ap biology lab #08

1Copyright © 2013 Quality Science Labs, LLC

Big Idea 4: Interactions What factors govern energy capture, allocation, storage, and transfer between

producers and consumers in a terrestrial ecosystem?

Please be sure you have read thestudent intro packet before you do this lab.

(If needed, the student intro packet is available at www.qualitysciencelabs.com/AdvancedBioIntro.pdf)

Lab Investigations SummaryPre-lab Questions

What is the Environmental Impact of Eating at Lower Trophic Levels?

Lab Investigation 8.1 Part 1 - Energy Transfer and Productivity

Energy Transfer and Productivity: Estimating Net Productivity of Producer Biomass and Energy Transfer from a Producer to the Primary Consumer Level of a Food Chain within an Ecosystem”

Part 2 - Student Guided Inquiry Investigation of a student-selected variable that affects the rate of fermentation and the production of the biofuel ethanol as determined by measuring CO2 production.

Lab 8Energy Dynamics

2 Copyright © 2013 Quality Science Labs, LLC

LAB 8 - Energy Dynamics

Big Idea 4: Interactions

What factors govern energy capture, allocation, storage, and transfer between producers and consumers in a terrestrial ecosystem?

BACKGROUND

Everything that lives needs energy. Energy is converted and lost as heat as it moves through ecosystems, and new energy is continually added to the earth in the form of solar radiation. Autotrophs convert the sun’s energy, usually through the process of photosynthesis, into organic compounds that store energy. Autotrophs are the primary producers and their production of new organic compounds (sugars) or biomass is referred to as primary production. The primary producers are either decomposed or consumed and their stored energy powers consumers and the higher trophic levels of the biotic community.

The organic energy-rich compounds (sugars) create biomass. The total amount of CO2 that is fixed by the plant in photosynthesis is the gross primary productivity (GPP). The net primary productivity (NPP) is the net amount of primary production after the costs of plant respiration (R) are included or NPP = GPP – R.

How do you measure primary production? There are two systems for measuring primary production — either by the rate of photosynthesis or the rate of increase in plant biomass.

•Rate of Photosynthesis: From the basic equation for photosynthesis, we know that six CO2 molecules are used for every six O2 and one sugar molecule produced. By placing plants in a closed system, we can either measure the depletion of CO2 per unit time, or the generation of O2, to get a direct measure of primary production. The NPP would be related to the GPP minus the O2 used up during respiration.

•Rate of Biomass Accumulation: To determine the primary production of a crop some seeds are planted. At the end of one year samples of the entire plants including the roots that were contained in one square meter are harvested. The samples are dried to remove any variation in water content, and then weighed to get the “dry weight.” Thus, the measure of primary production would be grams/m2/yr of crop including stems, leaves, roots, flowers, and fruits but minus the mass of any vegetation that may have blown away or otherwise lost. What has been measured? It isn't GPP because some of the energy produced by photosynthesis went to meet the metabolic needs of the plants themselves or was lost to insects and other such things. Is it NPP?

• In recent years it has also become possible to estimate GPP and R in large plants or entire forests using tracers and gas exchange techniques. These measurements now form the basis of this investigations into how primary production affects the carbon dioxide content of our atmosphere.


Another way to evaluate trophic levels is to examine the amount of carbon that is being passed on to each trophic level, either in the form of decomposition, metabolism, reproduction, food for predators, or the amount of carbon released into the atmosphere in the form of CO2. Can you calculate the amount of carbon released in to the atmosphere by the herbivores?

If you calculated 60 g/m2, you are correct. The herbivores receive 125 g/m2 from grass, but lose 5 g/m2 to predators and 60 g/m2 to decomposition and the soil. What remains is 60 g/m2 of carbon that goes to the atmosphere via respiration.

In this lab you will investigate the use of plant sugars by yeast to power growth, reproduction, and storage of energy as biomass as it gets passed on through a food chain. Yeast convert sugar to ethanol and carbon dioxide and release energy during the process of fermentation. The production of carbon dioxide is used as an indicator of the amount of energy converted by the yeast. Assuming the ratio of energy per biomass production is constant, the carbon dioxide is also an indirect indicator of biomass production. In Lab Investigation 8.1, you will measure the volume of CO2 produced, calculate the rate of production, and relate it directly to the amount of energy transferred from the primary producer and indirectly to the biomass production by the primary consumer — the yeast.

As you progress through the pre-labs and the yeast fermentation investigations, you might also consider the conversion of energy and production of biomass with your own personal impact on the environment. On what trophic levels do you predominantly eat?

Lab Investigation 8.1 Part 1 will establish a baseline for inquiry Lab Investigation 8.1 Part 2 on testing the effects of a variable that could possibly increase ethanol yield and potentially impact the production of biofuels.

Carbon Flow in a Grassland Ecosystem

Grass Herbivores Predators125 g/m2 5 g/m2

60 g/m21 g/m2

336 g/m2

4 g/m2

Soil/Decomposers

125 g/m2(litter)

250 g/m2(roots)

RespirationRespiration

Respiration

How much carbon (in g/m2) is releasd into the atmosphere as a result of the metabolic activity of herbivores? Give your answer to the nearest whole number.


PREPARATION

Materials and Equipment are listed with each lab separately.

Timing and Length of Lab Activities This Pre-lab does not require lab bench time and could be done in class or after

school. Lab Investigation 8.1 Part 1 for yeast fermentation is designed to establish a baseline for the rate of production of CO2 and ethanol by yeast with a 15 minute data collection. The entire lab should take two periods to conduct the lab, collect data, and analyze and discuss the data. The Lab Investigation 8.1 Part 2 - Student Guided Inquiry will take two periods.

Learning objectives aligned to standards and science practices (SP)

•To design and conduct an experiment to investigate a question about energy capture and energy flow in an ecosystem (2D1 and SP 4.2, 7.2)

•To explain community/ecosystem energy dynamics, including energy flow, NPP, and primary and secondary producers/consumers (4A6 and SP 2.2, 6.1, 6.2)

•To use mathematical analyses in energy accounting (2D1 and SP 5.1)

•To make the explicit connection between biological content and the investigative experience (2D1 and SP 1.3, 3.2)

•To evaluate the human impact on changes at local levels (4B4 and SP 5.1)

General Safety Precautions Use general microbiology practices in working with the yeast by using household

bleach for prepping surfaces before and after labs, mainly to prevent contamination from other microorganisms.


Pre-lab Questions

What is the Environmental Impact of Eating at a Lower Trophic Level?

"Three hundred trout are needed to support one man for a year. The (300) trout in turn, must consume 90,000 frogs, that must consume 27 million grasshoppers that live off of 1,000 tons of grass."

-- G. Tyler Miller, Jr., American Chemist (1971)

The purpose of this activity is to calculate and compare human food needs at different trophic levels, using the data to construct a biomass pyramid. You will also analyze the advantages and disadvantages of eating at lower trophic levels on a global scale.

What is a Trophic Level?Trophic levels are the feeding position in a food chain such as primary

producers, herbivore, primary carnivore. Green plants form the first trophic level, the producers. Herbivores form the second trophic level, while carnivores form the third and even the fourth trophic levels. Ecological pyramids are built based on these trophic levels and can show numbers of organisms, biomass, or energy flow.

What is a Biomass Pyramid?An ecological pyramid of biomass shows the relationship between biomass and

trophic level by quantifying the amount of biomass present at each trophic level of an ecological community at a particular moment in time. It is a graphical representation of biomass (total amount of living or organic matter in an ecosystem) present in weight per unit of area in different tropic levels. Typical units for a biomass pyramid could be grams or kilograms per meter2.

In the following scenario, you will be analyzing the energy needs and necessary quantities to support different trophic levels of organisms on a farm.

10,000 Kilocalories/m2/year available for primary consumers

1,000 Kilocalories/m2/year available in the bodies of primary consumers

100 Kilocalories/m2/year in secondary comsumers

10 kilocalories/m2/year

PrimaryProducers

PrimaryConsumers

SecondaryConsumers

TertiaryConsumers

(Herbivores)

(Predators)

(Predators)

Trees -Shrubs - Ferns - Grasses - Flowers

Rabbits - Squirrels - Deer - Sparrow - Mice

Fox - Racoon Badger - Goose - Frog

GoldenEagle


Scenario and Assumptions for the Following Exercises: In this scenario, the owner of a corn farm raises geese for food and insect control.

Geese will eat grasshoppers and other insect pests and ticks (which is a good thing). They also act as a “watchdog” by making a lot of noise when intruders approach their territory. The farmer allows the geese free range in his fields during the day and provides sheltered roosts for them at night.

For purposes of the following exercises, you may make the following assumptions:

•The farmer lives on 1 goose/day for a year;

•1 goose eats 250 grasshoppers/day;

•1,000 grasshoppers have a mass of 1 Kg;

•1 grasshopper requires about 30 g of corn/year;

•1 human requires about 600 grasshoppers/day;

•Dry corn has about 3.65 cal/g.

•Grasshoppers only reproduce to feed the geese or human. (While unrealistic, this will help illustrate the scenario.)

Exercises –Show all your math using proper units

1. Calculate the number of grasshoppers a goose needs per year.

2. How many grasshoppers are needed for a year’s supply of geese for the farmer each year?


3. What is the total mass, in kilograms, of the grasshoppers needed to feed all the geese for one year?

4. How many kilograms of corn are needed to feed all the grasshoppers for one year?

5. Estimates of early Native American hunter-gather societies indicate that a person could collect about 90 kg (200 lb) of grasshoppers per hour, when they are abundant. How many people could the grasshoppers feed compared to the one person that the goose fed?

6. The farmer needs to consume 3,000 calories/day. If he ate only corn instead of the goose or the grasshoppers, how many people would his corn crop feed? (See your response to #4.)


7. Draw a biomass pyramid using the data you have developed to this point. Why do most food webs not have a fourth or fifth trophic level?

8. Should people generally eat at a lower trophic level? It seems, by a simple analysis, that the Earth could support many more people if we all ate at a lower trophic level.

a. List two advantages and two disadvantages for eating at a lower trophic level.

b. On average, cows produce 19 kg of protein/acre/year and corn produces 120 kg of protein/acre/year. Relate these data to the fact that people in the less-developed countries usually eat at lower trophic levels than those in developed countries.

9. Comment on the success of omnivores, such as coyotes, rats, and humans, and the fact that they can eat at many trophic levels.


10. List the foods you have eaten over the last 5 days:

a. Identify what trophic level each food came from.

b. Estimate what percent of the mass of the food in your diet comes from the first and second trophic levels.

c. What percent of your diet comes from higher trophic levels?


LAB Investigation 8.1:Part 1

Energy Transfer and Productivity Lab as Demonstrated by Yeast Fermentation of Corn Sugar into Ethanol and Carbon Dioxide

In this lab, you will investigate the transfer of energy from corn, a producer of sugars, to yeast (and associated by products). Yeast is at the primary consumer level of a food chain within an ecosystem. When a consumer takes in food, energy is transferred from the biomass that exists in the organisms they consume. Organisms use this energy in three ways: to sustain existing biomass (to stay alive), to create growth, and to store energy in the form of new biomass including growth and reproduction. It is the energy stored as biomass that gets passed on through a food chain in an ecosystem.

Saccharomyces cerevisiae, also known as yeast, is a unicellular, eukaryotic sac fungus, which undergoes anaerobic fermentation to produce ethanol. Yeast changes sugar into ethanol and carbon dioxide and releases energy during the process of fermentation:

Fermentation uses yeast to convert the sugars in biomass into ethanol. This is the same process that has been used for thousands of years to make wine and beer. Some forms of biomass are made up of simple sugars that can be used directly, like sugars from sugar cane and sugar beets. Some are made up of starch, which is a chain of large numbers of sugar molecules that must first be broken down. Starch in crops such as corn, and woody crops such as trees and grasses fall into this category.

Fermentation, as opposed to cellular respiration, is a way of breaking down sugar molecules and harvesting chemical energy without using either oxygen or any electron transport system. Fermentation is an extension of glycolysis (the first step in cellular respiration) that allows continuous generation of ATP (adenosine triphosphate). There are two common types of fermentation, differing in the end products. One is alcohol production, which is typically done by bacteria or yeast. The second is lactic acid fermentation without the production of CO2, which is done by certain fungi and bacteria in production of cheese and yogurt; and also seen in human muscle cells for making lactic acid and ATP when oxygen is scarce.

Measuring the production of CO2 over time is an indicator of the amount of glucose used by the yeast, thus the amount of energy transferred. Assuming the ratio of glucose used per biomass production is a constant, CO2 is also an indirect indicator of biomass production at the primary consumer level.

In this lab investigation, you will measure the volume of CO2 produced, calculate the rate of production, and relate it directly to the amount of energy transferred from the primary producer and indirectly to the biomass production by the primary consumer — the yeast.

C6H12O6 (glucose) (Fermentation)

2 C2H5OH(ethanol)

→ + 2 CO2(gas) + energy (carbon dioxide)


Materials:•Yeast packet

•Beakers, 50 mL (2) and plastic 150 mL

•Graduated cylinder, 10 mL

•Corn syrup (dark) 1 mL*

•Distilled water*, (It should be about 25-27 °C.)

•Food coloring (red)*

•Syringe, 5 mL

•Tall glass jar or water glass* (to hold inverted respirometer)

•Serological graduated pipet, 1 mL

•Stopwatch

•Thermometer

•Tape **items not included

Preparations: 1. Prepare a yeast suspension: First check your yeast packet

for expiration data and verify that it has not expired. This is important and expired dates could give you poor lab results. Put 50 mL of 25-27 °C distilled water in a 150-mL plastic beaker and mix in the dry yeast.

2. Prepare a 5% corn syrup solution: Use the 10-mL graduated cylinder to measure out 9 mL of 25-27 °C distilled water into a 50-mL glass beaker. Mix into the distilled water in the glass beaker 1 mL of dark corn syrup by gently swirling the solution until the corn syrup is completely dissolved. (This is a 10% solution of corn syrup; when 10 mL of yeast is added in Step 3, it will get diluted and result in a 5% solution).

3. Using a 10-mL graduated cylinder, measure out 10 mL of the yeast suspension and transfer it into the beaker. Allow the yeast suspension to incubate for 5 minutes, with occasional swirling. Check the temperature and record. Keep the solution about room temperature (around 25-27 °C). (Caution: if you warm it in a microwave, every 5 seconds will raise it about 10 °C).

4. Construct a respirometer: Draw up exactly 3 mL of the yeast suspension (after the 5 min. incubation in Step 3) into a 5-mL syringe. Invert the syringe as shown in Figure 8.1a. IF there are any trapped air bubbles, flick it in the middle with your thumb and finger, the air bubble(s) will rise to the top, and push the syringe slightly to let them out.


Now draw 1 mL of air above the liquid. Before attaching the 1-mL serological pipet to the syringe, draw up a drop of red food coloring through the pipet past the 0 mark as shown in Figure 8.1a. Complete the assembly of the respirometer by gently attaching the pipet to the syringe and taping it in place. (If you press too hard, the top of the pipet will crack and break.) Gently set it upside down into your tall glass jar.

5. As soon as the water droplet reaches the 0 mL mark, begin taking measurements at 1 minute intervals and record the data. You can mark measurements using either the top or the bottom of the droplet, but be consistent. Decrease the time interval to 30-second readings after the first three minutes as the rate of CO2 production increases. Continue until Table 8.1a is filled.

Time (min.)

Reading (mL)

Time (min.)

Reading (mL)

Time (min.)

Reading (mL)

0

Pipet

Colored Droplet

Yeast

Syringe

Table 8.1a

Figure 8.1a


Data Analysis:

1. Plot the raw data on graph paper and draw a line through the linear part of the curve. Using only the linear part of the data, calculate the slope of the line as change in volume over change in time. This yields the rate of fermentation in units of mL of CO2 per minute.

2. The independent variable (time - min.) is plotted on the x-axis and the dependent variable (CO2 released - mL) is plotted on the y-axis. The slope gives you the rate of fermentation and the production of ethanol.

Discussion 3. What was the primary producer and what was the primary

consumer in this investigation?

4. How does your calculated slope for the rate of CO2 production during fermentation of yeast and corn syrup equate to biomass and energy transfer?


Part 2 - Student Guided Inquiry

This is an investigation of a student-selected variable and how it affects the rate of fermentation and the production of the biofuel ethanol as determined by measuring CO2 production.

In this portion of the lab, you will design a study to look at the effects of a variable of your choice on fermentation rates in yeast. The higher the fermentation rate, the more ethanol can be produced in a given time. Ethanol can be used as a fuel or an additive in gasoline blends. In fact, biofuel refers most commonly to ethanol, which is produced through the fermentation of carbohydrates by yeast. The by-products are CO2 and ethanol. Ethanol has become a valuable energy source as an alternative to fossil fuels.

Ethanol, when blended with gasoline at between 5-10% is called gasohol. This mixture has several advantages over pure gasoline as an energy source. The presence of an oxygen atom in ethanol allows gasohol to burn cleaner than regular gasoline, which reduces emissions of CO, nitrogen oxides, and hydrocarbons.

The following is the molecular structure of ethanol showing the oxygen atom that allows gasohol to burn cleaner than regular gasoline:

A significant question in the alternative energy resources is “What can be controlled to increase the efficiency of ethanol production?” There are many variables that could potentially affect the rate of yeast fermentation. Some of the variables to consider that may affect the fermentation in yeast cells and ultimately increase or decrease the ethanol production are described below:

Variables to consider testing for increase yields of ethanol production by yeast include:

•Type of carbohydrate: grain crops (corn syrup), fruits (fructose), cellulose, milk sugar (lactose);

•The optimum temperature for fermentation (or what are the effects of different temperatures on yeast fermentation?);

•Concentrations of carbohydrate (50%, 25%, 12.5%, 6.25%);

•Different species of yeast;

•Environmental conditions like pH (what is the effect of varying pH on yeast fermentation?);


•Concentration of salt (how does varying the salt (NaCl) concentration affect the rate of yeast fermentation?);

•Osmolarity [Osmolarity refers to the total concentration of sugars or salts in the fermentation solution, which affects water flow into or out of the cells. What is the effect of adding sorbitol (which cannot be utilized by yeast for fermentation) along with glucose on the rate of fermentation?];

•Ethanol concentration (What are the effects of varying the initial ethanol concentration in the fermentation mixture on yeast fermentation?);

Use the rate or total volume of CO2 production as an indicator of the production of ethanol.

Procedures:Once you select your driving question, start with your experimental design (ExD). Identify your independent and dependent variables, your hypothesis, your control, and your test set-up.

Step 1: Select your driving question to investigate.Step 2: Fill in the ExD (Experimental Design) form on the next page to

plan your experiment. Identify your independent and dependent variables, your hypothesis, your control, and your test set-up.

Step 3: Design data tables and collect data.Step 4: Analyze the data.Step 5: Summarize your conclusions.


Experimental Design (ExD) FormComplete this ExD pre-lab planning form before beginning your lab

1. Independent variable: (What is the cause agent? What are you changing?)

2. Dependent variable: (What is being measured?)

3. Lab set-up:

ExperimentalGroups

Number of Trials

4. Control: (What is the experimental group being compared to?)

5. Hypothesis: (Use an “if ” [Independent Variable], “then” [Dependent Variable] format. State the cause and e�ect relationship between the I.V. and the D.V. It must be testable.)

6. Lab title: (�e e�ect of ____[I.V.] ____on ____[D.V.]____.)

7. Experimental constants: (Name at least six variables NOT altered during the experiment.)

8. Sketch of experimental set up with labels:

9. Detailed procedure:


Discussion questions to consider

1. Did the results of your experiment support or contradict your hypothesis? If not, what conclusions would you draw from your results?

2. How does the trend in your graph compare with the predicted results from you original experimental plan? Describe any difference you observe.

3. How do your results compare to information about the effect of you variable from literature sources?

4. Does the variable you tested have a stimulating or inhibiting effect on fermentation?

5. What are the implication of you result to improving biofuel production?

ap biology lab #08

Documents

primary producers

energy capture

new energy

suns energy

co2 production

net primary productivity

gross primary productivity

rate of photosynthesis