Objective
Students will discover the transfer of energy and matter between
marine organisms from a molecular perspective, including the contribution
of the microbial loop to the traditional marine food web
Background | Materials | Procedure | Discussion
Background
As human beings, we have evolved to rely heavily on our
sense of sight. Our vision is an important tool to gather information
and understand what is happening around us. But even our excellent
vision has limitations - we can only see things within a certain
size range 
Couldn’t quite read that? Well, the point is that many things are too small for us to see, including much of the life and matter on this planet. We tend to be more familiar and comfortable with things when they are on a scale large enough that we can see them. As a result, most of us don’t usually think of how things happen on very small scales – but it’s important that we do because all living things are not only composed of molecules, they also rely on molecules for their energy to live (including us!).
Let’s take an example of a person eating an apple. How does the energy from the apple actually get into their body and become energy they can use? You can watch them take bites, and know that they chew and swallow the pieces, and that those pieces provide them with energy. End of story, right? … not quite. Those bites of apple make their way to the stomach where digestive enzymes break down the pieces into smaller and smaller pieces, and eventually into molecules, that are absorbed into cells in our stomach and intestines and carried by our bloodstream.
Ultimately, energy in living organisms is used or created at the molecular level. Organisms break down their food into molecules, and then use those molecules to create energy for respiration (the basic functions that keep us alive) or store it to build other molecules for growth. So, you can see (well, actually you can’t) that energy and matter are truly transferred at the molecular level for living things.
What about the flow of energy and matter between organisms in the marine environment? We’re able to see large organisms feed and grow in the ocean, but are things that happen at the molecular level important in the ocean as well? Click on the link below to find out …
It was only 30 years ago that scientists first began to understand that bacteria and other microbes play a big role in the cycling of matter and energy in the ocean. Without the microbial loop, a large portion of organic carbon on the planet would remain dissolved for thousands or millions of years before returning to the food web.
Bacteria are a critical link not only for recycling dissolved organic matter, but also for converting organic carbon to inorganic carbon through metabolic processes such as respiration. In fact, most heterotrophs (organisms that consume other organisms for energy) create inorganic carbon in the form of CO2 through respiration, including humans. This CO2 can then be used by many autotrophs (organisms that convert inorganic molecules into energy) such as plants, algae and cyanobacteria to create energy that helps fuel life for much of the rest of the planet. For example, CO2 created by bacteria as they “feed” on DOM and respire can be used by phytoplankton to perform photosynthesis and create their own energy.
All organisms rely on carbon-based molecules for at least part of their survival, growth and reproduction. In the next activity you’ll be asked to consider how matter and energy move through a marine food web by tracing the multiple pathways that can be taken by carbon as it transforms into different molecules. Good luck!
Materials
Computers with Internet access for groups of 2-4 students
For each group of students:
Game Board
Set of Destination Cards
Set of Fate Cards
For each student:
Set of Game Pieces
Copies of the student worksheet
-
Divide students into groups of 2-4 based on the available number of computers, or preferred group size
-
Have students read through the Background information and view the on-line Microbial Loop Tutorial
-
In their groups, provide the students with the ‘Get in the Loop’ Board Game materials and have them play the game using the following rules:
a. The game can be played by 1-4 players.
b. Each player should select a color for their game pieces - each color will have four pieces which represent a carbon compound (a fat, carbohydrate, protein or nucleic acid)
c. Determine which student in the group will start, and have them place any one of their four game pieces on the phytoplankton.
d. The student should select a Destination card. Each Destination card represents one group of organisms in the food web. If there is a black arrow pointing from your current location on the game board to the location you selected on the destination card then move your piece to that location and proceed to step “e”. If there is not a direct connection from your current location to the location on your destination card remain where you are and the next player goes in turn.
e. Once you have moved to your destination location select a Fate card. This card will determine whether you: a) remain in the organism to eventually be moved through organisms in the food web, b) excreted or lost from the system as dissolved organic matter, in which case you move your game piece to the DOM location, or c) are released as CO2 during respiration, in which case you move to the CO2 location.
f. Once your new location on the board is determined, select the proper carbon compound from your game pieces based on the information on the Fate card and place it at that location – allow the next player to go in turn.
g. The game ends when one of the players reaches the shark with one of their game pieces. However, once you reach the shark you must still select a Fate card to see if you remain in the shark (in which case you win), or return to the DOM or the CO2 (in which case you start all over again). -
Once the game is completed, have the students complete the discussion questions on their worksheets.
-
Your carbon molecule has finally been incorporated into the shark – now what? Draw and explain different ways for the carbon compounds to get back to the beginning of both pathways and eventually become part of another shark.
-
Why is there only one pathway out of the DOM?
-
It is estimated that only 10% of the particulate biomass at any one trophic, or feeding, level is incorporated into the biomass of the next level. This game does not accurately reflect these data. How could you change the game to make it more accurate? What would be the drawback to making that change?
-
For a carbon molecule that was not lost from the food web the probability of moving through the web as “particulate” carbon vs. “dissolved” carbon was 50/50. What does this tell you about the importance of the microbial loop in the marine food web?
-
I’m stuck …I’m stuck! There were times when you may have spent several turns in a row stuck at the same position on the game board. Is this a problem with the game, or does this reflect true conditions in the movement of carbon through the ecosystem? How do you know?
-
Your game pieces represent different carbon molecules - either a carbohydrate, nucleic acid, fat, or a protein. Why is there a need to have different game pieces rather than just using a single type of carbon molecule throughout the game? Write down your thinking and some evidence for your answer below.