iGCSE Biology Notes Biological molecules

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[h] iGCSE Biology Notes Biological molecules

[q] Why is water important? 

What is water for?

[a] 

• Most organisms are around 80% water, as the cytoplasm of all cells is mostly water.
• Almost all metabolic reactions occur in water. Metabolism is all the reactions happening in the body, keeping us alive.
• This is because water is an excellent solvent, substances dissolve in water so they can react and be transported (like in the blood plasma, which is also mostly water)

[q] What are biological compounds made of? 

What types of biological molecules are there? 

[a] 

• Biological molecules are polymers, which means they are made up of lots of smaller molecules called monomers.
• Carbohydrates such as starch, cellulose and glycogen are made up of sugars like glucose, and are made of the elements carbon, oxygen and hydrogen.
• Lipids are made up of glycerol and fatty acids, and are made of the elements carbon, oxygen and hydrogen too.
• Proteins are made up of amino acids, and are made up of carbon, oxygen, hydrogen, nitrogen and sulfur.

[q] How do we test for different biological molecules? 

What are the different food tests?

[a] 

• We use the iodine test to test for starch, a type of carbohydrate.
• Iodine solution is yellowbrown, but in the presence of starch is turns dark blue.

[q] How do we test for different biological molecules? 

What are the different food tests?

[a] 

• We use Benedict’s test to test for reducing sugars like glucose which makes up starch.
• Benedict’s solution is blue, but will turn to brick red through all the colours of the rainbow depending on how much glucose is present.
• This test requires heat.

[q] How do we test for different biological molecules? 

What are the different food tests?

[a] 

• We use the biuret test for proteins (which would also detect most enzymes)
• Biuret solution is blue, and it turns lilac/purple in the presence of protein

[q] How do we test for different biological molecules? 

What are the different food tests? 

[a] 

• We use the ethanol emulsion test to test for lipids, fats and oils.
• Ethanol is clear like water, but when you shake it in the presence of a lipid, then add it to some water, a milky layer will form at the top if lipid is presence.

[q] How do we test for different biological molecules? 

What are the different food tests? 

[a] 

• We use the DCPIP test for vitamin C (ascorbic acid)
• DCPIP is blue, and will turn lose its colour/go colourless in the presence of vitamin C.

[q] What is the structure of DNA? 

Use the information to identify the biological molecules in each food 

[a] 

• DNA is another polymer, made of monomers called nucleotides.
• Each nucleotide has one of the four bases represented by the letters A, T, C and G.
• Each DNA molecule has two strands which wrap around each other in a double helix shape.
• The strands link together, where A always matches to T, and C always matches to G.
• These bases are joined by hydrogen bonds.

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