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26 Dec 2025
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How Antibiotics and Antiseptics Affect Bacteria: Practical Guide
Gabriela
@gabriela.my.school.journey16
1 / 3
Setting Up Your Bacterial Culture
Getting bacteria to grow properly in the lab requires aseptic techniques – basically keeping everything sterile so you don't accidentally grow the wrong microorganisms. You'll be testing how different antibiotics and antiseptics affect bacterial growth by measuring something called the zone of inhibition.
Your independent variable is the type of antibiotic or antiseptic disc you use, whilst your dependent variable is the size of the zone of inhibition (the clear area where bacteria can't grow). Keep everything else constant – disc size, concentration, temperature, and incubation time.
The process starts with sterilising everything: your petri dish, agar, and work surfaces using heat or disinfectant. You'll use a sterilised inoculating loop (heated in a flame) to spread bacteria evenly across the agar surface, keeping the petri dish lid barely open to prevent contamination.
Top Tip: Always tape the lid with a cross pattern – this lets oxygen in whilst preventing harmful anaerobic bacteria from taking over, and store plates upside down so condensation doesn't drip onto your bacterial colonies.
Safety First in the Lab
Working with bacteria and chemicals means taking proper precautions to protect yourself and get accurate results. The main hazards you'll face include Bunsen burners, strong disinfectants, glass equipment, and potentially contaminated materials.
When using Bunsen burners to sterilise equipment, tie back hair and tuck in loose clothing. Always use the safety flame when not actively heating, and place heatproof mats underneath. Turn off gas supplies and let equipment cool before handling.
Strong disinfectants can irritate skin and eyes, so wear gloves and safety goggles throughout the experiment. Wash hands thoroughly after use. Glass petri dishes can break and cause cuts – check for chips or cracks before use and wear cut-resistant gloves when handling broken glass.
Remember: Dispose of used cotton buds and other contaminated materials properly, and always disinfect work surfaces before and after the experiment to prevent spreading infections.
Measuring Results and Drawing Conclusions
After 48 hours of incubation at 25°C, you'll see clear circular areas around some discs where bacteria couldn't grow – these are your zones of inhibition. The larger the zone, the more effective that antibiotic or antiseptic is at killing or preventing bacterial growth.
Measure the diameter of each zone using a ruler, then calculate the area using πr². If zones are irregularly shaped, take measurements from different positions around the clear zone and calculate a mean for accuracy.
The most effective treatment will have the largest zone of inhibition because it killed or prevented growth of the most bacteria. Your control disc (soaked in sterile water) should show no clear zone, proving that any inhibition is due to the active substance, not the paper disc itself.
Exam Success: Remember that contaminated cultures give invalid results because unwanted microorganisms interfere with bacterial growth – this is why aseptic technique is absolutely crucial for reliable data.
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4.9/5
App Store
4.8/5
Google Play
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
How Antibiotics and Antiseptics Affect Bacteria: Practical Guide
Gabriela
@gabriela.my.school.journey16
Ever wondered how doctors know which antibiotic will work best against a bacterial infection? This practical investigation shows you exactly how to test the effectiveness of antibiotics and antiseptics against bacteria in the lab, using proper scientific techniques to get... Show more
Setting Up Your Bacterial Culture
Getting bacteria to grow properly in the lab requires aseptic techniques – basically keeping everything sterile so you don't accidentally grow the wrong microorganisms. You'll be testing how different antibiotics and antiseptics affect bacterial growth by measuring something called the zone of inhibition.
Your independent variable is the type of antibiotic or antiseptic disc you use, whilst your dependent variable is the size of the zone of inhibition (the clear area where bacteria can't grow). Keep everything else constant – disc size, concentration, temperature, and incubation time.
The process starts with sterilising everything: your petri dish, agar, and work surfaces using heat or disinfectant. You'll use a sterilised inoculating loop (heated in a flame) to spread bacteria evenly across the agar surface, keeping the petri dish lid barely open to prevent contamination.
Top Tip: Always tape the lid with a cross pattern – this lets oxygen in whilst preventing harmful anaerobic bacteria from taking over, and store plates upside down so condensation doesn't drip onto your bacterial colonies.
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Safety First in the Lab
Working with bacteria and chemicals means taking proper precautions to protect yourself and get accurate results. The main hazards you'll face include Bunsen burners, strong disinfectants, glass equipment, and potentially contaminated materials.
When using Bunsen burners to sterilise equipment, tie back hair and tuck in loose clothing. Always use the safety flame when not actively heating, and place heatproof mats underneath. Turn off gas supplies and let equipment cool before handling.
Strong disinfectants can irritate skin and eyes, so wear gloves and safety goggles throughout the experiment. Wash hands thoroughly after use. Glass petri dishes can break and cause cuts – check for chips or cracks before use and wear cut-resistant gloves when handling broken glass.
Remember: Dispose of used cotton buds and other contaminated materials properly, and always disinfect work surfaces before and after the experiment to prevent spreading infections.
Sign up to see the contentIt's free!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Measuring Results and Drawing Conclusions
After 48 hours of incubation at 25°C, you'll see clear circular areas around some discs where bacteria couldn't grow – these are your zones of inhibition. The larger the zone, the more effective that antibiotic or antiseptic is at killing or preventing bacterial growth.
Measure the diameter of each zone using a ruler, then calculate the area using πr². If zones are irregularly shaped, take measurements from different positions around the clear zone and calculate a mean for accuracy.
The most effective treatment will have the largest zone of inhibition because it killed or prevented growth of the most bacteria. Your control disc (soaked in sterile water) should show no clear zone, proving that any inhibition is due to the active substance, not the paper disc itself.
Exam Success: Remember that contaminated cultures give invalid results because unwanted microorganisms interfere with bacterial growth – this is why aseptic technique is absolutely crucial for reliable data.
We thought you’d never ask...
What is the Knowunity AI companion?
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.
Where can I download the Knowunity app?
You can download the app from Google Play Store and 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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Most popular content: Antibiotics
Most popular content in Biology
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Can't find what you're looking for? Explore other subjects.
Students love us — and so will you.
4.9/5
App Store
4.8/5
Google Play
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