AQA A-Level Biology
3.1 Biological
Molecules
Mark scheme
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,1.
1 hydrogen bond represented as,
horizontal / vertical, dashed line between O on one molecule and H on the adjacent
molecule;
DO NOT CREDIT if >1 H bond is drawn between the same two molecules
2 hydrogen / H, bond label (on any drawn bond between 2 molecules);
3 (delta positive) δ+ on each drawn H
and (delta negative) (2) δ– on each drawn O;
if both molecules drawn, δ+ and δ– on all atoms.
ACCEPT d (lower case) for δ
[3]
2. ice floats
P1 (ice is less dense because) molecules spread out;
P2 molecules form a crystal structure / lattice / AW;
P3 ice forms an insulating layer / clearly described;
e.g. acts as a barrier to the cold
P4 water (below ice), does not freeze / still liquid / remains water / kept at higher
temperature;
S1 organisms do not freeze;
DO NOT ACCEPT die (because ‘survival’ stated in stem)
S2 animals / organisms, can still, swim / move;
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,S3 allows, currents / nutrients, to circulate;
solubility
P5 ions / named ion, polar / charged;
P6 ions /named ion, attracted to / bind to / interact with, water;
S4 (named) organisms / plants / animals, uptake / AW, minerals / named mineral /
nutrients;
ACCEPT obtain / enters / goes in / gets
S5 correct use of named, mineral / nutrient, in organism;
needs to be more specific than ‘for growth / metabolism’ suitable examples include
but are not limited to: nitrates for amino acids / protein / (named) nucleic acid /
phosphate for ATP / phospholipids / plasma membrane / magnesium for chlorophyll
etc
temperature stability
P7 many / stable, (hydrogen) bonds between molecules;
Many hydrogen bonds between molecules = 2 marks (gets P7 and H)
P8 at lot of energy to, force apart molecules / break bonds;
ACCEPT heat as an alternative to energy
P9 high (specific) heat capacity;
DO NOT CREDIT latent heat capacity
S6 temperature does not change much / small variation in temperature;
could refer to organisms or surrounding water
ACCEPT stays cool in summer / stays warm in winter
DO NOT CREDIT constant alone
S7 effect of temperature on, enzymes / metabolic rate;
ACCEPT any reference to temperature affecting enzyme activity / metabolic
rate
S8 gases remain soluble;
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, Award once in any section
H hydrogen bonds;
DO NOT CREDIT if in incorrect context
(e.g. they are strong bonds)
7 max
QWC - Award if you see a P mark and an S mark within the same section;
Look for the S mark first, then award QWC if there is a P mark in the same
section in the mark scheme
1
[8]
3. hydrolysis / hydrolytic;
hydrophilic;
ACCEPT phonetic spelling throughout
IGNORE head
[2]
4.
(i) X;
1
(ii)
1 substrate / PABA, and, inhibitor / sulfonamide, similar shape;
ACCEPT similar structure DO NOT CREDIT same
2 able to, bind / fit into / block, active site;
3 (shape) complementary to active site;
DO NOT CREDIT refs to PABA and sulfonamide being complementary to
each other or to the enzyme (alone)
4 both have, hex / benzene / 6-C, (ring);
5 both have, NH2 / amine;
alevelbiology.co.uk
3.1 Biological
Molecules
Mark scheme
alevelbiology.co.uk
,1.
1 hydrogen bond represented as,
horizontal / vertical, dashed line between O on one molecule and H on the adjacent
molecule;
DO NOT CREDIT if >1 H bond is drawn between the same two molecules
2 hydrogen / H, bond label (on any drawn bond between 2 molecules);
3 (delta positive) δ+ on each drawn H
and (delta negative) (2) δ– on each drawn O;
if both molecules drawn, δ+ and δ– on all atoms.
ACCEPT d (lower case) for δ
[3]
2. ice floats
P1 (ice is less dense because) molecules spread out;
P2 molecules form a crystal structure / lattice / AW;
P3 ice forms an insulating layer / clearly described;
e.g. acts as a barrier to the cold
P4 water (below ice), does not freeze / still liquid / remains water / kept at higher
temperature;
S1 organisms do not freeze;
DO NOT ACCEPT die (because ‘survival’ stated in stem)
S2 animals / organisms, can still, swim / move;
alevelbiology.co.uk
,S3 allows, currents / nutrients, to circulate;
solubility
P5 ions / named ion, polar / charged;
P6 ions /named ion, attracted to / bind to / interact with, water;
S4 (named) organisms / plants / animals, uptake / AW, minerals / named mineral /
nutrients;
ACCEPT obtain / enters / goes in / gets
S5 correct use of named, mineral / nutrient, in organism;
needs to be more specific than ‘for growth / metabolism’ suitable examples include
but are not limited to: nitrates for amino acids / protein / (named) nucleic acid /
phosphate for ATP / phospholipids / plasma membrane / magnesium for chlorophyll
etc
temperature stability
P7 many / stable, (hydrogen) bonds between molecules;
Many hydrogen bonds between molecules = 2 marks (gets P7 and H)
P8 at lot of energy to, force apart molecules / break bonds;
ACCEPT heat as an alternative to energy
P9 high (specific) heat capacity;
DO NOT CREDIT latent heat capacity
S6 temperature does not change much / small variation in temperature;
could refer to organisms or surrounding water
ACCEPT stays cool in summer / stays warm in winter
DO NOT CREDIT constant alone
S7 effect of temperature on, enzymes / metabolic rate;
ACCEPT any reference to temperature affecting enzyme activity / metabolic
rate
S8 gases remain soluble;
alevelbiology.co.uk
, Award once in any section
H hydrogen bonds;
DO NOT CREDIT if in incorrect context
(e.g. they are strong bonds)
7 max
QWC - Award if you see a P mark and an S mark within the same section;
Look for the S mark first, then award QWC if there is a P mark in the same
section in the mark scheme
1
[8]
3. hydrolysis / hydrolytic;
hydrophilic;
ACCEPT phonetic spelling throughout
IGNORE head
[2]
4.
(i) X;
1
(ii)
1 substrate / PABA, and, inhibitor / sulfonamide, similar shape;
ACCEPT similar structure DO NOT CREDIT same
2 able to, bind / fit into / block, active site;
3 (shape) complementary to active site;
DO NOT CREDIT refs to PABA and sulfonamide being complementary to
each other or to the enzyme (alone)
4 both have, hex / benzene / 6-C, (ring);
5 both have, NH2 / amine;
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