BIO181 Photosynthesis Worksheet

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Arizona State University *

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Biology

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Dec 6, 2023

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Name: BIO181 Worksheet: Photosynthesis How do light-dependent and light-independent reactions provide food for a plant? ___________________________________________________________________________ READ THIS: Plants are the original solar panels. Through photosynthesis a plant is able to convert electromagnetic (light) energy into chemical energy. This energy is used not only to keep the plant alive, but also to sustain all creatures that rely on the plant for food and shelter. Plants and photosynthetic algae are also the source of all oxygen on Earth, allowing the inhabitants of Earth to benefit from our most plentiful renewable energy resource. ___________________________________________________________________________ Note - This image is provided as a drawing. To edit it, draw on it, add circles or labels to it, double click the image while in Google Docs. Add in what you need to, then hit “Save and Close”. 1. Consider the organelle illustrated in Model 1. a. What is the name of this organelle? 1 chloroplast b. Is this organelle more likely to be found in animal cells or plant cells? 1 Plant cells 2. The structures inside the organelle in Model 1 are called thylakoids. What compound necessary for photosynthesis is contained in the thylakoids?

i chlorophyll 3. Consider the chemical reaction in Model 1. This represents photosynthesis. a. What substances are the reactants in photosynthesis? Include the name and chemical formula of each substance in your answer. 1 Carbon dioxide: CO2 2 Water: H2O b. Where in the organelle are these molecules stored before they are used in photosynthesis? 1 Before they are used in photosynthesis, carbon dioxide and water are not stored within the chloroplasts. Instead are taken up by the plant and transported to the chloroplasts when needed for photosynthesis. c. Is photosynthesis an endergonic or exergonic reaction? Support your answer with evidence from Model 1. 1 Photosynthesis is an endergonic reaction d. What is the energy source for photosynthesis? 1 sunlight 4. Photosynthesis occurs in two parts—the light-dependent reactions and the lightindependent reactions . a. What is another name for the light-independent reactions? 1 Calvin cycle b. In what part of the chloroplast do the light-dependent reactions occur? 1 thylakoid membranes of the chloroplast c. In what part of the chloroplast do the light-independent reactions occur? 1 stroma of the chloroplast 5. Considering your answers to Question 4, what compound is best able to absorb the light energy from the Sun and convert it into chemical energy? i chlorophyll is the compound best able to absorb light energy from the Sun and convert it into chemical energy

6. What substances are produced during photosynthesis? Include the name and chemical formula of each substance in your answer. i Glucose C6H12O6 ii Oxygen O2 7. Why is it necessary to have six CO 2 entering the chloroplast? i balanced equation emphasizes the conservation of mass and atoms Note - This image is provided as a drawing. To edit it, draw on it, add circles or labels to it, double click the image while in Google Docs. Add in what you need to, then hit “Save and Close”. 8. In Model 2, what shape or symbol represents a single electron?

i Small circle 9. In the light-dependent reactions electrons are released from molecules in two ways. a. Find two places in Model 2 where electrons are released from chlorophyll by a photon of light coming from the Sun. 1 Photosynthesis 1 and 2 b. Find one place in Model 2 where electrons are released from water molecules. 1 Inner thylakoid c. When the electrons are released from water molecules, what other products are formed? 1 Oxygen and hydrogen ions READ THIS: The light-dependent reactions of photosynthesis include three major processes: A. Excited electrons leave chlorophyll and reduce NADP + into NADPH. B. Excited electrons moving through the electron transport chain provide the free energy needed to pump hydrogen ions into the inner thylakoid. C. Hydrogen ions flowing out of the thylakoid via a protein channel provide the free energy needed to convert ADP to ATP. ___________________________________________________________________________ 10. In Model 2, label the diagram with “A,” “B,” and “C” to indicate where the three steps in the Read This! box are occurring. i “A" occurs in Photosystem II, "B" occurs in the ETC, and "C" occurs in the ATP synthase 11. The light-dependent reactions include an electron transport chain system that works in a very similar fashion to the electron transport chain in respiration. Briefly describe how this system works and what job it performs in the light- dependent reactions. (Your answer should include a discussion about concentration gradient.) i In the light-dependent reactions of photosynthesis, light energy is absorbed by chlorophyll in the thylakoid membrane, starting the splitting of water into oxygen, protons, and electrons. Then electrons are transferred through an electron transport chain, releasing energy that pumps protons across the thylakoid membrane, creating a

concentration gradient. The resulting proton flow back into the stroma through ATP synthase drives the synthesis of ATP, a crucial energy carrier. This process, known as chemiosmosis, mirrors the role of the electron transport chain in cellular respiration, demonstrating the conversion of light energy into chemical energy through the establishment and utilization of a proton gradient. 12. Refer to Model 2. a. Name the embedded protein complex found in the thylakoid membrane that uses excited electrons to reduce NADP + into NADPH. 1 ferredoxin-NADP+ reductase b. Name the embedded protein complex found in the thylakoid membrane that provides excited electrons to the electron transport chain. 1 photosystem II c. Name the embedded protein complex found in the thylakoid membrane that converts ADP to ATP using free energy from a flow of hydrogen ions. 1 ATP synthase 13. Once a chlorophyll molecule has released electrons it is no longer useful until those electrons are replaced. a. According to Model 2, what is the source of replacement electrons for those released from photosystem I? 1 electrons from Photosystem 2 b. According to Model 2, what is the source of replacement electrons for those released from photosystem II? 1 electrons from the split of water 14. Is carbon dioxide involved in the light-dependent reaction? i no 15. Refer to Model 2. a. Write a chemical reaction that summarizes all of the chemical reactions in the light-dependent reactions of photosynthesis starting with two water molecules.

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