Pedigrree Tasting Assignment
garinh
biol1009labmanual.pdf
1
Biol 1009 Lab Manual NOTE: You must complete at least 7 out of 8 labs to pass this course. The labs are not optional.
Contents Lab Exercise Page
1 Use of the Microscope 3
2 Enzyme Activity and Digestion of Carbohydrates and Proteins 13
3 Fermentation, Photosynthesis, and Respiration 19
4 The Structure of a Flower 28
5 Growth and Trophic Responses 31
6 Pedigree Tasting 39
7 Morphogenesis in Insects 44
8 The Ecological Community Structure 51
2
3
Lab Exercise 1: Use of the Microscope As part of the assignment for this lesson, complete the following lab exercise. Read through all of the lab exercise before you begin so that you’ll know what you’re expected to do, what equipment to gather, and the questions you’ll need to answer.
Write down your answers to the questions as you do the work. These are the questions you will answer in your lab report. Go to the Assignments tool on the course Web site to download the worksheet on which to enter your answers.
Timing note: A few hours, but you will need to arrange an appointment in advance. NOTE: Most students use the microscope that is set up on the U of M campus (see below). To avoid scheduling problems using this microscope, you do not have to complete this lab until the end of week 3. However, sometimes a lot of students wait until the end of week 3 to do this lab, so it’s best to schedule your microscope appointment early (see below).
Arranging to Use a Microscope If you live near the University of Minnesota, you may come to the St. Paul campus and use a microscope in the College of Biological Sciences instructional laboratories. To be sure a microscope is available for your use, please make an appointment by contacting Sandy Mand at [email protected] or call 6126262821. The preferred day and time for appointments is Friday, 9 a.m.–5 p.m., but other days and times can usually be arranged. Also be sure to call this number if you need to cancel your appointment. If you do not live near campus, contact a local grade school, high school, college, or laboratory to see if you may use one of their microscopes. Try to find some time that is convenient to both you and the lending institution. Many institutions will be gracious about letting you use their equipment on their premises. It will take you approximately three hours to complete this lab exercise.
4
Objectives In this exercise you will learn about the use and care of the compound light microscope. You will use it to examine plant and animal materials, prepare your own temporary slides, and make approximate measurements of viewed materials.
Supplies If possible, borrow the following equipment:
● compound light microscope with scanning, low, and highpower objectives ● slide with three different colors of thread* ● slide of plant tissue* ● slide of animal tissue* ● lens paper ● paper towels
*Note: If these slides are not available, be creative and make your own slides (e.g., human hair, aquarium water, etc.)
From the lab kit you will need:
● eye dropper ● clean slides and cover slips ● calibration film ● printed strip labeled “Biology”
You will need to supply:
● a sample from any natural body of water—pond, stream, etc.—or a sample
of water taken from an aquarium or fish bowl ● transparent tape
Notebook For this exercise and the other exercises in this course, you should have a notebook (any kind of notebook) in which to jot down data and observations. Of course, you may also write in this lab manual.
5
Write your initial answers to the questions in the exercises in the notebook. You will enter them later in a wordprocessing document for submission.
Procedure Locate the parts of the microscope using the figure on the next page. Although the microscope you use may differ from this illustration, the parts of most compound microscopes are located in approximately the same positions. You might ask the person who lends you the microscope for a quick lesson in its use.
Always carry the microscope using both hands, one hand grasping the arm and the other firmly supporting the base. Never tip a microscope, or the ocular may fall out and shatter. When using the microscope, rest it on the tabletop directly in front of you with the arm facing you. Do not place it too close to the edge of the table or you may knock it over. If the ocular is dusty or dirty, clean it with lens paper only—never with tissue or a handkerchief. Do not touch the lenses with your fingers or you will leave greasy smudges on them. When focusing the microscope, first watch from the side and raise the stage by turning the coarse adjustment knob. Continue focusing by looking through the ocular while lowering the stage. Always begin focusing a new slide by using the lowpower objective, usually designated with a “10X” on the tube supporting the lens.
If your microscope has a builtin illuminator, make sure the electric cord is plugged into an outlet and the illuminator button is switched on. When you place a slide on the stage, light from the illuminator passes successively through the substage condenser, iris diaphragm, slide, objective lens, and ocular lens to your eye. Prisms in the barrel focus the light passing through the objective lens, and the ocular lens magnifies the resultant image. The iris diaphragm controls the amount of light passing through the lenses. If the slide is darkly stained, you must use the maximum amount of light; if it is transparent, reduce the amount of light. The substage condenser concentrates the light on the specimen. The image is brought into focus with the two knobs that raise and lower the stage: the coarse adjustment (the larger outer knob) and the fine adjustment (the smaller inner knob).
6
The nosepiece contains three objectives: the scanning objective is usually labeled “4X” and magnifies the object four times; the lowpower objective is labeled “10X” and magnifies ten times; the highpower objective is usually labeled “40X” and magnifies the object forty times. The ocular has a 10X lens and magnifies the image ten times. To determine the total magnification of the set of lenses you are using, simply multiply the magnification of the ocular by the magnification of the objective. Thus, the combination of the 10X ocular and the 10X objective results in a magnification of 10 X 10 or 100 times the size of the object on the slide. Similarly, the 10X ocular and the 40X objective produce a compound magnification of 400 times.
Focusing on a Practice Slide
Turn the nosepiece so the lowpower objective, 10X, snaps into place. Prepare a practice slide by attaching the printed strip labeled “Biology” to a clean microscope slide. Use a small piece of transparent tape at each end to secure the strip. Insert the slide so that the paper label is on top.
7
Center one of the letters on the slide so that the beam of light passes through it. While watching from the side, raise the stage with the coarse adjustment knob until the bottom of the objective is about half an inch from the stage. Note which way you turned the knob; the opposite direction will lower it.
Since the label is relatively dense, open the iris diaphragm completely. A clear, circular field of light should be visible through the ocular. Look through the microscope and slowly lower the stage with the coarse adjustment until the lettering is resolved. Continue focusing with the fine adjustment until the letter is in perfect focus. Now swing the highpower objective into place and refocus with the fine adjustment knob only.
Return the microscope to low power and refocus. Slowly move the slide away from you while looking through the microscope. Jot down your answers to the following questions in your notebook. Later you will enter your answers on the worksheet for this lab and submit the document as your lab report for this lab exercise.
1. Which way does the image move?
Now move the slide toward you.
2. Which way does the image move?
Move the slide to the left.
3. In which direction does the image move? 4. If a protozoan were moving from left to right on a slide, which way would you move the slide to keep the protozoan in focus?
Understanding Depth of Focus
8
Place a slide of colored threads on the stage. After focusing on low power, switch to high power and determine which thread is on top, which is in the middle, and which is on the bottom. Microscopy allows you to observe different levels of material on a slide.
Observing Plant and Animal Cells (Prepared Slides)
Observe slides of plant and animal tissue under low and high power.
5. With the aid of chapter 4 of your text, determine which cell organelles can be observed with a light microscope. Why can’t the other structures be seen?
6. List the visible structures that plant and animal cells have in common. 7. Draw a plant or animal cell you have observed and label the cell type and the organelles. Include the drawing(s) in your report. Note: A major part of your lab grade will be based on the enthusiasm of your drawings. Detail, rather than artistic ability, will be stressed.
Making Wet Mount Slides
If you live near a natural body of water (e.g., a lake, a stream, or a temporary pond), you might find it interesting to collect a sample of water for observation under a microscope. If it is difficult for you to get a sample from a natural body of water, use water from an aquarium or a fish bowl. Possible sources might be a friend or a pet store. Collect your sample on the same day you will be using the microscope. Merely dip out a small quantity of water using any clean container. Keep the sample loosely covered so the organisms have access to oxygen.
To make your own slide of this material, take a clean glass slide and cover slip. Using an eye dropper, take a sample from the bottom of your container; most organisms are denser than water and tend to settle to the bottom. Place one drop of water in the center of the slide. Then place an edge of the cover slip on the slide
9
next to the drop so that the cover slip is at a 45degree angle to the boundary of the drop, as shown in the following diagram.
Allow the water to flow out along the edge of the cover slip, and then drop the cover slip onto the slide. The force exerted by the falling cover slip should drive out most of the air bubbles.
Make sure the bottom of the slide is dry, and then place the slide on the microscope stage and observe it under low power. When you think you see an organism, focus it clearly and switch to high power for further observation. Since this is a transparent slide, you will have the best resolution if you manipulate the iris diaphragm to allow in the least possible amount of light. When you have finished, clean the slide and cover slip with soap and water and dry them on paper towels. Make additional slides of your material. It often takes several attempts to become adept at making wet mount slides, so be patient.
8. What organisms did you observe? Make sketches of them on a separate sheet of paper. Include the drawings in your report.
Calibrating a Microscope
While it is interesting to be able to view cells under a microscope, it is also important to have some idea of the relative sizes of these structures. When you calibrate a microscope, you determine the diameter of the microscope field at each magnification. You can then estimate the size of microscopic structures by determining how many of them could be stretched across your field of view. For example, if the diameter of your lowpower objective is 1,500 micrometers and a protozoan takes up approximately onethird of the field, then it is approximately 500 micrometers in length. Remember that these will only be approximations, but they will be close enough to give you information about relative size.
10
As you learned above, by serially increasing the magnification, you can see smaller and smaller structures. But as you probably noticed from the first part of this lab exercise, as you increase the magnification, the diameter of the field decreases.
Place your calibration film on the microscope stage. Focus on the circle labeled #1. These circles will be referred to hereafter as standards. The distance between two adjacent parallel lines on standard #1 is 1.000 mm. This distance constitutes one division. We will consider one division to be equal to the distance between the left edges of two adjacent parallel lines. Figure 2 shows a field with three divisions.
Figure 2 The distance between the left edges of two adjacent lines on standards #2 and #3 are 0.635 mm and 0.453 mm, respectively.
Now measure the diameter of the field at 50X. Your microscope may have a scanning objective with a different magnification. Determine its total magnification and change the appropriate boxes in the table below. Align the left edge of a black line so that it is tangent to (just touching)
11
the outer edge of the microscope field. You should see an image similar to the one in Figure 2. Count the number of divisions across the field and record this number in the table. Next, without moving the slide, swing the 10X objective into alignment. Position a line tangent to the left edge and count the divisions across the field. Notice that as you increase the magnification, you see fewer divisions. Enter this value in the table. Repeat this procedure with the higherpower objective and with each standard. When you are finished, you will have three values for each standard.
Measurement of Field Diameters
Standard Mag. div./field mm/field µm/field
#1 1.000 mm/div
#2 0.635 mm/div
#3 0.453 mm/div
Convert the number of divisions to a numerical value, i.e., mm per field, by multiplying the number of divisions by the number of millimeters per division using the following formula:
mm per field = no. divisions per field X mm per division
Since one millimeter equals 1,000 micrometers, multiply the mm per field value by 1,000 to determine the number of micrometers per field.
9. Do the different estimates of a specific magnification agree with each other? If not, to what would you attribute the accuracy (or lack thereof) of the various estimates?
Greater accuracy can be achieved by using more finely divided rulers that have more points of reference.
12
10. Which standard had the most points of reference?
This is the standard you should use for all measurements. Use the most accurate measurement to estimate the height and width of the letter “B” on the “Biology” slide. Measure it at 50X (or a different scanning magnification) and express your results in both mm and µm.
11. height mm µm
width mm µm
12. Using a slide of either plant or animal tissue, measure the length and width (in micrometers) of a typical cell at low power (100X).
tissue (plant or animal?) Length µm Width µm
What to Include in Your Lab Report Using the document you downloaded from the Assignments tool, please write complete sentences (where appropriate) to the following requests for information.
1. Report the brand of microscope you used, the lending source, and list the
types of slides you observed.
2. Write your answers to questions 1 through 12, which are given throughout this lab exercise.
13
Lab Exercise 2: Enzyme Activity and Digestion of Carbohydrates and Proteins Remember to read through this lab exercise before you begin it. It should take you about three hours to complete after you germinate six corn seeds (see Preparation Note below).
Write down your answers to the questions as you do the work. These are the questions you will answer in your lab report. Go to the Assignments tool on the course Web site to download the worksheet on which to enter your answers.
Timing note: Your preparation begins four days before you start the lab. You may also need to buy or borrow some supplies ahead of time.
Objectives In this exercise you will observe some of the properties of enzymes. As you should recall from this lesson, enzymes catalyze chemical reactions. They may accelerate the reactions, in which simple molecules bond together to form more complex molecules (anabolism); they may catalyze the breakdown of larger molecules into their simpler components (catabolism); or they may accelerate reactions involving the conversion of one molecule into another molecule.
Digestion is primarily the result of the catabolic action of enzymes. Most people know that the stomach is acidic, but its acidity plays only a minor role in digestion. Most digestion is carried out by the digestive enzymes of the small intestine. (See pages 735743 of your text.) As you can see, each specific food substrate is digested by its own enzymes. For example, proteolytic enzymes always have proteins as their substrates. Metabolic reactions in plants are also catalyzed by proteins.
In this lab exercise you will test the activity of two different enzymes. Salivary amylase is an enzyme that catalyzes the breakdown of starch into reducing sugars such as glucose and maltose. Bromelin, an enzyme found in plants, breaks proteins down into peptides.
Part A: Carbohydrate Digestion in Plants 14
Supplies You will need the following items from the lab kit:
six corn seeds three 16 x 150 ml test tubes vermiculite 30 ml bottle containing Benedict’s* solution eye dropper petri dish
*This chemical is hazardous. Keep out of the reach of children.
You will need to supply these items:
small plastic or glass container (e.g., for cottage cheese, whipped cream, etc.) small saucepan for boiling test tubes mortar and pestle or sturdy knife
Preparation Note Four days prior to beginning this lab exercise, place six corn seeds in a container of moistened vermiculite so they can germinate. Cover the container and check it each day to see that the vermiculite remains moist.
Procedure
A. About four days after you place the seeds in vermiculite, the coleoptiles should appear. See page 643 (Figure 30.16d) in your textbook for an illustration.
15
B. Separate the coleoptiles from the seeds and dispose of the seeds. Grind the coleoptiles with a mortar and pestle, if available, or smash them with the blade of a large knife.
C. Place half of the macerated coleoptiles in a test tube with ten drops of water. Add twenty drops of Benedict’s solution to the test tube. Shake the tube to mix the contents, and allow it to stand at room temperature for five minutes.
Benedict’s solution consists of either sodium or potassium citrate, sodium carbonate, and cupric (copper) sulfate in a solution of water. When the solution is heated with a reducing sugar, such as glucose, a characteristic color (reddish brown) and precipitate appear. This indicates that the cupric ion, Cu++, has been reduced to the cuprous ion, Cu+. As in any redox reaction, if one substance is oxidized, another substance is reduced. In this reaction, the reducing sugar, glucose, is oxidized.
Note: This is a positive test that indicates the presence of a reducing sugar. Benedict’s solution and the substance in question must be heated together for two minutes in a boiling water bath.
Place the test tube in a small pan of boiling water and boil gently for two minutes. The pan should be small enough so that the test tube will not spill its contents.
1. Is there a color change in the solution? Is this a positive or negative Benedict’s test?
2. Which substance was
oxidized?
3. Which substance was reduced? Next, grind or macerate several dry, ungerminated corn seeds. Test them with Benedict’s solution, using the same procedure that you used for the coleptiles.
4. Do ungerminated corn seeds store sugar or starch?
16
5. What is responsible for the conversion of starch to sugar in a seedling?
6. Of what advantage to the plant is the presence of two forms of carbohydrates?
Part B: Protein Digestion
Supplies You will need to provide the following items:
one fresh pineapple (or two small cans of frozen pineapple juice concentrate) one egg saucepan small bowl and wooden spoon
Pineapple juice (either fresh or frozen) contains bromelin, which is a proteolytic enzyme. An egg is an animal product that is rich in protein.
Procedure
A. Cut two thin slices off the fresh pineapple. Mash them in a bowl with a wooden spoon until the juice is extracted. If fresh pineapple is unavailable, you may use frozen pineapple juice that has been thawed and warmed to room temperature. Do not use cold pineapple juice.
B. Boil an egg until hard boiled (about ten minutes). Peel the egg and discard the shell. Remove and chop the cooked egg white (discarding the yolk). Then add equal amounts (about half a teaspoon) of the egg white to two clean test tubes labeled A and B.
C. Place twenty drops of pineapple juice in a third test tube, and place it in a pan of boiling water for ten minutes.
17
D. Add twenty drops of fresh or thawed unboiled juice to tube A and twenty drops of boiled
juice to tube B. E. Shake the tubes for twenty seconds, and then allow them to rest for five minutes.
7. What happens to the egg white in the two tubes? Hint: you must carefully look at the edges of the cooked egg white.
8. What effect does boiling have on the enzyme bromelin?
9. Would you expect all enzymes to act similarly if they were boiled? Why?
Part C: Starch Digestion in Animals
Supplies You will need the following items from the lab kit:
six test tubes
You will need to supply the following items:
three soda crackers (saltines) small saucepan
Preparation Note Do not chew gum or eat anything for two hours prior to performing this exercise.
Procedure
18
A. Pulverize one soda cracker (one square) and place half of the crumbs in a clean test tube. Add twenty drops of water and twenty drops of Benedict’s solution. Shake the tube vigorously for twenty seconds, and then allow it to stand at room temperature for five minutes. Heat the tube in a boiling water bath for two
minutes.
10. Does a color change occur?
11. Is this a positive or negative test for a reducing sugar?
B. Now collect about a quarter inch of saliva in each of two clean test tubes. Test the saliva for reducing sugars and starch using the Benedict’s test. Repeat the same procedures as before.
12 Does your saliva contain reducing sugar?
13. Does it contain starch?
C. Collect more saliva in two clean test tubes labeled A and B. Slowly chew a portion of soda cracker (at least half of the cracker), and divide this mass between the two tubes. Shake the tubes to mix and allow them to rest at room temperature for five minutes.
D. Add Benedict’s solution to tube A. Carry out the same procedure as before.
14. Does the partially digested cracker contain reducing sugar?
15. Does it contain starch?
16. What was responsible for the conversion of carbohydrate from one form to another?
17. Where in the body does the final digestion of carbohydrates occur?
19
18. Would you expect to find the digestion of protein and fats occurring in the mouth? Explain.
What to Include in Your Lab Report Go to the Assignments tool on the course Web site to download the worksheet on which to enter your answers. Write complete sentences in response to questions 1 through 18 listed throughout this lab exercise.
Lab Exercise 3: Fermentation, Photosynthesis, and Respiration
Objectives The purpose of this exercise is to give you a chance to study three different modes of metabolism (fermentation, respiration, and photosynthesis) by preparing food products for your own consumption. The exercise is divided into two parts, which may be done simultaneously or separately. Your report should be written after you complete both parts.
Write down your answers to the questions in the exercise as you do the work. These are the questions you will answer in your lab report attached to the Assignments tool).
Timing note: This exercise will run for about six days, requiring short, daily observations or activities after the first day. You will need to gather some supplies ahead of time.
Part A: Fermentation In today’s modern society, we have many mechanisms of food preservation: refrigeration, freezing, canning, vacuum packaging, and gamma irradiation, for example, as well as the more traditional drying, salt or sugar “curing,” and fermentation. All of these food preservation methods have the same goal: to
20
prevent the growth of microorganisms that would destroy the food (i.e., make it unacceptable because of bad smell, bad taste, or potential for causing illness).
While the growth of unwanted microorganisms can be a problem, many food products are the result of microbial action on plant or animal material. Usually, this microbial action results in the formation of acid or alcohol that act as inhibitors of further microbial growth. Examples of food products resulting from microbial action (with “raw” food in parentheses) are bread and beer (grains), sauerkraut and kimchee (cabbage), cheese and yogurt (milk), and sausage (meat). In this exercise, you will study the biochemical process of fermentation by preparing yogurt and kimchee. Yogurt is prepared from milk, kimchee from cabbage. In both cases, the microorganisms ferment the available sugar (lactose in milk, glucose and fructose in cabbage), producing acid end products.
In people, when your muscles are working hard, oxygen may be used up very quickly so that oxidative phosphorylation cannot take place. Under these conditions, pyruvate cannot be broken down in the mitochondria. Instead, pyruvate is converted to lactic acid, which is excreted from the cell. This prevents the buildup of pyruvate, and allows glycolysis to keep running and supply your muscles with ATP. (Remember that pyruvate is produced from glucose during glycolysis.)
Supplies You will need the following item from the lab kit:
pH paper
You must provide the following supplies for yogurt:
2 tablespoons of dry milk 3 cups of milk (whole or 2 percent) 2–3 tablespoons of plain yogurt (look on the label for the words “live culture”). Vanilla yogurt will also work, but do not use yogurt with fruit (the cultures are not as healthy). a way to heat the milk two jars to hold the mixture
21
one cooler hot tap water
You must provide the following supplies for kimchee:
onehalf head of cabbage 2 tablespoons of pickling salt (This is noniodized salt that will not inhibit the
growth of the fermenting microorganisms. It is available in either the spice or the canning section of your grocery store. Or ask a neighbor who makes pickles for the small amount you need.) spices of your choice (e.g., cayenne pepper, garlic) two widemouth glass jars (canning jars are good, as are the short pickle jars that
have wide mouths) two leakproof plastic bags (or four bags, doublebagged) for weights
Procedure
For Yogurt
1. Measure 3 cups of milk into a saucepan. Add 2 tablespoons of dry milk. Mix well. Scald the milk mixture (scalding milk means bringing it to just about boiling, but not letting it actually boil). This can be done on a stovetop or in a microwave, or even over a campfire.
2. Allow the milk to cool. Divide it between the two jars. Add 2–3 tablespoons of unpasteurized yogurt to one jar (label it “starter culture added” because you have added a culture of live, yogurtproducing bacteria to it to start the fermentation). Label the other jar “no starter culture.” Mix each jar well. Remove a teaspoon of material from each jar and measure the pH of the solution. Record it in the data chart. Cover the jars with lids or foil.
3. Place both jars in a cooler and add very warm tap water (temperature should feel hot but
not scalding; if you have a thermometer, it should be at about 40–450 C) to the cooler, up to the level of milk in the jars. Cover the cooler and let the jars incubate for three to five hours
22
(if your cooler is not very good, you may need to change the water once during the incubation period to keep the jars warm), until the jar marked “starter culture added” has solidified. Remove a teaspoon of material from each jar and measure the pH of the milk product. Record the pH in the data chart on the following page. Make other observations. The “starter culture added” yogurt should smell sweet (not bitter or putrid), have a low pH, and be solid (tip jar), although there may be a small amount of extruded whey on the surface of the solidified milk (that’s okay). What is the appearance, smell, and pH of the milk that did not receive any starter culture? Place the jar of yogurt in the refrigerator until tomorrow. Discard the “no starter culture” milk down the drain (just as you would discard any spoiled milk).
4. When your yogurt is cold, add some fruit or granola and have a taste! Do not taste the milk from the “no starter culture” jar! (It is unlikely to cause any major problem, but it will taste bad and may cause a gagging reaction. Some people’s stomachs also get upset from sour milk.)
For Kimchee
1. Chop the onehalf head of cabbage into bite size pieces (do not grate—you want larger pieces). Mix in 2 tablespoons of pickling salt and the spices of your choice. Kimchee, a traditional Korean dish, is often made very hot and spicy with cayenne pepper. Add about 1 cup of water and mix well. Remove 1 teaspoon of the liquid and measure the pH. Record it on the data chart on the next page.
2. Divide the mixture into the two widemouth jars. Put water into the plastic bags and place one bag (or one doublebag) into each jar. These bags serve two functions: they act as weights to help pull/push liquid out of the cabbage leaves, and they act as seals to prevent oxygen from getting into the fermenting cabbage. It is important that the bags fit firmly and completely over the surface of the cabbage. It is also important that they do not leak more water into the fermentation.
3. Label one jar “for pH measurements.” You will use this daily to monitor the pH of the fermentation. The measurement of pH requires that the fermentation be opened, which can introduce oxygen and microorganisms that may spoil
23
the fermentation. You will keep the other jar for consumption, so label it “for consumption.”
4. Daily, remove one teaspoon of the liquid in the “for pH measurements” jar and measure the pH. Record it on the data chart below. When the pH of that jar has fallen to about 4.5 (usually within three to five days), check the pH of the other jar. If it is also about 4.5 (or lower), the kimchee is ready to taste. (Many prefer kimchee cold. If so, place the jar in the refrigerator overnight before tasting.)
Observations
Yogurt
Observations “starter culture added” “no starter culture”
pH at start
pH at end
Appearance and smell at end
Kimchee
Observations “for pH measurements” “for consumption”
measured pH on
measured pH on
measured pH on
measured pH on
measured pH on
24
measured pH on
appearance and smell at end
What to Include in Your Lab Report For Lab Report 3, Part A, answer the following questions:
1. What happened in both the yogurt and the kimchee? Explain using observations and your knowledge of the process of fermentation (see your text).
2. Does the acid end product alone cause coagulation (solidification) of the milk proteins? How could you test this?
3. What was the purpose of the “starter culture” in the yogurt production?
4. What are other fermented milk products? Do you think they all use the same starter culture?
5. Why wasn’t a starter culture needed for the kimchee (or was there one there)?
6. What do you imagine would happen if the yogurt or kimchee were aerated (oxygen added) during their production? (You may want to review Chapter 7 in your text for some help on this. Look at the alternative way pyruvate can be metabolized in the presence or the absence of oxygen.)
Additional Work if You Are Interested
1. If there is a cheese factory nearby, call for a tour. Other factories that produce fermented food products and may be close by are those producing sausage, pickles, beer, wine, or bread.
25
2. Look up other fermented food products online or in your local library. You may be surprised at what you find (e.g., coffee, black teas, chocolate, Tabasco sauce, vinegar).
Part B: Respiration and Photosynthesis To study respiration, you will be preparing bean sprouts. Bean seeds germinate and form sprouts in the presence of water and air (oxygen). The water rehydrates the dried tissue of the seed. Water is imbibed (absorbed by the seed) very quickly. This imbibition then triggers a series of events which, macroscopically, result in the formation of roots and shoots. Since the plant cannot photosynthesize until the leaves have been formed, the seedling relies on respiration of stored sugars for these early development events. This exercise will require you to rinse the seedlings twice a day for four to six days.
Supplies You will need the following item from the lab kit:
cheesecloth to cover the jars
You must provide the following supplies:
bean seeds (mung beans work very well for this experiment, although any bean
will be fine. Try navy or kidney or lima beans, all available dry, in bags, in the bean and rice section of the grocery store.) three glass jars, one with a cover (Old mayonnaise or peanut butter jars are fine.
Canning jars work well too.) three rubber bands or some string to attach the cheesecloth to the jars
Procedure
26
1. Put equal amounts of beans into each of the three jars, being sure not to fill any jar more than onefourth full of beans. Cover the beans with water until the water is about one to two inches above the top of the beans. Put a cheesecloth cover (two to three layers thick for strength) on each jar. Swirl the jar to sink any floating beans. Let the jars sit for two to three hours at room temperature (or overnight in the refrigerator). (What is the purpose of this soaking? Review the imbibition process in the introductory paragraph of Part B of this lab exercise.)
2. Pour off the soaking water (no need to remove the cheesecloth; the water will pour right through it).
3. Remove the cheesecloth cover from one jar, cover the jar with the jar cover, and label the jar “anaerobic.” Place this jar on its side out of sunlight (but on a table in a room that gets light is fine).
4. Label one of the other two jars “aerobic” and place it on its side next to the anaerobic jar.
5. Label the third jar “photosynthetic” and place it on its side on a windowsill (to get sunlight)
or under a lamp that you can leave on frequently.
6. Twice daily, rinse the seeds/seedlings in the “aerobic” and the “photosynthetic” jar. This can be done by pouring water right through the cheesecloth, swirling the jar, and pouring the water back out. Replace the jars on their sides in the appropriate incubation places.
Observations
1. Daily, record what is happening in each jar. Look for swelling of the beans, germination (appearance of roots and shoots), greening of the plant tissue, and presence of “unwanted guests” (i.e., molds that will look like cotton, or bacterial growth that will look more like mayonnaise or peanut butter).
2. After four to six days, your “aerobic” jar will contain “bean sprouts,” ready to add to a salad or stirfried for dinner. (They can be stored in the refrigerator for a
27
week or so.) What about the other two jars? What has happened in them? Can you eat the beans in the “photosynthetic” jar? Yes. Can you eat the beans in the “anaerobic” jar? (No, and you won’t want to once you smell them!)
3. Discard all unwanted beans into the garbage. Wash the jars with soapy water before reusing.
What to Include in Your Lab Report For Lab Report 3, Part B, answer the following questions:
1. What did you observe in each jar?
2. What metabolic processes were taking place in each jar?
3. Wasn’t oxygen in the “anaerobic” jar when you sealed it? What happened to the oxygen?
Summary Report Provide this summary report in addition to answering the questions for parts A and B.
• For the summary report for this exercise, compare and contrast the three modes of metabolism. What environmental conditions does each require?
28
Lab Exercise 4: The Structure of a Flower
Objectives The objectives of this exercise are to show you how much can be learned by “disassembling” a plant or animal, give you an opportunity to learn about the structure of the flower, and show you the value of the hand lens to the field biologist. This exercise is inserted here because the flower is the site of gamete formation in a plant.
Write down your answers to the questions in the exercise as you do the work. These are the questions you will answer in your lab report (attached to the Assignments tool).
Timing note: This exercise will take a few hours and can be completed in one day. You will need to acquire some flowers of specific types.
Introduction Over the centuries, biologists have learned a great deal by tearing things up. They have dissected plants and animals to look at their inner workings. By doing this, biologists found different organs and tissues that are essential to the organism. By doing additional experiments, they learned about the function of these organs and tissues. On a more microscopic level, they have “torn apart” cells and studied cell parts (like mitochondria or enzymes) and have even opened viral coats to see what is inside. While this “ripping apart” of organisms may seem like studying the functioning of a house by ripping off all its walls and scattering the furniture, biologists have had, until recently, very few other ways to see inside a living organism or cell.
Biologists still rely on this disassembling (called dissection) to give them information, to help them in identification, and to lead them to new questions about how life works and how it came to be what it is.
In this exercise, you will be dissecting flowers. You will start with flowers that have easily distinguishable parts, but you will then be asked to work with flowers in which
29
the parts are a bit more difficult to identify. Refer to page 827 in your text for an illustration of a flower and the terminology of its parts.
Supplies You will need the following items from the lab kit:
hand lens forceps razor blade
You must provide the following supplies:
at least three flowers of these types:
a. a lily, tulip, buttercup, or impatiens; b. a bell flower, snapdragon or morning glory; c. a sunflower or daisy
Procedure
1. You will need to collect or purchase a few flowers for this exercise. Your local greenhouse may give you free flowers since you can use slightly bruised flowers for this exercise. Your first dissection will be of a flower that has easily identifiable parts, such as a lily, tulip, buttercup, or impatiens. You will then progress to more difficult flowers.
a. Examine the flower. How many petals does it have? Can you distinguish between petals and sepals? Both lily and tulip are monocotyledonous plants. These plants (monocots) typically have petals in multiples of three. Dicots (dicotyledonous plants) like buttercup and impatiens typically have petals in multiples of four or five.
b. Carefully remove each set of floral organs (petals, sepals, stamen, and pistil), arranging each on a piece of paper in the order you have removed
30
them from the flower. If a flower has all of these parts, it is called a complete flower.
c. Using the hand lens, look for the parts that make up the stamen (the stalk or filament and the anthers or pollen sacs). Is there any pollen on the anthers? (What is pollen?) What is the purpose of the filament?
d. Using the hand lens, look for the parts that make up the pistil (the ovary, the style, and the stigma). Touch the top of the stigma. Is it ready to receive pollen (is it sticky)? Are there any pollen grains on the stigma? If not, and if it is sticky, shake some of the pollen grains from the anthers onto the stigma. Do they stick?
e. Cut through the ovary lengthwise and then crosswise. Using the hand lens, what do you see? An ovary may be subdivided into sections, each containing ovules. How many sections does this flower have? (This information is very useful when identifying plants. You may want to buy or borrow a field guide for identification of plants for your next hike in the woods.)
f. Draw a diagram of the flower you have dissected in the space below.
2. Now progress to a more difficult flower, such as a bell flower, snapdragon, or morning glory.
These flowers have fused petals. Repeat steps a through e.
3. Now, go on to a composite flower. The flowers you dissected earlier are called simple flowers. Composite flowers are those that have an aggregation of smaller flowers that form a “head.” Sunflowers and daisies are examples of composite flowers. Cut the head lengthwise. You will be able to see two types of flowers: those on the edges (in a circle around the edge) are called “ray florets,” and those in the middle are called “disc florets.” The disk florets are often in
31
various stages of blooming, with those near the edge blooming first. If the florets are large enough (such as those on sunflowers), dissect each and look for the flower parts you found on the earlier flowers.
4. Finally, go outside and pick any flower. Dissect it and describe what you see.
What to Include in Your Lab Report Go to the Assignments tool on the course Web site to download the worksheet on which to enter your answers.
1. Draw a diagram of a perfect flower. Label the parts and indicate the function of each part
(use your text for help with this). 2. What are the gametes of the flower and where are they found in the flower?
3. Draw a diagram of the flower you found outside. Is the flower simple or composite? Do you think it is the flower of a monocot or a dicot?
Lab Exercise 5: Growth and Trophic Responses
Objectives and Introduction The purpose of this exercise is for you to study growth in plants, including both the rate and direction of growth.
Organisms grow in two distinct ways: the cells may increase in number through mitosis, as you learned in the last lesson, or the cells may increase in size or mass. In plants, growth is restricted to certain areas called meristems. In this exercise, you will be determining the location of the meristematic region of the root and how this region responds to environmental stimuli such as gravity. You will also be able to observe the response of the shoot to gravity. Growth responses of plants to
32
environmental stimuli are called trophic responses, with response to gravity called gravitropism (previously called geotropism).
Write down your answers to the questions in the exercise as you do the work. These are the questions you will answer in your lab report (attached to the Assignments tool).
Timing note: This exercise will take several days to complete. It is divided into two sections, which should be done simultaneously.
Supplies You will need the following items from the lab kit:
fifteen pea seeds ruler with metric calibrations Sharpie extra fine point pen strip of filter paper short drinking straw two large petri dishes with lids one test tube one cork three pieces of large filter paper
You will need to provide these items:
paper towels and newspapers aluminum foil tall drinking glass cup tape
Preparation
33
1. Soak fifteen pea seeds in a cup of water for twentyfour hours. (If it has been a long time since you began this class, the seeds from the lab kit may not be viable. If they are not, you will need to buy replacement seeds to do this exercise. If you cannot find pea seeds, you may substitute bean seeds from the dry beans and rice section of the grocery store.)
2. Cut a piece of paper towel to fit the bottom of one of the petri dishes. Wet it and place it in the petri dish. Then place the soaked pea seeds on the paper. Cover the petri dish with its lid. Allow the seeds to germinate for two to three days. During this time, the epicotyls and roots will emerge. (See the illustration below.)
Part A: Growing Region of the Root
Procedure 1. Choose a seedling that has a straight root between 1.5 and 3.5 cm in length.
34
2. Working on a piece of newspaper or paper towel, place the metric ruler under the seedling to prepare to record the root length. Before marking the pea seedling with the Sharpie pen, blot the root to remove excess moisture. Apply gentle pressure with the pen so you do not damage the soft root tissues. (You may want to practice on several other pea seedlings to see how much pressure to apply.) Starting at the tip, use the Sharpie pen to mark the root in 1 mm intervals for a length of 8–10 mm (see the figure below).
a. Note: The first mark will be at the very tip of the seedling. Be careful that you don’t stain anything but the seedling. Do not let the seedling dry out while you continue to set up this experiment.
b. On a piece of paper, draw the root to full scale and label the positions of the ink marks.
You will turn this drawing in as part of your report.
3. Insert a thin strip of filter paper into the drinking straw.
4. Gently insert the root into the straw until the seedling rests on the edge of the straw.
5. Keeping the seedling and straw together, insert the straw into a clean test tube containing about one inch of water (see the figure on the next page). The filter
35
paper acts as a wick, supplying water to the seedling (so make sure the base of the filter paper is in the bottom of the test tube, while the straw supports the seedling).
6. Cork the test tube or cover it with a small piece of aluminum foil. Place the test tube in a tall drinking glass and allow the root to grow for two or three days.
7. After the seedling has grown for two or three days, remove it and measure the length of the root. Again draw the seedling to full scale, and label the positions of the root markings. Return the root to its “growth chamber.”
8. Continue to observe the seedling for the next few days, observing secondary root formation (side roots that emerge from the side of the original
36
root) and any growth of the shoot (stem and leaves of the plant). When do secondary (side) roots first appear? Are there any root hairs on these secondary roots? What advantages to the plant do these lateral roots provide?
Part B: Trophic Responses of the Root
Procedure
1. While you are determining the growing region of the root, also determine the growth response of the root to gravity. To perform this part of the experiment, you must again choose seedlings that have a straight root between 1.5 and 3.5 cm in length (the shorter length is preferred). Take four of these seedlings and mark the root with ink as with the root growth experiment.
2. Arrange the marked seedlings in a circle on a large piece of dry filter paper so that the roots all point toward the center. Imagining the filter paper as the face of a clock, the seeds should be at 12:00, 3:00, 6:00, and 9:00. Carefully tape each seed (not the root, just the seed) to the filter paper.
3. Put two pieces of filter paper into the large petri dish, add the piece of filter paper with the taped seeds, and wet the filter papers with tap water. The paper
37
should be uniformly moist with no excess water in the dish. Put the lid on the petri dish.
4. Slowly tip the petri dish on its edge so that the “12:00 seed” is at the top. The filter paper and seeds should stay in place on the bottom half of the dish (what is holding the filter paper there?). Cover the dish with foil and brace it to make it stay in the upright position.
5. Observe the growth of the roots over the next few days. In which direction are the roots growing? Was this growth in the same region as the growth you observed in the lone seedling you are measuring? Why did we exclude light? Does bending of the root in order to change direction require growth? Is there some elastic quality of the root that allows the bending? Or can the cells shrink on the inside of the curve, causing bending? What observations support your choice? What additional observations would you need to make or experiments would you need to do to determine if your choice is the right one?
What to Include in Your Lab Report Go to the Assignments tool on the course Web site to download the worksheet on which to enter your answers.
Part A: Growing Region of the Root
1. Include the two fullscale drawings of the root, one prepared just as you marked the root and one prepared after two to three days.
2. How much did the root grow? What was the total growth rate (i.e., how many millimeters per day)?
3. What portion of the root grew the most?
4. What other changes occurred in the seedling? What might be the role of gene expression in these changes?
38
5. Using your data and the information in your text, write a paragraph that summarizes the visual and cellular events in root growth.
Part B: Trophic Responses of the Root
1. Describe the results of the gravitropism experiment. What do you think is the mechanism of bending? (Hint: Think about cell elongation and cell division.) What additional observations would you need to make or experiments would you need to do to determine if this is the correct mechanism?
2. How would you test the seedling’s response to light? Design an experiment. (You do not need to perform this experiment unless you would like to.) You should include a hypothesis, experimental design, materials and methods, observations to be taken, and expected results if your hypothesis is correct.
Additional Work if You Are Interested 1. Perform the experiment you designed for Part B of your lab report.
2. Measure the growth rate of the roots of other seedlings and/or at other temperatures. For example, do pea seed roots grow faster at low temperatures (refrigerator or cool basement) than the roots of some plants that you don’t see emerge until later in the spring (e.g., morning glories)?
39
Lab Exercise 6: Pedigree Tasting
Objective The purpose of this exercise is to gather data and analyze the genetic transmission of a simple inherited characteristic (trait).
To do this study, you will need to find three generations of a family to participate in your study. We realize that you may not be able to gather information for your own family (because of separations of distance or emotion), so you are encouraged to enlist the help of a friend or co worker and his or her family in developing this pedigree.
The best of all possible situations is to have two sets of grandparents, a set of parents and their siblings (brothers and sisters), and the children of this parent pair. Attempt to get as close as you can to this best situation, but even professionals studying genetic inheritance in humans may find it impossible to obtain all data from one family because of death or the inability to locate a family member.
Write down your answers to the questions in the exercise as you do the work. These are the questions you will answer in your lab report (attached to the Assignments tool).
Timing note: This exercise will take a few hours to complete once you have obtained the “taste” data from your test family, though contacting relatives may take some time in advance.
Introduction While population studies of genetic transmission of traits in plants or animals often involve carefully selected matings, this is not possible in the human population. Instead, observations of traits within a family are made, a pedigree developed, and the results analyzed. These results can be used in genetic counseling (for example,
40
to help partners decide the risk of genetic abnormality in a current or future pregnancy).
Inherited characteristics that can be analyzed easily are those that are expressed regardless of environment (e.g., eye color or hair color); other characteristics such as height or weight may have a genetic influence, but are often influenced heavily by environment and are therefore hard to analyze. There are many traits that you could study, such as the presence of a “widow’s peak” (hairline forms a point in the center of the forehead) or attached earlobe, but for your pedigree, you will study the ability to taste certain chemicals. The chemicals have been added to strips of paper that are used in taste tests. The taste of some of these strips may be unpleasant, but the chemical itself is harmless. For simplicity, you can make the assumption that the ability to taste each of these chemicals is controlled by a single gene. In your analysis, you will be able to challenge this assumption.
Supplies You will need the following supplies from the lab kit:
taste strips (there are three different taste strips, plus one control [no
taste added] strip) These taste strips are color coded:
control paper is white
paper containing PTC (phenylthiocarbamide) is blue paper containing sodium benzoate is pink paper containing thiourea is yellow
You have been supplied with twenty strips of each. These can be easily mailed to relatives, as the chemicals are stable at normal temperatures.
Procedure
41
1. You will need to keep track of each person’s ability to taste or not taste each chemical. Use the data chart given below for this purpose. Use T for taste and N for no taste.
Name Relationship PTC thiourea Na benzoate
2. Start with yourself. Then you can instruct others how to taste the papers. Rinse your mouth with water. Place the control strip on your tongue and move it around so that any chemical on the paper can mix with your saliva. Since this is the control strip, this gives you the taste of the paper itself. Any other strips that taste like this should be marked as no taste.
3. Rinse your mouth again (and between each taste strip), and try the PTC strip (blue strip).
Record as T for taste something or N for no taste. Continue the taste test of the other strips, being sure to rinse between each strip.
42
4. Test your selected family, keeping careful notes on the chart. Remember, you are scoring taste versus nontaste.
5. Draw a familial pedigree for each chemical (three pedigrees total). A pedigree indicates the relationship between individuals tested, the sex of each individual, and the phenotype (in this case, taster or nontaster) of each individual. See page 253 in your text for an example of how a pedigree is set up. The figure below also indicates the format of a pedigree.
6. Analyze the data you have obtained. To begin with, analyze each pedigree separately and assume that the ability to taste each chemical is controlled by a single gene.
a. Using the pedigree developed for each chemical, determine whether tasting is controlled by a dominant or recessive gene. (How? Refer to your text on pages 336–337. Note that dominant genes usually show up as traits found in higher frequency in the population because both the homozygous and the heterozygous genotype give rise to the same phenotype. While higher frequency is not always true, it is a guideline that will help in your analysis.)
b. Based on your hypothesis of the dominance or recessiveness of tasting or nontasting, assign the gene a symbol (e.g., P for tasting PTC; p for nontasting, if tasting is assumed to be dominant). Then assign a genotype to one taster and one nontaster in your test family.
c. Analyze the pedigree to see if there is any linkage of this trait to either sex (which would indicate a sexlinked or sexlimited trait). Do you see any?
7. Now look at the pedigrees together. Analyze these for linkage between the three different traits tested. Linkage is indicated by nonindependent assortment. The genotypic and phenotypic ratios of linked genes differ from those of nonlinked genes. Refer to your text on page 352–356 for a further discussion of linkage and how to analyze your data.
43
What to Include in Your Lab Report Go to the Assignments tool on the course Web site to download the worksheet on which to enter your answers.
1. Send in the three pedigree charts you have developed. On each chart, indicate the genotype of one taster and one nontaster. Be specific about whether the trait is dominant or recessive. Did you see any sexlinkage of these traits?
2. In your analysis of the three charts together, did you decide the genes were linked or unlinked? What observations support your decision?
Additional Work if You Are Interested You may find that some individuals taste a chemical, but describe its taste differently than others. It is true that there may be more than one gene that is involved in the taste versus nontaste of these chemicals. Alternatively, there may be different alleles of the same gene that control the way the chemical is perceived (e.g., sweet, bitter, salty). If you wish, you could look at this question in more detail in your pedigree
44
(sodium benzoate tasting is the trait that shows this variety of perception). How might you determine whether the variation in perceptions is due to different genes or to different alleles of the same gene?
Lab Exercise 7: Morphogenesis in Insects
Order the milkweed bugs and food kit from Carolina Biological Supply Company. Wait until 2–3 weeks before you start this lab to place your order. The timing is important: if you order the bugs too soon, they will die before you are ready to begin. The lab itself will take several weeks to a month to complete.
Write down your answers to the questions in the exercise as you do the work. These are the questions you will answer in your lab report (attached to the Assignments tool).
Order the following items. Carolina Biological Supply Company will ship based on the date you select. They cannot guarantee the exact date of arrival; please plan to receive shipment on Wednesday, Thursday, or Friday of the week you select. Allow ten days before the expected delivery date.
Item 143816 Milkweed Bug (Oncopeltus fasciatus), Living, Eggs Item 143830 Milkweed Bug Food, 250 g
To order on the Web: http://www.carolina.com/home.do Phone: 800.334.5551 Fax: 800.222.7112 Email: [email protected]
Objectives The purpose of this experiment is to observe the morphological changes that occur during the development of an animal. Without a microscope, it is impossible to observe the developments at the cellular and subcellular level; however, observations at the macrolevel (postembryonic),
45
such as changes in body size and shape, are quite easy to make without a microscope. In this exercise, you will watch and record the development (morphogenesis) of an insect from egg to adult. This process takes about a month (more or less, depending on temperature), so be sure to start it when you have a month in which you can make frequent observations of the insect culture.
Introduction The milkweed bug (Oncopeltus fasciatus) is a member of the family Lygaeidae and the order Hemiptera in the class Insecta. This insect is common in many regions where the milkweed plant (Asclepias species) grows. The bugs you have been supplied with have been adapted, over generations, to use sunflower seeds as a complete food source. This means that if the bugs escape, they are unlikely to survive in the wild (or in your house!).
The illustration below shows one of the stages of milkweed bug development so that you have the proper terminology to describe what you are seeing.
For your observation, we have chosen an insect that goes through a gradual (“paurometabolous”) development, in which the insect form that hatches from the egg is quite similar to the adult and is called a nymph. There are several stages of development (you find out how many by observation) from the first nymph, called the first instar, to the final, winged adult stage. During the development, the insect is
46
growing in size and therefore reproductive capacity—an important consideration for a species during the race for food and survival. Since insects have external skeletons, growth requires molting of the exoskeleton. You will be able to find these molted skeletons in your insect culture during the course of this experiment. If you observe the culture carefully, you may be able to catch an insect in the process of a molting. Molting takes about fifteen minutes. Each molting releases a new instar stage, until the final molt, which releases the adult. The molted exoskeletons are called exuvia.
Other insects go through development stages in which the hatchling and intermediate stages do not resemble the adult (consider the dobson fly and its immature stage; the hellgrammite, available at any bait store; and the house fly or butterfly, in which the stages progress from egg to larval stages to pupa to adult). If you are interested, you can easily set up cultures of these other insects after you have gained experience with the milkweed bug. The most important things to consider are their food source and water supply.
Supplies You will need the following items:
milkweed bug eggs, ordered with your postcard from Carolina Biological Supply
You will need the following items from the lab kit:
cheesecloth dish towel cloth water cup with lid a hand lens
You must provide the following supplies:
a glass vessel to keep the bugs in (a quart canning jar works very well, or any
wellwashed, rinsed, and dried glass food jar) a rubber band to fasten cheesecloth or the dish towel cloth around the neck of
the vessel to
47
keep the bugs inside scissors sunflower seeds
Procedure Setup and Maintenance of the Insect Culture
1. Be sure the glass vessel is clean, dry, and free of soap residue.
2. Sprinkle about 2 teaspoons of sunflower seeds into the bottom of the vessel.
3. Punch a hole in the water cup’s lid. To make a wick for water, tear or cut off a piece of cheesecloth measuring about 1.5 inches by 12 inches. Roll this cheesecloth up lengthwise (i.e., from one end of the 12inch end to the other), and push this roll into the hole in the water cup’s lid. Fill the water cup with water and cover with the lid. Place in the bottom of the vessel.
4. Cut another piece of cheesecloth measuring about 2 inches by 18 inches. Fold this cheesecloth to give a 2inchwide piece. Place this piece as an insect ramp between the sunflower seeds and the wick on the water cup. Be sure this piece does not touch the wick.
5. Place the cotton containing milkweed bug eggs onto the bottom of the vessel.
6. Cut a piece of dish towel or cheesecloth to fit the top of the vessel, place it on the top, and secure it with a rubber band.
7. Place the culture in a warm, wellventilated room. Keep the culture out of the sun.
8. You will need to add sunflower seeds (and remove any that look moldy or otherwise rotten) and change the water and water wick weekly. During the winter or dry season, keep a close watch on the water since evaporation will occur quickly.
48
Observations
Observe the insect culture daily, if possible (yes, you may go away for a weekend, but you may miss something exciting!). These insects do not bite, so you can remove individuals from the jar and observe them closely with the hand lens. Observations you are expected to make include:
1. Record the number of eggs that have hatched each day. Did any fail to hatch?
2. Observe at least two insects each day for morphology. Use the hand lens supplied to observe detail that is hard to see without some magnification. Keep a daily log of your observations. This log will be used at the end of the exercise to summarize the development of the insect. In particular, look for changes in size, changes in morphology (these may be subtle; for example, watch the antennae and the wing size), duration of each instar stage, and time of emergence of adult. Drawings are very helpful.
3. While this exercise is designed to study the morphological changes occurring during the development of the insect, you may wish to watch for any behavioral changes that occur as well.
49
4. Optional: If you want to continue studying the milkweed bug after the adults emerge, you will need to add some cotton balls to provide a substrate for egglaying by the adults.
Ending the Exercise
At the end of the exercise, you should not release the adults into the wild. While it is unlikely they will be able to survive, and while some variety of the milkweed bug may be common in your area, the release of possible “exotic” species into an area is considered to be ecologically unsound. Many exotic species that have flourished in Minnesota include the Eurasian water milfoil, purple loosestrife, and zebra mussels. These species threaten the survival of native varieties that inhabit the same habitat. Two ways you can end this exercise are:
1. Give the milkweed culture to a school in your area. Be sure, however, to remind the teacher not to release the insects into the wild.
2. Kill the insects by freezing (thirty minutes in the freezer should be sufficient as these insects have not been preparing for an upcoming winter as they might be in the autumn in the wild) or by placing them in alcohol (rubbing alcohol or distilled alcohol such as vodka will both work) for thirty minutes, then discarding them in the (compostable) trash.
What to Include in Your Lab Report Go to the Assignments tool on the course Web site to download the worksheet on which to enter your answers.
1. In one or two pages, summarize the development of this insect. Include the number and duration of each instar stage and the time of emergence of the adult.
2. Answer the following questions relating to this exercise.
50
a. Which stage in the milkweed life cycle is depicted in the first figure in this exercise?
b. What other animals besides insects have external skeletons? Which have internal skeletons?
c. Based on your experience, describe the development of the human from infant to adult.
Are there stages similar to “instars,” or is the development much too gradual to identify specific stages?
Additional Work if You Are Interested
You may wish to look for “wild” milkweed bugs on milkweed if the season is right (summer and early fall are the best times to look for milkweed bugs).
As mentioned previously, you may wish to culture other insects. Insects may
be caught quite easily in a trap made from a plastic soda bottle.
1. First, remove the lid, wash the bottle, and then cut off the top of the bottle just below the shoulder.
2. Dry the inside of the bottle.
3. Put bait into the bottle and invert the bottle top into the
bottle bottom. a. For flying insects, leave the bottle upright.
b. For crawling insects, lay the bottle on its side. Insects will enter through the narrow top, but find it difficult to find their way out.
4. To culture these insects, be sure to provide food they prefer and water using a wicking system. Aquatic insects are easy to catch using just such a jar.
51
Lab Exercise 8: The Ecological Community Structure
Timing note: You must carry out this lab exercise during the growing season in your area. For Minnesotans, this means any time between April and early November. Plan ahead so that you can collect data at the appropriate time for your locale.
Write down your answers to the questions in the exercise as you do the work. These are the questions you will answer in your lab report (attached to the Assignments tool).
Objectives In this lab exercise, you will familiarize yourself with the concept of community structure by making sample plots in a community of your choice. You will be collecting both qualitative and quantitative data, reporting your observations, and answering questions. It may take you a few days to gather all the data necessary to complete this exercise.
Supplies From the lab kit you will need:
two sheets of graph paper
You need to provide the following items:
meter stick right triangle (optional) eight sticks or long nails hammer or rock heavy string
52
Procedure
1. Choose a natural terrestrial community within your locale. It can be of any type. Within the community, select two 1 x 2meter quadrants (rectangular areas) at random. Stake and rope off the quadrants, making sure that both quadrants are the same size. In order to distinguish between the plots, label them Plot 1 and Plot 2. Describe and record the physical characteristics of the plots (e.g., moisture, soil texture, degree of shade, etc.).
3. Make a chart for each plot containing a list of the various plant species that grow in it. Label each plant with a letter. Plant species that grow in both plots should be given the same letter. Otherwise, the plant species in Plot 1 should be labeled with different letters than those used to label the plant species in Plot 2. (You don’t have to identify the plants by name.)
4. Assign some height categories to the vegetation (e.g., 1–3 in., 4–5 in., 6–8 in., etc.), and record a height category for each plant species in each plot on a chart. Use the same height categories for both plots.
5. Count the number of individuals of each plant species in each plot and record this on a chart for each plot.
6. Make a chart of the animals found in each plot. Search for animals under logs, stones, leaves, and other cover, being careful to replace any object overturned. List the taxonomic groups of animals you’ve found (e.g., frogs, ants, turtles, etc.). List the number of individuals you found in each taxonomic group.
7. On the graph paper from your lab kit, record your data about each plot in the form of bar graphs showing the relative abundance of plants and animals. Use the same measures for each graph so that the data from the two plots can be compared.
8. On paper, report:
53
a. the number of plant species in each plot
b. the density of individual plant species in each plot
c. the height categories of plant species that were found in
both plots d. the number of animal taxonomic groups in
each plot
e. the density of individual animal groups in each plot
9. Explain whether the different physical features of the two quadrants are solely responsible for the differences in species composition.
10. How reliably do your chosen plots characterize the larger community? Are the physical and biotic characteristics uniform or variable when compared with the larger community? Explain.
What to Include in Your Lab Report Go to the Assignments tool on the course Web site to download the worksheet on which to enter your answers.
After you complete steps 1 through 10, write your results on the worksheet.
54
