Questions to think about:

Is water loss through transpiration harmful or beneficial for plants?

Is there a relationship between transpiration rate and photosynthesis rate?

If a bright and hot light is directed at a leaf and the stomata open, how could you determine if stomatal opening is due to the plant’s need for CO2 for photosynthesis or the plant’s need to cool itself?

If you compare the top and bottom surfaces of a leaf, do you expect the top to have more stomata, fewer stomata, or about the same number of stomata?

Stomata are found not only on leaves, but also on green stems. Would you expect to find them on woody stems, such as a large tree trunk? Why or why not?

Learning objectives for this week’s lab:

(1) Be able to explain transpiration to a fellow student.

(2) Be able to perform a leaf peel and identify stomata, accessory cells, guard cells, and epidermal cells.

(3) Be able to discuss why stomatal densities might differ within a leaf, among leaves from different parts of a large plant, and among leaves found on plant species specialized to different environments.

(4) Be able to generate and quantitatively test hypotheses about how light and leaf temperature influence transpiration rate in plants.

(5) Be able to interpret data from a potometer and explain what they tell us about transpiration rates.

Textbook Reading:

Cambell and Reece, 6th edition, pages 734, Fig. 35.19, 756-764, 825-826

fall 2004, Lab 9-1

Week 9 labREGULATION OF PLANT TRANSPIRATION

November 8-12, 2004

LAB OVERVIEW

PLANT PHYSIOLOGY: TRANSPIRATION

THE BIG PICTURE

In recitation you learned that transpiration is central to the proper functioning and survival of plants. Today in laboratory we explore several important components of transpiration, including relationships between the organization of leaf tissue, stem tissue, and whole-plant water balance.

BEFORE CLASS

Prepare for this week’s quiz by:

reading today’s lab handout and the textbook readings;

attending recitation lecture and reviewing your recitation notes;

DURING LAB

Learn the basic structure of angiosperm stems and leaves and complete worksheet 4.

Perform the Carnation transpiration experiment and record your observations.

Perform the leaf epidermal imprint activity. Record your data on Worksheet 1 and contribute your data to the class pool.

Quantify the effects of different variables on transpiration rates complete Worksheet 2.

ASSIGNMENT DUE AT THE BEGINNING OF

LAB NEXT WEEK

Complete Worksheets 1 and 2 during lab, but do not turn them in. You will need them so that your group members can collaborate to answer the questions on Worksheet 3. As a group, complete and turn in Worksheet 3.

Individually, you will turn in worksheet 4. Remember to do your own work on this worksheet (and on others unless specifically instructed to work as a group. There have been some issues in the past with students turning in worksheets with the same answers word-for-word. Even if they are not word-for-word the same, this can still be a violation of the honor code. BE CAREFUL and if you have questions, please ask your instructor!!!!)

fall 2004, Lab 9-2

Angiosperm diversity: MONOCOTS AND DICOTS; work individually and complete worksheet 4

When one examines various flowering plants, they fall into two groups, each with distinctive features: the subclass Dicotyledonae (dicotyledons or dicots) and the subclass Monocotyledonae (monocotyledons or monocots). The following indicates some generalities. (As is usual in biology, there are exceptions.)

MONOCOTS VS DICOTS

Examine three of the plants available in the lab and determine whether they are monocots or dicots. Record your observations on your data sheet.

fall 2004, Lab 9-3

Angiosperm Stems: work individually and complete worksheet 4In the lab this week, there will be prepared slides of cross-sections of stems, from both a dicot and a monocot. Examine the various cell and tissue types.

The outermost ring of cells is the epidermis. In the stem, epidermal cells are coated with a waxy cuticle. Inside the epidermis of the dicot stem is the cortex. This tissue consists of large, undifferentiated cells, called parenchyma cells. Some of them may contain chloroplasts, and thick-walled support cells.

Parenchyma cells make up most of the stem tissue and are stained light purple. In a dicot they also form the large, central pith. Now identify the vascular bundles (clusters of xylem and phloem). With toluidine blue, the phloem usually stains reddish-purple and lignin, a carbohydrate that stiffens cell walls and is often found in xylem, stains bluish-green.

Vascular bundles are arranged in different patterns in dicot and monocot stems. On your worksheet, draw an outline of your stem sections showing the epidermis and the arrangement of the vascular bundles for both types of stem. For the dicot stem, also label the cortex and pith. For the monocot you need only draw a representative sample of vascular bundles.

The xylem is most readily identified by the large diameter and thick walls of vessel members. The cells in the phloem are thinner walled, and consist of the sieve-tube members that transport organic compounds and their smaller, companion cells. The vascular bundles of corn are surrounded by a bundle sheath, made of fibers. Long strings of fibers associated with vascular bundles are the source of linen (made from flax, Linum) and natural rope (made from jute or hemp, Cannabis ).

A distinct difference between the dicot and monocot stems is the presence of brick-shaped cells of vascular cambium between the xylem and phloem. This secondary meristematic tissue gives rise to additional xylem and phloem in woody stems. Only dicots have vascular cambium and, therefore, only dicots can undergo lateral (woody) growth of the stem. Notice that the vascular cambium continues between the vascular bundles and encircles the stem.

Angiosperm Leaves: work individually and complete worksheet 4

The leaf is the principal lateral appendage of the stem and the principal organ of photosynthesis. Most leaves consist of a stalk, the petiole, and a broad, expanded part, the blade. Leaves are very diverse, and the structure of a leaf is to a great extent related to habitat and function. There are, however, basic differences between monocot and dicot leaves. Review these differences you learned during last week’s lab.

1. Syringa (lilac) leaf. Spend some time observing the prepared slide of a leaf under low power. It is important that you orient yourself. You will see variation in the size and orientation of the veins, or vascular bundles, which carry xylem and phloem in the leaf. The centrally located, largest vein is the midvein. Smaller veins are embedded in mesophyll, which is photosynthetic. Chloroplasts should be visible in cells in the mesophyll, as well as intercellular spaces. What is the function of these intercellular spaces?

If you examine a portion of the blade that is to one side of the midrib, you should be able to identify the upper epidermis. This has a relatively thin cuticle. Below it, there is a layer of palisade parenchyma. Running through the parenchyma are veins surrounded by rings of cells. Below the palisade parenchyma is spongy parenchyma. The palisade and spongy parenchyma together comprise the mesophyll. One the lower epidermis, you should see stomata, associated with substomatal chambers. What is the function of these chambers? More stomata occur on the lower than the upper surface. Why?

fall 2004, Lab 9-4

Water is a valuable resource for plants. The growth of plants is more likely to be limited by lack of water than by lack of any other factor — CO2, light, nitrogen or other minerals. Anyone who has neglected a houseplant knows this. Yet transpiration is the only way to lift water from a plant’s roots, and plants are constantly losing water through shoots, seeming to defeat the purpose of a plant’s extensive water-absorbing roots.

Why transpire, and, especially, why transpire so much? If a human being used as much water as a typical vascular plant, she would require consumption of about 40 liters of water every day. No one sweats that much. Think about why there is this difference. Plants need carbon dioxide to carry out photosynthesis in their chloroplasts and oxygen to carry out aerobic respiration in their mitochondria. People need oxygen to carry out aerobic respiration in their mitochondria. Why do plants move so much more water than we do?

This week’s lab focuses on this apparent paradox. Our focus is on individual leaves, but as you do the experiments you should think about transpiration as a normal function of individual plants, and of natural ecosystems, including the global ecosystem. Try to think about transpiration from two different perspectives.

First, explain how transpiration happens and how plants regulate the rate of transpiration.

Second, try to understand why transpiration happens and the manners in which plants (or leaves) acclimate and adapt to different environmental challenges such as high temperature or drought.

How transpiration happens

During the beginning part of the lab, you learned three things about the anatomy of vascular plants. First, leaves possess thick, impermeable cuticles to prevent the loss of water. Second, the inside of a leaf is occupied by intercellular air spaces that take up about 70% of the volume of the leaf. Third, the structures that connect these intercellular air spaces with the dry air outside the leaf are the microscopic openings in the leaf surface, the stomata.

Stomata can be opened and closed through the action of two guard cells, and many different factors regulate this opening or closing.

A biological clock exists in the guard cells of most plants, with stomata opening in the morning and losing at night, even if the plant is kept in either 24 hours of light or 24 hours of dark.

When a leaf is exposed to bright light, the blue wavelengths trigger guard cells to rapidly take up potassium ions (K+) through specialized channels in the cell membrane, an active transport process that requires ATP. Water then flows into the guard cell, increasing turgidity so that they stay open. These ions and the water will passively leave the guard cell when this light signal is removed.

The hormone ABA plays a role in regulating the closure of stomata; this role was discovered by studying mutant plants that lack ABA and cannot close their stomata. In non-mutants, high temperatures or water deficiency in the soil can cause the synthesis of ABA in leaf tissue. ABA alters permeability of plant cell membranes as well as properties of the cell walls of the guard cells.

fall 2004, Lab 9-5

INTRODUCTION TO TRANSPIRATIONTranspiration: (n.) evaporation of water from leaves and stems; occurs mostly through stomata

Other environmental factors can trigger stomatal opening as well, including low concentrations of CO2 intracellularly, a consequence of high rates of photosynthesis that can rapidly deplete the leaf’s supply. In a complementary fashion, high CO2 concentrations intracellularly, or high temperatures, can promote the stomata to close.

In today’s lab, you will have the opportunity to investigate the role of light, temperature, and ABA in the regulation of transpiration.

Why transpiration happens: pros and cons

As we noted earlier, the downside of transpiration is that it causes plants to lose water. This is clearly a problem when water is scarce and the rate at which a plant transpires exceeds the rate at which roots can absorb water. Over time, this leads to wilting, and eventually plant death. Given this cost of transpiration, why do all plants do it? One answer is that transpiration is an inevitable consequence of the plant’s need to take up CO2 from the atmosphere for photosynthesis. The stomata must be open to permit gas exchange, and transpiration occurs whenever the stomata are open.

Another answer is that transpiration actually helps the plant maintain leaf temperature. As water evaporates, heat dissipates, thereby cooling the leaf. (The same principle is behind sweating in humans.) Imagine how hot leaves could become in the middle of a hot summer day, in the blazing sun, without a cooling system. Finally, transpiration is the only mechanism plants can use to lift water from roots deep in the soil, through the xylem, to branches many meters above the ground.

The take-home message is that there are pros and cons to transpiration. It should therefore not surprise you that plants have evolved a complex set of mechanisms for controlling transpiration, so that they can maximize its benefits and minimize its costs. You should also realize that the regulation of stomata is not the only strategy for regulating water loss. Species adapted to different environmental challenges may have evolved differences in the density of stomata. Other strategies for tolerating water loss include altering leaf position, hairiness on leaves, changes in leaf surface area and thickness, stomata located in chambers sunken inside the leaf surface, shedding of leaves during very dry seasons, or even alternative photosynthetic pathways.

Your textbook provides additional background on this topic:

pp. 756-759 (6th ed.) on ascent of water through the xylem

Fig. 36.13 (6th ed.) diagrams how guard cells open and close stomata

fall 2004, Lab 9-6

Objectives Demonstrate transport through a xylem in a stem. Determine how environmental conditions affect this phenomenon.

Equipment2 (250 ml) narrow-mouth glass beakers2 short-stemmed white Carnation flowersfood coloringlight source (lamp)scalpel

Procedure1. Place 100 ml of distilled H20 into two glass beakers.

2. Add 10 drops of food coloring into each beaker.

3. Under running water, cut two Carnation stems (at a 45 degree angle) to a length of approximately 10 cm and VERY QUICKLY place them into your blue dye solution. Why do you need to cut the stems under water and put them under the surface of the solution so quickly?

4. Place one beaker under a lamp (flower about 8-10 cm from the light) and place the other beaker at your lab station.

5. Observe the flowers after 30 minutes and after 1 hour. Record your observations in the table below. Students may take flowers home after the experiment.

30 minutes 1 hour

Flower

under

lamp

Flower

under

ambient

light

fall 2004, Lab 9-7

Carnation experiment: Work in groups of 4

Objectives

Learn a method for examining the stomata on the epidermal surfaces of a leaf. Use the method to quantify the density of stomata on upper and lower leaf surfaces. Develop hypotheses about expected differences in stomatal density on upper and lower surfaces. Do a formal statistical test for differences in stomatal density on upper and lower leaf surfaces.

The reason you will work in groups of two is because you will need a MINIMUM sample size of EIGHT to perform a meaningful statistical analysis.

Hypothesis

Before you begin collecting data about the number of stomata on the upper and lower surfaces of a Spathiphyllum (Peace lily) leaf, think about whether and why you expect to find a difference.

You should also think about specific hypotheses that can be used to structure data collection, analysis, and interpretation. Recall the concept of a null hypothesis. A null hypothesis is appropriate in the absence of a biological reason to expect an alternative hypothesis. In the case of the Spathiphyllum leaf, an appropriate null hypothesis would be that the density of stomata on the upper and lower surfaces is similar, and so the difference between upper and lower surfaces is zero.

Logically, there are three different alternatives to this null hypothesis:

(1) A non-zero difference between upper and lower leaf surfaces, but no expectation of higher density on one surface or the other. This is called a “two-tailed” hypothesis.

(2) A difference between upper and lower surfaces greater than zero, because there are more stomata on the upper surface. This is called a “one-tailed hypothesis.”

(3) A difference between upper and lower surfaces less than zero, because there are more stomata on the lower surface. This is also a one-tailed hypothesis.

Is there a reason to prefer one of these three alternatives? That requires thinking about biology, specifically about how a leaf’s structure is suited to its functions: photosynthesis and transpiration. Do you really expect no difference between the stomatal density of upper and lower leaf surfaces? If not, what difference do you expect? Write an alternative hypothesis in the space provided on the worksheet, as well as the biological rationale for your hypothesis.

Equipment and supplies

Nail polishCut leaf from SpathiphyllumGlass slidesSlide labels or labeling tapeMicroscope

fall 2004, Lab 9-8

Spathiphyllum epidermal imprints and estimation of stomatal density: Work in groups of 2

Procedure

1. Obtain two microscope slides. Label one slide “upper surface” and the other “lower surface” by writing on the end of the slides with a Sharpie pen.

2. Observe a peace lily plant (Spathiphyllum), choose a leaf with a long petiole, and note its upper and lower leaf surfaces Then, cut the leaf from Spathiphyllum and bring it to your lab station.

3. Evenly place one coat of nail polish on part of the upper and lower surfaces of the leaf. Do not let the coated leaf touch the lab table or your fingers. (You’ll only need enough to put on your microscope slide, but make your polished part a bit bigger so you’ll have some room for error.)

4. Tape the petiole of the leaf on the edge of the lab bench (or the edge of the fume hood) and allow it to hang until dry.

5. When dry, peel a layer of the nail polish from the upper surface of the leaf and place it on the appropriately labeled glass slide. You do not need to add water or a coverslip.

6. Do the same for a layer of the nail polish from the lower surface.

7. Examine your epidermal imprint at 40X and 100X magnifications.

8. In the field of view at 100X, sketch and label the following structures in the space provided on the worksheet: (a) stomata, (b) guard cells, (c) accessory cells, and (d) epidermal cells.

9. In a single field of view at 100X, count the number of stomata on the upper surface of the leaf. Record this information in the space provided on the worksheet and also give it to your instructor so that it can be added to the master data sheet for the class. Since your counts are based on a standard area (one field of view at 100X magnification), this is an estimate of stomatal density.

10. In a single field of view at 100X, count the number of stomata on the lower surface of the leaf. Record this number in the space provided on the worksheet and give to your instructor so that it can be added to the master data sheet for the class.

fall 2004, Lab 9-9

Analysis

Your data are perfectly good data (remember that “data” is plural and that “datum” is singular). There’s not really such a thing as good or bad data. Some people mistakenly believe that if data doesn’t support a hypothesis, it is bad. Remember that this is how the scientific process works. It can be a GOOD thing to not support an incorrect hypothesis. Even though your data are “good,” let’s think about their limitations.

First, one difference between just two data points is not very convincing or satisfying evidence. By pooling data from all sections, we can evaluate hypothesized differences between upper and lower leaf surfaces more rigorously by examining many leaves. We can look at a mean difference.

If we do find a difference, so what? We want to do more than say that the means are “pretty different.”To evaluate data more rigorously, we need to consider variation from leaf to leaf.

Consider the following hypothetical data:

Lower UpperDifference

between upper and lower

group 1 33 32 1

group 2 40 62 22

group 3 35 140 105

mean 36 76 40

The means in the table above tell you that there tend to be more stomata on the upper surface, but they don’t tell you that this difference can be very tiny (group 1) or very large (four times greater for group 3). Calculating the standard deviation can help to supplement the mean by summarizing how far around the mean a given data point is likely to range.

You should calculate both the mean and standard deviation for the class data. Since the data will be available in an Excel spreadsheet, the easiest way to do the calculation is with Excel. If you don’t know how to do this, your lab instructor will show you how to do it using a sample data set. You can also ask someone at the computer help desk, a computing RA, a fellow student, or use the help menu in Excel.

There is a table on the worksheet for recording these values.

In the Excel spreadsheet, you can also conduct the paired t-test. Use the cursor to choose an empty cell in the spreadsheet where you can enter the commands for the t-test, and where the spreadsheet software will display the result (which will be a single number called a p-value; see below.) Go to the “Insert” pull-down menu at the top of the spreadsheet window, and choose “Function” from the pop-up menu. You’ll see a dialog box with two lists of options. First, on the left list, choose “Statistical” and then you need to look through the list of options in the right window. Scroll through the long list in this right-hand window and choose “TTEST” and click “OK.”

You should get a dialog box with four blank windows: “Array 1”, “Array 2”, “Tails”, and “Type.” In the “Array 1” window, you should enter the range of data values in the first column. (If you click on the icon at the right of the window, the pop-up menu will collapse and you can highlight the column of numbers using the mouse. Clicking on the icon in the collapsed menu will return the dialog box to its original size so that you can move to the next blank window.) Repeat this procedure for the “Array 2” window and the second column of density data.

fall 2004, Lab 9-10

In the “Tails” window, specify “1” or “2” depending on the nature of your alternative hypothesis. (See previous page and your worksheet.)

Finally, in the “Type” window, specify “1” because that is how you chooses a paired t-test. Our data is “paired” because each group in the class uses the same leaf to estimate stomatal density on the upper and lower surfaces. (It is also possible to conduct an independent t-test— often referred to as just “t-test”. When would such a test be used? Let’s consider a study of leaf area that compares shade-grown and sun-grown violets. There’s no natural pairing of any given shade leaf with a corresponding sun leaf. So a regular, or independent, t-test would be conducted.)

The result you will get (shown in a cell in your spreadsheet) is called a P-value. The P-value is a probability. A small P-value tells you that it’s rare or unlikely to get a difference that large (or larger) by chance. How rare is significantly rare? A P-value of less than 0.05, or 5%, is commonly used in biological research. (If you were conducting experiments to test a new type of nuclear fuel, a smaller and more stringent P-value cut-off might be appropriate.)

If our data show a difference between upper and lower leaf surfaces, and if the P-value from a paired t-test is small enough, we will be able to say that the difference is statistically significant. The magnitude of the difference is not what matters. What matters how large the difference is relative to the variation in data set. There is a space on the worksheet for your P-value, and you should mark it with an asterisk if it is less than 0.05 and therefore statistically significant.

(One way to think about P-values: what if 100 students each randomly scrambled the values for the upper and lower leaf surfaces, rather than having the upper surface data points in one column and the lower surface data points in the other column. How many students would find a difference as big or bigger than the one you found? If it’s five or fewer, that corresponds to P < 0.05.)

A P-value of less than 0.05 means that there is less than a 5% chance that the difference you found between the two groups was due to chance.

Remember that the MINIMUM size for this statistical test is EIGHT samples! Think about why it would be less meaningful with a smaller sample size.

fall 2004, Lab 9-11

Objectives: Quantify transpiration rate in an angiosperm leaf using a potometer. Investigate how transpirations rates change in response to environmental factors. Gain additional experience in proposing null and alternative hypotheses, designing experiments, and

collecting and analyzing data.

Equipment and supplies:

ring stand with three clampslatex tubing T-tubing connector(large cotton balls)hydrangea stembeaker filled with watersquare green tray with ~1.5 in. H2Orazor blade1 mL pipettefunneltubing clamp

Procedure

Each person in your group will need to participate in this exercise. Before beginning, check that everyone in your group has read through the procedure and understands their role.

Set up the potometer using the following diagram and instructions.

Group member 1: Places finger over tip of B.

Group member 2: Keeps funnel full to the top at ALL times, even if this means spilling some water by overfilling the funnel.

Group member 3: Controls the clamp.

Group member 4: Removes air bubbles from the tubing A, cuts the stem, and puts the stem into tubing A.

fall 2004, Lab 9-12

Quantifying transpiration rate using a potometer: Work in groups of four

These instructions sound complicated, but it is really a fairly simple process. There are multiple important tips for making sure everything goes smoothly. Please READ over the instructions thoroughly before beginning.

1. Have one group member put her index finger over the tip of the pipet at B and keep this tightly sealed until instructed. Make sure that tubing A is in the green tray and is under the surface of some water in the tray, with about 1.5 inches of water in the bottom of the tray (do NOT fill the tray yet, you need room to keep adding more water throughout the set-up).

2. Keeping the clamp at C partially open, have one member of your group add water to the funnel (this person should vigilantly make certain that the funnel is filled almost to the top AT ALL TIMES). Keep adding water until the tubing from the funnel to A is completely filled with water. Have a group member make CERTAIN that there are NO NO NO NO NO air bubbles in the tubing (can you tell this is important?). If there are air bubbles, squish the tubing gently with your fingers to remove the bubbles. The funnel MUST remain FULL with water at all times, even if this means that it is sometimes overfilled and some water gets spilled. Your instructor or TA can assist you. Once the tubing is completely free of air bubbles, have a group member tighten the clamp FIRMLY (this works best if the tubing is in the center of the clamp).

3. Keep the A tubing under the surface of the water until instructed to remove it. Choose a stem that has a larger diameter than the inside of your latex tubing at A. Bring the stem to your green tray AS QUICLY AS POSSIBLE (why?). NEVER let the cut end out from under the surface of the water and try not to get the leaves wet. Cut the stem with a new razor blade at least 1-2 inches from the end. The diameter of the stem should be slightly larger than the inside diameter of tubing A. You may need to cut above the next internode because you MUST be able to get an air-tight seal between the stem and the tubing.

4. Insert the freshly cut stem into the tubing about 1cm (you need an air-tight seal). Be careful not to crush the stem or get the leaves wet (why?). Stand the stem up using the ring stand clamp. Rest the stem in the clamp, but do not tighten the clamp enough to damage the stem.

5. Have the person holding a finger over tip B remove her finger. Open the clamp to let water into pipet B. CLOSE the clamp when the pipet is full. You may need to raise or lower the pipet in order to have the level of the water come close to its tip (if so, don’t close the clamp until you have finalized the level of the pipet). The funnel-filler should remain diligent and make sure the funnel is full at all times (to prevent the introduction of air bubbles into the system). The clamp must be CLOSED FIRMLY so that when the plant at A transpires, it will pull water from the pipet at B, not from the funnel. If the water in the pipet approaches the bottom of the mL markings, more water can be added by opening the clamp while the funnel is kept full.

Establishing a control transpiration rate

As the plant transpires, an air bubble will be drawn down the pipet at B and the rate of transpiration can be measured by timing the movement of the meniscus. Do not let the air bubble get lower than the numbers on your pipet or you will no longer be able to accurately measure volume.

The pipet at B is calibrated in milliliters (mL), so the transpiration rate in mL/hour can be calculated. You can calculate this by measuring how far the bubble moves over a certain period of time. For example, if the bubble moves 5 mL in 10 minutes, the rate would e 0.5 mL/min. What would this rate be in mL/hour? Measure the transpiration during a period of at least 10 minutes.

How do environmental factors affect transpiration?

Add water to the funnel and refill the pipet. Design and conduct your own experiment testing the effect of an altered environmental condition. Record your experimental design, results, and conclusions on Worksheet 2.

fall 2004, Lab 9-13

Group Member Names _______________________________________________________________________________

Signatures ________________________________________________________________________________________

Day/Time/Instructor ___________________________________ BC Bio 2003, Fall 2004

LAB 8, WORKSHEET 1: LEAF PEEL HYPOTHESES AND ANALYSES

Null hypothesis: Stomatal density on upper and lower surfaces will be the same; the difference in stomatal densities should be zero.

Alternative hypothesis:

Biological rationale for your alternative hypothesis:

Sketch and label:

(a.) guard cells

(b.) stomata

(c.) accessory cells

(d.) epidermal cells

fall 2004, Lab 9-14

Your Group’s Stomatal Density Data

Number of stomata Magnification

Upper surface

Lower surface

Your instructor will also ask you to add your data to the master data sheet for the class.

Class stomatal density data

Mean density of stomata Standard deviation

Upper surface

Lower surface

Difference

P-value from paired t-test

Pooled data will be provided in an Excel spreadsheet. Use Excel for calculations and for conducting statistical tests.

fall 2004, Lab 9-15

Group Member Names _____________________________________________________________________________

Signatures ______________________________________________________________________________________

Day/Time/Instructor ___________________________________BC Bio 2003 Fall 2004

LAB 8, WORKSHEET 2: RATE OF TRANSPIRATION IN SPATHIPHYLLUM LEAVES

Environmental condition(s) you are testing:

Null hypothesis:

Alternative hypothesis(es):

Results: (don’t forget that you are comparing your control and experimental transpiration rates)

Analysis/Conclusions:

fall 2004, Lab 9-16

Group Member Names _____________________________________________________________________________

Signaturesto indicate that all group members have contributed to this assignment equally

_______________________________________________________________________________________________

Day/Time/Instructor ___________________________________ BC Bio 2003 Fall 2004

LAB 8, WORKSHEET 3: INTERPRETATION AND SYNTHESIS

The members of each group should collaborate and turn in a single assignment. Be sure to work together on every question so that you will be prepared for the final exam. All group members will receive the same grade.

Turn in your typed answer to these questions on a separate sheet stapled to this worksheet. Be sure that all group member names and signatures are on this sheet and on the attachment.

1. In addition to your completed worksheets. Turn in your data from the Carnation experiment in the table below:

CARNATION EXPERIMENT DATA TABLE30 minutes 1 hour

Flower under lamp

Flower at lab station

2. If a bright and hot light is directed at a leaf and the stomata subsequently open, how could you determine if stomatal opening is due to the plant’s need for CO2 for photosynthesis or the plant’s need to cool itself (through transpiration)? Design an experiment to answer this question.

3. If a bright, hot light is directed at a leaf and the stomata subsequently close, come up with null and alternative hypotheses to determine why this closure occurs. Design an experiment to test your hypotheses.

4. Explain how the carnation experiment, leaf peel activity, and transpiration experiment are conceptually related.

5. Did the carnation experiment and the transpiration experiment differ in any way(s) other than the use of a potometer?

6. Does stomatal density relate to transpiration rate? Explain.

7. Generally, how is ABA involved in regulating transpiration rate? Explain.

8. Do you think high humidity would increase or decrease transpiration rate? Why?

9. Both water and carbon dioxide levels within the leaf will affect stomatal opening and closure. Which response system do you think takes precedence over the other and why?

10. Was there a difference in the density of stomata on the top and bottom of the leaves of Spathiphyllum? How big was the difference? What were the results of your paired t-test? Does this indicate that the difference was statistically significant? Is statistical significance the same thing as biological significance? How would you determine whether a difference is biologically significant? What is the functional or ecological importance of the difference that you found, if any?

Lab 8-17

Names _______________________________________________Day/Time/Instructor ___________________________________BC Bio 2003 Fall 2004

LAB 8, WORKSHEET 4: Angiosperm stems and leaves

Monocots and Dicots—Complete the following table:

Plant name

flower parts in multiples of 3, 4, 5 or other?

(if no flowers, write “no flowers”)

leaf veins parallel or netted/branched?

secondary growth absent or present?

(only if you can tell; if you can’t tell, say so)

other observations?

conclusion: monocot or dicot?

Lab 8-18

Worksheet 4 continued. Stem and leaf anatomy.

1. Labeled diagrams of monocot and dicot stem cross sections. Don’t forget to give final magnification levels and the names of the plants you are drawing.

MONOCOT DICOT

magnification level ____________ magnification level ________

2. Labeled diagram of a lilac leaf cross section.

Lab 8-19

Worksheet 4 continued. Angiosperm organs (you may need to look up some of this information in your textbook.)

Leaf Stem Flower

Function(s)?

Specialized tissues or structures involved in major function(s)

Meristem present? Determinate or indeterminate?

Can organ undergo secondary growth?

Does meiosis occur in organ? If so, where?

Are vascular tissues present?

Is epidermis present?

If present, does epidermis have cuticle?

If present, does epidermis have stomata?

How do these organs differ between monocot and dicot?

Lab 8-20