AST 248 HW for Chapter 5
Ryan Richards
Review Questions
Briefly describe the six key properties that appear to be shared by most living organisms
on Earth.
1) Order: The internal structure of all living organisms is ordered i.e., not randomly
oriented. The book notes that order doesn’t make something alive. The example they give
is a book.
2) Reproduction: Living organisms reproduce either asexually like bacteria or sexually like
humans and plants. This leads to the growth of a species.
3) Growth and Development: Living organisms grow and develop with a direct correlation
to their ancestral history or heredity. Of course other factors may influence how
organisms develop such as their environment.
4) Energy Utilization: Living organisms use energy to create and maintain cell production,
growth and the ability to reproduce. For example, in humans we create energy by
breaking down glucose in a process known as cellular respiration. As some may know
from biology, this occurs in the mitochondria. The processes involved in cellular
respiration are glycolysis, the Citric Acid cycle and the electron transport chain (I said
this to enrich your learning experience).
5) Response to the Environment: Living organisms interact with their environmental
surroundings and respond to any changes. For example, the weather influences how we
may dress. The book gives the example of simple organisms moving to region where the
temperature is suitable for growth.
6) Evolutionary Adaptation: Over time, organisms evolve to be more adapted to their
environment.
Why do we say that living cells are carbon-based? Briefly discuss whether life elsewhere
could be based on something besides carbon.
We say living cells are carbon-based because carbon atoms are essential in creating more
complicated molecules such as proteins etc. What makes carbon atoms so special are their
bonding properties (quiz 4). Carbon can form stable single, double, and triple bonds with other
molecules as well as form long chains and bend itself. It would be difficult for life to form from
something other than carbon. Carbon is in group 14 of the periodic table so we may expect other
elements of this group to have similar properties like silicon. However, as you progress down the
group, the atoms become bigger and have different bonding properties than carbon. Silicon
weakly bonds with other atoms making them less stable.
Quick Quiz
Which of the following is not a key property of life? (c) the ability to violate the second law of
thermodynamics
In case you forgot, the second law of thermodynamics says that the entropy of any closed system
should increase with time. It also says that heat moves from an area of hotter temperature to
colder temperature. Another formulation is that heat cannot move from a colder temperature to a
hotter temperature. Interestingly we know of an everyday piece of equipment that does this, a
refrigerator. However it doesn’t violate this law because it does work, you need to do work to
move heat from a colder temperature to a warmer temperature. That is why the back of your
refrigerator is so hot; it’s doing work.
Which of the following is not considered a key piece of evidence supporting a common
ancestor for all life on Earth? (a) the fact that all life on Earth is carbon-based.
People belong to the domain (a) Eukarya
Generally speaking an extremophile is an organism that (a) thrives in conditions that would
be lethal to humans and other animals
Investigate Further
Rock Life? How do we know that a rock is not alive? In terms of the properties discussed in
this chapter, clearly describe why a rock does not meet the criteria for being alive.
Keeping the above conditions in mind, we clearly see that a rock is not alive. The only property
that a rock has in common with living organisms is order. However, a rock cannot reproduce
and it doesn’t utilize energy. These are a few of the criteria that distinguish rocks from living
organisms.
A Separate Origin? Suppose that we someday discover life on Mars. How might we be able
to determine whether it shares a common origin with life on Earth (perhaps suggesting that
life traveled on meteors between the two planets) or has a complete separate origin?
Explain clearly.
We begin by analyzing the question. If Martian life and Earth life shared a common origin, we
would look for properties that share a common trait by coincidence. One example to determine if
life on earth has a common ancestor is looking at the chirality of amino acids. Chirality simply
means mirror image. Living cells on Earth have adapted to using left-handed amino acids to
create proteins. If life on Mars also shares this same abundance of using left-handed amino acids,
this would be a good way to check if there was a common origin between life on the two planets.
Another example would be looking at the structural unit of energy, ATP. All life on Earth use
ATP for energy storage. If life on Mars uses this same molecule for energy storage, it would
offer more evidence for a common origin of life.