Name______Period_____

Modeling Energy Transfer in an Ecosystem

Honors Biology

Pre- Lab Questions:

  1. Define the following:
  2. Autotroph:
  3. Heterotroph:
  4. Trophic level:
  5. Primary consumer:
  6. Secondary consumer:
  7. Tertiary consumer:
  8. Quaternary consumer:
  9. Decomposers:
  10. Biomass:
  11. Food chain:
  12. Primary production:

2. Create a food chain below with the following organisms: frogs, humans, oats, trout, grasshoppers.

3. Put the organisms above into the energy pyramid below, labeling them with their trophic levels.

4. Where does the energy in the pyramid above initially come from?

5. About how much energy will one level receive from the previous level? Explain why.

* As part of your pre-lab, read through the introduction and define any words that are new to you on the back of

the lab so you are fully prepared for the lab.*

Introduction:

All organisms within an ecosystem interact with each other and one of the most fundamental ways in which they interact is by eating and being eaten. The producers in an ecosystem are able to make sugar for their own use through a process called photosynthesis. Photosynthesis is an anabolic process in which producers convert solar energy into chemical energy. They obtain carbon dioxide from the atmosphere and also take in water. They are able to capture energy from sunlight and convert it into simple sugars that they can then use for energy. Oxygen is also released as a byproduct during this process. Other organisms can then consume the producers to obtain their chemical energy. They obtain this energy from the sugars of the producer through a catabolic process called cellular respiration. During the process of cellular respiration organisms take in sugar from eating as well as oxygen from the air and are left with ATP (adenosine triphosphate-an energy carrying molecule easily used by cells), water, and carbon dioxide. The equations for these processes can be seen below:

As plants and other producers collect the solar energy and store it as sugar, they are also burning that sugar and using the energy to run their own life processes. Fortunately for heterotrophic organisms, they now have useable energy that can be provided to organisms within that ecosystem through consumption. This is what becomes the biomass. Biomass is the dry weight which contains energy in the form of calories. Unfortunately for consumers, the energy transfer between trophic levels is not 100% efficient. In fact, about 90% of the energy is lost as entropy (heat) when transferred to the next trophic level. (Note: this loss is a rough average). This transfer of approximately 10% of energy to the next level is referred to as the10% rule. Although we are unlucky in the fact that we only get 10% of the producers energy (if we eat the producer directly), biomass is a renewable energy source and can be regrown in a relatively short period of time.

Your Scenario:

An ecologist has genetically engineered his oat grain crop to contain more than 4 times the calories yield than typical grain. You will be determining just how many consumers can be supported by 1 acre of the oat grain by investigating the biomass of this oat grain over the course of a year. Oat grain is a plant crop that feeds many primary consumers in nature. You will be looking at how many primary producers affect the ecosystem’s total energy and how many consumers it can support. Primary producers take solar energy and convert it into chemical energy in the form of sugar. Plants can ONLY convert approximately 1.2% of the energy available to it from the sun. Using what you know about the 10% rule you will be calculating the number of organisms that you would be able to support in an ecosystem with your 1 acre of oat grain.

Your group has received a 1/100th sample of the oat grain harvested from the field to calculate the primary production. From there you will be using the “Helpful Information Appendix” to create a biomass and energy pyramid for the ecosystem. The organisms in the ecosystem are the same organisms that yo made your energy pyramid for during your pre-lab.

Procedure:

PART A: PRIMARY PRODUCTION GRAIN CALCULATIONS*Show all work in space provided*

  1. First you must determine the mass of the oats. Place your weigh boat on the scale and tare it so that the mass of the weigh boat will not be added to the mass of the oats, then add your oats.

Mass of oats for 1/100th of the acre (don’t forget units!):______

  1. Now calculate the total mass of the oatsharvested from the 1 acre property: ______
  1. Using the appendix, determine the total energy in the oats. ______
  1. Using your answer from step 3 and other information from the appendix, determine how many primary consumers (grasshoppers) can be fed for the year. (Round to nearest whole #)
  1. What is the amount of grasshopper TISSUE (biomass) in grams that can be supported at this trophic level?______
  1. Based on the fact that the number of calories calculated in the oat grain is 10% of the transferred energy, how much was used by the oat plant and lost as entropy?______

PART B- NUMBER OF SECONDARY CONSUMERS SUPPORTED

  1. To start, you must determine how many calories are present at the grasshopper’s trophic level ______
  1. How many calories are needed by 1 frog for 1 year? ______
  1. How many frogs can be supported for one year? (round to nearest whole number)
  1. What is the amount of frog TISSUE (biomass) in grams that can be supported at this trophic level?______

PART C- NUMBER OF TERTIARY CONSUMERS SUPPORTED

  1. Calories in frog biomass = ______
  1. How many calories are needed by 1 trout for 1 year? ______
  1. What is the # of trout that can be supported for 1 year? ______(round to nearest 100th)
  1. What is the amount of trout TISSUE (biomass) in grams that can be supported at this trophic level?______

PART D- NUMBER OF QUATERNARY CONSUMERS SUPPORTED

  1. Calories in trout biomass = ______
  1. How many calories are needed by 1 human for 1 year? ______
  1. What is the # of humans that can be supported for 1 year? ______(decimal ok)
  1. What is the amount of human TISSUE (biomass) in grams that can be supported at this trophic level?______

Helpful Information Appendix

Oat grain
Grasshopper
Frog
Trout
Human / Biomass = (grams measured)
8.15 calories/gram when eaten
Need 724 calories/yr to survive
biomass= 35 g/organism
2.05 calories/gram when eaten
Need 1,800 calories/yr to survive
biomass= 127 g/organism
1.4 calories/gram when eaten
Need 4,670 calories/yr to survive
biomass= 675 g/organism
0.65 calories/gram when eaten
Need 730,000 calories a year to survive
biomass= 50,000 g/organism

Questions:

  1. Construct each of the 3 ecological pyramids for this ecosystem: biomass, energy, numbers in the space below. Be sure to label the pyramids. (*You will need to estimate the amount of energy at the quaternary consumer level*)
  1. Explain how food chains/webs in an ecosystem are limited by primary production. (Cite at least 2 pieces of data)
  1. How might a farmer increase primary production of crops? Explain. (give at least 2 suggestions)