STUDENT INSTRUCTION AND ANSWER SHEET

Activity 2: Concept Introduction-Who Lives Where?

Most scientists agree that the Earth is approximately 4.5 billion years old. By the time the Earth was approximately 1 billion years old microscopic organisms had found a way to live on the volatile young Earth. However, it would take another 3 billion years before plants and animals would appear. We see that humans, plants and animals have been around for only a very short time in comparison to the time that microscopic organisms have existed. During the last three billion years these tiny life forms have gone through a tremendous evolution so as to adapt to the changing conditions on Earth. They can be found living in almost any environment imaginable. Of great interest to scientists is the unique way that these tiny organisms live in conditions in which all other forms of life fail. By better understanding how these life forms interact with their surroundings we hope to better understand how life could exist in the extreme environments found on other planets and moons in our solar system and beyond.

In this activity you will investigate three hypothetical environments and three bacterial life forms that could exist on Earth. For each we have provided a table with a partial list of characteristics that describe: (1) how the different environments support life and (2) the different needs of each bacteria in order to live within a particular environment. It will be your task to examine the characteristics that are provided for each environment and bacteria and then, based on this information, you will need to complete each table by deciding which bacteria could live in which environment.

In the table below we have listed the characteristics for each environment and bacteria. In the column next to each characteristic are the possible range of values that you will need to consider when matching each bacteria with its environment.

A. Complete (fill in) each of the tables for these hypothetical environments and bacteria by determining which of the bacteria could live in which of the environments.

B. State which bacteria (A, B, or C) you decided could live in which environment (X, Y, or Z.)

C. How did you choose which environment bacteria A could live in? How did you rule out the other environments? What characteristics of the other environments made them too extreme for bacteria A? What were the determining/limiting characteristics for the other bacteria and their corresponding environments? Explain your reasoning.

D. If the number of photons that arrive at environment Y were to decrease to nearly zero would the bacteria that you chose still be able to live in this environment? Explain why, or why not.

E. Would your answer to part D change if we were instead considering environment X or Z and the corresponding bacteria? Explain your reasoning.

F. Which of the bacteria use a carbon source that is organic and which of them use a source of inorganic carbon?

To describe how bacteria interact with their environment it is useful to consider the different ways the bacteria use energy and produce or consume food. To describe these different processes we use the following labels.

By combining the label for how the bacteria uses energy (chemo or photo) with the label that describes the type of carbon source needed by the bacteria (autotroph and heterotroph) we can generate a label that describes the interaction between the bacteria and its environment.

G. Label bacteria A, B, and C using the labels above.

H. Which of these bacteria live anaerobically and which live aerobically? Explain how you know.

I. Life forms that can live in extreme environments are often given special names. For instance a "thermophile" can live at extremely high temperatures near the boiling temperature of water. A "psychrophile" can live at extremely cold temperatures near the freezing temperature of water, and a "halophile" is able to live in conditions that have an extremely high concentration of salts.

Which of these hypothetical bacteria (A, B, or C) is a thermophile, a psychrophile or a halophile?