B3 - Biological Molecules

Question 1

What are monomers and polymers?

Answer 1

Monomers are the building blocks of more complex molecules, called polymers. Polymers consist of repeating molecular units.

Question 2

What are natural polymers?

Answer 2

Proteins, carbohydrates and lipids are described as natural polymers or biopolymers because they are built up from smaller molecules into much larger structures by living cells.

Question 3

What are protein molecules made up from?

Answer 3

Protein molecules are made up from long chains of amino acids.

Question 4

Why does the chain of amino acids in a protein have a special shape?

Answer 4

Due to cross-linkages

Question 5

What happens to the protein when subjected to high temperatures?

Answer 5

The protein loses its shape and becomes denatured because these cross-linkages are broken and so the protein loses its original properties.

Question 6

What do all carbohydrates contain?

Answer 6

carbon, hydrogen, and oxygen.

Question 7

What are the types of carbohydrates?

Answer 7

Monosaccharides, disaccharides, polysaccharides

Question 8

What is a monosaccharide?

Answer 8

Sugars with a single carbon ring, e.g. glucose and fructose

Question 9

What is a polysaccharide?

Answer 9

carbohydrates that have many glucose molecules joined together. e.g. strach

Question 10

What is a disaccharide?

Answer 10

sugars with 2 carbon rings, e.g. maltose and sucrose.

Question 11

What are lipids?

Answer 11

LIpids are fats and oils that contain carbon, hydrogen, and oxygen.

Question 12

What is a molecule of fat made up from?

Answer 12

A molecule of fat is made of 3 molecules of an organic acid called fatty acid, combined with 1 molecule of glycerol.

Question 13

Where do lipids form?

Answer 13

LIpids form part of the cell membrane and the internal membranes of the cell such as the nuclear membrane.

Question 14

What are the steps to Benedict’s test for glucose?

Answer 14

1. Add 1cm of Benedict’s solution to 1cm of food or glucose in a test tube.
2. Heat the mixture in a water bath without boiling.

Question 15

In Benedict’s test for glucose, how do we know that glucose is present?

Answer 15

A brick-red colour is positive for glucose. With sucrose, a negative test remains a blue colour.

Question 16

What are the steps for the test for sucrose?

Answer 16

1. Add 10 drops of 2M HCl to 1cm of food or sucrose in a test tube.
2. Heat gently in a water bath without boiling.
3. Add 0.5 cm of Benedict’s solution and heat gently without boiling in a waterbath.

Question 17

In the test for sucrose, how do we know that sucrose is present?

Answer 17

The mixture should turn blue.

Question 18

How do you test for starch?

Answer 18

Add 2 drops of iodine solution to 1cm solution of food or starch.

Question 19

In the test for starch, how do we know starch is present?

Answer 19

A black/blue colour indicates the presence of starch.

Question 20

What are the steps to the ethanol emulsion test for fats and oils?

Answer 20

1. Dissolve substances to be tested in ethanol (2ml).
2. Allow to settle for 2 minutes.
3. Empty any clear liquid into a test tube containing 2ml of distilled water.

Question 21

In the ethanol emulsion test, how do we know fats and oils are present?

Answer 21

A milky emulsion shows fats are present, if the mixture remains clear, no fats are present.

Question 22

How is water important as a solvent?

Answer 22

• Dissolved substances can be easily transported around organisms - e.g. xylem and phloem of plants and dissolved food molecules in the blood.
• Digested food molecules are in the alimentary canal but need to be moved to cells all over the body - without water as a solvent, this would not be possible.
• Toxic substances such as urea and substances in excess of requirements such as salts can dissolve in water which makes them easy to remove from the body in urine.
• Water is also an important part of the cytoplasm and plays a role in ensuring metabolic reactions can happen necessary in cells.

Question 23

What are the steps to the biuret test for proteins?

Answer 23

• To a 1 cm solution of food in a test tube, add an equal amount of 5% NaOH.
• Dribble a small amount of 1% CuSO4 solution down the side of the test tube.

Question 24

What indicates the presence of protein in the biuret test for proteins?

Answer 24

A purple ring at the interface indicates the presence of protein.