Biological molecules Questions with
Correct Answers
Large molecules often contain carbon. Explain why this is. - ANSWERSCarbon atoms
readily link to one another to form a chain.
Explain why Benedict's reagent turns red when heated with a reducing sugar. -
ANSWERSSugar donates electrons that reduce blue copper(II) sulfate to orange
copper(I) oxide.
(Semi-quantitative use of Benedict's test) Suggest a ways in which different
concentrations of reducing sugar could be estimated. - ANSWERS1. Compare colour
changes.
2. Dry the precipitate in each sample and weigh it. The heavier the precipitate the more
reducing sugar is present.
(Semi-quantitative use of Benedict's test) Explain why it is not possible to distinguish
between very concentrated samples, even when their concentrations are different. -
ANSWERSOnce all the copper(II) sulfate has been reduced to copper(I) oxide, further
amounts of reducing sugar cannot make a difference.
To hydrolyse a disaccharide it can be boiled with hydrochloric acid but if hydrolysis is
carried out by an enzyme a much lower temperature (40 degrees C) is required. Explain
why. - ANSWERSEnzymes are denatured at higher temperatures and this prevents
them functioning.
From the following list of carbohydrates, choose one or more that most closely fit each
of the statements below.
alpha-glucose starch cellulose beta-glucose glycogen
1. Stains deep blue with iodine solution.
2. Is known as 'animal starch'.
3. Found in plants.
4. Are polysaccharides. - ANSWERS1. Starch
2. Glycogen
3. Starch, cellulose, beta-glucose, alpha-glucose
4. Starch, cellulose glycogen
, From the following list of carbohydrates, choose one or more that most closely fit each
of the statements below.
alpha-glucose starch cellulose beta-glucose glycogen
5. Monosaccharide found in starch.
6. Has a structural function.
7. Can be hydrolysed.
8. Easily moves in and out of cells by facilitated diffusion. - ANSWERS5. Alpha-glucose
6. Cellulose
7. Starch, cellulose, glycogen
8. Alpha-glucose, beta-glucose
Fill in the missing words:
Fats and oils make up a group of lipids called ( 1 ) which, when hydrolysed, form ( 2 )
and fatty acids. A fatty acid with more than one C=C is described as ( 3 ). In a
phospholipid the number of fatty acids is ( 4 ); these are described as ( 5 ) because they
repel water. - ANSWERS( 1 ) Triglycerides
( 2 ) Glycerol
( 3 ) Polyunsaturated
( 4 ) Two
( 5 ) Hydrophobic
List differences between a triglyceride molecule and a phospholipid molecule. -
ANSWERSTriglyceride: 3 fatty acids, no phosphate group, non-polar.
Phospholipid: 2 fatty acids, 1 phosphate group, hydrophilic head and hydrophobic tail.
Organisms that move (e.g. animals) and parts of organisms that move (e.g. some plant
seeds) use lipids rather than carbohydrates as an energy store. Suggest one reason
why this is so. - ANSWERSLipids provide more than twice as much energy as
carbohydrate when they are oxidised. If fat is stored, the same amount of energy can be
provided for less than half the mass. It is a lighter storage product - a major advantage if
the organism is motile.
Explain why the quaternary structure of collagen makes it a suitable molecule for a
tendon. - ANSWERSIt has three polypeptide chains wound together to form a strong,
rope-like structure that has strength in the direction of pull of a tendon.
Suggest how the cross-linkages between the amino acids of polypeptide chains
increase the strength and stability of a collagen fibre. - ANSWERSPrevents the
individual polypeptide chains from sliding past one another and so they gain strength
because they act as a single unit.
The points where one collagen molecule ends and the next begins are spread
throughout the fibre rather than all being in the same position along it. Explain why this
arrangement of collagen molecules is necessary for the efficient functioning of a tendon.
- ANSWERSThe junctions between adjacent collagen molecules are points of
Correct Answers
Large molecules often contain carbon. Explain why this is. - ANSWERSCarbon atoms
readily link to one another to form a chain.
Explain why Benedict's reagent turns red when heated with a reducing sugar. -
ANSWERSSugar donates electrons that reduce blue copper(II) sulfate to orange
copper(I) oxide.
(Semi-quantitative use of Benedict's test) Suggest a ways in which different
concentrations of reducing sugar could be estimated. - ANSWERS1. Compare colour
changes.
2. Dry the precipitate in each sample and weigh it. The heavier the precipitate the more
reducing sugar is present.
(Semi-quantitative use of Benedict's test) Explain why it is not possible to distinguish
between very concentrated samples, even when their concentrations are different. -
ANSWERSOnce all the copper(II) sulfate has been reduced to copper(I) oxide, further
amounts of reducing sugar cannot make a difference.
To hydrolyse a disaccharide it can be boiled with hydrochloric acid but if hydrolysis is
carried out by an enzyme a much lower temperature (40 degrees C) is required. Explain
why. - ANSWERSEnzymes are denatured at higher temperatures and this prevents
them functioning.
From the following list of carbohydrates, choose one or more that most closely fit each
of the statements below.
alpha-glucose starch cellulose beta-glucose glycogen
1. Stains deep blue with iodine solution.
2. Is known as 'animal starch'.
3. Found in plants.
4. Are polysaccharides. - ANSWERS1. Starch
2. Glycogen
3. Starch, cellulose, beta-glucose, alpha-glucose
4. Starch, cellulose glycogen
, From the following list of carbohydrates, choose one or more that most closely fit each
of the statements below.
alpha-glucose starch cellulose beta-glucose glycogen
5. Monosaccharide found in starch.
6. Has a structural function.
7. Can be hydrolysed.
8. Easily moves in and out of cells by facilitated diffusion. - ANSWERS5. Alpha-glucose
6. Cellulose
7. Starch, cellulose, glycogen
8. Alpha-glucose, beta-glucose
Fill in the missing words:
Fats and oils make up a group of lipids called ( 1 ) which, when hydrolysed, form ( 2 )
and fatty acids. A fatty acid with more than one C=C is described as ( 3 ). In a
phospholipid the number of fatty acids is ( 4 ); these are described as ( 5 ) because they
repel water. - ANSWERS( 1 ) Triglycerides
( 2 ) Glycerol
( 3 ) Polyunsaturated
( 4 ) Two
( 5 ) Hydrophobic
List differences between a triglyceride molecule and a phospholipid molecule. -
ANSWERSTriglyceride: 3 fatty acids, no phosphate group, non-polar.
Phospholipid: 2 fatty acids, 1 phosphate group, hydrophilic head and hydrophobic tail.
Organisms that move (e.g. animals) and parts of organisms that move (e.g. some plant
seeds) use lipids rather than carbohydrates as an energy store. Suggest one reason
why this is so. - ANSWERSLipids provide more than twice as much energy as
carbohydrate when they are oxidised. If fat is stored, the same amount of energy can be
provided for less than half the mass. It is a lighter storage product - a major advantage if
the organism is motile.
Explain why the quaternary structure of collagen makes it a suitable molecule for a
tendon. - ANSWERSIt has three polypeptide chains wound together to form a strong,
rope-like structure that has strength in the direction of pull of a tendon.
Suggest how the cross-linkages between the amino acids of polypeptide chains
increase the strength and stability of a collagen fibre. - ANSWERSPrevents the
individual polypeptide chains from sliding past one another and so they gain strength
because they act as a single unit.
The points where one collagen molecule ends and the next begins are spread
throughout the fibre rather than all being in the same position along it. Explain why this
arrangement of collagen molecules is necessary for the efficient functioning of a tendon.
- ANSWERSThe junctions between adjacent collagen molecules are points of
