Materials Included In Kit

Additional Materials Required

Prelab Preparation

Prepare the fertilizer water.

1. The fertilizer water can be made in advance but will grow algae if exposed to light.
2. Add 2 mL fertilizer concentrate to 2 L of aged tap water or bottled water in a labeled container.
3. Store in a cool dark place in a sealed bottle.

Safety Precautions

Mealworms are considered to be a clean and safe organism. The Flinn Mealworm Diet contains wheat and those with gluten allergies should be especially diligent. Wash hands thoroughly with soap and water before leaving the laboratory. Please consult current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Never release living specimens into the local ecosystem. Mealworms make excellent food for many amphibians, birds, fish, and reptiles. Otherwise the mealworms or adult beetles must be euthanized prior to disposal. The wheat can be considered Type VI Biological Waste and disposed of in the normal garbage.

Lab Hints

• Enough materials are provided in this kit for 8 groups of students. This lab will last for several weeks. Most days only a few minutes will be needed to maintain the plants and animals and to take notes or photos. Setup, harvesting, drying and planning days will take most or all of a 50-minute lab period.
• The health and safety of any animals used in this lab must be considered prior to ordering or collecting the animals. Longterm maintenance or euthanasia should be considered and planned for ahead of time. Most states require special collection permits before plants or animals can be captured from local ecosystems. No plants or animals used in a laboratory should be released into the wild. Purchased specimens may be invasive. Purchased or collected specimens may have become infected or become ill while captive and therefore may harm the local ecosystem.
• Contact Flinn Scientific for a guide on how to maintain a long term culture of mealworms. Request publication 10584. Mealworms are often used as a food source for amphibians, birds, fish and reptiles. Adult beetles are a food source for amphibians, birds and reptiles. Pupae do not move and are not suitable as a food source for those animals that require moving prey.
• If no laboratory oven is available, it is possible to dehydrate the wheatgrass using a food dehydrator. The wheatgrass should remain in the dehydrator for a minimum of six hours.
• If desired, allow students to determine the dry mass of the mealworms. Small insects such as mealworms are typically placed in a freezer overnight to euthanize them. The percent dry mass provided in the Background section was determined by euthanizing and then drying 30 of each life stage in a laboratory oven using the same procedure outlined in the Baseline Activity. These data are comparable to published data.
• It is possible to use window screen to sift the wheat bran and remove the fecal matter and eggs in order to estimate the amount of wheat bran consumed. This step was purposely omitted because small pieces of wheat bran will sift the screen and skew the results. If students think of this step you may wish to allow them to discover this on their own.

Teacher Tips

• Have students construct a bomb calorimeter using the Flinn Scientific’s free write-up “Soda Can Calorimeter.” Contact Flinn Scientific and request publication 10861.

Further Extensions

Alignment with the Concepts and Curriculum Framework for AP^® Biology 

Big Idea 2: Biological systems utilize free energy and molecular building blocks to grow, to reproduce and to maintain dynamic homeostasis.

Enduring Understandings
2A1: All living systems require constant input of free energy.
2A3: Organisms must exchange matter with the environment to grow, reproduce and maintain organization.
2D1: All biological systems from cells and organisms to populations, communities, and ecosystems are affected by complex biotic and abiotic interactions involving exchange of matter and free energy.

Big Idea 4: Biological systems interact, and these systems and their interactions possess complex properties.

Enduring Understandings
4A5: Communities are composed of populations of organisms that interact in complex ways.
4A6: Interactions among living systems and with their environment result in the movement of matter and energy.

Learning Objectives

• The student is able to explain how biological systems use free energy based on empirical data that all organisms require constant energy input to maintain organization, to grow, and to reproduce (2A1 & SP 6.2).
• The student is able to justify a scientific claim that free energy is required for living systems to maintain organization, to grow, or to reproduce, but that multiple strategies exist in different living systems (2A1 & SP 6.1).
• The student is able to predict how changes in free energy availability affect organisms, populations, and ecosystems (2A1 & SP 6.4).
• The student is able to refine scientific models and questions about the effect of complex biotic and abiotic interactions on all biological systems from cells and organisms to populations, communities, and ecosystems (2D1 & SP 1.3, SP 3.2).
• The student is able to design a plan for collecting data to show that all biological systems are affected by complex biotic and abiotic interactions (2D1 & SP 4.2, SP 7.2). 
• The student is able to analyze data to identify possible patterns and relationships between a biotic or an abiotic factor and a biological system (2D1 & SP 5.1).
• The student is able to apply mathematical routines to quantities that describe interactions among living systems and their environment, which result in the movement of matter and energy (4A6 & SP 2.2).
• The student is able to predict the effects of a change of matter or energy availability on communities (4A6 & SP 6.4).

Science Practices
1.3: The student can refine representations and models of natural or man-made phenomena and systems in the domain.
1.4: The student can use representations and models to analyze situations or solve problems qualitatively and quantitatively.
2.2: The student can apply mathematical routines to quantities that describe natural phenomena.
3.1: The student can pose scientific questions.
3.2: The student can refine scientific questions.
4.2: The student can design a plan for collecting data to answer a particular scientific question.
5.1: The student can analyze data to identify patterns or relationships.
6.1: The student can justify claims with evidence.
6.2: The student can construct explanations of phenomena based on evidence produced through scientific practices.
6.4: The student can make claims and predictions about natural phenomena based on scientific theories and models.
7.2: The student can connect concepts in and across domains to generalize or extrapolate in and/or across enduring understandings and/or big ideas.

Sample Data

Mealworm Data

Wheatgrass Data

Answers to Questions

Opportunities for Inquiry

1. Consider the following questions while reflecting upon your observations of the wheatgrass, the mealworms and the data collected.
   1. How many kilocalories were transferred from food to Tenebrio biomass over the course of the experiment?
      {11154_Answers_Equation_1}

      0.01g x 0.36 x 6.5 kcal/g = 0.02 kcal Essentially, it was unchanged.

   2. How many kilocalories of free energy were transformed to chemical energy in wheatgrass from the first harvest to the second harvest?

      Δ dry mass x 4.0 kcal/1 g
      (0.28 g – 0.18 g) x 4.0 kcal/1 g = 0.40 kcal
      The amount of free energy converted to chemical energy was 0.40 kilocalories.

   3. Was it necessary to add water to the wheatgrass containers? Why?

      Yes, it is necessary to add water to the wheatgrass containers. Some of the water is used by the plant but much of it evaporates.

   4. Why it was necessary to mass more than one plant and then calculate the average mass?

      The mass gained by a single plant would not necessarily represent the normal change in mass. Also, the actual gain per plant is extremely small. It is good protocol to use more than one specimen when working with such small changes in mass.

   5. Calculate the net primary productivity in grams per square meter per week for the population of wheat plants.

      1) Calculate the area of the container (πr²) in meters. = π(0.054)2 = 0.0092m²
      2)

      {11154_Answers_Equation_2}
   6. Describe the changes in the wheat bran and other solids found in the Tenebrio culture container.

      The flakes of tan wheat bran are gradually consumed. A fine tan powder begins to appear in the container.

   7. Calculate the net primary productivity in grams per meter per week for the population of Tenebrio.

      Unable to calculate this since the mass stayed constant in this closed system.

   8. Did the mealworm container change mass over the weeks of the experiment? What does this indicate about the conservation of matter and energy in a closed system? (That is a system in which nothing is added or removed.)

      No, the mass did not substantially change within the Tenebrio culture. This supports the law of conservation as mass was neither created nor destroyed. The Tenebrio consumed the wheat bran and used the macromolecules for metabolism and growth. Waste was excreted. Another possible student answer may discuss the fact that the change in mass is too small to be measured with the equipment available in the school’s lab.

   9. Did the mealworms grow or progress from larvae to pupae to adult beetles during the experiment? What does this indicate about the conservation of matter and energy in a closed system? (That is a system in which nothing is added or removed.)

      The mealworms do change over the course of the experiment. Depending upon the larval stage of the original culture, they may progress from mealworm to pupae or mealworm to adult beetle.

   10. Are there ways to increase the net productivity of either the wheat or the mealworms?

       Answers may include suggestions such as adding vitamins or nutrients to the Tenebrio culture or optimizing plant growth.

   11. What environmental factors may affect the net productivity?

       Optimal conditions should increase net productivity whereas cold temperatures, a lack of light or other less-than-optimal conditions will decrease net productivity.

   12. How can the respiration rate be determined for the wheat or the Tenebrio?

       A respirometer can be used to determine the respiration rate of both the wheat and the Tenebrio.

   13. Is the net primary productivity different for a dicot or another small animal?

       This is an experimental choice. The data table below shows the net primary productivity of radishes. Radishes are a dicot.

       {11154_Answers_Table_3}

References

AP Biology Investigative Labs: An Inquiry-Based Approach. College Entrance Examination Board: New York, 2012.

Biology: Lab Manual. College Entrance Examination Board: New York, 2001.

Introduction

Energy is essential for life. Energy flows through biochemical pathways within cells but it also flows from one organism to another as food. Energy enters into a food web either as solar energy captured as part of photosynthesis or as chemical energy captured by chemosynthetic bacteria in specialized ecosystems. No matter the source, this energy is used to create complex energy rich macromolecules which are either used immediately to maintain homeostasis or are stored for later use. Consumers feed on organisms in order to acquire complex energy rich macromolecules for their own needs. This investigation demonstrates how ecologists determine the flow of energy along a simple food chain.

Concepts

• Community modeling
• Ecological pyramid
• Net primary productivity
• Energy conservation
• Conservation of mass
• Producers vs. consumers

Background

Food chains and food webs are pictorial representations of the flow of energy from one organism to another (see Figure 1). Most often these diagrams focus on a food chain based on the Sun’s energy being captured by photosynthesis. A similar chain forms in some of the deepest areas on Earth where chemosynthetic bacteria capture energy from sulfur vents on the sea floor and other harsh environments. Since the Sun food chain is the most common, that is the one we will focus on in this investigation.

Determining the total amount of energy available is not as simple as measuring the amount of light energy that hits the Earth’s surface. Some ecosystems are more efficient than others when it comes to capturing energy. Aquatic ecosystems are vast but capture 1% or less of the Sun’s energy that falls on the oceans. Tropical rain forests are able to capture up to 3%. The rest of the energy becomes heat. But how were these numbers determined? Special solar energy meters that only measure the energy in the wavelengths used for photosynthesis were developed many years ago. These expensive meters measure the maximum energy available but are useless in determining the actual energy captured in the ecosystem.

In order to determine the actual amount of energy captured, scientists must measure the dry mass of all life within that ecosystem. The mass is converted to energy using calories per gram, a known constant for each organism. This will be discussed in more depth later in the lab. Since ecosystems are complex, scientists harvest part of the ecosystem or use a simplified model system to make an estimate of the whole.

A great place to start is with plant life. Plants use water, carbon dioxide, trace nutrients, and light to grow and carry out metabolic functions. Plants convert these raw materials into macromolecules, which have mass and store energy. Gross primary productivity is a measure of the total amount of energy converted by plants during photosynthesis and includes accounting for the energy in the waste products of photosynthesis and respiration. This is not easily measured because the waste products are oxygen and carbon dioxide. Scientists are generally interested in the amount of energy available to the next trophic level, or net primary productivity. The total mass of all the plants in an ecosystem at a given time is the biomass of the ecosystem. The added dry biomass that grows within a measured area over a specific amount of time is the net primary productivity. This is reported in grams per square meter per week, or as kilograms per square meter per year, depending on the type of ecosystem and nature of the study.

When plants grow from tiny seeds to large organisms, it may seem that they create mass from nothing. However, the law of conservation of mass states that mass cannot be created or destroyed, simply rearranged into different molecules. Where does the dry mass come from? Living things are carbon-based organisms; fats, carbohydrates, and proteins are primarily carbon, hydrogen, and oxygen. Therefore, the mass of the plant mainly comes from carbon dioxide and, to a lesser extent, water.

Primary consumers, those that eat plants, are not able to capture 100% of the plant’s biomass for growth. They use most of the energy they acquire from plants just to maintain homeostasis. In addition, not all of the plant is digestible and a large fraction is lost as fecal waste, heat, and waste gases. Only a fraction of the energy acquired is used to make more cells (growth). By massing the animal over time, the net secondary productivity can be determined.

The productivity loss at each level determines the total number of trophic levels that are able to exist in that ecosystem. This is represented by an ecological pyramid (see Figure 2). A primary consumer assimilates plants and uses most of the plant’s biomass for metabolism. On average, 5–20% of the primary consumer’s biomass is converted to growth. A predator (secondary consumer) then eats the primary consumer. Again, much of the herbivore is used to maintain homeostasis in the predator leaving less biomass for growth. This means that the predator must consume numerous herbivores to maintain itself and to grow. When this predator is consumed by another predator, the amount of biomass available for the next animal on the food chain is once again reduced. A population study would show very few top predators in an ecosystem but thousands of plants. Biomass is typically reported as a dry mass because water content can vary greatly and does not contribute energy. Consider the differences in the mass of the prairie grass in a one square meter area of prairie in a drought year versus a rainy year. By drying the prairie grasses the mass of the macromolecules from one year to the next can be compared. Therefore, calculations must be done on dried plants and animals. The percent dry weight can be calculated by massing the plants when they are harvested then drying them in a controlled environment and reweighing the same plants.

The law of conservation of energy also applies to ecosystems. The amount of energy used by the plant for metabolism and growth and lost as waste must equal the amount of energy captured by that plant. Similarly, the amount of energy consumed by the predator must equal that of its metabolism, wastes, and growth. Different biomolecules have different amounts of energy available for use. The amount of energy available in a plant or animal is measured in calories. A calorie is the amount of heat needed to increase the temperature of 1 gram of water by one degree Celsius. Calories are measured in an instrument called a bomb calorimeter. One gram of dry material is compressed into a disk. When this disk is used as fuel to heat water the change in the temperature of the water can be measured to determine the number of calories contained in the original sample. The Calories listed on a food label are actually kilocalories. The food unit is always capitalized while the scientific unit of measure is not. Carbohydrates and proteins have about 4 kcal per gram dry weight. Fats have about 9 kcal per gram dry weight. These numbers are true for plant fats, carbohydrates and proteins as well as for animal fats, carbohydrates and proteins. The ratio of fats, carbohydrates, and proteins in plants and animals may vary greatly depending upon the species and age of the organism. For example, a young shoot may contain mostly carbohydrates and protein whereas the seeds of a mature plant may contain mostly proteins and fats.

In this activity, the plant used is wheat, which is a monocot cereal grain and an important food crop. The type used in this experiment is a hard red winter wheat. The grain seeds are harvested for bread and other foodstuffs. Young blades of wheat, called wheatgrass, can also be used as food. Wheatgrass has an overall dry weight energy value of about 4 kcal per gram. The wheat seed contains the endosperm, the embryo called the wheat germ, and the hard outer layers called the wheat bran. In this activity, wheat bran will be used as the food source for mealworms. Wheat bran has an overall dry weight energy value of about 4 kcal per gram.

Mealworms are the larval form of the Tenebrio molitor beetle. These larvae are used by hobbyists and zoologists as an important food source for many amphibians, birds, fish, reptiles, and small mammals. The mealworm is easily cultivated in wheat bran. One metabolic pathway used by the larvae converts carbohydrates in the wheat bran into the metabolic water the larva needs to survive. In the lab this means that they do not need extra water added to their culture thereby eliminating one experimental variable. Since they are used as a food source, the energy content of the Tenebrio has been determined. Like most living things their caloric value and dry weight varies according to their stage in life. The larvae have an overall energy value of 6.5 kcal/g and are 36% dry weight. The pupae have an overall energy value of 6.4 kcal/g and are 35% dry weight. The adult beetles have an overall energy value of 5.8 kcal/g and are 34% dry weight.

Experiment Overview

The Baseline Activity explores the net productivity for wheat and one of its predators, the mealworm. Daily observations allow for the study of the life cycle of a metamorphic animal and the growth of a monocot plant. The results of this baseline activity provide a procedure and model for open-inquiry and student-designed experiments—see the Opportunities for Inquiry section.

Materials

Safety Precautions

No parts of this laboratory are considered hazardous. Do not handle living animals unnecessarily. Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines.

Procedure

Baseline Activity: Setup

Part A. Wheat

1. Use a dissecting needle or a dissection pin to poke at least 30 holes into the bottom of two of the containers. Move the dissection needle or pin around when forming each hole to ensure each hole remains open.
2. Label the container as instructed so it can be identified later.
3. Measure the area of the container in square meters.
4. Fill the two containers about halfway with vermiculite.
5. Thoroughly wet the vermiculite with the dilute fertilizer solution.
6. In each container, distribute 100 wheat seeds evenly on top of the wet vermiculite.
7. Cover the seeds with a light layer of vermiculite.
8. Place a piece of plastic wrap over the top of the container while the wheat plants sprout.
9. Place the containers in the planting trays in the grow area. The grow lights should be raised as the plants grow so they are always about 6 inches above the wheat plants.

Part B. Mealworms

1. Use a dissection needle or a dissection pin to poke at least 30 holes into the lid of the container. Move the dissection needle or pin around when forming each hole to ensure each hole remains open for air exchange.
2. Measure the area of the container in square meters.
3. Mass the container and write this on the side of the container.
4. Mass 10–20 g of mealworm diet (wheat bran) in a weighing dish. Record the mass. Transfer to the empty container. Wipe out the weighing dish with a paper towel.
5. In the weighing dish, mass 10–15 mealworms; record the mass. Transfer to the container with the wheat bran. Keep the weighing dish for future measurements.
6. Record the combined mass of the container, wheat bran and mealworms.
7. Label the container as instructed so it can be identified later.
8. Place the aerated lid onto the container and place the mealworm culture in a designated area.

Baseline Activity

1. Make daily observations and maintain the wheat and mealworms for 2–3 weeks.
   1. Plant maintenance:
      1. Water the wheat as necessary.
      2. Add vermiculite as needed to the wheat containers. The vermiculite holds water but compresses over time. This is especially important over the weekend when plants may dehydrate and die.
      3. Remove the plastic wrap once the wheat seeds have grown enough to touch it.
   2. Animal care:
      1. Once adults emerge add small pieces of apple to the culture. The adult Tenebrio do not eat wheat bran and will cannibalize the pupa instead.
      2. As the culture progresses it may be necessary to add more wheat bran and to collect deceased animals and sheds. Keep track of the mass of any added wheat bran and anything removed from the culture.
2. Once a week:
   1. Mass the entire mealworm container, wheat bran and Tenebrio.
   2. Gently collect all of the Tenebrio (mealworms, pupae and beetles) into a weighing dish and mass them.
   3. Determine the mass of the solids within the container, including wheat bran, fecal matter and eggs (if adults are present).
3. Once the wheat reaches a height of 4 inches, harvest the entire wheat crop from one of the two containers:
   1. Record the number of days since planting.
   2. Gently remove all of the vermiculite from the roots. Note: This can be a time consuming process. Remove as much vermiculite as possible, then use a tub of water to rinse off most of the remaining vermiculite. Use gently running water to completely remove the vermiculite. Note: Do not rinse large amounts of vermiculite down the drain. It will clog the pipes.
   3. Pat the wheatgrass dry and mass.
   4. Calculate the average mass per plant.
   5. Create an aluminum tray using the aluminum foil (see Figure 3).
      {11154_Procedure_Figure_3}
   6. Mass the aluminum tray.
   7. Place the wheatgrass onto the tray and place into a 105 °C laboratory oven. Allow the wheatgrass to dry for 24–48 hours.
   8. After the wheatgrass has dried, mass again to determine the dry weight.
   9. Calculate the average dry mass per plant.
4. Allow the remaining container of wheatgrass to grow one or two more weeks, and then harvest the remaining wheat crop using the same procedure as in step 3.

Opportunities for Inquiry

1. Consider the following questions while reflecting upon your observations of the wheatgrass, the mealworms and the data collected.
   1. How many kilocalories were transferred from food to Tenebrio biomass over the course of the experiment? Use 6.5 kcal/g for the dry mass and 36% for the percent dry weight.
   2. How many kilocalories of free energy were transformed to chemical energy in wheatgrass from the first harvest to the second harvest? Use 4.0 kcal/g for the dry mass.
   3. Was it necessary to add water to the wheatgrass containers? Why?
   4. Why was it necessary to mass more than one plant and then calculate the average mass?
   5. Calculate the net primary productivity in grams per meter per week for the population of wheat plants.
   6. Describe the changes in the wheat bran and other solids found in the Tenebrio culture container.
   7. Calculate the net secondary productivity in grams per meter per week for the population of Tenebrio.
   8. Did the mealworm container change mass over the weeks of the experiment? What does this indicate about the conservation of mass in a closed system? (That is a system in which nothing is added or removed.)
   9. Did the mealworms grow or progress from larvae to pupae to adult beetles during the experiment? What does this indicate about the conservation of mass in a closed system? (That is a system in which nothing is added or removed.)
   10. Are there ways to increase the net productivity of either the wheat or the Tenebrio?
   11. What environmental factors may affect the net productivity?
   12. How can the respiration rate be determined for the wheat or the Tenebrio?
   13. Is the net primary productivity different for a dicot or another small animal?
   14. Of the factors identified in the above questions, which can be replicated as an experiment in the laboratory?
2. Plan, discuss, execute, evaluate and justify an experiment to test a question regarding the relationship between a plant and its predator, ways to influence the productivity of plants or animals or determine the productivity of a different species.
   1. Decide upon one question that your group would like to explore.
   2. Develop a testable hypothesis.
   3. Discuss and design a controlled procedure to test the hypothesis.
   4. List any safety concerns and the precautions that will be implemented to keep yourself, your classmates and your instructor safe during the experimental phase of this laboratory.
   5. Determine what and how you will collect and record the raw data.
   6. How will you analyze the raw data to test your hypothesis?
   7. Share your hypothesis, safety precautions, procedure, data tables and proposed analysis with your instructor prior to beginning the experiment.
   8. Once the experiment and analysis are complete, evaluate your hypothesis and justify why or why not the hypothesis was supported by your data.
   9. Present and defend your findings to the class.
   10. Make suggestions for a new or revised experiment to modify or retest your hypothesis.