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Mariela Hilario
12/7/2025
AP Biology
AP Bio:Eellular Energetics~unit 3 review
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Dec 7, 2025
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AP Biology Unit 3: Cellular Energetics Review
Mariela Hilario
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Photosynthesis: Capturing Energy from Light
Organisms are divided into autotrophs (producers that make their own food) and heterotrophs (consumers that get energy by eating other organisms). Photosynthesis is an endergonic process requiring energy input, transforming light energy into chemical energy stored in glucose.
Photosynthesis takes place in chloroplasts containing the green pigment chlorophyll, which absorbs light energy. These chloroplasts are found in the mesophyll tissue of leaves, with stomata (pores) allowing CO₂ to enter and O₂ to exit during the process.
The process has two main stages. Light reactions occur in the thylakoid membrane where light energy is captured by photosystems I and II. Water is split, releasing oxygen, and energy is transferred through electron transport chains to produce ATP and NADPH. The Calvin cycle uses these energy carriers in the stroma to incorporate CO₂ into sugar molecules called G3P, requiring 9 ATP and 6 NADPH for each complete cycle.
Try This! Draw a simple diagram connecting the light reactions to the Calvin cycle, showing how ATP and NADPH move between them. This visual connection will help you understand how these processes work together.
Cellular Respiration: Releasing Energy from Food
Cellular respiration is the exergonic process that breaks down glucose to release stored energy for cellular work. The equation C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP shows how oxygen helps extract maximum energy from sugar.
The process begins with glycolysis in the cell's cytosol, which splits glucose into two pyruvate molecules while generating 2 ATP and 2 NADH. The pyruvate molecules then enter mitochondria where they're converted to acetyl-CoA through a process that releases CO₂ and creates 2 more NADH.
Next, the citric acid cycle (Krebs cycle) in the mitochondrial matrix completely breaks down the carbons from acetyl-CoA into CO₂, producing more electron carriers (NADH and FADH₂). Finally, oxidative phosphorylation uses these electron carriers in the inner mitochondrial membrane. The electron transport chain pumps H⁺ ions across the membrane, creating a gradient that drives ATP production through ATP synthase, generating 30-36 ATP molecules.
Remember this! Aerobic respiration (with oxygen) produces up to 38 ATP total, while anaerobic respiration (without oxygen) produces only 2 ATP through fermentation processes like those that create alcohol or lactic acid.
Enzymes and Energy Concepts
All metabolic reactions can be categorized as either anabolic (building larger molecules from smaller ones using energy) or catabolic (breaking down larger molecules to release energy). Similarly, reactions are either exergonic (releasing energy) or endergonic (requiring energy input).
Enzymes are specialized proteins that dramatically speed up biochemical reactions by lowering the activation energy needed to start them. Each enzyme has a specific active site where the substrate fits like a lock and key. Enzymes can be affected by temperature, pH, and chemicals that alter their shape, potentially causing denaturation.
Enzyme activity can be regulated through allosteric regulation when molecules bind to locations other than the active site. Activators like cofactors (minerals) and coenzymes (vitamins) increase enzyme activity, while inhibitors decrease it. Feedback inhibition occurs when the product of a reaction stops the enzyme from making more product.
Make connections! Plants have evolved different photosynthetic adaptations: C3 plants perform normal photosynthesis, C4 plants separate processes spatially within the plant, and CAM plants separate processes temporally (at different times) to conserve resources in harsh environments.
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I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
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Brad T
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Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
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Greenlight Bonnie
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I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
Aubrey
iOS user
Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
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This app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
Thomas R
iOS user
Knowunity is the BEST app I’ve used in a minute. This is not an ai review or anything this is genuinely coming from a 7th grade student (I know 2011 im young) but dude this app is a 10/10 i have maintained a 3.8 gpa and have plenty of time for gaming. I love it and my mom is just happy I got good grades
Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
Aubrey
iOS user
Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
Paul T
iOS user
AP Biology Unit 3: Cellular Energetics Review
Mariela Hilario
@marielahilario_pkkw
AP Biology Unit 3 covers the essential energy processes that power life - photosynthesis and cellular respiration. These biochemical pathways explain how organisms capture, store, and use energy through complex molecular transformations that happen inside cells.
Photosynthesis: Capturing Energy from Light
Organisms are divided into autotrophs (producers that make their own food) and heterotrophs (consumers that get energy by eating other organisms). Photosynthesis is an endergonic process requiring energy input, transforming light energy into chemical energy stored in glucose.
Photosynthesis takes place in chloroplasts containing the green pigment chlorophyll, which absorbs light energy. These chloroplasts are found in the mesophyll tissue of leaves, with stomata (pores) allowing CO₂ to enter and O₂ to exit during the process.
The process has two main stages. Light reactions occur in the thylakoid membrane where light energy is captured by photosystems I and II. Water is split, releasing oxygen, and energy is transferred through electron transport chains to produce ATP and NADPH. The Calvin cycle uses these energy carriers in the stroma to incorporate CO₂ into sugar molecules called G3P, requiring 9 ATP and 6 NADPH for each complete cycle.
Try This! Draw a simple diagram connecting the light reactions to the Calvin cycle, showing how ATP and NADPH move between them. This visual connection will help you understand how these processes work together.
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Cellular Respiration: Releasing Energy from Food
Cellular respiration is the exergonic process that breaks down glucose to release stored energy for cellular work. The equation C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP shows how oxygen helps extract maximum energy from sugar.
The process begins with glycolysis in the cell's cytosol, which splits glucose into two pyruvate molecules while generating 2 ATP and 2 NADH. The pyruvate molecules then enter mitochondria where they're converted to acetyl-CoA through a process that releases CO₂ and creates 2 more NADH.
Next, the citric acid cycle (Krebs cycle) in the mitochondrial matrix completely breaks down the carbons from acetyl-CoA into CO₂, producing more electron carriers (NADH and FADH₂). Finally, oxidative phosphorylation uses these electron carriers in the inner mitochondrial membrane. The electron transport chain pumps H⁺ ions across the membrane, creating a gradient that drives ATP production through ATP synthase, generating 30-36 ATP molecules.
Remember this! Aerobic respiration (with oxygen) produces up to 38 ATP total, while anaerobic respiration (without oxygen) produces only 2 ATP through fermentation processes like those that create alcohol or lactic acid.
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Enzymes and Energy Concepts
All metabolic reactions can be categorized as either anabolic (building larger molecules from smaller ones using energy) or catabolic (breaking down larger molecules to release energy). Similarly, reactions are either exergonic (releasing energy) or endergonic (requiring energy input).
Enzymes are specialized proteins that dramatically speed up biochemical reactions by lowering the activation energy needed to start them. Each enzyme has a specific active site where the substrate fits like a lock and key. Enzymes can be affected by temperature, pH, and chemicals that alter their shape, potentially causing denaturation.
Enzyme activity can be regulated through allosteric regulation when molecules bind to locations other than the active site. Activators like cofactors (minerals) and coenzymes (vitamins) increase enzyme activity, while inhibitors decrease it. Feedback inhibition occurs when the product of a reaction stops the enzyme from making more product.
Make connections! Plants have evolved different photosynthetic adaptations: C3 plants perform normal photosynthesis, C4 plants separate processes spatially within the plant, and CAM plants separate processes temporally (at different times) to conserve resources in harsh environments.
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What is the Knowunity AI companion?
Our AI companion is specifically built for the needs of students. Based on the millions of content pieces we have on the platform we can provide truly meaningful and relevant answers to students. But its not only about answers, the companion is even more about guiding students through their daily learning challenges, with personalised study plans, quizzes or content pieces in the chat and 100% personalisation based on the students skills and developments.
Where can I download the Knowunity app?
You can download the app in the Google Play Store and in the Apple App Store.
Is Knowunity really free of charge?
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The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
Thomas R
iOS user
Knowunity is the BEST app I’ve used in a minute. This is not an ai review or anything this is genuinely coming from a 7th grade student (I know 2011 im young) but dude this app is a 10/10 i have maintained a 3.8 gpa and have plenty of time for gaming. I love it and my mom is just happy I got good grades
Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
Aubrey
iOS user
Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
Thomas R
iOS user
Knowunity is the BEST app I’ve used in a minute. This is not an ai review or anything this is genuinely coming from a 7th grade student (I know 2011 im young) but dude this app is a 10/10 i have maintained a 3.8 gpa and have plenty of time for gaming. I love it and my mom is just happy I got good grades
Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
Aubrey
iOS user
Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
Paul T
iOS user