AQA A-LEVEL BIOLOGY PAPER 1
QUESTIONS AND ANSWERS GRADED
A+
klarge molecules often contain carbon. why? - they can readily form bonds with other carbon atoms. this
forms a 'backbone'. other atoms can then attach.
describe benedicts test for reducing sugars - add equal volumes of the sugar sample and benedicts
reagent.
heat the mixture in a water bath for 5 minutes.
brick red precipitate will form.
what is a reducing sugar? - a sugar that can reduce (give electrons to) another chemical.
describe the benedicts test for non reducing sugars - with food sample, add an equal volume of dilute
hydrochloric acid in a test tube.
place test tube in water bath for 5 mins.
add sodium hydrogencarbonate solution.
heat resulting solution with an equal volume of benedicts. solution for 5 minutes.
turns orange/brown.
what does dilute hydrochloric acid do in the benedicts test for non reducing sugars? - it hydrolyses any
disaccharide into monosaccharides, thus also forming reducing sugars.
describe the structure of starch - chains of alpha glucose
some chains are branched= amylopetcin
some chains are coiled= amylose
,what purpose does the structure of amylose serve? - makes the molecule compact so it is stored more
easily.
what purpose does the structure of amylopectin serve? - more surface area for enzymes to work on,
thus glucose molecules can be released at a much quicker rate.
how is the structure of starch suited to its function? - 1. starch is insolube so it doesnt affect water
potential
2. it is large enough that it doesnt diffuse out of cells
3. compact enough so that a lot of it can be stored in a small space
4. branched= each end can simultaneously be acted on by enzymes, so glucose is quickly released
how is the structure of glycogen suited to its function? - 1. insoluble, so no effect on water potential of
cell
2. insoluble, so doesnt diffuse out of cells
3. compact, a lot of it can be stored in a small space
4. very highly branched= each end can simultaneously be acted on by enzymes, so glucose is quickly
released
why do animals need highly branched glycogen? - because animals metabolic rate is faster than plants
and so needs glucose to be released quicker.
describe the structure of cellulose - made up of straight chains of beta glucose
the chains are parallel to each other, so H bonds form cross-linkages
all the H bonds together strengthens the cellulose
forms microfibrils
draw alpha and beta glucose -
how does the structure of triglycerides relate to their properties? - 1. triglycerides have a high ratio of
energy-storing carbon-hydrogen bonds to carbon atoms, so its a good source of energy.
, 2. low mass to energy ratio, so theyre good energy storage molecules.
3. large and non-polar, therefore insoluble, therefore don't affect osmosis.
4. high ratio of hydrogen to oxygen atoms, so can release water when oxidised, hence provide a source
of water
what are the roles of lipids? - 1. source of energy
2. waterproofing
3. insulation
4. protection
how does the structure of phospholipids relate to their properties? - 1. polar, therefore will position itself
to form a bilayer
2. the structure allows them to form glycolipids by combining with carbohydrates within the cell-surface
membrane. these are important in cell recognition.
draw the structure of an amino acid -
draw how a dipeptide forms -
what is meant by 'primary sequence' of a protein - The unique sequence of amino acids that make up a
protein or polypeptide chain
what is meant by 'secondary sequence' of a protein - The way in which the primary structure of a
polypeptide chain folds e.g. alpha helix or beta pleated sheets. shape is held by H bonds.
what is meant by 'tertiary sequence' of a protein - This is the overall 3-D structure of the protein.
The shape of the protein is held together by H bonds and ionic bonds and disulfide bridges.
what is meant by 'quaternary sequence' of a protein - If a protein is made up of several polypeptide
chains that are linked in various ways, the way they are arranged is called the quaternary structure.
QUESTIONS AND ANSWERS GRADED
A+
klarge molecules often contain carbon. why? - they can readily form bonds with other carbon atoms. this
forms a 'backbone'. other atoms can then attach.
describe benedicts test for reducing sugars - add equal volumes of the sugar sample and benedicts
reagent.
heat the mixture in a water bath for 5 minutes.
brick red precipitate will form.
what is a reducing sugar? - a sugar that can reduce (give electrons to) another chemical.
describe the benedicts test for non reducing sugars - with food sample, add an equal volume of dilute
hydrochloric acid in a test tube.
place test tube in water bath for 5 mins.
add sodium hydrogencarbonate solution.
heat resulting solution with an equal volume of benedicts. solution for 5 minutes.
turns orange/brown.
what does dilute hydrochloric acid do in the benedicts test for non reducing sugars? - it hydrolyses any
disaccharide into monosaccharides, thus also forming reducing sugars.
describe the structure of starch - chains of alpha glucose
some chains are branched= amylopetcin
some chains are coiled= amylose
,what purpose does the structure of amylose serve? - makes the molecule compact so it is stored more
easily.
what purpose does the structure of amylopectin serve? - more surface area for enzymes to work on,
thus glucose molecules can be released at a much quicker rate.
how is the structure of starch suited to its function? - 1. starch is insolube so it doesnt affect water
potential
2. it is large enough that it doesnt diffuse out of cells
3. compact enough so that a lot of it can be stored in a small space
4. branched= each end can simultaneously be acted on by enzymes, so glucose is quickly released
how is the structure of glycogen suited to its function? - 1. insoluble, so no effect on water potential of
cell
2. insoluble, so doesnt diffuse out of cells
3. compact, a lot of it can be stored in a small space
4. very highly branched= each end can simultaneously be acted on by enzymes, so glucose is quickly
released
why do animals need highly branched glycogen? - because animals metabolic rate is faster than plants
and so needs glucose to be released quicker.
describe the structure of cellulose - made up of straight chains of beta glucose
the chains are parallel to each other, so H bonds form cross-linkages
all the H bonds together strengthens the cellulose
forms microfibrils
draw alpha and beta glucose -
how does the structure of triglycerides relate to their properties? - 1. triglycerides have a high ratio of
energy-storing carbon-hydrogen bonds to carbon atoms, so its a good source of energy.
, 2. low mass to energy ratio, so theyre good energy storage molecules.
3. large and non-polar, therefore insoluble, therefore don't affect osmosis.
4. high ratio of hydrogen to oxygen atoms, so can release water when oxidised, hence provide a source
of water
what are the roles of lipids? - 1. source of energy
2. waterproofing
3. insulation
4. protection
how does the structure of phospholipids relate to their properties? - 1. polar, therefore will position itself
to form a bilayer
2. the structure allows them to form glycolipids by combining with carbohydrates within the cell-surface
membrane. these are important in cell recognition.
draw the structure of an amino acid -
draw how a dipeptide forms -
what is meant by 'primary sequence' of a protein - The unique sequence of amino acids that make up a
protein or polypeptide chain
what is meant by 'secondary sequence' of a protein - The way in which the primary structure of a
polypeptide chain folds e.g. alpha helix or beta pleated sheets. shape is held by H bonds.
what is meant by 'tertiary sequence' of a protein - This is the overall 3-D structure of the protein.
The shape of the protein is held together by H bonds and ionic bonds and disulfide bridges.
what is meant by 'quaternary sequence' of a protein - If a protein is made up of several polypeptide
chains that are linked in various ways, the way they are arranged is called the quaternary structure.
