HW #4

1) Why is water so important for life on Earth? List the three major roles that water plays in metabolism.

A liquid of some kind is needed to allow organic chains and molecules to travel and interact. Water can get very warm, in contrast to other liquids on planets such as methane which is very cold in liquid form. Reactions happen faster in warmer temperatures than cold ones, allowing cellular respiration and other reactions to go quicker. Water also carries chemicals in and out of cells to ensure they get the nutrients they need.

 2) What do we mean by an “RNA World” and why do scientists suggest that such a world preceded the current “DNA World”?

The "RNA World"  was early in Earth's life when prokaryotes and other simple life forms were the only things inhabiting Earth. RNA was the original  genetic code, and its  simple design was easy to create. RNA was the precursor to the development of DNA. Eukaryotes, complex life, is based on DNA. At some point in the evolutionary chain, RNA found a way to pair up and replicate, and with replication came larger multicelled organisms.

 3) Summarize the three major environment requirements for life. Overall, what “litmus test” seems appropriate for constraining our search for habitable worlds, and why? 

One of the basic requirements of life are elements such as O, N, C, and H can combine in various ways to form larger organic molecules. Other requirements include energy and liquid water. Energy from sunlight works if the planet is close enough to the sun, and chemical energy is also another source of energy but needs atmosphere or liquid water. Liquid water is by far the most important requirement for life. It is a solvent that allows for molecules to move around and undergo reactions. A good "habitability test" would be to see how far away the planet is from its sun, in regards to the size of the sun. Since water plays such a vital role in all of the processes of life, we should look at planets that have the conditions for liquid water. There is the possibility to life based on something other than carbon, but water would still be  needed  to facilitate  transportation and movement within and between cells.