor.

This observation supports presence of some biotic factor.

If it's true that the generation of white film is bacterial growth then specimen are susceptible to gamma radiation. And if the white film production is due to some abiotic factor then the film production reaction is repressed by gamma radiation.

Microscopic appearance

On microscopic examination of specimen, they appeared like cocci. This observation supports presence of some biotic factor.

This actually supports the presence of bacteria in the culture media.

DNA staining

The results of DNA isolation and staining deny the presence of nucleic acids, and hence biotic form.

As per our knowledge, every living organism on the earth posses nucleic acid (DNA/RNA; ss/ds) as the genetic material. Since EtBr staining shows absence of nucleic acids , there is no living specimen present in the culture. EtBr can also indicate the presence of ssDNA or ssRNA strands.

DNA presence

Similar to above explanation. The results obtained with this experiment do not support the presence of nucleic acids and hence any living specimen.

Nucleic acids absorbs at 260nm (both ss and ds).

Protein presence

Negative results of coomassie blue staining do not support the presence of some biotic factor.

Proteins are considered as the basic structural unit of any living thing. Negative results of coomassie blue staining do not support the presence of some biotic factor.

The above results do not allow to hypothesize that there is the presence of biotic component in the culture. The reasons for this contradiction are already explained in the table.