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0
D
defne
13/12/2025
Biology
GCSE triple biology paper 1 - B8
95
•
13 Dec 2025
•
GCSE Triple Biology Paper 1 - Photosynthesis (B8)
D
defne
@defneguvenn
1 / 10
Plant Cells and the Photosynthesis Equation
Ever wonder what makes plants so different from animals? Plant cells have three special features that animal cells don't: a cell wall for structure, a vacuole to store water, and chloroplasts to capture sunlight. These are all designed for one main job - photosynthesis!
The photosynthesis equation is dead simple: carbon dioxide + water → oxygen + glucose (using sunlight). In chemical symbols, that's 6CO₂ + 6H₂O → 6O₂ + C₆H₁₂O₆.
Photosynthesis is an endothermic reaction, meaning it takes in energy from light. Plants use some glucose straight away for respiration, but most gets converted into starch for storage - think of it as the plant's packed lunch for later!
💡 Quick tip: Remember that photosynthesis is basically the opposite of respiration - plants take in CO₂ and release O₂, whilst we do the reverse.
How Leaves Are Perfect for Photosynthesis
Leaves are basically photosynthesis factories, and they're brilliantly designed for the job. They're thin so gases can easily reach all the cells, and wide and flat to create a massive surface area for catching sunlight.
Inside leaves, you'll find loads of chloroplasts packed with chlorophyll - that's the green stuff that actually captures light energy. The veins act like a transport system, with xylem carrying water in and phloem taking glucose away to other parts of the plant.
Air spaces throughout the leaf allow CO₂ to flow in and O₂ to flow out by diffusion. On the underside, tiny pores called stomata control this gas exchange - they're like little doorways that can open and close.
💡 Remember: Guard cells control the stomata - when they're inflated (turgid), stomata open; when they collapse (flaccid), stomata close.
Variegated Plants and Testing for Starch
Variegated plants have those cool green and white patterned leaves you see in gardens. But here's the thing - they actually grow more slowly than fully green plants because the white bits contain no chlorophyll.
Less chlorophyll means less photosynthesis, which means less glucose production for growth. It's like trying to cook with half your kitchen equipment missing!
You can prove this using the iodine test. When you add iodine to a leaf, areas with starch turn blue-black (positive result). On variegated leaves, only the green parts turn blue-black because that's where photosynthesis happened. The white parts stay unchanged because no chlorophyll = no photosynthesis = no starch.
💡 Exam tip: This is a classic required practical - make sure you know that iodine tests for starch and turns blue-black when starch is present.
Limiting Factors - What Slows Photosynthesis Down
A limiting factor is anything that puts the brakes on photosynthesis. The main culprits are light intensity, temperature, CO₂ concentration, and chlorophyll levels.
Light intensity works exactly as you'd expect - more light equals faster photosynthesis, less light equals slower photosynthesis. It's like having a dimmer switch on the whole process.
Temperature is trickier because chlorophyll is actually an enzyme. It works best at 30-37°C (body temperature range). Too cold and the enzyme is sluggish; too hot and the enzyme denatures (breaks down permanently). CO₂ concentration matters because air only contains about 0.04% CO₂, so there's often not enough to go around.
💡 Key point: On sunny days, CO₂ is usually the limiting factor because plants quickly use up all the available CO₂ around them.
The Inverse Square Law and Light
Here's some physics mixed into your biology! The inverse square law explains why moving a light source affects photosynthesis so dramatically.
As distance from the light increases, light intensity decreases much faster than you might expect. The intensity is inversely proportional to the square of the distance. This means if you double the distance, the light intensity doesn't just halve - it becomes four times weaker!
The formula is: light intensity ∝ 1/distance². This relationship is crucial for understanding experimental results when investigating photosynthesis rates.
💡 Maths connection: This law appears in physics too (with gravity and electromagnetic forces), so understanding it here helps across multiple subjects.
Investigating Photosynthesis - The Required Practical
This is a classic GCSE required practical that you absolutely need to know! Aquatic plants like pondweed produce visible oxygen bubbles when they photosynthesise, and you can count these bubbles to measure the rate.
Your independent variable is the distance between pondweed and light source. Your dependent variable is the number of bubbles produced. Keep everything else constant (control variables): temperature, mass of sodium hydrogen carbonate solution, and size of pondweed.
The method is straightforward: place pondweed in a boiling tube filled with sodium hydrogen carbonate solution (releases CO₂), position an LED light source at measured distances, and count bubbles. Use LEDs because they don't produce much heat - you don't want temperature messing up your light intensity investigation!
💡 Practical tip: Always leave 5 minutes for acclimatisation at each distance before counting bubbles - this ensures accurate results.
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very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
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I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
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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 apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
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
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
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
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
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 apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
GCSE Triple Biology Paper 1 - Photosynthesis (B8)
D
defne
@defneguvenn
Photosynthesis is one of the most important processes on Earth - it's how plants make their own food using sunlight! Understanding how this works, and what affects it, is crucial for your biology GCSE and helps explain how all life... Show more
Plant Cells and the Photosynthesis Equation
Ever wonder what makes plants so different from animals? Plant cells have three special features that animal cells don't: a cell wall for structure, a vacuole to store water, and chloroplasts to capture sunlight. These are all designed for one main job - photosynthesis!
The photosynthesis equation is dead simple: carbon dioxide + water → oxygen + glucose (using sunlight). In chemical symbols, that's 6CO₂ + 6H₂O → 6O₂ + C₆H₁₂O₆.
Photosynthesis is an endothermic reaction, meaning it takes in energy from light. Plants use some glucose straight away for respiration, but most gets converted into starch for storage - think of it as the plant's packed lunch for later!
💡 Quick tip: Remember that photosynthesis is basically the opposite of respiration - plants take in CO₂ and release O₂, whilst we do the reverse.
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How Leaves Are Perfect for Photosynthesis
Leaves are basically photosynthesis factories, and they're brilliantly designed for the job. They're thin so gases can easily reach all the cells, and wide and flat to create a massive surface area for catching sunlight.
Inside leaves, you'll find loads of chloroplasts packed with chlorophyll - that's the green stuff that actually captures light energy. The veins act like a transport system, with xylem carrying water in and phloem taking glucose away to other parts of the plant.
Air spaces throughout the leaf allow CO₂ to flow in and O₂ to flow out by diffusion. On the underside, tiny pores called stomata control this gas exchange - they're like little doorways that can open and close.
💡 Remember: Guard cells control the stomata - when they're inflated (turgid), stomata open; when they collapse (flaccid), stomata close.
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Variegated Plants and Testing for Starch
Variegated plants have those cool green and white patterned leaves you see in gardens. But here's the thing - they actually grow more slowly than fully green plants because the white bits contain no chlorophyll.
Less chlorophyll means less photosynthesis, which means less glucose production for growth. It's like trying to cook with half your kitchen equipment missing!
You can prove this using the iodine test. When you add iodine to a leaf, areas with starch turn blue-black (positive result). On variegated leaves, only the green parts turn blue-black because that's where photosynthesis happened. The white parts stay unchanged because no chlorophyll = no photosynthesis = no starch.
💡 Exam tip: This is a classic required practical - make sure you know that iodine tests for starch and turns blue-black when starch is present.
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Limiting Factors - What Slows Photosynthesis Down
A limiting factor is anything that puts the brakes on photosynthesis. The main culprits are light intensity, temperature, CO₂ concentration, and chlorophyll levels.
Light intensity works exactly as you'd expect - more light equals faster photosynthesis, less light equals slower photosynthesis. It's like having a dimmer switch on the whole process.
Temperature is trickier because chlorophyll is actually an enzyme. It works best at 30-37°C (body temperature range). Too cold and the enzyme is sluggish; too hot and the enzyme denatures (breaks down permanently). CO₂ concentration matters because air only contains about 0.04% CO₂, so there's often not enough to go around.
💡 Key point: On sunny days, CO₂ is usually the limiting factor because plants quickly use up all the available CO₂ around them.
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The Inverse Square Law and Light
Here's some physics mixed into your biology! The inverse square law explains why moving a light source affects photosynthesis so dramatically.
As distance from the light increases, light intensity decreases much faster than you might expect. The intensity is inversely proportional to the square of the distance. This means if you double the distance, the light intensity doesn't just halve - it becomes four times weaker!
The formula is: light intensity ∝ 1/distance². This relationship is crucial for understanding experimental results when investigating photosynthesis rates.
💡 Maths connection: This law appears in physics too (with gravity and electromagnetic forces), so understanding it here helps across multiple subjects.
Sign up to see the contentIt's free!
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Investigating Photosynthesis - The Required Practical
This is a classic GCSE required practical that you absolutely need to know! Aquatic plants like pondweed produce visible oxygen bubbles when they photosynthesise, and you can count these bubbles to measure the rate.
Your independent variable is the distance between pondweed and light source. Your dependent variable is the number of bubbles produced. Keep everything else constant (control variables): temperature, mass of sodium hydrogen carbonate solution, and size of pondweed.
The method is straightforward: place pondweed in a boiling tube filled with sodium hydrogen carbonate solution (releases CO₂), position an LED light source at measured distances, and count bubbles. Use LEDs because they don't produce much heat - you don't want temperature messing up your light intensity investigation!
💡 Practical tip: Always leave 5 minutes for acclimatisation at each distance before counting bubbles - this ensures accurate results.
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Our AI Companion is a student-focused AI tool that offers more than just answers. Built on millions of Knowunity resources, it provides relevant information, personalised study plans, quizzes, and content directly in the chat, adapting to your individual learning journey.
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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
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
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
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
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 apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
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
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
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
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
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 apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user