Photosynthesis Essential Questions: How does the process of photosynthesis store energy? What are the steps of Photosynthesis? Why is photosynthesis important for life on Earth?

Recap: Where does our energy come from? We know that the source of all energy comes from the SUN! Since we can’t eat sunshine to get our energy, we must rely on plants via a process called photosynthesis. We can obtain their energy by directly eating the plant. Or we can get energy indirectly by eating other animals who got their energy from eating plants. It will be important to stress to the student’s that while all the energy the earth has is obtained from the sun, plants play a vital role in capturing that energy and transferring the energy to other forms of life. Stating that, “we can’t eat sunshine” is silly and obvious, but will also remind student of our great dependency on the role of plants to trap the sun’s energy for us. Is photosynthesis exothermic or endothermic? Endothermic: Stores Energy!

Photosynthesis Overview Photo = light Synthesis = putting together Photosynthesis is the process that plants use to trap the sun’s energy and build carbohydrates (called glucose) that store energy Happens in 2 phases: 1) The Light (light-dependent) reaction creates ATP, releases Oxygen. 2) The Dark (light-independent) reaction uses those ATP molecules (from the light reaction) to make glucose.

Overview of Photosynthesis Products Reactants In which organ does photosynthesis take place? Root, Stem, Leaf, Flower or Fruit? The LEAF!

Where does photosynthesis occur? The top of the leaf is where photosynthesis occurs. The Chloroplast is the cell organelle where photosynthesis occurs. In the chloroplasts are pigments that absorb wavelengths of light.

Where are the chloroplasts? Thinking about where a chloroplast lives is like giving directions to where you live in your hometown. The Chloroplast You Leaf State Mesophyll Cell County Chloroplast City Granum Neighborhood Thylakoid House on Street Students should understand that while chloroplasts are in the leaf, they are much smaller and are packaged a certain way. While the actual structures names are present, the teacher should stress the organization and intricate design of the leaf. By comparing the location of the chloroplast in the leaf to the location of a person in their home, this helps students to realize some form of the scale involved and some of the complexity to the organization of the leaf. This slide should help break the misconception that leafs are just randomly stuffed with green vesicles.

Sunlight is made up of ALL the colors together. Pigments reflect the color of light that we see. They absorb the other colors. Look at the graph, right. Where is absorption the lowest? Where is it the highest? Chlorophyll (a and b) absorb all colors except green so it is reflected! Eye – http://www.thirdeyehealth.com/images/clear-eye.jpg Sunlight is made up of ALL the colors together. Pigment molecules reflect the color of light that we see. They absorb the other colors. That means that chlorophyll, which appears green, reflects green light and absorbs the other wavelengths of light. That means chlorophyll absorbs a lot more light than it reflects, which is a good thing!

Why do leaves change color in the fall? Remember- chlorophyll is the pigment that captures sunlight and what gives plants their green color. In order for chlorophyll to be produced, sunlight is needed. Year round, many different color pigments are present, but the green from the chlorophyll prevents those colors from showing through. In Fall, trees reabsorb chlorophyll leaving the other pigments visible! A common question students have is why the leaves change color in the fall. Tying color change into this lecture will help students make a connection between color change and photosynthesis. The website for the video is http://www.cnr.vt.edu/dendro/dendrology/leaf.swf CLICK HERE TO WATCH A TIME-LAPSE OF A LEAF CHANGING COLOR!

Light-Dependent Reactions 1:2 1st stage of photosynthesis requires light. (Light dependent) Light energizes electrons and are passed from the chlorophyll to the electron transport chain. The Electrons come from splitting molecules of water. This process is called photolysis: Each water molecule supplies… ½ molecule of Oxygen gas 2 Hydrogen ions 2 Electrons ETC = series of proteins embedded in the thylakoid membrane of the chloroplast. As the electron passes on the chain between chlorophyll molecules, it loses a bit of energy at each protein. I’m free to leave out of the stomata!

Light-Dependent Reactions 2:2 After the electron has passed through the first chain, it enters a second electron chain so any e- (light) energy isn’t wasted. A carrier molecule called NADP+ is used (when with an electron it binds with a Hydrogen ion and becomes NADPH.) Binds to the electron and stores the energy from the electron in a chemical form. NADPH plays a role in the formation of Carbohydrates. Summary: Converts ADP and NADP+ into ATP and NADPH with Oxygen gas. Haha! What am I?

What happens to plants when there is no sunlight? Chlorophyll is “turned off.” Plants produce lots of glucose--enough to last them through the night and several cloudy days. However, plants cannot store excess glucose. Instead, plants convert the excess glucose to starch. Starches are long term energy storage molecules and make the cellular components of plants. like cellulose for their cell walls! When they need glucose for energy they convert the starch back to glucose. Since students have just been taught that photosynthesis occurs in sunlight, they will automatically wonder what happens when there is no sunlight. While chlorophyll is never really “turned off,” this is a simple way for students realize that the plant must have to do something else since it can no longer make use of chloroplasts. While it’s not extremely important that students remember the term “starch,” this will help students with the concept that glucose is something that can be changed into different forms and reconsituted again by simple transformations.

Light-Independent Reactions Does not need light! (Also called the “Dark Reaction.”) Called the Calvin Cycle. Uses CO2 to form 6 Carbon Sugars. (Carbohydrates) Takes place in the stroma of the chloroplast. Called a Cycle because the end products can be used again to initiate the process. Uses the NADPH and ATP produced in the earlier light reactions. Otherwise the dark reaction could not occur!

http://www.tracy.k12.ca.us/thsadvbio/animations/Photosynthesis.swf Calvin Cycle The Calvin cycle uses the ATP and NADPH from the light dependent reaction to create sugar. Reactant: Carbon Dioxide Product: a 6 Carbon Sugar Calvin’s in the Dark about Photosynthesis!

What’s the big deal about Photosynthesis? The Calvin Cycle removes Carbon Dioxide from the Earth’s atmosphere and creates sugars. Plants can use those sugars for food or to make larger molecules like cellulose for growth and development. When we eat plants (or herbivores) eat plants, we use the energy stored in the carbohydrates. A byproduct of our breathing is Carbon Dioxide, which is used by plants for photosynthesis. It is also a greenhouse gas contributing to global warming. Without plants to harvest the sun’s energy, there would be no life for animals on Earth! Photosynthesis Song! http://www.youtube.com/watch?v=R_17euLU_EM&feature=related

So, back to the original question…. CLICK HERE TO WATCH THEM GROW! So, back to the original question…. Where does the mass of a tree come from? Revisit your original thought… Were you right? Are you surprised by the answer? Another misconception that students often have is the misconception that plants get most of their mass from the soil that they are planted in. You will probably need to point out to students that carbon dioxide is what makes up the bulk of a plant’s mass. You may then want to mention that carbon dioxide is used by the plant for so many things (its structure, energy, biosynthesis). Seeing that carbon dioxide is present in so many of the plant’s functions may help students understand why carbon dioxide makes up the bulk of a plant’s mass. The website for the video is http://www.youtube.com/watch?v=3nRVZPJdXOo Answer: The Mass of a tree comes from the Carbon from atmospheric CO2 taken in during photosynthesis! Gets converted into cellulose!

Activity: Photosynthesis Exit Ticket Complete the exit ticket so I can assess your understanding of Photosynthesis. Make sure to write down further questions you have! Turn it into the box before you leave class today!