Environmental Literacy Project Michigan State University Plants Lesson 2, Activity 2: Using Molecular Models to Explain Photosynthesis Answering the Three Questions for plants in the light
The Movement Question Where are atoms moving from? Where are atoms moving to?
Which atoms and molecules move so that plants can do photosynthesis? water carbon dioxide oxygen glucose
How do glucose water, carbon dioxide and oxygen move for a plant leaf to photosynthesize? water carbon dioxide oxygen glucose
Plants make glucose from carbon dioxide and water in their leaves.
What happens inside the leaf cell as it photosynthesizes? Chemical change
What is Photosynthesis? Photosynthesis is the secret of plant growth. Plants do photosynthesis so they can grow (gain biomass).
The Carbon Question: What is happening to carbon atoms? What molecules are carbon atoms in before photosynthesis? How are the atoms rearranged into new molecules during photosynthesis? The Energy Question: What is happening to energy? What forms of energy are involved in photosynthesis? How is energy changing from one form to another during photosynthesis?
Photosynthesis happens when light energy from the sun, carbon dioxide, and water are used to make sugar and oxygen. (the sugar is then used to build the plant s mass; the O 2 is released as waste)
Using your poster and modeling kits, make a model of how matter and energy are transformed during photosynthesis.
Rules of Molecular Bonding Reminder: Atoms in stable molecules always have a certain number of bonds to other atoms: Carbon: 4 bonds Oxygen: 2 bonds Hydrogen: 1 bond This means that if you have a carbon atom, for example, all 4 of its prongs should be attached to other atoms. There should not be empty prongs. Oxygen atoms do NOT bond to other oxygen atoms if they can bond to carbon or hydrogen instead.
Making the Reactant Molecules: Carbon Dioxide and Water Photosynthesis occurs when plants combine carbon dioxide (CO 2 ) and water (H 2 O) to produce glucose (C 6 H 12 O 6 ) and oxygen (O 2 ). Show how this can happen: 1. Get the atoms you will need to make your molecules. Can you figure out from the formula for sugar how many C, H, and O atoms you will need? a. You will need 6 carbon atoms to make one sugar molecule. How many CO 2 molecules will you need to make for the reactants? b. You will need 12 hydrogen atoms to make one sugar molecule. How many H 2 O molecules will you need to make for the reactants? 2. Use the bonds to make models of carbon dioxide (CO 2 ) and water (H 2 O). Remember that CO 2 has double bonds. 3. There are no high-energy bonds (C-C and C-H) in carbon dioxide or water. Add 12 twist ties to the reactant side of your poster to represent light energy. Add a light energy card. 4. Compare your molecules to the pictures on the next slide. Are they the same?
Photo of reactant molecules: CO 2 (carbon dioxide) and H 2 O (water) Start by making the molecules of the reactants and energy units of light. Put them on the reactants side, then rearrange the atoms and energy units to show the products. Carbon dioxide Water Chemical change Reactants Products Remember: Atoms last forever (so you can rearrange atoms into new molecules, but can t add or subtract atoms). Energy lasts forever (so you can change forms of energy, but energy units can t appear or go away). 13
When you re done, what will it look like? Arrange your atoms so that the water and carbon dioxide are transformed to glucose and oxygen.
Making the Product Molecules: Glucose and Oxygen Photosynthesis occurs when carbon dioxide (CO 2 ) and water (H 2 O) react to produce glucose (C 6 H 12 O 6 ) and oxygen (O 2 ). Show how this can happen: 1. Break the bonds in the reactant molecules and recombine the atoms into sugar (C 6 H 12 O 6 ) and oxygen (O 2 ). How many oxygen molecules can you make? 2. Identify the high-energy bonds (C-C and C-H) by putting twist ties on them. How many high energy bonds does a molecule of sugar have? Where does the energy for those bonds come from? 3. Compare your molecules to the pictures on the next slide. Are they the same?
Photo of product molecules: H 6 C 12 O 6 (sugar) and O 2 (oxygen) Start by making the molecules and energy units of the reactants and putting them on the reactants side, then rearrange the atoms and energy units to show the products.. Glucose Chemical change Oxygen Reactants Products Remember: Atoms last forever (so you can rearrange atoms into new molecules, but can t add or subtract atoms). Energy lasts forever (so you can change forms of energy, but energy units can t appear or go away). 16
Comparing photos of reactant and product molecules Compare the atoms and energy units on the reactant and products sides.. Glucose Carbon dioxide Water Chemical change Oxygen Reactants Products Remember: Atoms last forever (so you can rearrange atoms into new molecules, but can t add or subtract atoms). Energy lasts forever (so you can change forms of energy, but energy units can t appear or go away). 17
What happens to atoms and energy in photosynthesis? Carbon Dioxide Chemical change Glucose Reactants Water Products Light energy Oxygen 18
What happens to carbon atoms in photosynthesis? Carbon Dioxide Chemical change Glucose Reactants Water Products Light energy Carbon atoms in carbon dioxide become part of glucose molecules. Oxygen 19
What happens to oxygen and hydrogen atoms in photosynthesis? Carbon Dioxide Chemical change Glucose Reactants Water Products Light energy Oxygen and hydrogen atoms become part of glucose and oxygen gas molecules. Oxygen 20
What happens to light energy in photosynthesis? Carbon Dioxide Chemical change Glucose Reactants Water Products Light energy Light energy is transformed into chemical energy. Oxygen 21
What happens to atoms and energy in photosynthesis? Carbon Dioxide Chemical change Glucose Reactants Water Products Light energy Atoms last forever! Energy lasts forever! Oxygen 22
Writing a Chemical Equation Writing in symbols: Chemists use an arrow to show how reactants change into products: [reactant molecule formulas] [product molecule formulas] Saying in words: Chemists read the arrow as yield or yields : [reactant molecule names] yield(s) [product molecule names] Equations must be balanced: Atoms last forever, so reactant and product molecules must have the same number of each kind of atom. Try it: can you write a balanced chemical equation to show the chemical change for photosynthesis?
Chemical Equation for Photosynthesis 6H 2 O + 6CO 2 C 6 H 12 O 6 + 6O 2 (in words: water and carbon dioxide yield glucose and oxygen) 24
How can we answer the Carbon Question and the Energy Questions now? The Carbon Question: What is happening to carbon atoms? What molecules are carbon atoms in before photosynthesis? How are the atoms rearranged into new molecules during photosynthesis? The Energy Question: What is happening to chemical energy? What forms of energy are involved in photosynthesis? How is energy changing from one form to another during photosynthesis?
The Carbon and Energy Questions Carbon: carbon atoms move from CO 2 molecules in the air (inorganic) to C 6 H 12 O 6 molecules in the plant (organic). Energy: energy is transformed from light energy into chemical energy in the highenergy (C-C and C-H) bonds of the glucose molecule.
The Three Questions for plants in the light Where are atoms moving from? Where are atoms moving to? What molecules are carbon atoms in before the change? What other molecules are involved? Chemical change What molecules are carbon atoms in after the change? What other molecules are produced? What forms of energy are in the reactants? What forms of energy are in the products? Remember: Atoms last forever and Energy lasts forever 27