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AP® Investigation #5

Cell Processes: Photosynthesis – Teacher’s Guide

Kit # 3674-05

Table of Contents Call “Us” at 1.800.955.2660 for Technical Assistance

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Abstract. . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 General Overview . . . . . . . . . . . . . . . . . . . . . . 1 Recording Data. . . . . . . . . . . . . . . . . . . . . . . . 2 Material Requirements/Checklist . . . . . . . . . . . . . . 4 curriculum alignment . . . . . . . . . . . . . . . . . . . . 5 Learning Objectives. . . . . . . . . . . . . . . . . . . . . . 6 Time Requirements . . . . . . . . . . . . . . . . . . . . . . 5 Safety Precautions. . . . . . . . . . . . . . . . . . . . . . 7 Pre-Lab Preparations. . . . . . . . . . . . . . . . . . . . . 8 Student guide contents Background. . . . . . . . . . . . . . . . . . . . . . . 11 Part 1: Cell Size & Diffusion. . . . . . . . . . . . . . . 13 Part 2: Modeling Osmosis in Living Cells. . . . . . . . 17 Part 3: Osmosis in Living Plant Cells . . . . . . . . . . 21 Assessment Questions/Additional Questions (Optional) 24 MATERIAL SAFETY DATA SHEETS. . . . . . . . . . . . . . . . . .

**AP® and the Advanced Placement Program are registered trademarks of the College Entrance Examination Board. The activity and materials in this kit were developed and prepared by WARD’S Natural Science Establishment, which bears sole responsibility for their contents..

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Cell Processes: Photosynthesis – Teacher’s Guide

Kit # 3674-05

abstract This lab illustrates the ability of plants to capture, store, and use energy from light for growth and reproduction. Part 1 is a structured inquiry activity in which students will visualize the pigments present in various plant leaves through the use of basic paper chromatography techniques. Part 2 is a guided inquiry activity in which the students will indirectly measure the rate of photosynthesis under specific environmental conditions using the floating disc assay. Students will also study the structure of plant leaves and their component cells in order to understand the interactions of the cells with the environment that enable uptake of specific components necessary for photosynthesis, and expulsion of waste products that result from cellular metabolism. Part 3 is an open inquiry activity, in which students design an experiment that allows them to further explore the process of photosynthesis.

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Cell Processes: Photosynthesis – Teacher’s Guide

Kit # 3674-05

general Overview The College Board has revised the AP Biology curriculum to begin implementation in the fall of 2012. Advanced Placement (AP) is a registered trademark of the College Entrance Examination Board. The revisions were designed to reduce the range of topics covered, to allow more depth of study and increased conceptual understanding for students. There is a shift in laboratory emphasis from instructor-designed demonstrations to student-designed investigations. While students may be introduced to concepts and methods as before, it is expected that they will develop more independent inquiry skills. Lab investigations now incorporate more student-questioning and experimental design. To accomplish this, the College Board has decreased the minimum number of required labs from 12 to 8 while keeping the same time requirement (25% of instruction time devoted to laboratory study). The College Board has defined seven science practices that students must learn to apply over the course of laboratory study. In brief, students must: 1. Use models 2. Use mathematics (quantitative skills) 3. Formulate questions 4. Plan and execute data collection strategies 5. Analyze and evaluate data 6. Explain results 7. Generalize data across domains The College Board published 13 recommended laboratories in the spring of 2011. They can be found at: http://advancesinap.collegeboard.org/science/biology/lab Many of these laboratories are extensions of those described in the 12 classic labs that the College Board has used in the past. The materials provided in this lab activity have been prepared by Ward’s to adapt to the specifications outlined in AP Biology Investigative Labs: An Inquiry-Based Approach (2012, The College Board). Ward’s has provided instructions and materials in the AP Biology Investigation series that complement the descriptions in this College Board publication. We recommend that all teachers review the College Board material as well as the instructions here to get the best understanding of what the learning goals are. Ward’s has structured each new AP investigation to have at least three parts: Structured, Guided, and Open Inquiry. Depending on a teacher’s syllabus, s/he may choose to do all or only parts of the investigations in scheduled lab periods. The College Board requires that a syllabus describe how students communicate their experimental designs and results. It is up to the teacher to define how this requirement will be met. Having students keep a laboratory notebook is one straightforward way to do this.

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Cell Processes: Photosynthesis – Teacher’s Guide

Kit # 3674-05

Recording Data in a Laboratory Notebook All of the Ward’s Investigations assume that students will keep a laboratory notebook for studentdirected investigations. A brief outline of recommended practices to set up a notebook, and one possible format, are provided below. 1. A composition book with bound pages is highly recommended. These can be found in most stationary stores. Ward’s offers several options with pre-numbered pages (for instance, item numbers 32-8040 and 15-8332). This prevents pages from being lost or mixed up over the course of an experiment. 2. The title page should contain, at the minimum, the student’s name. Pages should be numbered in succession. 3. After the title page, two to six pages should be reserved for a table of contents to be updated as experiments are done so they are easily found. 4. All entries should be made in permanent ink. Mistakes should be crossed out with a single line and should be initialed and dated. This clearly documents the actual sequence of events and methods of calculation. When in doubt, over-explain. In research labs, clear documentation may be required to audit and repeat results or obtain a patent. 5. It is good practice to permanently adhere a laboratory safety contract to the front cover of the notebook as a constant reminder to be safe. 6. It is professional lab practice to sign and date the bottom of every page. The instructor or lab partner can also sign and date as a witness to the veracity of the recording. 7. Any photos, data print-outs, or other type of documentation should be firmly adhered in the notebook. It is professional practice to draw a line from the notebook page over the inserted material to indicate that there has been no tampering with the records. For student-directed investigations, it is expected that the student will provide an experimental plan for the teacher to approve before beginning any experiment. The general plan format follows that of writing a grant to fund a research project. 1. Define the question or testable hypothesis. 2. Describe the background information. Include previous experiments. 3. Describe the experimental design with controls, variables, and observations. 4. Describe the possible results and how they would be interpreted. 5. List the materials and methods to be used. 6. Note potential safety issues. (continued on next page) ©2012, Ward’s Natural Science All Rights Reserved, Printed in the U.S.A.

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Cell Processes: Photosynthesis – Teacher’s Guide

Kit # 3674-05

Recording Data in a Laboratory Notebook (continued) After the plan is approved:   7. The step-by-step procedure should be documented in the lab notebook. This includes recording the calculations of concentrations, etc., as well as the weights and volumes used.   8. The results should be recorded (including drawings, photos, data print outs, etc.).   9. The analysis of results should be recorded. 10. Draw conclusions based on how the results compared to the predictions. 11. Limitations of the conclusions should be discussed, including thoughts about improving the experimental design, statistical significance, and uncontrolled variables. 12. Further study direction should be considered. The College Board encourages peer review of student investigations through both formal and informal presentation with feedback and discussion. Assessment questions similar to those on the AP exam might resemble the following questions, which also might arise in peer review: •

Explain the purpose of a procedural step.

Identify the independent variables and the dependent variables in an experiment.

What results would you expect to see in the control group? The experimental group?

How does XXXX concept account for YYYY findings?

Describe a method to determine XXXX.

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Cell Processes: Photosynthesis – Teacher’s Guide

Kit # 3674-05

Materials checklist MATERIALS PROVIDED IN KIT

MATERIALS NEEDED BUT NOT PROVIDED

Units per kit

Description

Timers

1

Aluminum foil, 12” x 25’ roll

Light source

2

Bottle, 60 mL

Baby spinach leaves

20

Syringe, NON-sterile, 10 mL

Light sensor ( item 9200003 or other)

1

Sodium bicarbonate, 50 g

Thermometer

1

Film, Rainbow: 8-1/2 x 11, 4 (available for use in Open Inquiry lab)

Variety of collected plant leaves

1

Pipet, pkg/15, 6’’ Grad.

Distilled water

16

Medicine cup, polypropylene

Rubber band

1

ScholAR Chemistry New MSDS CD

Forceps

8

One-hole paper Punch

Ruler

2

Disposable Petri dish, pkg/20

Wax pencil, pencil

1

Disposable pipet. 9”

Ring stand with ring

1

Buffer set: Includes envelopes of pH 2-11 (one each, for a total of 10 envelopes), 500 mL buffer (available for use in Open Inquiry lab)

Light bulbs variety (40 watt, 100 watt, 150 watt suggested )

1

Chromatography paper strips, 1 pkg.

Balance or scale

1

2’ Parafilm

Coins (quarters or dimes)

8

Glass vial, capsule cap #4

Scissors

1

Chromatography Solvent, 30 mL, pkg./ 4

Gloves, safety goggles, lab aprons

3

Translucent plastic cups, pkg. 15

Lab notebook

1

Instructions (this booklet)

Microscope and slide Clear nail polish, petroleum jelly

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©2012, Ward’s Natural Science All Rights Reserved, Printed in the U.S.A.

Fume hood

Or

Visit “Us” on-line at www.wardsci.com for U.S. Customers www.wardsci.ca for Canadian Customers

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Liquid soap (dishwashing liquid)

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Cell Processes: Photosynthesis – Teacher’s Guide

Kit # 3674-05

This lab activity is aligned with the 2012 AP Biology Curriculum (registered trademark of the College Board). Listed below are the aligned Content Areas (Big Ideas and Enduring Understandings), the Science Practices, and the Learning Objectives of the lab as described in AP Biology Investigative Labs: An Inquiry Approach (2012). This is a publication of the College Board that can be found at http://advancesinap.collegeboard.org/science/biology/lab.

Curriculum alignment Big Ideas ‹ Big Idea 2: Biological systems utilize energy and molecular building blocks to grow, to reproduce, and to maintain homeostasis. Also connects to: ‹ Big Idea 1: The process of evolution drives the diversity and unity of life. ‹ Big Idea 4: Biological systems interact, and these interactions possess complex properties Enduring Understandings ‹ 1B1: Organisms share many conserved core processes and features that evolved and are widely distributed among organisms today. ‹ 2A1: All living systems require constant input of free energy. ‹ 2A2: Organisms capture and store free energy for use in biological processes. ‹ 2B3: Eukaryotic cells maintain internal membranes that partition the cell into specialized regions (e.g., chloroplasts). ‹ 4A2: The structure and function of subcellular components, and their interactions, provide essential cellular processes. ‹ 4A6: Interactions among living systems and with their environment result in the movement of matter and energy. Science Practices ‹ 1.4 The student can use representations and models to analyze situations or solve problems qualitatively and quantitatively. ‹ 2.2 The student can apply mathematical routines to quantities that describe natural phenomena. ‹ 3.1 The student can pose scientific questions. ‹ 6.1 The student can justify claims with evidence. ‹ 6.2 The student can construct explanations of phenomena based on evidence produced through scientific practices. ‹ 7.2 The student can connect concepts in and across domain(s) to generalize or extrapolate in and/ or across enduring understandings and/or big ideas.

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Cell Processes: Photosynthesis – Teacher’s Guide

Kit # 3674-05

learning objectives ‹ The student is able to describe specific examples of conserved core biological processes and features shared by all domains or within one domain of life, and how these shared, conserved core processes and features support the concept of common ancestry for all organisms (1B1 & SP 7.2.. ‹ The student is able to justify the scientific claim that organisms share many conserved core processes and features that evolved and are widely distributed among organisms today (1B1 & SP 6.1.. ‹ The student is able to justify the scientific claim that free energy is required for living systems to maintain organization, to grow, or to reproduce, but that multiple strategies exist in different living systems (2A1 & SP 6.1.. ‹ The student is able to use representations to pose scientific questions about what mechanisms and structural features allow organisms to capture, store, and use free energy (2A2 & SP 1.4, SP 3.1.. ‹ The student is able to use representations and models to describe differences in prokaryotic and eukaryotic cells (2B3 & SP 1.4). ‹ The student is able to construct explanations based on scientific evidence as to how interactions of subcellular structures provide essential functions (4A2 & SP 6.2.. ‹ The student is able to apply mathematical routines to quantities that describe interactions among living systems and their environment, which result in the movement of matter and energy (4A6 & SP 2.2..

Time Requirements Part 1: Plant Pigments and Chromatography (Structured Inquiry)

45 minutes. Optional to start Part 2 during solvent migration.

Part 2: Floating Disc Assay (Guided Inquiry)

45 minutes

Part 3: Open Inquiry

Varies, depending on students’ experimental designs

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Cell Processes: Photosynthesis – Teacher’s Guide

Kit # 3674-05

Safety Precautions Lab-Specific Safety ‹ Chromatography solution (used in paper chromatography) an irritant to the skin and eyes, use with precaution. ‹ Chromatography solvent is extremely flammable, a serious health hazard, and moderately reactive. Use this chemical in an approved fume hood. General Safety ‹ The teacher should be familiar with safety practices and regulations in their school (district and state). The teacher should know what needs to be treated as hazardous waste and how to properly dispose of non-hazardous chemicals or biological material. ‹ Consider establishing a safety contract that students and their parents must read and sign off on. This is a good way to identify students with allergies to things like latex so that you (and they) will be reminded of what particular things may be risks to individuals. A good practice is to include a copy of this contract in the student lab book (glued to the inside cover). ‹ Students should know where all emergency equipment (safety shower, eyewash station, fire extinguisher, fire blanket, first aid kit etc.) is located. ‹ Make sure students remove all dangling jewelry and tie back long hair before they begin. ‹ Remind students to read all instructions, Material Safety Data Sheets (MSDSs) and live care sheets before starting the lab activities and to ask questions about safety and safe laboratory procedures. Appropriate MSDSs and live care sheets can be found on the last pages of this booklet. Additionally, the most updated versions of these resources can be found at www.wardsci.com, under Living Materials http://wardsci.com/article.asp?ai=1346. (Note that in this particular lab, there are no live materials that require a live care sheet. ‹ In student directed investigations, make sure that collecting safety information (like MSDSs) is part of the experimental proposal. ‹ As general laboratory practice, it is recommended that students wear proper protective equipment, such as gloves, safety goggles, and a lab apron. At end of lab: ‹ All laboratory bench tops should be wiped down with a 20% bleach solution or disinfectant to ensure cleanliness. ‹ Remind students to wash their hands thoroughly with soap and water before leaving the laboratory.

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Cell Processes: Photosynthesis – Teacher’s Guide

Kit # 3674-05

Pre-Laboratory Preparation Notes

For all parts of the lab: 1. Make copies of Student Guide.

Copy pages __ to __ of the student copymaster prior to starting class.

Part 1: Structured Inquiry – Plant Pigments & Chromatography 1. Obtain and cut chromatography paper strips to fit the chromatography vial. 2. Obtain fresh baby spinach leaves, coins. 3. A fume hood will be necessary for working with the chromatography solvent. Part 2: Guided Inquiry – Floating Disc Assay 1. Soak the baby spinach leaves.

Prepare the leaves by soaking them in water overnight under a light source. This initiates the process of photosynthesis, and the intercellular spaces fill with air (increasing buoyancy).

2. Prepare 0.2% sodium bicarbonate solution

Add 2 grams to 1 L of distilled water and mix. (1 g into 100 mL = 1%)

3. Dilute the soap solution. To prepare the diluted soap solution, add 5.2 mL of dishwashing liquid to 250 mL 0.2% sodium bicarbonate solution. Mix gently and allow the solution to sit in order to dissipate the soap suds.

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Cell Processes: Photosynthesis – Teacher’s Guide

Kit # 3674-05

Background OBJEcTIVES ‹ Design a plan for collecting data to show that all biological systems are affected by complex biotic and abiotic interactions. ‹ Use models to predict and justify that changes in the subcomponents of a biological polymer affect the functionality of the molecule. ‹ Analyze data to identify how molecular interactions affect structure and function.

Growth and reproduction are heavily energy-dependent processes that have driven organisms to evolve strategies, structures, and processes that enable them to capture, utilize, and store free energy. Free energy is available in the environment in a multitude of forms, and autotrophs and heterotrophs employ different approaches to harvest the energy they need to live. Photosynthesis and chemosynthesis enable autotrophs (or primary producers) to obtain free energy directly from their surroundings, whereas heterotrophs seek sources of food, and utilize the energy stored in carbon compounds produced by other organisms. Autotrophs are “self-feeders”. This name is derived from Greek: auto meaning “self”, and trophos meaning “feeder”. Multicellular plants are examples of photoautotrophs, organisms that produce organic molecules from light energy. Photosynthesis is the name of the process whereby photoautotrophs capture free energy from light in the environment for use in growth, reproduction, and maintaining homeostasis.

The set of chemical reactions involved in photosynthesis transforms the substrates carbon dioxide and water, into glucose (a simple carbohydrate) and oxygen. The chemical bonds of the glucose molecule serve to store the transformed light energy until it is harvested in the process of respiration. Measuring the oxygen produced in this reaction is one way to measure the rate of photosynthesis. In plants, chloroplasts are required to capture the energy that drives the reaction. Chloroplasts are membrane-bound organelles that contain a variety of photoreactive pigments, including the primary photosynthetic pigments - chlorophylls. Chlorophyll absorbs light energy in the red and blue parts of the spectrum and reflects green to our eyes, making the chlorophyll, and thus plants, look green to us. Accessory pigments in chloroplasts and leaves have other roles in regulating light energy. For example, yellow/orange/red carotenoids (continued on next page)

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Cell Processes: Photosynthesis – Teacher’s Guide

Kit # 3674-05

Background (COntinued) Notes

absorb ultraviolet light that can damage DNA. The pigments in chloroplasts are embedded in stacks of membrane and are therefore expected to be hydrophobic. Some of the common pigments found in leaves are listed in order from most polar (hydrophilic) to least polar (hydrophobic) as follows: chlorophyll b, chlorophyll a, phaeophytin b, phaeophytin a, xanthophylls, carotene. The terrestrial plant cells that are specialized for photosynthesis (and thus contain most of the chloroplasts and chlorophyll) are in the leaves. The structure of the leaf has evolved to regulate the photosynthetic reaction by regulating how the substrates of carbon dioxide and water are brought together with light to form carbohydrates and release oxygen. Guard cells, in the lower epidermis of the leaf, form pores called stomata that can be opened or closed to regulate gas exchange in the leaf under different environmental situations. One of the substrates for the photosynthetic reaction, CO2, enters the leaf through the open stomata. The other substrate, water, enters the leaf mostly through the vascular system of the plant, the xylem tubules. The palisade cell layer of a leaf has access to both substrates and consists of cylindrical cells that contain large numbers of chloroplasts. These are the cells primarily responsible for photosynthesis and thus energy capture in the plant. One of the products of photosynthesis, carbohydrates, can be transported out to other parts of the plant through the phloem of the vascular system. The other product, oxygen, passes into the spongy mesophyll layer containing air chambers, which expand as the oxygen is produced then released through the stomata into the environment. Alternatively, the carbohydrates and oxygen can be used as substrates for respiration in the leaf cells.

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Cell Processes: Photosynthesis – Teacher’s Guide

Notes

Kit # 3674-05

Safety Precautions ‹ When working with the chromatography solvent, use a chemical hood or proper ventilation. ‹ As general safe laboratory practice, it is recommended that you wear proper protective equipment, such as gloves, safety goggles, and a lab apron. ‹ As general lab practice, read the lab through completely before starting, including any Material Safety Data Sheets (MSDSs) and live materials care sheets at the end of this booklet as well as any appropriate MSDSs for any additional substances you would like to test. One of the best sources is the vendor for the material. For example, when purchased at Wards, searching for the chemical on the Ward’s website will direct you to a link for the MSDS. (Note: There are no live materials care sheets included in this particular lab.) At the end of the lab: ‹ All laboratory bench tops should be wiped down with a 20% bleach solution or disinfectant to ensure cleanliness. ‹ Wash your hands thoroughly with soap and water before leaving the laboratory.

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Cell Processes: Photosynthesis – Teacher’s Guide

Kit # 3674-05

Part 1 – Structured INQUIRY: plant pigments and chromatography

Procedure Tips ‹ When performing this lab activity, all data should be recorded in a lab notebook. You will need to construct your own data tables, where appropriate, in order to accurately capture the data from the investigation. ‹ If directed to do so by your teacher, this part of the lab may be done at the same time as Part 2 of the lab.

MATERIALS needed PER LAB GROUP q q q q q q q q q q q

1 Chromatography vial, with cap (provided) 1 Wax pencil 1 Disposable transfer pipet (provided) 1 mL Chromatography solvent (acetone:ethyl alcohol::1:1. (provided) 1 Chromatography paper strip (provided) 1 Sharp pencil 1 Ruler (metric) 1 Pair of scissors 1 Piece of fresh (pre-soaked) spinach 1 Coin (a quarter works well) 1 Pair of forceps

Part 1 – PROCEDURE: Structured inquiry 1. Obtain a chromatography paper strip. ‹

Figure 1

NOTE: Be sure to handle the chromatography strip of paper by the edges. Do not touch the surface of the strip with your fingertips as the oils from your fingers will interfere with the chromatogram.

2. Measure 1.5 cm from one end of the chromatography strip and lightly draw a pencil line across the width of the strip. This is the point of application (see Step 6). 3. Use a pair of scissors to cut off two small pieces below the pencil line to form a pointed end (see Figure 1). The pointed end will be referred to as the bottom end of the chromatogram. 4. Obtain a well-hydrated leaf of spinach which, has been presoaked to jump-start the process of photosynthesis. Place it over the line of the chromatography strip. Rub or roll the ribbed edge of a coin over the spinach leaf to extract the pigments. Repeat 510 times with different portions of the spinach leaf, making sure you are rubbing the coin over the pencil line (see Figure 2). Figure 2 (continued on next page) ©2012, Ward’s Natural Science All Rights Reserved, Printed in the U.S.A.

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Cell Processes: Photosynthesis – Teacher’s Guide

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PROCEDURE – Part 1: Structured Inquiry (continued) Notes

5. Obtain a chromatography vial from your teacher and label it with your initials using a permanent marker or wax pencil. ‹

CAUTION: Steps 6-11 should be performed under a fume hood or in a well ventilated area.

6. Go to a fume hood or a well ventilated area and remove the cap from the chromatography vial. Using a disposable pipette, add 1 mL of chromatography solvent to the vial. The solvent is a volatile organic compound (hydrophobic) and a fume hood is required to capture the volatile fumes. 7. Carefully place the chromatography paper strip into the vial so that the pointed end is barely immersed in the solvent. Do not immerse the pigments into the solvent. 8. Cap the vial and leave it undisturbed. Observe as the solvent is drawn up by the chromatography paper strip by capillary action. 9. Record the different colors you observe as they separate along the strip. 10. When the solvent reaches approximately 1 cm from the top of the strip, remove the cap from the vial. Using forceps, remove the strip from the vial. This is your chromatogram. 11. The solvent will evaporate quickly; immediately use a pencil to mark the location of the solvent on the front of the chromatography paper strip. ‹

NOTE: You will need this location to identify the distance the chromatography solvent traveled.

12. List and record the pigment colors or names. Once the strip has completely dried, mark the middle of each pigment band on the chromatography paper strip with a pencil. 13. Using a metric ruler, measure the distance from the original pencil line with the spinach extract to the solvent front and each mark you made on the pigment bands (see Figure 3). Record these distances in millimeters (mm). 14. Calculate the Rf value for each pigment on your chromatogram.

Figure 3

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Rf =

Distance traveled by component from point of application Distance traveled by solvent from point of application

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Cell Processes: Photosynthesis – Teacher’s Guide Procedure TipS ‹ When performing this lab activity, all data should be recorded in a lab notebook. You will need to construct your own data tables, where appropriate, in order to accurately capture the data from the investigation. ‹ If directed to do so by your teacher, this part of the lab may be done at the same time as Part 1 of the lab.

Kit # 3674-05

Part 2 – GUIDED INQUIRY: floating disc assay MATERIALS needed PER LAB GROUP q q q q q q q q

10 mL 100 mL 1 1 1 1 1 1

0.2% sodium bicarbonate solution (with dish soap added) 0.2% sodium bicarbonate solution Disposable beaker 100 mL (or plastic cup) One-hole punch Timer Light source 10 mL syringe Piece of fresh (pre-soaked) spinach

Part 2 – PROCEDURE: guided inquiry 1. Obtain a leaf of spinach that is well hydrated, and has been presoaked to jump-start the process of photosynthesis. 2. Use a one-hole punch to cut discs from the leaf (at least 10 discs per trial). ‹

Each trial requires at least 10 leaf discs. When cutting discs, avoid major veins, aberrant tissue, and leaf edges. Make an effort to obtain consistent discs.

3. Remove the plunger from the barrel of a 10 mL syringe. Place your finger over the outflow hole to block leakage. Fill the barrel of the plunger 1/2 full with bicarbonate/dish soap mixture. ‹

NOTE: The liquid soap in the sodium bicarbonate aids in wetting the normally hydrophobic surface of the leaf. The surface tension of the water is broken by the addition of the soap, and the leaf surface can become wet with the solution in order to allow it to infiltrate the pores on the leaf surface, and fill the intercellular spaces in the spongy mesophyll.

4. Place the leaf discs inside the barrel, tap to get them down to the fluid. Replace the plunger at the top the syringe barrel and invert so that the air bubble will float to the tip. Push the plunger in enough to expel most of the air.

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Cell Processes: Photosynthesis – Teacher’s Guide

Kit # 3674-05

PROCEDURE – Part 2: GUIDed Inquiry (continued) Notes

5. Hold your finger over the hole at the end of the syringe again and draw back on the plunger to form a vacuum within the chamber of the syringe. Hold this for 10 seconds while swirling the syringe to wet the leaf discs. Repeat until all of the leaf discs sink under normal pressure. This means that the solution has infiltrated the spongy layer of the leaf. ‹

Do not use leaf discs that do not sink.

Additional soap may be added if leaves will not sink.

A negative control may be set up with water and soap, but no bicarbonate.

6. Remove the plunger from the syringe and pour the discs and solution into a clear plastic cup containing 0.2% sodium bicarbonate (or plain water for a negative control) at a depth of about 3 cm. Be sure to place all of the discs in the bottom of the cup. The sodium bicarbonate serves as the source of CO2 necessary for photosynthesis to occur. Keep the depth of the solution in the cup consistent throughout the trials. 7 Place the reaction vessels under a bright light source. Start the timer immediately. ‹

Hint: Put the light source as close to the experimental beakers as possible

8. Record the number of discs that are floating at 30 second intervals. 9. Graph your results over time for bicarbonate and water-only conditions. 10. Explain your results

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Cell Processes: Photosynthesis – Teacher’s Guide

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Part 2 assessment questions 1. Which pigment migrated the farthest on the chromatogram? Explain how this migration occurred.

Answers will indicate that the same number and color pigments migrated in the same order up the chromatography strip. Explanations should include references to the relative solubility of the pigments in the chromatography solvent based on their relative polarities. Students should use logical reasoning and data from their experiment as evidence to support their conclusions.

2. What does the Rf value represent? If you were to perform your experiment on a chromatography paper twice the length of the one used, would your Rf values still be the same?

The Rf value indicates the distance moved of the pigment (from the point of sample application) relative to the distance moved of the solvent (from the point of sample application). The length of the paper does not affect the Rf values.

3. How do plant pigments and the absorption spectrum relate to photosynthesis?

Students should discuss the roles of various pigments in photosynthesis, the pigments present in various plants, and how light of different wavelengths is available to/utilized by plants with different pigments to optimize photosynthesis for that organism.

4. Name at least four parameters that will affect the rate of photosynthesis as measured by this investigation. How does each parameter have bearing on the reactions of photosynthesis?

Some parameters are: temperature, pH, light intensity, wavelength, availability of CO2, availability of water. There will be an optimal or peak range for each of these parameters, with the rate of photosynthesis tapering off as the optimal conditions are not satisfied.

5. What might happen if you were to remove all light from the setup after the discs have all become buoyant? Describe what you would see. Explain why this would occur with relation to cellular processes like respiration.

If all light were removed after the discs become buoyant then the rate of photosynthesis would drop off sharply, and the competing process of cellular respiration would take over, utilizing the available O2 and glucose in the leaf discs (that were produced by photosynthesis), producing CO2, and eventually causing the discs to sink. Cellular respiration occurs in both the light and dark. Photosynthesis is the dominant reaction in the presence of light, but cannot occur without light, so cellular respiration takes over in the dark. What is measured with O2 production in the light is the net rate of photosynthesis and respiration.

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Cell Processes: Photosynthesis – Teacher’s Guide EXPERIMENT DESIGN Tips The College Board encourages peer review of student investigations through both formal and informal presentation with feedback and discussion. Assessment questions similar to those on the AP exam might resemble the following questions, which also might arise in peer review: ‹ Explain the purpose of a procedural step. ‹ Identify the independent variables and the dependent variables in an experiment. ‹ What results would you expect to see in the control group? The experimental group? ‹ How does XXXX concept account for YYYY findings? ‹ Describe a method to determine XXXX.

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Part 3: Cell Processes: Photosynthesis open inquiry: design an experiment What questions occurred to you as you performed the investigations? Now that you are familiar with photosynthetic pigments, chromatography, and a photosynthesis rate assay, design an experiment to investigate one of your questions. Questions may include: How is the rate of photosynthesis in leaves related to pigments in the leaf? How does the amount or wavelength of light affect the rate of photosynthesis? Does temperature or pH affect the rate of photosynthesis? Is there a variation in chloroplast density in different leaves that affects photosynthesis? Does the age of the leaf or plant that it came from affect the rate of photosynthesis? Does the habitat in which the plant evolved affect pigments or rates of photosynthesis? Does the time of year that the leaf was collected affect pigments or photosynthetic rate? What other aspects of the leaf or plant environment might affect photosynthetic rates? Before starting your experiment, plan your investigation in your lab notebook. Have your teacher check over and initial your experiment design. Once your design is approved, investigate your hypothesis. Be sure to record all observations and data in your laboratory sheet or notebook. Use the following steps when designing your experiment. 1. Define the question or testable hypothesis. 2. Describe the background information. Include previous experiments. 3. Describe the experimental design with controls, variables, and observations. 4. Describe the possible results and how they would be interpreted. 5. List the materials and methods to be used. 6. Note potential safety issues. After the plan is approved by your teacher: 7. The step by step procedure should be documented in the (continued on next page)

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Part 3: open inquiry (continued) Notes

lab notebook. This includes recording the calculations of concentrations, etc. as well as the weights and volumes used. 8. The results should be recorded (including drawings, photos, data print outs). 9. The analysis of results should be recorded. 10. Draw conclusions based on how the results compared to the predictions. 11. Limitations of the conclusions should be discussed, including thoughts about improving the experimental design, statistical significance and uncontrolled variables. 12. Further study direction should be considered.

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