Ever wondered what makes up the food you eat every... Show more
Combined Science
Engineering
SociologySign 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
3
0
R
revision
07/12/2025
Biology
Biology - Nutrition and Food Tests
121
•
7 Dec 2025
•
Understanding Nutrition and Food Tests in Biology
R
revision
@user014
1 / 3
The Three Main Components of Our Diet
Carbohydrates are your body's favourite energy source, and they come in two main types. Simple carbohydrates include sugars like glucose and lactose that give you quick energy bursts. Complex carbohydrates are more interesting - they're made of loads of simple sugars joined together, like starch (which plants use to store energy) and cellulose (which gives plant cell walls their strength).
Fats and lipids might sound scary, but they're essential for your body. Made from fatty acids and glycerol, they're brilliant energy stores and can be either solid fats or liquid oils at room temperature. Think of them as your body's long-term energy savings account.
Proteins are the real workhorses of your body. Built from 20 different amino acids, they can form countless combinations to create everything from structural support (like collagen in your skin) to enzymes that speed up chemical reactions. It's like having a massive LEGO set where different combinations create completely different functions.
Quick Tip: Remember that complex carbohydrates are just simple sugars holding hands in long chains - this makes them easier to remember for exams!
Food Tests You Need to Know
Testing for different nutrients in food is simpler than you might think, and these four tests are exam favourites. Each test uses a specific chemical reagent that changes colour when it finds what it's looking for.
The starch test uses iodine solution, which starts yellow-brown but turns blue-black when starch is present. For proteins, you'll use Biuret reagent - it goes from blue to purple when it detects protein molecules. Fat testing involves ethanol, which stays colourless until you add water and it turns into a white, cloudy emulsion.
Reducing sugars (like glucose) are tested with Benedict's reagent in a boiling water bath. The blue reagent transforms into a brick-red precipitate when sugar is present - the more sugar, the more dramatic the colour change.
You can also measure energy content by burning food and seeing how much it heats up water. Weigh your food sample, record the water temperature, burn the food under a boiling tube of water, then measure the temperature rise.
Exam Alert: Remember the colour changes - blue to purple for protein, yellow-brown to blue-black for starch, and blue to brick-red for reducing sugars!
Why School Lab Results Differ from Real Values
Your energy content results in school labs are always lower than what manufacturers claim on food packets, but there's a perfectly good scientific reason for this. The problem isn't your technique - it's the limitations of school equipment.
Most energy from burning food escapes and heats the surrounding air instead of the water you're measuring. Some food doesn't burn completely, leaving unburnt bits that still contain energy. Plus, heat gets wasted warming up the glass test tube rather than just the water.
Professional solutions would involve burning food in a pure oxygen supply for complete combustion, enclosing the entire apparatus to prevent heat loss, and using heat transfer coils to get energy directly into the water. These improvements would give much more accurate results.
Understanding these limitations shows you're thinking like a real scientist - recognising that experimental conditions affect results and knowing how to improve methods.
Real World Connection: Food manufacturers use bomb calorimeters - sealed chambers that capture all the energy released, giving them those precise calorie counts you see on packaging!
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.
Most popular content: Energy
Most popular content in Biology
Most popular content
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
Understanding Nutrition and Food Tests in Biology
R
revision
@user014
Ever wondered what makes up the food you eat every day? Your diet is built from three main biological molecules that keep your body running: carbohydrates, fats, and proteins. Understanding these molecules and how to test for them is crucial... Show more
The Three Main Components of Our Diet
Carbohydrates are your body's favourite energy source, and they come in two main types. Simple carbohydrates include sugars like glucose and lactose that give you quick energy bursts. Complex carbohydrates are more interesting - they're made of loads of simple sugars joined together, like starch (which plants use to store energy) and cellulose (which gives plant cell walls their strength).
Fats and lipids might sound scary, but they're essential for your body. Made from fatty acids and glycerol, they're brilliant energy stores and can be either solid fats or liquid oils at room temperature. Think of them as your body's long-term energy savings account.
Proteins are the real workhorses of your body. Built from 20 different amino acids, they can form countless combinations to create everything from structural support (like collagen in your skin) to enzymes that speed up chemical reactions. It's like having a massive LEGO set where different combinations create completely different functions.
Quick Tip: Remember that complex carbohydrates are just simple sugars holding hands in long chains - this makes them easier to remember for exams!
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
Food Tests You Need to Know
Testing for different nutrients in food is simpler than you might think, and these four tests are exam favourites. Each test uses a specific chemical reagent that changes colour when it finds what it's looking for.
The starch test uses iodine solution, which starts yellow-brown but turns blue-black when starch is present. For proteins, you'll use Biuret reagent - it goes from blue to purple when it detects protein molecules. Fat testing involves ethanol, which stays colourless until you add water and it turns into a white, cloudy emulsion.
Reducing sugars (like glucose) are tested with Benedict's reagent in a boiling water bath. The blue reagent transforms into a brick-red precipitate when sugar is present - the more sugar, the more dramatic the colour change.
You can also measure energy content by burning food and seeing how much it heats up water. Weigh your food sample, record the water temperature, burn the food under a boiling tube of water, then measure the temperature rise.
Exam Alert: Remember the colour changes - blue to purple for protein, yellow-brown to blue-black for starch, and blue to brick-red for reducing sugars!
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
Why School Lab Results Differ from Real Values
Your energy content results in school labs are always lower than what manufacturers claim on food packets, but there's a perfectly good scientific reason for this. The problem isn't your technique - it's the limitations of school equipment.
Most energy from burning food escapes and heats the surrounding air instead of the water you're measuring. Some food doesn't burn completely, leaving unburnt bits that still contain energy. Plus, heat gets wasted warming up the glass test tube rather than just the water.
Professional solutions would involve burning food in a pure oxygen supply for complete combustion, enclosing the entire apparatus to prevent heat loss, and using heat transfer coils to get energy directly into the water. These improvements would give much more accurate results.
Understanding these limitations shows you're thinking like a real scientist - recognising that experimental conditions affect results and knowing how to improve methods.
Real World Connection: Food manufacturers use bomb calorimeters - sealed chambers that capture all the energy released, giving them those precise calorie counts you see on packaging!
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.
3
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Mock Exam
Quiz
Flashcards
Essay
Similar content
Lipids in Biology
Explore the essential concepts of lipids, including fatty acids, phospholipid bilayers, and lipid metabolism. This summary covers key topics for AS Level Biology Unit 1.1, focusing on the structure and function of lipids in cell membranes and their role in energy storage and protection.
Biology12
Lipids and Cardiovascular Health
Explore the role of lipids in health, focusing on saturated and unsaturated fatty acids, cholesterol metabolism, and their impact on cardiovascular diseases. This summary covers lipid functions, including energy storage, insulation, and protection, as well as the biochemical structure of triglycerides and phospholipids. Ideal for students studying biology and health sciences.
Biology12
Understanding Lipids
Explore the structure, functions, and types of lipids, including triglycerides, phospholipids, and cholesterol. This summary covers key concepts such as fatty acids, ester bonds, and the roles of lipids in biological membranes and energy storage. Ideal for A-Level Biology students.
Biology12
Understanding Triglycerides
Explore the structure, functions, and significance of triglycerides in lipid metabolism. This summary covers key concepts such as energy storage, insulation, and the role of triglycerides in cellular respiration. Ideal for A-Level Biology students studying biological molecules and membrane lipids.
Biology12
Understanding Lipids
Explore the structure, function, and types of lipids, including triglycerides, phospholipids, and cholesterol. This summary covers key concepts such as lipid solubility, energy storage, and membrane fluidity, essential for AQA A-level Biology. Ideal for students seeking to grasp the role of lipids in biological systems.
Biology12
Biological molecules - Lipids
OCR a level biology - lipids
Biology13
Most popular content: Energy
Most popular content in Biology
Most popular content
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