|From Mrs. Mazen...
Biology is the study of life. If we are going to study life, we must explore and define what being alive means. We can start by getting in touch with ourselves. Conversely, we may consider what being dead or inanimate means. Next, we can start to describe our feelings of what life is. In our classroom, we have and will continue to explore the question "What is life?", the origin of life, and evolution.
In our quest, we will discuss the work of many past and present scientists. This week we discussed two basic theories of how life beganspontaneous generation or abiogenesis and biogenesis. Abiogenesis is the theory that life comes from non-living matter. Biogenesis is the theory that life comes from life. We discussed the ideas of Aristotle, Francesco Redi, John Needham, Lazzaro Spallanzani and Louis Pasteur.
Our class is repeating Pasteur's experiment with the swan-necked flasks. Students are observing their flasks on a daily basis for any signs of life. At the end of a week, we will examine the broths microscopically for the presence of living organisms.
In addition, we discussed Oparin's idea that life was preceded by a long period of chemical evolution. He based his hypothesis on what scientists thought the Earth was like after it was formed. Oparin hypothesized that organic molecules were formed from the atmospheric gases and collected in the water. He thought that some of these organic molecules may have concentrated as areas dried up or by molecules adhering to solid surfaces. In addition, parts of protein molecules may have ionized (become charged). An organized layer of water molecules may then have formed around these charged proteins forming precell droplets called coacervates.
This week we attempted to make coacervates using a solution of gelatin (source of protein), a solution of gum arabic (carbohydrate), and hydrochloric acid. Most of the class was able to see coacervate formation.
Our discussion continued with an examination of Stanley Miller and Harold Urey's work. Basically, they set out to test Oparin's hypothesis. Together they constructed an apparatus to recreate the conditions that may have been present in the early atmosphere. Their experiment produced many organic compounds including some amino acids. Amino acids are the building blocks of proteins. As far as we know, no form of life without proteins exists.
In an attempt to define some of the characteristics of life we discussed the cell theory. In addition, we compared and contrasted eukaryotic and prokaryotic cells. As part of this discussion, we talked about how eukaryotes may have evolved and Lynn Margulis's Endosymbiotic theory. We will continue to discuss this theory as we learn more about cells. When the Gram Stains of the broth's from our experiment are made, we will be able to see bacterial cells (prokaryotic). Previously, we examined slides with amoebae (eukaryotes).
As we move forward, we will begin to study the biochemistry of life. Next week we will review some basic chemistry and then take a look at some of the interactions in living organisms. We have already discussed the three basic components of metabolism: digestion, respiration, and synthesis. Now we will look at each of these on the molecular level. As we acquire knowledge about the biochemistry of life, our definition of life will evolve.
As an assignment, I asked each student to write an essay describing what life is and how they think life originated. It will be interesting to see how their opinions evolve from this point in the year through the end of the school year will just be so interesting.
I hope that all of my students enjoy studying life. Together we will watch, learn, struggle, and celebrate our findings. As we work together, each of us will share our opinions and feelings. Our thinking about life will evolve just as all life evolves.
|Origin of Life Theories|
|Now that you've heard about most of the theories that are out there, who do you believe? Some students have submitted their interpretations here.|
|Read Student Theories|
More Origin of Life Resources
After life originates, it needs a place to live. The next subject for investigation is the cell. In the next few weeks, "BioPoint" will feature student presentations and demonstrations about the cell.