Chapter 3.3 Photosynthesis

How Do Cells Capture Energy?

How Do Animals Capture Energy?

How Do Animals Capture Energy?

How Do Plants Capture Energy?

SUNLIGHT is the ultimate source of energy in the biosphere Nearly ALL living things obtain energy directly or indirectly from sunlight captured by plants

Food Chains Show the Flow of Energy

Energy Pyramids Show the Amount of Energy at Each Feeding Level 2nd Level Consumer 1st Level Consumer Producer

Energy is Stored in Food Autotrophs make their own food Heterotrophs eat others to get food HETEROTROPH HETEROTROPH AUTOTROPH

How do AUTOTROPHS make their food? Photosynthesis

Photosynthesis Happens in Chloroplasts

Photosynthesis Has TWO Stages PHOTO = Capturing light energy SYNTHESIS = Using the energy to make sugar PHOTO SYNTHESIS

Capturing Sun’s Light Energy Chlorophyll pigments in the thylakoids capture energy. Energy splits water and O2 is released. Hydrogen carries energy to the stroma. PHOTO

Using Energy to Make Food Energy from the 1st “photo” reaction is used to make sugar in the stroma. Hydrogen (H) combines with Carbon dioxide (CO2) to form SUGAR C6H12O6 SYNTHESIS

How does a plant get water and carbon dioxide?

Leaves Have Stomata for Gas Exchange

Your Turn: Look at the Stomata on Leaves Location: Underside of leaf

Photosynthesis Equation Sunlight + Come up with an image of your own (or use mine) that helps you remember the products and reactants of photosynthesis. Draw and label your image.

What environmental factors could influence the rate of photosynthesis? In other words…. What affects how quickly a plant grows? Light Energy

What happens to the sugar plants make? Brainstorm your ideas…

What happens to the sugar plants make? 3 Important Uses: Mitochondria break glucose down for ATP energy. ATP energy runs cellular activity. (in plants) 2. Plants store sugar for later use. Sugar is stored as starch in roots and in seeds. 3. Animals eat plants and use the sugar and starch as their food (source of energy). (Mitochondria again)

Review What are the reactants and products of photosynthesis? Student Misconceptions and Concerns 1. Students often do not fully understand how the burning of fossil fuels contributes to global warming. They might wonder, “How does the burning of fossil fuels differ from the burning of ethanol produced from crops?” Students might not realize that the carbon in fossil fuels was removed from the atmosphere hundreds of millions of years ago, while the carbon in crops was removed much more recently, when the crops were grown. The use of ethanol as an alternative is complicated by the typical reliance upon fossil fuels for ethanol production. 2. Some students do not realize that plant cells also have mitochondria. Instead, they assume that the chloroplasts are sufficient for the plant cell’s needs. But nearly 50% of the carbohydrates produced by plant cells are used for cellular respiration (involving mitochondria). 3. Students may not connect the growth in plant mass to the fixation of carbon during the Calvin cycle. It can be difficult for many students to appreciate that molecules in air can contribute significantly to the mass of plants. 4. Students may understand the overall chemical relationships between photosynthesis and cellular respiration, but many struggle to understand the use of carbon dioxide in the Calvin cycle. Photosynthesis is much more than gas exchange. 5. Students who have not read all of Chapter 7 may not realize that glucose is not the direct product of photosynthesis. Although glucose is shown as a product of photosynthesis, a three-carbon sugar is directly produced (G3P). A plant can use G3P to make many types of organic molecules, including glucose. (The authors address the production of G3P under the section “The Calvin Cycle” later in this chapter.) Teaching Tips 1. When introducing the diverse ways that plants impact our lives, consider challenging your students to come up with a list of products made from plants that they encounter regularly. Perhaps you might only list those encountered in a single day of college life. The list can be surprising and help to build up your “catalog of examples.” 2. The living world contains many examples of adaptations to increase surface area. Some examples are the many folds of the inner mitochondrial membrane, the highly branched surfaces of fish gills and human lungs, and the highly branched system of capillaries in the tissues of our bodies. Consider relating this broad principle seen elsewhere to the extensive folding of the thylakoid membranes. 3. In our world, energy is frequently converted to a usable form in one place and used in another. For example, electricity is generated by power plants, transferred to our homes, and used to run computers, create light, and help us prepare foods. Consider relating this common energy transfer to the two-stage process of photosynthesis. 4. You might wish to discuss the evolution of chloroplasts from photosynthetic prokaryotes if you will not address this subject elsewhere in your course. 5. Figure 7.3 is an important visual organizer that notes the key structures and functions of the two stages of photosynthesis. This figure reminds students where water and sunlight are used in the thylakoid membranes to generate oxygen, ATP, and NADPH. The second step, in the stroma, reveals the use of carbon dioxide, ATP, and NADPH to generate carbohydrates. 6. The thylakoid space and the intermembrane space of a mitochondrion have analogous roles. Students might be encouraged to create a list of the similarities in structure and function of mitochondria and chloroplasts through these related chapters. 22