4. Biological Molecules (Cambridge IGCSE Biology 0610 for exams in 2023, 2024 and 2025)

Summary

This IGCSE study video covers biological molecules, focusing on carbohydrates, fats, and proteins—organic molecules essential for life. It explains the structure of monosaccharides, disaccharides, and polysaccharides in carbohydrates, and the composition of fats from fatty acids and glycerol. Proteins are described as chains of amino acids, with variations leading to diverse protein structures. The video also details food tests for identifying starch, reducing sugars, proteins, fats, oils, and vitamin C, and concludes with an overview of DNA's double helix structure and base pairing.

Takeaways

• 🌿 The bodies of living organisms are composed of various chemicals, including carbohydrates, fats, and proteins, which are organic molecules containing carbon, hydrogen, and oxygen.
• 🍬 Carbohydrates are large molecules made up of simple sugar molecules like monosaccharides (e.g., glucose), disaccharides (e.g., maltose), and polysaccharides (e.g., starch, glycogen, or cellulose).
• 🍯 Fats, or lipids, are made from fatty acids and glycerol, with oils being liquid fats at room temperature, and each fat molecule consisting of one glycerol molecule bonded to three fatty acid chains.
• 🥚 Proteins are composed of long chains of amino acids, with about 20 different types that can be arranged in various orders to create a vast array of proteins.
• 🧪 Food tests can identify the presence of starch, reducing sugars, proteins, fats, oils, and vitamin C in food samples through specific reactions and color changes.
• 🟣 The starch test involves adding iodine solution, which turns blue-black in the presence of starch, indicating its presence.
• 🟠 The reducing sugar test uses Benedict's solution, which changes from blue to orange or brick red when heated with a food sample containing reducing sugars.
• 🟣 The protein test involves the addition of biuret reagent, which turns from blue to violet or purple, confirming the presence of protein in the food sample.
• 🥛 The fat and oil test mixes the food sample with ethanol, and when added to cold water, a cloudy or milky emulsion indicates the presence of fats or oils.
• 🟢 The vitamin C test uses dcpip solution, which turns colorless when mixed with a food sample containing vitamin C, indicating its presence.
• 🧬 DNA, or deoxyribonucleic acid, is the molecule containing the genetic instructions for all organisms, structured as a double helix with two strands held together by base pairs (A-T and C-G).

Q & A

What are the three main categories of molecules found in living organisms?

The three main categories of molecules found in living organisms are carbohydrates, fats, and proteins.

Why are carbohydrates, fats, and proteins referred to as organic molecules?

Carbohydrates, fats, and proteins are referred to as organic molecules because they all contain carbon, hydrogen, and oxygen, with proteins also containing nitrogen and sometimes sulfur.

What is the simplest form of sugar molecules known as?

The simplest form of sugar molecules is known as monosaccharides, with glucose being an example.

How are maltose and starch related to glucose molecules?

Maltose is formed when two glucose molecules join together, and starch is a polysaccharide formed when many glucose molecules join together.

What are the basic units of fats or lipids?

The basic unit of fats is one glycerol molecule chemically bonded to three fatty acid chains.

What is the difference between oils and fats?

Oils are fats that are liquid at room temperature.

How many different amino acids are there, and what do they form when combined?

There are about 20 different amino acids, and when combined, they form long chains that make up protein molecules.

What happens when iodine solution is added to a food sample containing starch?

When iodine solution is added to a food sample containing starch, the color changes from orange-brown to blue-black.

How is the presence of reducing sugars in a food sample tested?

The presence of reducing sugars in a food sample is tested by adding Benedict's solution, heating it in a water bath, and observing a color change from blue to orange or brick red.

What color change indicates a positive test for protein in a food sample?

A positive test for protein in a food sample is indicated by a color change from blue to violet or purple when biuret solution is added.

How can the presence of fats or oils in a food sample be determined?

The presence of fats or oils in a food sample can be determined by mixing the sample with ethanol, adding it to cold water, and observing the formation of a cloudy or milky emulsion.

What is the structure of a DNA molecule, and how are the two strands held together?

A DNA molecule consists of two strands wound around each other in a double helix. The strands are held together by hydrogen bonds between pairs of bases, which always pair up in the same way: adenine (A) with thymine (T), and cytosine (C) with guanine (G).

Outlines

00:00

🧬 Introduction to Biological Molecules

This segment introduces the topic of biological molecules from the Cambridge IGCSE syllabus. It explains that living organisms are composed of various chemicals, with carbohydrates, fats, and proteins being the three main categories of molecules. These molecules are organic, containing carbon, hydrogen, and oxygen, with proteins also containing nitrogen and sulfur. The paragraph delves into the structure of these molecules, describing carbohydrates as large molecules made from simple sugar molecules like monosaccharides, disaccharides, and polysaccharides. Fats are discussed as large molecules composed of fatty acids and glycerol, with oils being liquid fats. Proteins are highlighted as complex molecules made from amino acids, which can be arranged in various orders to form a vast array of different proteins. The video also touches on food tests to identify the presence of these molecules in food samples.

05:02

🔬 Food Tests for Biological Molecules

This part of the script focuses on various food tests used to detect the presence of biological molecules such as starch, reducing sugars, proteins, fats, oils, and vitamin C. The iodine test for starch is described, where the addition of iodine solution to a food sample containing starch turns the solution blue-black. The Benedict's solution test for reducing sugars is explained, where heating the solution with the food sample changes the color from blue to orange or brick red if reducing sugars are present. The Biuret test for proteins is mentioned, which turns the solution violet or purple when proteins are detected. The emulsion test for fats and oils is described, where mixing the food sample with ethanol and cold water results in a cloudy or milky emulsion if fats or oils are present. Lastly, the DCPIP test for vitamin C is explained, where the addition of the food sample to a blue DCPIP solution causes the blue color to disappear, indicating the presence of vitamin C. The segment concludes with an introduction to the structure of DNA, highlighting its double helix form composed of two strands held together by hydrogen bonds between base pairs.

Keywords

💡Carbohydrates

Carbohydrates are a class of organic molecules that are composed of carbon, hydrogen, and oxygen. In the context of the video, carbohydrates are described as large molecules made up of simple sugar molecules, such as monosaccharides, disaccharides, and polysaccharides. Glucose is given as an example of a monosaccharide, maltose as a disaccharide, and starch, glycogen, or cellulose as polysaccharides. These molecules are essential for energy storage and provide structural support in living organisms.

💡Fats or Lipids

Fats, also known as lipids, are another category of organic molecules that are composed of fatty acids and glycerol. The video explains that fats are large molecules made from these smaller units, with the basic unit being a glycerol molecule bonded to three fatty acid chains. Fats serve as a dense source of energy and are also important for cell membrane structure. Liquid fats at room temperature are referred to as oils.

💡Proteins

Proteins are complex organic molecules made up of amino acids. The video highlights that there are about 20 different amino acids that can be arranged in various orders to create a vast array of proteins. Proteins are crucial for the structure, function, and regulation of the body's tissues and organs. An example from the script is that different combinations of amino acids result in different proteins, which is fundamental to the diversity of life.

💡Monosaccharides

Monosaccharides are the simplest form of carbohydrates and are single sugar molecules. Glucose, as mentioned in the video, is an example of a monosaccharide. These molecules are the building blocks for more complex carbohydrates and are important energy sources for living organisms.

💡Disaccharides

Disaccharides are carbohydrates formed by the joining of two monosaccharide molecules. Maltose, formed from two glucose molecules, is an example given in the video. Disaccharides play a role in the digestion process and are broken down into monosaccharides to be absorbed by the body.

💡Polysaccharides

Polysaccharides are complex carbohydrates composed of many sugar molecules linked together. Starch, glycogen, and cellulose are examples of polysaccharides discussed in the video. They serve various functions, such as energy storage in the form of glycogen and structural support in plants through cellulose.

💡Amino Acids

Amino acids are the building blocks of proteins, with the video noting that there are about 20 different types. These molecules are linked together in chains to form proteins, which are essential for life. The sequence in which amino acids are arranged determines the structure and function of the resulting protein.

💡Food Tests

Food tests are methods used to identify the presence of certain molecules in food samples. The video outlines tests for starch, reducing sugars, proteins, fats, and oils, and vitamin C. These tests are important for understanding the nutritional content of food and are demonstrated through various color changes and reactions.

💡Iodine Test

The iodine test is a specific food test mentioned in the video to detect the presence of starch. When iodine solution is added to a food sample containing starch, the color changes from orange-brown to blue-black, as illustrated by the example of a potato.

💡Benedict's Solution

Benedict's solution is used in the food test for reducing sugars. When added to a food sample and heated, a color change from blue to orange or brick red indicates the presence of reducing sugars. This test is crucial for identifying the types of sugars present in food.

💡DNA

DNA, or deoxyribonucleic acid, is the molecule that contains the genetic instructions for all living organisms. The video describes DNA as a double helix structure composed of two strands held together by hydrogen bonds between pairs of bases. The bases pair up in a specific way (A with T and C with G), which is essential for DNA replication and the transmission of genetic information.

Highlights

Introduction to IGCSE study buddy for biology revision

Topic 4 focuses on biological molecules

Living organisms' bodies are made of chemicals, including carbohydrates, fats, and proteins

These molecules are organic, containing carbon, hydrogen, and oxygen

Proteins contain additional nitrogen and small amounts of sulfur

Carbohydrates are large molecules made of simple sugar molecules

Monosaccharides are the simplest form of sugar molecules, like glucose

Disaccharides like maltose are formed when two sugar molecules join

Polysaccharides are formed when many glucose molecules join, like starch and glycogen

Fats or lipids are large molecules made from fatty acids and glycerol

Liquid fats at room temperature are called oils

Proteins are made of long chains of amino acids

There are about 20 different amino acids that can be arranged in various orders

Different combinations of amino acids result in different proteins

Food tests can identify the presence of starch, reducing sugars, proteins, fats, and oils

Iodine solution turns blue-black in the presence of starch

Benedict's solution changes color to indicate the presence of reducing sugars

Biuret solution changes color to violet or purple in the presence of protein

Fats and oils can be detected by mixing with ethanol and observing a cloudy emulsion

Vitamin C can be tested with dcpip solution, which turns colorless in its presence

DNA structure consists of two strands in a double helix, held together by base pairs

Base pairs in DNA always pair up in the same way: A with T and C with G

Summary of chapter 4 on biological molecules

Transcripts

hi everyone welcome to IGCSE study buddy

where you can revise biology topics from

the Cambridge IGCSE syllabus

this video summarizes topic 4 biological

molecules

the bodies of all living things are made

of many different kinds of chemicals

the three main categories of molecules

in living organisms are carbohydrates

fats

and proteins

since these molecules contain carbon

they are known as organic molecules

these are the chemical elements present

in these molecules so as you can see

carbohydrates fats and proteins all

three contain carbon hydrogen and oxygen

but only protein has nitrogen

additionally and proteins even contain

small amounts of sulfur

let's look into these chemical elements

in more detail we need to know that

large molecules are made from smaller

molecules

the first is carbohydrates they are

large molecules made up of simple sugar

molecules

the simplest form of sugar molecules are

also known as monosaccharides

glucose is an example of a

monosaccharide

when two glucose molecules join together

maltose is formed which is a

disaccharact

when lots of glucose molecules join

together starch glycogen or cellulose

can form they are called polysaccharides

this picture illustrates the three types

of carbohydrates

a monosaccharide is a single sugar

molecule a disaccharide is when two

sugar molecules are linked

a polysaccharide is when many sugar

molecules are linked examples of many

glucose molecules join together are

starch glycogen or cellulose

the next category of biological

molecules are fats or lipids

fats are large molecules made from

smaller units of fatty acids and

glycerol

their basic unit is one glycerol

molecule chemically bonded to Three

fatty acid shades

fats that are liquids at room

temperature are called oils

so this picture shows that each fat

molecule consists of one glycerol

molecule bonded to Three fatty acid

chains

next is proteins protein molecules are

made of long chains of smaller molecules

joined end to end

these smaller molecules are called amino

acids there are about 20 different amino

acids the amino acids can be arranged in

any order resulting in hundreds of

thousands of different proteins

so different combinations of these amino

acids will give rise to different

proteins even a small difference in the

order of the amino acids results in a

different protein being formed

here's an illustration of amino acids

that when combined forms a protein

next we'll be looking into food tests

different tests can be performed on food

to identify if they contain starch

reducing sugars proteins fats and oils

or vitamin C

let's first take a look at the test for

starch in order to find out if some food

contains starch we should add drops of

iodine solution to the food sample if

the food sample contains touch the color

will change from orange brown to blue

black

here's a picture to show this test as

you can see a few drops of iodine are

poured onto a potato since potatoes

contain starch the orange brown color of

the iodine turns blue black

the next food test is for reducing

sugars we must first add Benedict

solution into the food sample solution

in the test tube

Heat at 60 to 70 degrees Celsius in a

water bath for 5 minutes

take the test tube out of the water bath

and observe the color

if reducing sugars are present in the

food sample the solution will turn from

Blue to orange or brick red

this diagram shows the food test for

reducing sugars

Benedict's solution is added to the food

sample which is heated in a water bath

and if the color changes from Blue to

Orange it confirms a positive test of

reducing sugars

the next food test is for proteins add

drops of buy red solution to the food

sample a positive test will show a color

change from Blue to Violet or purple

this illustration shows what happens

when a food sample is tested for protein

since the color changed from Blue to

purple it means that the food sample

contains protein now the test for fats

and oils the food sample is mixed with

two cubic centimeters of ethanol and

shaken

the ethanol is added to an equal volume

of cold distilled water

a positive test will show a cloudy or

milky Emulsion forming

so if we want to check if a food sample

contains fats or Oils we must mix the

food sample with ethanol then we must

add that to some cold water

if the food sample contains fat cell

oils a white cloudy Emulsion will form

the final food test we'll be learning

about is the test for vitamin C

add 1 cubic centimeters of dcpip

solution to a test tube dcpip is blue in

color

add a small amount of the food sample as

a solution

a positive test will show the blue color

of the dye disappearing

this picture shows that when the blue

dcpip solution is mixed with the food

sample the blue color turns colorless

and disappears this confirms that the

food sample contains vitamin C

finally we'll be learning about the

structure of a DNA molecule DNA or

deoxyribonucleic acid is the molecule

that contains the instructions for

growth and development of all organisms

it consists of two strands of DNA wound

around each other in what is called a

double helix

each strand contains chemicals called

bases

hydrogen bonds between Pairs of bases

hold the strands together

the bases always pair up in the same way

a with t or adenine with thymine

and C with g that is cytosine with

guanine

full names are not required to be known

for the exams just the letters but you

must know which base bonds with which

here's a picture to better understand

the structure of a DNA molecule you may

notice the double-stranded helix held

together by base cats the base pairs are

held together by hydrogen bonds

the base pairs always pair up in a

particular way a pairs with t and c

pairs with g

so that sums up the main things to be

learned in chapter 4 biological

molecules

hope you found it useful thank you for

watching and please don't forget to

subscribe to IGCSE study buddy for more

biology revision videos bye