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Yujun Ge
12/13/2025
Biology
Passive Transport
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Dec 13, 2025
•
Understanding Passive Transport in Cell Biology
Yujun Ge
@yujunge_jflh
1 / 4
Understanding Passive Transport
Passive transport is the movement of substances across cell membranes without using energy. It all starts with solutions - a mixture of a solute (the dissolved substance like sugar or salt) and a solvent (the substance doing the dissolving, often water).
Diffusion happens when molecules naturally move from areas of high concentration to areas of low concentration. A special type of diffusion called osmosis focuses specifically on water molecules moving across cell membranes. These movements follow the concentration gradient - basically the difference in solute concentration from one area to another.
When molecules are evenly distributed throughout a space, we call this equilibrium. Though molecules are still moving, there's no net change in their distribution. In a hypotonic solution, there's a higher concentration of solute inside the cell than outside, causing water to flow into the cell until balance is reached.
💡 Think of concentration like a crowd at a concert. Diffusion is like people naturally spreading out from a packed area to less crowded spaces without being told to move.
Cell Responses to Different Solutions
When a cell is placed in a hypertonic solution (where there's more solute outside than inside the cell), water rushes out of the cell seeking equilibrium. This can dramatically affect how cells function and maintain their shape.
For plant cells, water pressure against the cell wall creates turgor pressure, which helps plants stay upright and rigid. When plants lose too much water in hypertonic environments, plasmolysis occurs - the cell membrane shrinks away from the cell wall, resulting in a wilted, flaccid cell.
Animal cells react differently to water imbalances. In hypotonic environments (more water outside than inside), excessive water enters the cell, potentially causing cytolysis - where the cell swells and may burst from the pressure.
🔑 Remember this: Plant cells have walls for protection against bursting, while animal cells don't, making them more vulnerable to water pressure changes.
Balancing Acts: Isotonic Solutions and Facilitated Diffusion
In an isotonic solution, the concentration of solutes inside and outside the cell is equal. Water still moves in both directions across the membrane, but there's no net change in cell volume - perfect balance is maintained.
Not all molecules can easily cross cell membranes on their own. Facilitated diffusion solves this problem by using special protein channels in the membrane to help larger or charged molecules pass through. Unlike active transport, this still requires no energy because molecules move down their concentration gradient.
The difference between simple diffusion and facilitated diffusion is like comparing walking through an open field versus using a bridge to cross a river - the bridge (protein channel) makes crossing possible without requiring extra energy.
🧪 Science in action: In lab experiments, we can observe diffusion using indicators like Benedict's solution (turns red in the presence of glucose) and iodine (turns black when it contacts starch).
Observing Diffusion in Action
Lab demonstrations bring diffusion concepts to life. In a typical experiment, we might place glucose and starch inside a semipermeable bag (representing a cell) and immerse it in a solution containing water and iodine.
The results tell us what can and cannot pass through the membrane. When the bag turns black, it shows that iodine molecules moved from outside to inside and reacted with starch. Since the outside solution doesn't turn black, we know starch molecules are too large to pass through the membrane.
When Benedict's solution turns red after testing the outside solution, it confirms that glucose molecules moved from inside the bag to the outside environment, demonstrating selective permeability of the membrane.
🔬 Visual indicators make invisible molecular movements visible! This is how scientists can "see" processes happening at the microscopic level.
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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
Understanding Passive Transport in Cell Biology
Yujun Ge
@yujunge_jflh
Dive into the world of cellular transport where we explore how molecules move in and out of cells. Understanding passive transport is key to grasping how cells maintain balance and exchange materials with their environment without using energy.
Understanding Passive Transport
Passive transport is the movement of substances across cell membranes without using energy. It all starts with solutions - a mixture of a solute (the dissolved substance like sugar or salt) and a solvent (the substance doing the dissolving, often water).
Diffusion happens when molecules naturally move from areas of high concentration to areas of low concentration. A special type of diffusion called osmosis focuses specifically on water molecules moving across cell membranes. These movements follow the concentration gradient - basically the difference in solute concentration from one area to another.
When molecules are evenly distributed throughout a space, we call this equilibrium. Though molecules are still moving, there's no net change in their distribution. In a hypotonic solution, there's a higher concentration of solute inside the cell than outside, causing water to flow into the cell until balance is reached.
💡 Think of concentration like a crowd at a concert. Diffusion is like people naturally spreading out from a packed area to less crowded spaces without being told to move.
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Cell Responses to Different Solutions
When a cell is placed in a hypertonic solution (where there's more solute outside than inside the cell), water rushes out of the cell seeking equilibrium. This can dramatically affect how cells function and maintain their shape.
For plant cells, water pressure against the cell wall creates turgor pressure, which helps plants stay upright and rigid. When plants lose too much water in hypertonic environments, plasmolysis occurs - the cell membrane shrinks away from the cell wall, resulting in a wilted, flaccid cell.
Animal cells react differently to water imbalances. In hypotonic environments (more water outside than inside), excessive water enters the cell, potentially causing cytolysis - where the cell swells and may burst from the pressure.
🔑 Remember this: Plant cells have walls for protection against bursting, while animal cells don't, making them more vulnerable to water pressure changes.
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Balancing Acts: Isotonic Solutions and Facilitated Diffusion
In an isotonic solution, the concentration of solutes inside and outside the cell is equal. Water still moves in both directions across the membrane, but there's no net change in cell volume - perfect balance is maintained.
Not all molecules can easily cross cell membranes on their own. Facilitated diffusion solves this problem by using special protein channels in the membrane to help larger or charged molecules pass through. Unlike active transport, this still requires no energy because molecules move down their concentration gradient.
The difference between simple diffusion and facilitated diffusion is like comparing walking through an open field versus using a bridge to cross a river - the bridge (protein channel) makes crossing possible without requiring extra energy.
🧪 Science in action: In lab experiments, we can observe diffusion using indicators like Benedict's solution (turns red in the presence of glucose) and iodine (turns black when it contacts starch).
Sign up to see the contentIt's free!
Access to all documents
Improve your grades
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By signing up you accept Terms of Service and Privacy Policy
Observing Diffusion in Action
Lab demonstrations bring diffusion concepts to life. In a typical experiment, we might place glucose and starch inside a semipermeable bag (representing a cell) and immerse it in a solution containing water and iodine.
The results tell us what can and cannot pass through the membrane. When the bag turns black, it shows that iodine molecules moved from outside to inside and reacted with starch. Since the outside solution doesn't turn black, we know starch molecules are too large to pass through the membrane.
When Benedict's solution turns red after testing the outside solution, it confirms that glucose molecules moved from inside the bag to the outside environment, demonstrating selective permeability of the membrane.
🔬 Visual indicators make invisible molecular movements visible! This is how scientists can "see" processes happening at the microscopic level.
We thought you’d never ask...
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?
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
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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