write a hypothesis that the leaf disk assay is designed to test

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Study Photosynthesis with the Floating Leaf Disk Assay

Cup filled with a solution and leaf disks on the bottom. One leaf disk is floating to the surface.

Plants carry out photosynthesis to produce sugars that they need as an energy source to live and grow. During photosynthesis, oxygen—a gas that many living beings need to survive—is released. This makes photosynthesis one of the most important biological processes on Earth. In Part 1 of this lesson plan, students will utilize the floating leaf disk assay to demonstrate the production of oxygen gas during photosynthesis. They will then continue to design and conduct their own experiments in Part 2 of the lesson in order to investigate variables that affect the rate of photosynthesis in plants.

Remote learning adaptation: This lesson plan can be conducted remotely. The Engage section of the lesson can be skipped or done over a video call, then students can work independently during the Explore sections, using the Student Worksheet and the Leaf Disk Assay Video as a guide. Students will need to obtain their own materials such as a light source and a plastic syringe. For Part 2 of the lesson, students can adjust the independent variable they will investigate according to the materials available to them. The data analysis in the Reflect sections and the presentations of the results can be done over a video call, or by sharing a poster or slides on a class drive.

Learning Objectives

NGSS Alignment

MS-LS1-6 . Construct a scientific explanation based on evidence for the role of photosynthesis in the cycling of matter and flow of energy into and out of organisms.

Materials needed for the 'Study Photosynthesis with the Floating Leaf Disk Assay' lesson.

For each student group of 3:

For teacher:

Extra materials for independent student investigations:

Background Information for Teachers

Every living organism needs energy to survive, to grow, and to reproduce. Humans and animals eat foods with carbohydrates, proteins, and fats to produce the energy they need to survive. But plants do not eat. They make their own energy source in the form of energy-rich carbohydrates (sugars) through a process called photosynthesis. Photosynthesis is a multi-step, enzyme-mediated process that converts light energy into chemical energy. During photosynthesis, plant cells use light energy (such as light emitted from the Sun), water (H 2 O), and carbon dioxide (CO 2 ) as reactants to produce sugar molecules (C 6 H 12 O 6 ) and oxygen (O 2 ) (Figure 1):

A schematic drawing of a plant showing all the plant parts above and underground. In the soil, arrows labeled H2O point to the plant roots. Yellow arrows coming from the top indicate sunlight shining onto the plant. An arrow labeled CO2 is pointing toward the plant leaves. An arrow labeled O2 and another arrow labeled C6H12O6 are pointing away from the plant leaves.

Photosynthesis takes place in the chloroplasts within the plant's cells. The chloroplasts contain special pigments that react to light. Chlorophyll is one of the pigments that can absorb light in the blue and red spectrum from the visible light spectrum. Chlorophyll does not absorb light in the green spectrum of light, but reflects it instead. This is why leaves with chlorophyll usually appear green. During the first part of photosynthesis—the light-dependent reaction—chlorophyll and other pigments harness the light energy to produce NADPH and ATP, which are two types of energy-carrier molecules. At the same time, water is split into oxygen (O 2 ) and protons (H + ). The next stage is light-independent and is often referred to as the dark reaction. In this step, the two energy-carrier molecules NADPH and ATP are utilized in a series of chemical reactions called the Calvin cycle. In the Calvin cycle, the plants take carbon dioxide (CO 2 ) from the air and use it to ultimately make sugars such as glucose or sucrose. These sugars can be stored for later use by the plant as an energy source to fuel its metabolism and growth.

Photosynthesis is responsible for replenishing Earth's atmosphere with oxygen that we breathe. Thus, it is not only crucial for plants, but also for all organisms that rely on oxygen for their survival. Many factors affect how quickly plants are able to conduct photosynthesis. Without enough light or water, for example, a plant cannot photosynthesize very quickly. Similarly, the concentration of carbon dioxide—another reactant in photosynthesis—affects how fast photosynthesis can occur. Temperature also plays a significant role, as photosynthesis is an enzyme-mediated reaction. This is because at high temperatures, enzymes can get damaged and thus become inactivated. Other factors that affect the rate of photosynthesis are the light intensity, the amount of chlorophyll or other color pigments in a plant, and the color of light.

In this lesson plan, students will place 10 disks in the baking soda solution at the same time. A good way to collect data is to count the number of floating disks at the end of a fixed time interval; for example, after every minute until all disks are floating. The time required for 50% of the leaves to float represents the Effective Time (ET 50 ). ET 50 can be determined by timing when the fifth leaf floats, or by graphing the number of disks floating over time, as shown in Figure 3. An ET 50 of 11.5 minutes (min), for example, as shown in Figure 3, would mean that after 11.5 min 50% of the leaves (5 out of the 10) floated on top of the baking soda solution. In the context of oxygen production, you could also say that an ET 50 value of 11.5 min means that it took 11.5 min to produce enough oxygen to make 50% of the leaf disks float.

A scatter plot graph showing exemplary results for a leaf disk assay.

The x-axis shows time in minutes. The y-axis shows the number of floating leaf disks. After 7 minutes the first leaf disk floats, after 11 minutes 4 leaf disks float, at 12 minutes 7 leaf disks float, at 13 minutes 8 leaf disks float, and after 14 minutes all 10 leaf disks float. A red line indicates at what time 50% (5) leaf disks float (at about 11.5 minutes). This time is labeled Effective Time ET50.

Reaction rates are usually expressed as the concentration of reactant consumed or the concentration of product formed per unit of time. As mentioned above, we can use the ET 50 as a proxy for how much oxygen has been produced to make half of the leaf disks float. This means that the ET 50 value is proportional to the inverse of the rate of oxygen production, or proportional to the inverse of the rate of photosynthesis. The reciprocal of ET 50 or 1/ET 50 can thus be used as a simple measure of the rate of photosynthesis.

This lesson plan has two parts. In the first part, students use the leaf disk assay to explore how plants make energy using photosynthesis. In the second part, students design and conduct experiments that use the leaf disk assay to investigate several variables that have the potential to affect the rate of photosynthesis. This allows students to apply and review scientific concepts involved in photosynthesis, such as cell structure and function, enzyme activity, energy use and storage, and reaction rates.

Prep Work (15 minutes)

Engage (10 minutes), explore (45 minutes), reflect (45 minutes), make career connections, lesson plan variations, explore our science videos.

write a hypothesis that the leaf disk assay is designed to test

Experiment 6: Photosynthesis

Terms in this set (19)

Students also viewed, floating leaf disk photosynthesis.

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C.W., a 36-year-old woman, was admitted several days ago with a diagnosis of recurrent inflammatory bowel disease (IBD) and possible small bowel obstruction (SBO). C.W. is married, and her husband and 11-year-old son are supportive, but she has no extended family in the state. She has had IBD for 15 years and has been taking mesalamine (Asacol) for 15 years and prednisone 40 m g / 40 \mathrm{mg} / 40 mg / day for the past 5 years. She is very thin; at 5 feet 2 inches ( 157 c m ) (157 \mathrm{~cm}) ( 157 cm ) , she weighs 86 l b s ( 39 k g ) 86 \mathrm{lbs}(39 \mathrm{~kg}) 86 lbs ( 39 kg ) and has lost 40 l b s ( 18 k g ) 40 \mathrm{lbs}(18 \mathrm{~kg}) 40 lbs ( 18 kg ) over the past 10 years. She averages 5 to 10 loose stools per day. C.W's life has gradually become dominated by her disease, with anorexia, lactase deficiency, profound fatigue, frequent nausea and diarrhea, frequent hospitalizations for dehydration, and recurring, crippling abdominal pain that often strikes unexpectedly. The pain is incapacitating and relieved only by a small dose of diazepam (Valium), oral electrolyte solution (Pedialyte), and total bed rest. She confides in you that sexual activity is difficult: "It always causes diarrhea, nausea, and lots of pain. It's difficult for both of us." She is so weak she cannot stand without help. You indicate complete bed rest on the nursing care plan.

C.W.s condition deteriorates. On the third day after admission she experiences intractable abdominal pain and unrelenting nausea and vomiting. C.W. is taken to the operating room because of probable SBO and is readmitted to your unit from the postanesthesia care unit. During surgery, 38 inches ( 96 c m ) (96 \mathrm{~cm}) ( 96 cm ) of her small bowel was found to be severely stenosed, with 2 areas of visible perforation. Much of the remaining bowel is severely inflamed and friable. A total of 5 feet ( 152 c m ) (152 \mathrm{~cm}) ( 152 cm ) of distal ileum and 2 f e e t ( 61 c m ) 2 \mathrm{feet}(61 \mathrm{~cm}) 2 feet ( 61 cm ) of colon have been removed, and a temporary ileostomy was established. She has a Jackson-Pratt (JP) drain to bulb suction in her right lower quadrant (RLQ), and her wound was packed and left open. She has 2 peripheral IV lines, a Salem Sump nasogastric tube (NGT), and a Foley catheter. Her vital signs (VS) are 112 / 72 , 86 , 24 , 100. 8 ∘ F ( 38. 2 ∘ C 112 / 72,86,24,100.8^{\circ} \mathrm{F}\left(38.2^{\circ} \mathrm{C}\right. 112/72 , 86 , 24 , 100. 8 ∘ F ( 38. 2 ∘ C ) (tympanic). You attach her NGT to low-continuous wall suction per the postoperative orders. What else will you note about the drainage?

X-rays with a wavelength of 0.125 n m 0.125 \mathrm{~nm} 0.125 nm are scattered from a cubic array (of a sodium chloride crystal), for which the spacing of adjacent atoms is a = 0.282 n m a=0.282 \mathrm{~nm} a = 0.282 nm . (a) If diffraction from planes parallel to a cube face is considered, at what angles θ \theta θ of the incoming beam relative to the crystal planes will maxima be observed? (b) Repeat part (a) for diffraction produced by the planes shown in Fig., which are separated by a / 2 a / \sqrt{2} a / 2 .

Photochemical Efficiency of Light at Different Wavelengths

The rate of photosynthesis, measured by O 2 \mathrm{O}_2 O 2 production, is higher when a green plant is illuminated with light of wavelength 680 n m 680 \mathrm{~nm} 680 nm than with light of 700 n m 700 \mathrm{~nm} 700 nm . However, illumination by a combination of light of 680 n m 680 \mathrm{~nm} 680 nm and 700 n m 700 \mathrm{~nm} 700 nm gives a higher rate of photosynthesis than light of either wavelength alone. Explain.

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Photosynthetic Flotation

Light leaves leaves light..

Photosynthetic organisms capture energy from the sun and matter from the air to make the food we eat, while also producing the oxygen we breathe. In this Snack, oxygen produced during photosynthesis makes leaf bits float like bubbles in water.

Video Demonstration

Tools and materials.

Pour 150 mL of bicarbonate solution into the cup. Try to avoid making suds.

Hold the syringe with the tip up, and expel the air by gently pushing on the plunger.

Set up your light fixture so that it is suspended about 12 inches (30 cm) above the table. You may want to use a ring stand for this.

To Do and Notice

Turn on the light, start a timer, and watch the leaf disks at the bottom of the cup. Notice any tiny bubbles forming around the edges and bottoms of the disks. After several minutes, the disks should begin floating to the top of the solution. Record the number of floating disks every minute, until all the disks are floating.

How long does it take for the first disk to float? How long does it take for half the disks to float? All the disks?

When all the disks have floated, try putting the cup in a dark cabinet or room, or cover the cup with aluminum foil. Check the cup after about fifteen minutes. What happens to the disks?

What’s Going On?

Plants occupy a fundamental part of the food chain and the carbon cycle due to their ability to carry out photosynthesis, the biochemical process of capturing and storing energy from the sun and matter from the air. At any given point in this experiment, the number of floating leaf disks is an indirect measurement of the net rate of photosynthesis.

In photosynthesis, plants use energy from the sun, water, and carbon dioxide (CO 2 ) from the air to store carbon and energy in the form of glucose molecules. Oxygen gas (O 2 ) is a byproduct of this reaction. Oxygen production by photosynthetic organisms explains why earth has an oxygen-rich atmosphere.

The equation for photosynthesis can be written as follows:

6CO 2 + 6H 2 O + light energy → C 6 H 12 O 6 + 6O 2

In the leaf-disk assay, all of the components necessary for photosynthesis are present. The light source provides light energy, the solution provides water, and sodium bicarbonate provides dissolved CO 2 .

Plant material will generally float in water. This is because leaves have air in the spaces between cells, which helps them collect CO 2 gas from their environment to use in photosynthesis. When you apply a gentle vacuum to the leaf disks in solution, this air is forced out and replaced with solution, causing the leaves to sink.

When you see tiny bubbles forming on the leaf disks during this experiment, you’re actually observing the net production of O 2 gas as a byproduct of photosynthesis. Accumulation of O 2 on the disks causes them to float. The rate of production of O 2 can be affected by the intensity of the light source, but there is a maximum rate after which more light energy will not increase photosynthesis.

To use the energy stored by photosynthesis, plants (like all other organisms with mitochondria) use the process of respiration, which is basically the reverse of photosynthesis. In respiration, glucose is broken down to produce energy that can be used by the cell, a reaction that uses O 2 and produces CO 2 as a byproduct. Because the leaf disks are living plant material that still require energy, they are simultaneously using O 2 gas during respiration and producing O 2 gas during photosynthesis. Therefore, the bubbles of O 2 that you see represent the net products of photosynthesis, minus the O 2 used by respiration.

When you put floating leaf disks in the dark, they will eventually sink. Without light energy, no photosynthesis will occur, so no more O 2 gas will be produced. However, respiration continues in the dark, so the disks will use the accumulated O 2 gas. They will also produce CO 2 gas during respiration, but CO 2 dissolves into the surrounding water much more easily than O 2 gas does and isn’t trapped in the interstitial spaces.

Going Further

Try changing other factors that might affect photosynthesis and see what happens. How long does it take for the disks to float under different conditions? For example, you can compare the effects of different types of light sources—lower- or higher-wattage incandescent, fluorescent, or LED bulbs. You can change the temperature of the solution by placing the beaker in an ice bath or a larger container of hot water. You can increase or decrease the concentration of sodium bicarbonate in the solution, or eliminate it entirely. You can try to identify the range of wavelengths of light used in photosynthesis by wrapping and covering the beaker with colored gel filters that remove certain wavelengths.

Teaching Tips

This experiment is extremely amenable to manipulations, making it possible for students to design investigations that will quantify the effects of different variables on the rate of photosynthesis. It is helpful to have students familiar with the basic protocol prior to changing the experimental conditions.

Ask your students to think carefully about how to isolate one variable at a time. It is important to hold certain parts of the experimental setup constant—for example, the distance from the light source to the beaker, the type of light bulb used, the temperature of the solution, the height of the solution, and so on. Certain treatments may eliminate photosynthesis altogether—water with no bicarbonate, very low temperature, and total darkness.

A typical way to collect data in this assay is to record the number of disks floating at regular one-minute time intervals. This is easily graphed, with time on the x-axis and number of floaters on the y-axis.

To make comparisons between treatments, the number traditionally used is the time point at which half of the disks in the sample were floating, also known as the E50.

This experiment was originally described in Steucek, Guy L., Robert J. Hill, and Class/Summer 1982. 1985. “Photosynthesis I: An Assay Utilizing Leaf Disks.” The American Biology Teacher , 47(2): 96–99.

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Designing an experiment to test the rate of photosynthesis

This activity will allow students to measure the rate at which the photosynthesis process occurs. Students will work in small groups to design an experiment with one independent variable and test this variable on spinach leaf disks. The punched out leaf disks will initially sink in a test tube of water but will float as photosynthesis occurs. Students will write a lab report including, hypothesis, experimental design, data collection / analysis, and conclusion (findings). Students will speculate on further investigations that could be done and discuss how the rate at which photosynthesis occurs has vast implications for human survival on the planet.

Expand for more detail

Activity Classification and Connections to Related Resources Collapse

Grade level, learning goals.

-Photosynthesis

-Guard cells

-Wave lengths of light

-Global climate change

-Carbon sequestration

-Independent variable

-Dependent variable

-Qualitative data

-Quantitative data

Context for Use

Description and teaching materials.

-Meter stick -Baking soda -Different species of plant (other than spinach) -Weak acids / weak bases to change the pH of the solution -Other materials as students design experiments would some substances inhibit photosynthesis? (act as weed killers?) The teacher will now demonstrate to students the basic technique that will be used to measure the rate of photosynthesis. Students can follow along with the directions found in their handout / lab report (see experimental design, steps 1-5 in sample lab report within the assessment section) The main focus of the investigation depends on students knowing how to make the spinach leaf disks and make them sink in water. All students will be guided to use this technique . They can now practice this technique (see experimental design and the following web site http://www.elbiology.com/labtools/Leafdisk.html discuss the process of choosing a variable for the experiment. Pick a testable question to answer when doing the experiment. Give students time to design experiment and do a trial run. Teacher will help coach the students as they finalize / modify the experimental design to include a testable question with only one variable. The final experimental design will be written out using diagrams /drawings to illustrate the setup. Students can now plan / design an appropriate data table . (include proper units of measure, titles, all labeling) Finally, students will complete the experiment, analyze and discuss findings, and report findings to class. Class discussion will connect the lab to world issues; food availability, global climate change.

Teaching Notes and Tips

References and resources.

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COMMENTS

Floating Leaf Disk Photosynthesis Flashcards | Quizlet
Write a hypothesis that this experiment is designed to test. A syringe containing sodium bicarbonate and in the most intense light will have the most floating disks because the photosynthetic rate would be the fastest. Which serves as a control? Water beaker What variables are tested in this experiment?
Use Floating Leaf Disks to Study Photosynthesis
Conduct the leaf disk assay for each condition or variation that you choose to test. Remember to record the number of floating leaf disks in a data table and do each experiment in triplicates. Note: It is very important that you only test one variation at a time in your experiment.
Solved 2. Write a hypothesis that the Leaf Disk Assay is ...
Question: 2. Write a hypothesis that the Leaf Disk Assay is designed to test. (If I test 4 syringes in light and in the dark, the study with light will have more floating disks because the photosynthetic rate would be fastest. Data Table 2 T have included sample data for the first row for you to refer to when completing the laboratory experiment.
Study Photosynthesis with the Floating Leaf Disk Assay
In the first part, students use the leaf disk assay to explore how plants make energy using photosynthesis. In the second part, students design and conduct experiments that use the leaf disk assay to investigate several variables that have the potential to affect the rate of photosynthesis.
Experiment 6: Photosynthesis Flashcards | Quizlet
what three stat tests will be used to analyze the class' data. mean rate of floating leaf disks, 95% confidence interval, and students t-test. if the experimental system is working correctly then. the rate of floating leaf disks in low light will be sig greater than the rate of floating leaf disks in dark light.
Photosynthetic Flotation: Biology & Physics Science Activity ...
Because the leaf disks are living plant material that still require energy, they are simultaneously using O 2 gas during respiration and producing O 2 gas during photosynthesis. Therefore, the bubbles of O 2 that you see represent the net products of photosynthesis, minus the O 2 used by respiration.
IMG_4381.jpg - Activity 2: Leaf Disk Assay Overview 2. Write ...
Write a hypothesis that the Leaf Disk Assay is designed to test. Data Table 2: Leaf Disk Assay, | Course Hero IMG_4381.jpg - Activity 2: Leaf Disk Assay Overview 2.... Doc Preview Pages 1 Total views 27 Cumberland County College BIO Intro to Biology AgentFireGrasshopper4 11/18/2020 End of preview Upload your study docs or become a member.
Designing an experiment to test the rate of photosynthesis
Preparation of the leaf disks: 1) Use the cork borer (to cut out the number of disks needed for your experiment). 2) Put disks in a syringe and suck up 5 cc (5 ml) of .2% sodium bicarbonate (baking soda) 3) Put finger over end of syringe, pull back on plunger to about the 35 cc mark (on a 60 cc syringe) and hold this position for 30 seconds.