AQA AS BIOLOGY ACTUAL TEST SCRIPT
WITH SOLVED QUESTIONS AND VERIFIED
ANSWERS
●● starch is a carbohydrate often stored in plant cells.
describe and explain two features of starch that make it a good storage
molecule. (2 marks)
Answer: 1. starch is insoluble so does not affect the water potential
2. starch is a branched molecule which makes it compact
●● which test identifies the presence of starch?
Answer: iodine/potassium iodide test
A solution of iodine and potassium iodide in water has a light
orange/brown colour. If it is added to a sample that contains starch, the
colour turns a deep blue.
●● what test identifies the presence of reducing sugars?
Answer: Benedict's reagent
,Any change from its initial blue colour indicates formation of copper I
sulphate which indicates the presence of a reducing sugar.
To test for the presence of reducing sugars, a food sample is dissolved in
boiling water. Then a small amount of BR is added and the solution
starts to cool. Over the next 10 minutes, the solution should change
colour. If the solution changes to blue then no glucose is present.
●● describe what a mole is and what is meant by a molar solution
Answer: the mole is the unit for measuring the amount of a substance
a molar solution is a solution that contains one mole of solute in each
litre of solution.
●● explain bonding and the formation of molecules
Answer: covalent bonding:
atoms share a pair of electrons in their outer shells. as a result, the outer
shell of both atoms is filled and a more stable compound, called a
molecule, is formed.
ionic bonding:
ions with opposite charges attract one another.
this electrostatic attraction is an ionic bond.
e.g. the positively charged sodium ion Na+ and negatively charged
chloride ion Cl- form an ionic bond to make sodium chloride.
, ionic bonds are weaker than covalent bonds.
hydrogen bonding:
a molecule with an uneven distribution of charge is said to be polarised/a
polar molecule. the negative region of one polarised molecule and the
positively charged region of another attract each other.
a weak electrostatic bond is formed between the two.
although each bond is individually weak, they can collectively form
important forces that alter the physical properties of molecules e.g. in
water
●● describe polymerisation and state what macromolecules are.
Answer: polymerisation is the process by which polymers are formed,
by linking monomers together to form longer chains.
a macromolecule is a very large molecule, created by the polymerisation
of many smaller subunits.
●● describe condensation and hydrolysis
Answer: reactions that produce water by the joining together of sub-
units are called condensation reactions.
the formation of a polypeptide from amino acids and polysaccharide
starch from monosaccharide gluocse are both condensation reactions.
WITH SOLVED QUESTIONS AND VERIFIED
ANSWERS
●● starch is a carbohydrate often stored in plant cells.
describe and explain two features of starch that make it a good storage
molecule. (2 marks)
Answer: 1. starch is insoluble so does not affect the water potential
2. starch is a branched molecule which makes it compact
●● which test identifies the presence of starch?
Answer: iodine/potassium iodide test
A solution of iodine and potassium iodide in water has a light
orange/brown colour. If it is added to a sample that contains starch, the
colour turns a deep blue.
●● what test identifies the presence of reducing sugars?
Answer: Benedict's reagent
,Any change from its initial blue colour indicates formation of copper I
sulphate which indicates the presence of a reducing sugar.
To test for the presence of reducing sugars, a food sample is dissolved in
boiling water. Then a small amount of BR is added and the solution
starts to cool. Over the next 10 minutes, the solution should change
colour. If the solution changes to blue then no glucose is present.
●● describe what a mole is and what is meant by a molar solution
Answer: the mole is the unit for measuring the amount of a substance
a molar solution is a solution that contains one mole of solute in each
litre of solution.
●● explain bonding and the formation of molecules
Answer: covalent bonding:
atoms share a pair of electrons in their outer shells. as a result, the outer
shell of both atoms is filled and a more stable compound, called a
molecule, is formed.
ionic bonding:
ions with opposite charges attract one another.
this electrostatic attraction is an ionic bond.
e.g. the positively charged sodium ion Na+ and negatively charged
chloride ion Cl- form an ionic bond to make sodium chloride.
, ionic bonds are weaker than covalent bonds.
hydrogen bonding:
a molecule with an uneven distribution of charge is said to be polarised/a
polar molecule. the negative region of one polarised molecule and the
positively charged region of another attract each other.
a weak electrostatic bond is formed between the two.
although each bond is individually weak, they can collectively form
important forces that alter the physical properties of molecules e.g. in
water
●● describe polymerisation and state what macromolecules are.
Answer: polymerisation is the process by which polymers are formed,
by linking monomers together to form longer chains.
a macromolecule is a very large molecule, created by the polymerisation
of many smaller subunits.
●● describe condensation and hydrolysis
Answer: reactions that produce water by the joining together of sub-
units are called condensation reactions.
the formation of a polypeptide from amino acids and polysaccharide
starch from monosaccharide gluocse are both condensation reactions.
