Читать книгу Astrobiology - Charles S. Cockell - Страница 135

1 Give at least one reason why compartmentalization (for example using a membrane) has been regarded as a defining characteristic of life. Do you agree that it is an essential feature of a living thing?

2 Describe three differences between a prokaryotic and eukaryotic cell.

3 Microbes are sometimes said to be “simple.” Discuss this statement with respect to what you know about microbes, their internal structures, and other capacities. Do you think microbes today reflect the characteristics of the earliest life forms?

4 Explain the process of translation, describing quantitatively the concept of the “degeneracy of the genetic code.”

5 An alien genetic code has been found that has six bases in its code and only two positions in each codon. Can it encode for the same diversity of amino acids as terrestrial life? Compare the degeneracy of this code to the terrestrial genetic code. What about an alien code with two bases and four positions in its codons?

6 Compare a plasmid and a virus.

7 Some microbes are motile. Discuss how this attribute could be useful in an extreme environment, such as inside a deep ice sheet. Why might this characteristic have evolved in the first place?

8 Explain the importance of endosymbiosis in evolution.