Topic 4 Revision - Year 9

The chemical elements found in carbohydrates are ...

• carbon

• hydrogen

• oxygen

• nitrogen

Answer explanation

The chemical elements found in carbohydrates are carbon, hydrogen, and oxygen.

Nitrogen is NOT a component of carbohydrates.

The chemical element is not found in lipids?

• carbon

• hydrogen

• oxygen

• nitrogen

Answer explanation

The chemical element nitrogen is not found in lipids.

Lipids primarily consist of carbon, hydrogen, and oxygen.

You can produce an amino acid by combining glucose with the mineral ...

• potassium ions

• sodium ions

• magnesium ions

• nitrate ions

Answer explanation

To produce an amino acid, glucose needs to be combined with the mineral nitrate ions.

This combination allows for the synthesis of the amino acid.

To test for the presence of reducing sugar in a sample, the reagent used is ...

• iodine

• Benedict's solution

• ethanol and water

• Biuret's reagent

Answer explanation

To test for the presence of reducing sugar in a sample, Benedict's solution is used.

Benedict's solution is a reagent that changes color in the presence of reducing sugars.

This solution is commonly used in laboratory tests to detect the presence of reducing sugars, such as glucose, fructose, galactose, maltose, and lactose.

To test for the presence of starch in a sample, the reagent used is ...

• iodine

• Benedict's solution

• ethanol and water

• Biuret's reagent

Answer explanation

To test for the presence of starch in a sample, iodine is used as the reagent.

The iodine reacts with starch to form a blue-black color, indicating the presence of starch.

To test for the presence of lipids in a sample, the reagent used is ...

• iodine

• Benedict's solution

• ethanol and water

• Biuret's reagent

Answer explanation

To test for the presence of lipid in a sample, ethanol and water are used as the reagent.

Ethanol is added first because lipids (fats) are miscible (mixable) with ethanol, so ethanol is used to extract any fats from a sample.

To test for the presence of protein in a sample, the reagent used is ...

• iodine

• Benedict's solution

• ethanol and water

• Biuret's reagent

Answer explanation

To test for the presence of protein in a sample, Biuret's reagent is used.

This reagent reacts with proteins, forming a violet colour (or purple/mauve/lilac).

In a Benedict's test, if the result of the colour change is from blue to yellow-green precipitate, this means there is ...

• no reducing sugar present

• traces of reducing sugar present

• moderate amount of reducing sugar present

• large amount of reducing sugar present

Answer explanation

In the Benedict's test, a blue to yellow-green precipitate indicates the presence of traces of reducing sugar. This means that there is a very small amount of reducing sugar present, not a large or moderate amount.

In an ethanol emulsion test, the result observed is the mixture turning from clear to cloudy, which means ...

• starch is present

• protein is present

• lipid is present

• reducing sugar is present

Answer explanation

If the mixture turns from clear to cloudy, it indicates the presence of lipids.

This change occurs because lipids are miscible (mixable) in ethanol i.e. ethanol helps to physically breakdown large fat droplets. Once water is added, an emulsion is formed, causing the cloudiness.

The sub-unit of carbohydrate molecule is ...

Answer explanation

The carbohydrate molecule is composed of smaller sub-units, glucose which is a monosaccharide.

Glucose is a simple sugar that is commonly found in many foods and is an important source of energy for the body.