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Study GuideBiology–Photosynthesis1. Photosynthesis DefinedMany living things on Earth—especiallygreen plants—can make their own food. They do this usingvery simple materials likecarbon dioxideandwater. To turn these simple molecules into food, theyneedenergy, and that energy comes fromsunlight. This food-making process is calledphotosynthesis.1.1 How Energy Moves Through a Plant CellPhotosynthesis and energy use in plant cells are closely connected. Here’s the big picture:•Chloroplastscapture light energy from the sun•That energy is used to makeglucose (C₆H₁₂O₆), a sugar that stores energy•Oxygen (O₂)is released as a waste product•The glucose and oxygen are then used in themitochondria•In the mitochondria, energy is released and used to makeATPfrom ADP and phosphate•Carbon dioxide (CO₂)andwaterare released and reused in photosynthesisThis creates a continuous cycle of energy use and recycling inside the cell.

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Study Guide1.2 What Is Photosynthesis?Photosynthesisis the process by which organisms use light energy to make carbohydrates, such asglucose. It allows plants to store energy in a form they can use later.Photosynthesis happens intwo main stages, each with a specific role.Stage 1: Capturing Light EnergyIn the first stage, light energy excitesenergy-rich electrons. These electrons move through a seriesofcoenzymes and other molecules.As this happens:•The energy from the electrons istrapped•ATPis produced•NADPH(nicotinamide adenine dinucleotide phosphate hydrogen) is formedBoth ATP and NADPH store energy and act as energy carriers for the next stage.

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Study GuideStage 2: Making CarbohydratesIn the second stage, the energy stored inATP and NADPHis used to combinecarbon dioxidemolecules.Thisprocess:•Buildscarbohydrates•Produces organic molecules such asglucose•Stores energy in chemical bonds that the plant can use later2. Quiz Photosynthesis1. QuestionFill in the blank:Which of the following statements about photosynthesis isFALSE?Answer Choices•Carbon dioxide molecules are bound into carbohydrates during the second half of theprocess.•It is a catabolic process that releases the energy stored in glucosemolecules.•Oxygen is released as a waste product.Correct AnswerIt is a catabolic process that releases the energy stored in glucose molecules.Why This Is CorrectPhotosynthesis is ananabolic process, not a catabolic one. Ituses energy (from sunlight)to buildglucose molecules from carbon dioxide and water.The other statements are true:

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Study Guide•Carbon dioxide is fixed into carbohydrates during the Calvin cycle (the second half ofphotosynthesis).•Oxygen is released as a waste product during the light-dependent reactions when water issplit.2.QuestionFill in the blank:How does photosynthesis occur?Answer Choices•Glucose is broken down into carbon dioxide using theenergy of the sun.•The products of the light reaction are used to create glucose from carbon dioxide.•The sunlight directly powers ATP synthase, which catalyzes the creation of glucose.Correct AnswerThe products of the light reaction are used to create glucose from carbon dioxide.Why This Is CorrectPhotosynthesis occurs intwo main stages:1.Thelight reactions, which capture energy from sunlight and produce energy-rich molecules(ATP andNADPH).2.TheCalvin cycle, which uses those products tobuild glucose from carbon dioxide.The other options are incorrect because:•Glucose breakdown happens duringcellular respiration, not photosynthesis.•Sunlight doesnot directly createglucose; it first powers the light reactions, which thensupport glucose production.

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Study Guide3. ChloroplastPhotosynthesis takes place inside a special cell structure called thechloroplast. Chloroplasts arefound in theleavesandgreen stemsof plants—anywhere the plant can capture sunlight.3.1What Is a Chloroplast Like Inside?Chloroplasts are relativelylarge organelleswith a detailed internal structure designed forphotosynthesis.Inside each chloroplast is a watery, protein-rich fluid called thestroma. The stroma is where somephotosynthetic reactions take place and where important enzymes are found.3.2Grana and Thylakoids: The Energy CentersFloating in the stroma are many small membrane structures that look likestacks of coins.•Each stack is called agranum•The plural form isgrana•Each “coin” in the stack is athylakoidThethylakoid membranesare especially important. Many of the key reactions of photosynthesisoccur right in these membranes, where light energy is captured and converted into chemical energy.3.3A Helpful ComparisonThylakoids in chloroplasts are similar in function to thecristaefound in mitochondria. In bothorganelles, folded membranes increase surface area and make energy-related reactions moreefficient.4. Quiz Chloroplast1. QuestionFill in the blank:Which of the following statements about the chloroplast isFALSE?

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