Lesson 7 How Do Plants Make Their Own Food

Brainstorm What is our evidence that plants do not get their food from the soil? If plants do not get their food from the soil, where do they get it? What is the role of the plant‘s roots in photosynthesis?

Brainstorm What is the role of water in photosynthesis? What other substances do plants need for photosynthesis? What substances do plants produce during photosynthesis?

Introduction What is food for plants? Which of these food molecules is produced through photosynthesis? After plants produce carbohydrate subunits during photosynthesis, they need to store them. What happens to subunits of carbohydrates before they can be stored? How have we tested for starch previously? What color does iodine turn when starch is present? Not present?

Continued Introduction What have you learned that plants also need to carry out photosynthesis? What happens to a plant when you take away water? Light? Based on this, do you expect that plants that are grown in the dark will have starch in them? What about plants that are grown in the light? Why?.

Part I :Starch I have been growing a geranium plant for several days with some of the leaves covered by aluminum foil and some of the leaves uncovered. You will compare the amount of starch you find in the covered and uncovered leaves using the iodine test How does covering the leaves in aluminum foil affect how much light they get? Which of these leaves can carry out photosynthesis?

Expected Results This is Evidence that plants use light energy to make food molecules (glucose). After plants produce glucose, they build it up into starch for storage, which you found evidence of using the iodine test. The production of glucose is one part of the chemical reaction of photosynthesis. Now you are going to investigate if there are other products of this chemical reaction.

Part II: Oxygen Production Can the elodea carry out photosynthesis like the geranium? Is the elodea able to carry out photosynthesis to make its own food now? Observe the elodea. What substance do you think the plants are producing? How could you test your hypothesis? We are going to record the observation of DO for 30 minutes

Summing It Up What have we learned today about photosynthesis? What is our evidence? We have found that plants can produce glucose and oxygen in the light. What has to be happening inside the plants in the light for these two substances to be produced? What are the reactants of photosynthesis? Or said another way, what do plants need to make oxygen and glucose?

Lesson 7.2 How Do I Know That Plants Use Carbon Dioxide

Brainstorm We know the same atoms that we find in the products of photosynthesis are found in the reactants. What are the products of photosynthesis, and what atoms make up these products? We know that the reactants must be made of carbon, hydrogen, and oxygen atoms. What evidence have we collected so far that shows plants use substances with any of these atoms? Compare the types of atoms contained in the products of photosynthesis to the types of atoms in water. What is missing? Where do you think plants get the carbon atoms they need to make carbohydrates?

Gather evidence to determine if plants in the light use carbon dioxide to make food during photosynthesis The probe yields quantitative (numerical) data about the concentration of CO 2 in the air. The plants (elodea) that you are going to work with to get evidence that plants use CO 2 to make food live in the water. A beaker with BTB solution is here. BTB is a qualitative indicator for CO 2. You can tell if CO 2 is present by the color of the BTB solution

Experiment How do you expect the color of the BTB to change if the plant is using CO 2 in the light? Why? How do you expect the color of the BTB to change if the plant is not using CO 2 or is producing it in the light? Why?

Experimental Desing Is this a good setup? Explain. How can you be sure that it is the plant using the CO 2 that is causing the BTB to change color? What will be different about the control and experimental tubes? What will be the same about the control and experimental tubes?

How To Collect Data After this discussion, you should have two identical test tubes—one with the elodea and one without. Both should be filled to the top with yellow BTB (to reduce the amount of air), and you should cover or cork both tubes. If you want to measure a change in color of the BTB solution, when should you record data?

Creating A Data Table “How could you label the columns and rows of the table appropriately so that you can organize the data you will collect?” Label the chart. Make observations about the color of the BTB solution in each tube and record it. Record your predictions about whether plants use carbon dioxide. We will place the tubes under a strong source of light or in the sun. Times may vary for a color change depending on the light source. It may take as little as 15 minutes; you may see a color change by the end of the class; or you may need to make your observations the next day. The BTB solution with the elodea will change back to a blue- green color.

Expected Results

Filling Out Chart

Synthesizing Your Learning Synthesize the evidence relating to the reactants, products, and energy conversions involved in photosynthesis. You now have evidence for the chemical reaction of photosynthesis: CO 2 + H 2 0 → O 2 + C 6 H 12 O 6. Each experiment you did provided you with a piece of this chemical reaction. Now you are going to review all of the evidence you collected so that you can write a complete scientific explanation about how plants make food molecules.

Brainstorm before writing…. What evidence do you have that plants use carbon dioxide in the light to make food molecules? What evidence do you have that plants use water in the light to make food molecules? You will use models to show that water plays a role in photosynthesis in the next activity. What evidence do you have that plants produce oxygen in the light when they make food molecules?

Just a little more….. What evidence do you have that plants produce food molecules in the light? What is your evidence that plants need light energy to carry out photosynthesis? Based on these pieces of evidence, you will write a scientific explanation about photosynthesis. Atoms in carbon dioxide and water rearrange in the cells of plants to form oxygen and glucose. You have gathered evidence that each of these reactants and products are involved in photosynthesis. In the next lesson, you will model this chemical reaction so that you can build a greater understanding of how it happens.

Activity 7.3 What Do Plants Produce in the Light?

Review What type of energy do plants need for this chemical reaction? Why do they need it? What are the reactants? What are the products? What happens to this chemical reaction if there is no light? No reactants? What do we still need more evidence for? Why?

Activity We will use models to determine if CO 2 + H 2 O → O 2 + C 6 H 12 O 6 is the chemical reaction for photosynthesis. Use the gumdrops to make: One Model of Carbon Dioxide and One Model of Water. Arrange the atoms to form the reactants—carbon dioxide and water Do these reactants equal that product listed above?

Scientific Principle Photosynthesis is a chemical reaction that uses energy from the sun and the reactants of carbon dioxide and water to form glucose and oxygen. In a chemical reaction, no atoms can be created or destroyed.

Guiding Questions How many atoms of carbon are in the products? How many are in the reactants? How many molecules of carbon dioxide must you have in the reactants to have the right number of carbons for the products? Explain. NOW make six molecules of carbon dioxide and make six molecules of water. NOW form the products of photosynthesis. Start with glucose

Questions to Answer After Activity How many atoms of hydrogen are in the products? How many are in the reactants? How many molecules of water must you have in the reactants to have the right number of hydrogen for the products? Explain How many molecules of oxygen did you form?” 6 CO H 2 O → 6 O 2 + C 6 H 12 O 6. It is called photosynthesis. (WRITE IN NOTES)

Synthesizing Is water involved in this chemical reaction? How do you know?” What makes photosynthesis a chemical reaction? What is needed for photosynthesis? What is the function of photosynthesis? Why can animals not perform photosynthesis? Describe the chemical reaction of photosynthesis. What is your evidence?

Partner Questions What are the reactants? How many molecules react? What is your evidence? What are the products? How many molecules are produced? What is your evidence? What happens to the atoms in the molecules of the reactants to form the products? Are atoms created or destroyed in this chemical reaction? What is your evidence? Describe what happens to light energy during photosynthesis. What is your evidence?

Partner Questions 2 What is your evidence that plants use light energy? What is your evidence that plants can provide energy in food molecules? Is energy created or destroyed during this energy conversion? Why? Why is photosynthesis important for plants?

Final Thoughts The purpose of photosynthesis is for plants to create the food molecules that they will use for energy and building materials. Plants use the energy in food molecules, not light, to do things. Food molecules provide plants with energy through cellular respiration just like in animals. Why is photosynthesis important for animals, including us?