Chlorophyll

Introduction: (Initial Observation)

Chlorophyll is the part of the plant that gives plants their green color. Chlorophyll is a green substance with a complex chemical structure. Each molecule of chlorophyll is made of carbon, hydrogen, oxygen, nitrogen and magnesium atoms.

Have you ever wondered why green plants are all slightly different colors? or why leaves change color during the fall season?

Almost all plant leaves contain chlorophyll.

Chlorophyll is required for plants so they can use the light energy to build their own food.

In this project you will perform experiments with chlorophyll.

Information Gathering:

Do some research on the topic of chlorophyll. Try to find pertinent information on what happens when chlorophyll is heated or when plants do not get sunlight.
Keep track of where you got your information from.

Following are samples of information that you may find.

Have you ever wondered why green plants are all slightly different colors ? Well there is more than one kind of chlorophyll, and there are other photosynthetic pigments. When you extract these pigments from leaves and separate them using chromatography you will see that they are all slightly different colors.

As the nights get shorter and cooler, the tree must protect itself for winter. Its stems, twigs, and buds are tough enough to withstand winter, but not so its fragile broad, thin leaves. The watery sap in leaf cells freezes easily. So the tree seals off its leaves and sheds them.

To begin the sealing-off process, the tree grows a corky membrane between each branch and leaf stem. The membrane hinders the flow of nutrients into the leaf which stops the leaf from making new chlorophyll. The old chlorophyll quickly decomposes and the leaf’s green color fades.

If the leaf contains carotene, birch trees for example, the fading leaf changes from green to yellow. Carotene, a more stable compound than chlorophyll, persists in leaves even after all the chlorophyll is gone. The leaves of those trees now look yellow.

More about Chlorophyll

• Chlorophyll is the part of the plant that gives plants their green color. It absorbs the sunlight and turns the energy from the sun into usable energy.
• Chlorophyll is the molecule that absorbs sunlight and uses its energy to synthesize carbohydrates from CO2 and water. This process is known as photosynthesis and is the basis for sustaining the life processes of all plants. Since animals and humans obtain their food supply by eating plants, photosynthesis can be said to be the source of our life also.
• Plants make their own food. They take water from the ground through their roots. They take a gas called carbon dioxide from the air. They turn water and carbon dioxide into food using sunlight and something called chlorophyll. Chlorophyll is green. It gives leaves their green color.
• Winter days are short and dry. Many plants stop making food in the fall. The chlorophyll goes away. Then we can see orange and yellow colors. These colors were in the leaves all summer, but the green covered them up. Some leaves turn red. This color is made in the fall, from food trapped in the leaves. Brown colors are also made in the fall. They come from wastes left in the leaves.

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

1. Do Plants Need Sunlight To Be Green? (See experiment 1)
2. What happens when chlorophyll is heated? (See experiment 2)
3. Is chlorophyll a hydrophilic or hydrophobic substance?

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

This is how you define variables for the question 1.

Independent variable (also known as manipulated variable) is the light.

Dependent variable (also known as responding variable) is the color of the leaves.

Hypothesis:

Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.

Following are sample hypothesis corresponding to the suggested questions above.

1. My hypothesis is that plants do need sunlight in order to be green. This may be the reason that leave fall off of trees in the winter.
2. My hypothesis is that nothing will change when chlorophyll is heated.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Experiment 1: Do Plants Need Sunlight To Be Green?

Introduction: In this experiment we cover some green leaves of a plant with black construction paper that can fully block the light. We will also cover a few other leaves with clear material. In this way any possible change in the leaves can be attributed to the light, not to the cover. We inspect the leaves daily and look for any change.

Materials:

• A plant with broad leaves. (Could be either inside or outside)
• Black or dark construction paper.
• Transparent material, such as a plastic bag.
• Scissors.
• Tape.

Procedure:

1. Cut two pieces of black construction paper large enough to fully cover each of 5 leaves.
2. Sandwich each of the five leaves between two pieces of construction paper (while the leaves are attached).
3. Repeat steps 1 and 2 using the transparent material and cover five different leaves.
4. Each day for five days remove the construction paper and the transparent material from one leaf each.
5. Record your observations of the changes for both types of leaf covers.

Your results table may look like this:

Related Notes:

As summer ends and autumn comes, the days get shorter and shorter. This is how the trees “know” to begin getting ready for winter.
During winter, there is not enough light or water for photosynthesis. The trees will rest, and live off the food they stored during the summer. They begin to shut down their food-making factories. The green chlorophyll disappears from the leaves. As the bright green fades away, we begin to see yellow and orange colors. Small amounts of these colors have been in the leaves all along. We just can’t see them in the summer, because they are covered up by the green chlorophyll.
The bright reds and purples we see in leaves are made mostly in the fall. In some trees, like maples, glucose is trapped in the leaves after photosynthesis stops. Sunlight and the cool nights of autumn turn this glucose into a red color. The brown color of trees like oaks is made from wastes left in the leaves.
It is the combination of all these things that make the beautiful colors we enjoy in the fall.

Experiment 2: What Happens When Chlorophyll is Heated?

Introduction: Many foods contain vegetables; however, they don’t look green. It is possible that for some reason (such as heat or exposure to other food substances) chlorophyll is loosing or changing its color. In this experiment we test the effect of heat on chlorophyll.

Materials:

• A type of vegetable such as spinach or broccoli.
• A pot and some water.

Procedure:

Take the vegetable and cook it over medium heat in a bit of water. Observe the vegetable. You will see that the vegetable will soon change color to a bright green. Yet after the cooking the vegetable for some time longer, you will find the vegetable will turn into another color. What color does the vegetable turn and why?

Experiment 3: Is Chlorophyll a hydrophobic or hydrophilic?

Definitions (from Wikipedia, The free encyclopedia):

1. Hydrophobe (from the Greek (hydros) “water” and (phobos) “fear”) in chemistry refers to the physical property of a molecule that is repelled by water. Hydrophobic molecules in water often cluster together.
2. Hydrophile, from the Greek (hydros) “water” and φιλια (philia) “friendship”, refers to a physical property of a molecule that can bond with water.
   A hydrophilic molecule or portion of a molecule is one that typically is electrically polarized and capable of hydrogen bonding, enabling it to dissolve more readily in water than in oil or other “non-polar” solvents.
3. Polar Molecules:
   In chemistry, a polar molecule is a molecule in which the centers of positive and negative charge distribution do not converge. These molecules are characterized by a dipole moment which measures their polarity.

Polar compounds are highly soluble in other polar compounds, and virtually insoluble in nonpolar compounds.

Introduction: In order to find out is chlorophyll is a hydrophobic or hydrophilic substance, we try to dissolve it in water and oil. If chlorophyll is hydrophilic, it must dissolve in water and change the color of water to green. If chlorophyll is hydrophobic, it must dissolve in oil and change the color of oil to green.

Material:

1. 100 mL vegetable oil (the lighter colored oils will work better). Instead of oil, you may want to use acetone or isopropyl alcohol. It is easier to filter these two solvents. Mineral spirit and mineral oil may also be used. Gloves, additional care, air ventilation and fire safety measures are required if you choose to use anything other than vegetable oil. Acetone, alcohol and mineral spirit are highly flammable.
2. 100 mL water
3. 100 grams Green leaf (geranium, spinach, …)
4. filter paper and funnel

Procedure:

1. Place the green leaves in a grinder or mortar and grind it to fine paste.
2. Divide the grinded leaves in two equal part. Add one part to the water and add the other part to the oil.

3. Stir each mixture for about 5 minutes.

4. Filter each mixture separately.

5. Compare the colors of filtered water and filtered oil. Which one has dissolved more chlorophyll?

Experiment 4:  What Color is transmitted by Chlorophyll?

Objective:

To determine the color transmitted by chlorophyll.
(Source: Guide to more of the best science fair projects, page 43)

Hypothesis:

If the color transmitted by the chlorophyll pigment is green then I should get a green colored glow on the screen underneath.

Material:

• Rubbing alcohol 50 ml
• A clear plastic cup
• A plant leaf such as a geranium leaf
• Flash light
• White paper

Caution:

Take help from an adult to handle rubbing alcohol. Keep it away from nose and mouth. My mother helped me to conduct this experiment.

Procedure:

1. Take about 50 ml of rubbing alcohol in a clear plastic cup. Add small pieces of a plant leaf by tearing the leaf.
2. Keep on stirring the contents of the cup for about an hour and then remove the leaf pieces. Now the liquid containing plant pigments is ready for the experiment.
3. Keep a white sheet of paper on the flat surface. This would be the screen.
4. Hold the glass about 4 inches (10 cm) above the screen.
5. Shine the light above the glass as shown in the figure on the left.
   This is a home made spectrophotometer.
6. The color seen on the screen is the color transmitted through the leaf pigment.

Result:

I observed a green colored glow on the screen. This experiment shows that all other colors of the natural light are absorbed and only green passed through the chlorophyll.

Conclusion:

So the color transmitted by the chlorophyll pigment is green. Thus…

[The color transmitted]= [All the colors making up the white color] – [The colors absorbed]

Materials and Equipment:

List of material may vary based on the question and the experiment that you select for your project. Each experiment has its own list of material. Your final list of material may be different from the samples provided above.

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.

In addition to your results table, you include some general information in your report or display board. Following are some valuable information.

This experiment explain why trees change color in autumn:

Chlorophyll is the part of the plant that gives the plants their green color. Plants take water form the ground through their roots. They take a gas called carbon dioxide from the air. Plants use sunlight to turn water and carbon dioxide into glucose. Glucose is a kind of sugar. Plants use glucose as food for energy and as a building block for growing. The way plants turn water and carbon dioxide into sugar is called photosynthesis. A chemical called chlorophyll helps make photosynthesis happen. In other words, chlorophyll absorbs the sunlight and turns the energy from the sun into usable energy.

Winter days are short and dry. During these months, there is not enough light or water for photosynthesis. The trees will rest, and live off the food they stored during the summer. They begin to shut down their food-making factories. The green chlorophyll disappears from the leaves. Then we can see orange and yellow colors. These colors were in the leaves all summer, but the green covered them up.

Calculations:

If you do any calculations for your project, write your calculations in this section of your report.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.

Conclusion:

Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.

References:

Visit your local library and find books related to chlorophyll and photosynthesis. List such books and your online references in the references/ bibliography of your report.

Following are some online references.

Why do leaves turn color in the fall?

Leaf Pigments

Chlorophyll and photosynthesis