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Photosynthesis

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Introduction

Before beginning this exercise, it is necessary to understand that photosynthesis uses light energy to synthesize carbohydrate from carbon dioxide. The equation is below.

\[\mathrm{6CO_2 + 6H_2O + Energy \rightarrow C_6H_{12}O_6 + 6O_2}\]

This process requires light for some of the reactions.

It is also necessary to understand that the plant is constantly undergoing cellular respiration according to the equation below.

\[\mathrm{C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + Energy}\]

Notice that these two equations appear to be opposites.

When plants are exposed to light, photosynthesis and cellular respiration both occur. In the dark, only cellular respiration occurs.

We will study photosynthesis in an aquatic plant ( Elodea ) We can measure the rate of photosynthesis and cellular respiration by measuring the amount of CO 2 given off or taken up by the plant.

Carbon dioxide combines with water to form carbonic acid (H 2 CO 3 ) which dissociates into hydrogen ions (H + ) and bicarbonate ions (HCO 3 - ). The pH drops due to the presence of hydrogen ions.

\[\mathrm{CO_2 + H_2O \leftrightarrow H_2CO_3 \leftrightarrow H^+ + \sideset{ }{_{3}^{-}}{HCO}}\]

Respiring plants release CO 2 into the water, causing the pH to decline. During photosynthesis, plants take up CO 2 and the pH increases.

Using the pH Probe

Set up the pH probe by following the instructions given in the link below.

Instructions for setting up and using the pH probe.

Procedure for Measuring Photosynthesis

Create a hypothesis for this experiment.

Be sure to use tap water for the experiments below. Distilled water should not be used.

After the probe is set up (see the step above), obtain two large test tubes for this experiment. A ring stand can be used to hold the tubes as shown in the photograph below.

Rinse both tubes and stoppers thoroughly with tap water to remove any traces of contaminants that might affect pH.

Fill each tube with tap water to approximately 2 cm from the top.

Cut a sprig of Elodea that is long enough to fill the entire length of one tube but not protrude from the water. The length of the stem can be adjusted, if necessary, by cutting a piece from the base of the stem. Put the plant in one of the tubes. The other tube will serve as a control.

Clamp the two tubes on a ring stand to hold them.

Insert one pH probe into each test tube.

When the pH stabilizes, record the pH in each tube and then turn on the lamp and begin timing the experiment. The pH probes can be kept in the tubes until the experiment is finished.

Record the pH of the water in each tube every 10 minutes for one hour. Your data table will have 7 pH readings for each tube.

You should begin the chromatography procedure (below) while waiting to take pH readings.

Chromatography

During photosynthesis, light energy is absorbed by photosynthetic pigments. Chlorophyll A is the main photosynthetic pigment but chlorophyll B, carotenes, and xanthophylls also absorb light. Each pigment absorbs a specific range of colors but all of them together enable the plant to use a larger amount of light. These pigments absorb red and blue light best and absorb green the least. Plants look green; because the green light is not absorbed by the plant; it is reflected.

Chromatography is a technique used to separate the components of a mixture. In this investigation, you will use chromatography to separate and identify several photosynthetic pigments in a solution prepared from spinach leaves.

Paper chromatography can be used to separate the components of a mixture based on their polarity. Some of the mixture is placed on one end of a piece of paper and that end of the paper is immersed in a nonpolar liquid (see the diagram below).

As the liquid moves up the paper, the molecules of the sample mixture will also move. Polar molecules within the sample will spend most of their time bound to the polar surface of the paper and will therefore not move very much. Nonpolar molecules, however, will spend most of their time dissolved in the liquid as it moves up the paper. When the liquid reaches the top of the paper, these molecules will also have traveled most of the way to the top. The two types of molecules (polar and nonpolar) are now separated.

It is useful to determine the relative distance moved by a particular kind of molecule using chromatography. This value is known as R f . For example, if the molecules move half as far as the solvent traveled, the R f = 0.5. If the molecules moved 1/4 the distance, the R f = 0.25. The maximum value for R f is therefore 1.0.

Using a pencil, put a small dot in the center of a strip of chromatography paper 2 cm. from one end.

Put a hole in the other end of the paper so that it can be suspended on a wire clip inserted in a cork stopper as shown in the photograph above. The paper should be able to reach to within 1 cm of the bottom of the tube but not touch the bottom.

When the apparatus is adjusted properly, remove the paper so that you can add pigment extract.

Caution - The remainder of this procedure should be conducted under the hood because the vapors from the chemicals used are toxic and carcinogenic (cause cancer).

Use a micropipette to place a 5 ul of pigment extract on the dot that you marked on the paper. The extract should be placed directly on top of the dot. It will spread, producing a small circular spot. Allow the spot to dry for 1 minute and repeat this procedure 4 more times for a total of 5 applications of pigment extract. Allow the spot to dry between each application.

While waiting for the paper to dry after the fifth application, add chromatography solvent to the bottom of the chromatography tube. Add enough solvent so that the end of the chromatography paper will be immersed in the solvent but the spot with pigment extract will remain above the solvent. It is important not to immerse the pigment spot. This tube should be kept under the hood at all times.

When the spot has dried, suspend the paper vertically in a chromatography tube. If possible, keep the paper from touching the sides of the tube.

Check the movement of the solvent after 20 minutes. The paper should be removed before the solvent reaches the top of the paper.

Before the solvent dries, draw a line on the paper that shows how far the solvent moved. One end of the paper should have a dot that indicates where the pigments were applied and the other end should have a line that indicates how far the solvent traveled.

Allow the paper to dry under the hood. After the paper is dried, you may bring it out from under the hood.

Do not discard the chromatography solution down the drain, discard it in the beaker provided under the hood.

The photosynthetic pigments will be separated in the following order beginning with the highest R f : beta-carotenes, xanthophylls, chlorophyll a, chlorophyll b. Beta-carotenes are orange or orange-yellow, xanthophylls are yellow, chlorophyll A is blue-green, and chlorophyll B is olive-green.

The proportion of the total distance moved by the spot is often calculated in chromatography procedures. To calculate this value, you must first measure the distance moved by the solvent. This can be done by measuring the distance from the spot to the top of the paper. Next, measure the distance moved by each of the pigments.

R f = distance moved by the pigment/distance moved by the solvent

For each of the pigments (beta-carotenes, xanthophylls, chlorophyll a, chlorophyll b) record the distance moved and the Rf.

One member of your group should paste the chromatogram in their notebook. The names of the members of your group should be listed next to the chromatogram.

Create a graph of your results from the photosynthesis experiment. Put time on the X-axis and pH on the Y-axis. If you have a notebook with quad-ruled pages, you can draw the graph directly in your notebook. If not, use graph paper or use a computer graphing program such as Excel or LibreOffice. Adjust the graph so that the minimum value of the Y-axis is a number that is slightly less than the minimum value observed in the table above. The maximum value should be equal to or slightly greater than the maximum value of the data. For example, suppose that the minimum pH that you measured was 5.9 and the maximum was 7.3. You could make the minimum on the graph 5.5 and the maximum 7.5. Be sure that you clearly identify the two lines on the graph. For example, you could use circles for points on one line and squares for points on the other line.

• What will happen to the pH of water when CO 2 is dissolved in the water?
• Write the equation that describes what happens when CO 2 is dissolved in water.
• What will happen to the pH of water when CO 2 is removed from the water?
• Two kinds of metabolic reactions caused the pH to change in the tube with the plant. One of these processes caused the pH to increase, the other caused it to decrease. Name these processes and tell which causes the pH to increase and which causes the pH to decline.
• The two processes listed above had opposite effects on the pH. Why did the pH increase in the light tube if both of these process were occurring at the same time?
• Explain why the values produced from the tube with the plant do not reflect the total photosynthesis (total CO 2 consumption) of the plant. [Hint - Think about your answer to questions 4 and 5.]
• Explain why the pH of the tube with the plant might stop increasing toward the end of the 60 minute time period. The diagram above may be helpful for answering this question.

Contributors

Michael J. Gregory, Ph.D. ( Clinton Community College)

Photosynthesis Lab

Photosynthesis is one of the most important anabolic chemical reactions that allows life to exist on Earth. With water, light energy from the sun, and carbon dioxide from the air, photosynthetic organisms are able to build simple sugars. Organisms that can make their own food are called autotrophs , and are at the base of the food chain. The basic reaction is:

6 C O 2 + 12 H 2 O + e --> 2 C 6 H 12 O 6 + 6 O 2

carbon dioxide + water + light energy --> glucose + oxygen

Oxygen molecules are colored to show their fate. Oxygen from CO 2 ends up in glucose. Oxygen from water becomes free O 2

Photosynthesis has two stages. Stage 1 requires light. Stage 2 can work in the light or in the dark. The energy accumulated in Stage 1 is used to drive Stage 2.

• The light reaction is used to convert sunlight into chemical energy stored in ATP and another energy storage molecule called NADP .
• The light-independent reaction or Calvin Cycle takes carbon dioxide and fixes it in three-carbon molecules which will eventually be synthesized into glucose.

Experiment : We will conduct a simple experiment using spinach leaves to demonstrate that, in the presence of light and carbon dioxide, leaf tissues produce gas bubbles. While we cannot prove in this experiment that the bubbles are oxygen without a gas probe, we can demonstrate, by use of a control, that the bubbles only form when the leaves are submerged in a sodium bicarbonate solution (which releases CO 2 ) and not when they are submerged in pure water. We can also demonstrate that the bubbles only form in the presence of strong light, by moving the experiment into the dark and making further observations. Finally, we could experimentally vary the light intensity to demonstrate the effect of light intensity on the process.

When we dissolve baking soda (NaHCO 3 ) in water, carbonic acid (H 2 CO 3 ) and sodium hydroxide (NaOH) are formed. The carbonic acid then breaks down into water and carbon dioxide gas, which is why dissolving baking soda in water causes it to fizz.

NaHCO 3 + H 2 O --> H 2 CO 3 + NaOH

H 2 CO 3 --> H 2 O + CO 2 (gas)

• Fresh spinach leaves
• Metal paper hole punch
• 10 mL or larger plastic syringe (without needle) - get one from your local pharmacy
• Baking soda solution (dissolve some baking soda powder in water)
• Liquid dish soap solution (dissolve 5 mL in 250 mL of water)
• Cup 1: Detergent solution
• Cup 2: Baking soda solution (treatment)
• Cup 3: Water (control)
• Light source (fluorescent is good because it produces light without much heat)
• Use the metal hole punch to cut out 20 circular disks from the fresh spinach leaves, 10 for a control and 10 for a treatment.
• Separate the two parts of the syringe, drop 10 of the spinach disks inside, reassemble the syringe.
• Push the plunger almost to the bottom but don't crush the disks.
• Control or treatment
• For the treatment , draw up a small amount ~1 mL of detergent solution, and then draw the baking soda solution up to ~3-5 mL
• For the control , draw up a small amount ~1 mL of detergent solution, and then draw the water up to ~3-5 mL
• Point the syringe upward, tapping the sides, so that any air bubbles rise, and gently squeeze the syringe until liquid begins to come out.
• Put a finger on the end of the syringe, and draw the plunger back slightly, creating a partial vaccum.
• Repeat until the leaf disks are suspended in the solution. This action forces the liquid into the interior of the leaf.
• Watch this video of the process to make sure you're doing it right.
• Pour the contents of control and treatment syringes into two labelled clear plastic cups.
• Swirl the liquid to try to keep the disks from sticking to each other or the sides of the cups and then let them sit.
• Turn on a bright light, and monitor the disks every minute. Count how many disks are floating during each of the next 15 minutes.
• After all (or most) of the disks are floating, put the cups in the dark (a shoebox or a closet) and monitor for the next 15 minutes.
• Record how many disks remain floating after each minute until all (or most) of them have sunk.

Watch this demonstration to see how to make the leaf disks sink.

In the light, you should expect to see the disks in the control solution (water) stay on the bottom, but the disks in the treatment solution (baking soda) should begin to rise as they use the CO 2 to undergo photosynthesis and produce oxygen bubbles. The bubbles should cause the disks to float. After you remove the light and place the cups in the dark, the treatment disks should stop undergoing photosynthesis and the disks should begin to sink.

For comparison purposes, each lab group that does this procedure should report the time at which half (5) of the disks is floating. In the example below, that time would be about 11.5 minutes. You can use this Excel spreadsheet to record your data and it will auto-generate a graph for you.

Some or all of the submerged disks should begin to float within about 15 minutes

Questions :

• How does the suction help the leaf disks to sink?
• How does the detergent help the leaf disks to sink?
• Why don't the leaf disks soaking in the water (control) float?
• What is the purpose of the baking soda solution?
• What is the purpose of the light reaction?
• Why do the leaf disks in the baking soda solution (treatment) begin to float?
• Why do the leaves begin to sink again in the dark?
• Why don't the leaves in the baking soda solution continue to produce oxygen in the dark?
• Why do we use the half-way mark as a point of comparison rather than the point at which all the disks are floating?
• If the light-independent reaction can run without light, why does oxygen production (and presumably glucose production) stop?

References :

http://media.collegeboard.com/digitalServices/pdf/ap/bio-manual/Bio_Lab5-Photosynthesis.pdf

http://www.biologyjunction.com/5b-photoinleafdiskslesson.pdf

https://www.youtube.com/watch?v=XV9FOWleErA

http://www.berwicksclasses.org/AP%20Biology/Biology%20Assignments/AP%20BIOLOGY%20Lab%204.htm

http://www.kabt.org/2008/09/29/video-on-sinking-disks-for-the-floating-leaf-disk-lab/

Jove Lab Bio

Lab 7: photosynthesis — procedure.

• NOTE: In this experiment you will separate pigments from spinach leaves using chromatography paper. Individual pigments travel along the paper at different rates and may have different colors. By calculating the relative distance the pigments travel, their resolution factor, and comparing them with literature values, you can identify different pigments. HYPOTHESES: In this exercise the experimental hypothesis is that there will be multiple pigments within the spinach leaves that absorb different wavelengths of sunlight. The null hypothesis is that there is only one type of pigment within the spinach leaf.
• Use a pencil to make a line two centimeters from one end of the chromatography paper.
• Then, lay a pipe cleaner horizontally across the top of a clean 400 mL beaker.
• Place the pencil-marked side of the chromatography strip at the bottom of the beaker.
• Next, wrap the paper around the pipe cleaner so that the bottom edge is barely touching the bottom of the beaker and then secure it with a paperclip.
• When the paper is secured around the pipe cleaner, remove it from the beaker, and then place a patted-dry spinach leaf over the marked line on the chromatography paper.
• Roll a coin over the spinach leaf along the pencil line going back and forth multiple times and applying steady pressure. When the leaf is removed, a green line should be clearly present.
• Next, place 8 mL of chromatography solvent in the beaker.
• Lower the chromatography strip into the beaker so that the edge of the paper touches the solvent but the green line does not. Adjust the pipe cleaner if needed.
• Without disturbing the beaker, observe the solvent as it moves up the paper and the individual pigments separate.
• When the solvent has traveled half way up the chromatography paper, which will take approximately 10 minutes, and the pigments have separated into well-defined bands, remove the paper from the beaker.
• Mark how far the solvent traveled with a pencil and then allow the paper to dry. NOTE: The solvent evaporates quickly.
• Next, record the number of visible bands and describe their color and relative size.
• Measure how far the solvent and pigments traveled, and record this information for each pigment in Table 1. Click Here to download Table 1
• Dispose of the chromatography solvent in a waste container under a fume hood. Throw the chromatography strips into the regular trash, and then clean the beakers with soap and water.
• NOTE: In this experiment you will indirectly observe photosynthesis and cellular respiration using a floating leaf disc in a solution. During photosynthesis, air bubbles will cause the leaves to float, and during respiration, the discs will sink. HYPOTHESES: In this exercise, the experimental hypothesis is that the leaf discs will have a greater rate of photosynthesis in the bicarbonate solution, because bicarbonate provides added CO 2 to fuel photosynthesis, causing more leaf discs to float. Additionally, all of the discs will sink in dark conditions as they perform cellular respiration. The null hypothesis is that there will be no difference in the rate of photosynthesis, and therefore the number of floating discs, between the bicarbonate and water, or light and dark treatments.
• To place leaf discs under vacuum, first remove the plungers from two 20 mL syringes, and then place 10 leaf discs inside each syringe tube. Label one syringe “bicarbonate”, and label the other syringe “water”.
• Replace the plungers and push the plunger until only a small amount of air remains in the syringe. Take care not to damage the leaf discs.
• Pull 5 mL of the bicarbonate solution into one of the syringes. Invert and swirl the syringe to suspend the leaf discs in solution.
• Push as much air out as possible without expelling the solution or damaging the leaf discs.
• Then pull 5 mL of the water solution into the other syringe and swirl it as previously described (step 3).
• To create a vacuum, hold one finger over the tip of the syringe while pulling back on the plunger. Hold this for 10 seconds while swirling the syringe to keep the leaf discs in suspension.
• Then, release the vacuum. NOTE: The discs should have absorbed the solution into the air spaces in their tissues and you should see them sink. If the discs don't sink, you can repeat the vacuum creation up to three times.
• Next, add 50 mL of bicarbonate solution to a plastic cup or a glass beaker, and then gently add the discs from the bicarbonate vacuum syringe.
• For the control, add the same amount of water to an identical cup, and then add the leaf discs from the water vacuum syringe. Label the containers appropriately.
• Place both cups under a light source.
• Every five minutes record the number of discs floating on the surface of the cup in Table 3 until 20 minutes have passed. Click Here to download Table 3
• Next, remove the cups from the light source and then swirl them so that the discs at the surface intermix with any gases also at the surface.
• Move the cups to a dark place. Every five minutes record the number of leaf discs floating at the surface until 20 minutes have passed. Swirl the cup each time before placing it back in the dark.
• To clean up, dispose of the leaf discs in the trash, and pour the bicarbonate solution down the drain. Wash the syringes and cups thoroughly.
• NOTE: In the first experiment, you observed how far pigments from spinach leaves traveled on chromatography paper. Different pigments absorb light at different wavelengths.
• Using colored pens or pencils, draw the positions of the pigment bands and the solvent on Figure 3.
• Calculate the retention factor, or Rf values for the pigments, which is done by dividing the distance the pigment in question moved up the paper from the line by the distance the solvent moved up the paper from the line.
• Compare your calculated Rf values to those in Table 2 to determine the identity of the pigment. Click Here to download Table 2
• Record these data in Table 1. NOTE: In the second experiment, you observed floating and sinking leaf discs as an indirect measurement of photosynthesis and respiration.
• Graph the results with time and minutes on the x-axis and number of floating discs on the y-axis. Use two different lines to represent the water control and the bicarbonate treatment.
• Add a line to the graph to indicate the point where the discs were removed from the light condition and placed into the dark.
• Next, starting with the bicarbonate condition, use the graph to determine the point at which 50% of the leaf discs were floating. This is referred to as the effective time, or ET50. NOTE: You will notice that the discs likely hit the 50% floating mark once in the light condition and then again in the dark condition.
• Your water samples may or may not have reached the ET50 mark. If they did, add the line for this sample also.
• Finally, compare your ET50 values and graphs with the rest of the class.

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Science Projects > Life Science Projects > Test for Starch in Plants  

Test for Starch in Plants

Photosynthesis is the process in which green plants (primarily) convert energy from the sun’s light into usable, chemical energy. Plants require energy for growth, reproduction, and defense. Excess energy, created from photosynthesis, is stored in plant tissue as starch. Starch is a white and powdery substance. It houses glucose, which plants use for food. The presence of starch in a leaf is reliable evidence of photosynthesis. That’s because starch formation requires photosynthesis.

( Adult supervision required. )

Starch Testing Experiment

What you need:.

• Beaker or glass jar
• Saucepan on the stove
• Ethyl alcohol
• Iodine solution

Test for starch in plants:

1. Place one of the plants in a dark room for 24 hours; place the other one on a sunny windowsill.

2. Wait 24 hours.

3. Fill the beaker or jar with ethyl alcohol.

4. Place the beaker or jar in a saucepan full of water.

5. Heat the pan until the ethyl alcohol begins to boil.

6. Remove from the heat.

7. Dip each of the leaves in the hot water for 60 seconds, using tweezers.

8. Drop the leaves in the beaker or jar of ethyl alcohol for two minutes (or until they turn almost white).

9. Set them each in a shallow dish.

10. Cover the leaves with some iodine solution and watch.

What Happened:

The hot water kills the leaf and the alcohol breaks down the chlorophyll, taking the green color out of the leaf. When you put iodine on the leaves, one of them will turn blue-black and the other will be a reddish-brown. Iodine is an indicator that turns blue-black in the presence of starch. The leaf that was in the light turns blue-black, which demonstrates that the leaf has been performing photosynthesis and producing starch.

Try the test again with a variegated leaf (one with both green and white) that has been in the sunlight. A leaf needs chlorophyll to perform photosynthesis — based on that information, where on the variegated leaf do you think you would find starch?

Buy Testing For Starch Experiment Kit

More Life Science Projects:

•   Make a Leaf Skeleton
•   Make a Butterfly Feeder
•   Make Spore Print Art
•   Make Spider Web Art

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Synopsis of the Experiment

• What Happens
• Lab Objectives
• Equipment/ Logistics Required
• Summary of What is Due
• Keyword Descriptors

What Happens:       In this three week lab, students use the technique of making clear nail polish impressions of leaf stomata to generate and test an hypothesis of their choice about how leaf stomata density might vary under different environmental conditions. First, students learn how stomata density affects leaf carbon, water, heat budgets, and photosynthesis. Then, students design their own study to compare stomata density among leaves that differ in biophysical environment on their campuses. Over the next two weeks, students collect and analyze their data (graphs and t-tests), and present their results in an in-class symposium.

______________________________________________________________

Lab Objectives: At the conclusion of this multiweek lab, students will:

• students will have a basic understanding of structure and function of leaf stomata as well as the role of stomata in regulating gas and heat exchange in vascular plants,
• Students will have actually done science - they will have generated a testable hypotheses, collected data, analyzed data, tested their hypothesis, and they will have reported their research results to their peers.

Equipment/ Logistics Required:

• a one page co-authored research proposal composed according to the guidelines below (due at the end of the first lab),
• answers to any four of the questions for further thought contained in this handout (due in lab on the second week - students work alone on these),
• clearly labeled copies of students' original data including the actual slides taped to a plastic slide holder (due in class at the end of the second lab),
• co-authored stomata results report composed according to the guidelines below and presented in class (due at the beginning of the third lab), and

Keyword Descriptors:

• Science & Math
• Sociology & Philosophy
• Law & Politics

How to Write Hypothesis for Lab Report

• How to Write Hypothesis for…

What Is a Real Hypothesis?

A hypothesis is a tentative statement that proposes a possible explanation for some phenomenon or event. A useful hypothesis is a testable statement that may include a prediction.

When Are Hypotheses Used?

The keyword is testable. That is, you will perform a test of how two variables might be related. This is when you are doing a real experiment. You are testing variables. Usually, a hypothesis is based on some previous observations such as noticing that in November many trees undergo color changes in their leaves and the average daily temperatures are dropping. Are these two events connected? How?

Any laboratory procedure you follow without a hypothesis is really not an experiment. It is just an exercise or demonstration of what is already known.

How Are Hypotheses Written?

• Chocolate may cause pimples.
• Salt in soil may affect plant growth.
• Plant growth may be affected by the color of the light.
• Bacterial growth may be affected by temperature.
• Ultraviolet light may cause skin cancer.
• The temperature may cause leaves to change color.

All of these are examples of hypotheses because they use the tentative word “may.”. However, their form is not particularly useful. Using the word may do not suggest how you would go about proving it. If these statements had not been written carefully, they may not have even been hypotheses at all. For example, if we say “Trees will change color when it gets cold.” we are making a prediction. Or if we write, “Ultraviolet light causes skin cancer.” could be a conclusion. One way to prevent making such easy mistakes is to formalize the form of the hypothesis.

Formalized Hypotheses example: If the incidence of skin cancer is related to exposure levels of ultraviolet light , then people with a high exposure to uv light will have a higher frequency of skin cancer.

If leaf color change is related to temperature , then exposing plants to low temperatures will result in changes in leaf color .

Notice that these statements contain the words, if and then. They are necessary for a formalized hypothesis. But not all if-then statements are hypotheses. For example, “If I play the lottery, then I will get rich.” This is a simple prediction. In a formalized hypothesis, a tentative relationship is stated. For example, if the frequency of winning is related to the frequency of buying lottery tickets . “Then” is followed by a prediction of what will happen if you increase or decrease the frequency of buying lottery tickets. If you always ask yourself that if one thing is related to another, then you should be able to test it.

Formalized hypotheses contain two variables. One is “independent” and the other is “dependent.” The independent variable is the one you, the “scientist” control, and the dependent variable is the one that you observe and/or measure the results. In the statements above the dependent variable is underlined and the independent variable is underlined and italicized .

The ultimate value of a formalized hypothesis is it forces us to think about what results we should look for in an experiment.

For the “ If, Then, Because ” hypothesis…you would use: “ IF pigs and humans share the same nutritional behaviors, THEN their internal organs should look relatively the same BECAUSE of similar function and composure.” That is an example. For the “If, Then, Because” you should follow this guideline:

IF X and Y both do or share this, THEN this should be found/confirmed, BECAUSE of this fact or logical assumption.

Example Question : How does the type of liquid (water, milk, or orange juice) given to a plant affect how tall the plant will grow? Hypothesis : If the plant is given water then the plant will grow the tallest because water helps the plant absorb the nutrients that the plant needs to survive.

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Author:  William Anderson (Schoolworkhelper Editorial Team)

Tutor and Freelance Writer. Science Teacher and Lover of Essays. Article last reviewed: 2022 | St. Rosemary Institution © 2010-2024 | Creative Commons 4.0

16 Comments

How would I write a hypothesis about a flying pig lab?

your lab hypothesis should have been written before the experiment. The purpose of the hypothesis was to create a testable statement in which your experimental data would either support or reject. Having a hypothesis based on a logical assumption (regardless of whether your data supports it) is still correct. If there is a disagreement between your hypothesis and experimental data it should be addressed in the discussion.

So you can go ahead an choose a hypothesis for either increase or decrease of adipogenesis after the inducement of insulin and not be wrong….as long as it is correctly formatted (see examples above).

Hey, I am having trouble writing my hypothesis.. I am supposed to write a hypothesis about how much adipogenesis was produced after the inducement of insulin. However, after proceeding with the experiments the results were On/Off .. meaning it will increase, decrease, increase, etc.. so it wasnt a constant result. It was supposed to be increasing.

please help!!!

this is very helpful but i don’t know how i would structure my hypothesis. i’m supposed to come up with a hypothesis related to the topic ‘how does mass effect the stopping distance of a cart?’. Could you help?

Thank you so much, it really help alot.:)

This is a rather difficult usage of this construct. It would most likely follow

“If the empirical formula of (enter compound’s name) is (enter compound’s formula) then it would be expected that combustion of _________ would yield _________, because (enter your rationale)

Need more background info.

For the “If, then, because” hypothesis I am doing an experiment to determine the empirical formula by using combustion but I am unsure on how to formulate the hypothesis using this structure.

For the “If, Then, Because” hypothesis…you would use: “IF pigs and humans share the same nutritional behaviors, THEN their internal organs should look relatively the same BECAUSE of similar function and composure.” That is an example. For the “If, Then, Because” you should follow this guideline:

Thanks, really helpful. Just one question, what about the ‘because’ part? right after the ‘if’ and ‘then’ parts?

I really need help for onion skin lab hypothesis for class

@Lauren An if/and statement is not usually apart of the convention. What exactly do you need help with?

Is there such thing as a if/and statement? I am in 8th grade science an I need to know for my lab report due tomorrow.HELP!!!!

Would have been better if more examples were given

If the purpose of your lab is “To obtain dissecting skills in an observational lab,” you can’t really formulate a testable hypothesis for that. I’ll assume you are doing some kind of pig or frog dissection. Often teachers give general outlines of skills that students are meant to ascertain from an experiment which aren’t necessarily what the actual experiment is directly testing. Obviously to do the dissection lab you need to obtain dissection skills but testing that would be rather subjective unless the teacher provided you with standards or operationally defined “dissecting skills”. If I were you, I would obviously mention it in the introduction of your lab but I am not sure if your teacher wants you to actually format it as a hypothesis; you can ask your teacher for clarification. If making a hypothesis from each purpose was some arbitrary exercise assigned to you then, it could look like this:

“If a student has successful acquired dissection skills, then they will be able to complete this observational lab with satisfactory competence because they utilized these newly acquired skills.”

For the “If, Then, Because” hypothesis…you pretty much have it. You would modify what you posted: “IF pigs and humans share the same nutritional behaviors, THEN their internal organs should look relatively the same BECAUSE of similar function and composure.” That is an example. For the “If, Then, Because” you should follow this guideline:

Thanks for this, it proved to be helpful. However, I do have a few questions. Obviously different teachers or instructors have their own requirements for their classes. How would you write an appropriate Question to follow each purpose in your lab report? For example: If the purpose was, “To obtain dissecting skills in an observational lab,” what question could you formulate with the purpose? (which is answered in the hypothesis)

And if a teacher requires the hypothesis to be in the format “If, Then, Because” how should this be written? I can actively complete the if and then, but I’m unsure how to incorporate the “because’ statement. For example, “If pigs and humans share the same nutritional behaviors, then their internal organs should function comparably and look relatively the same.” (how do i incorporate because?)

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