-
(a) Describe how a nerve impulse crosses a cholinergic synapse.
[9](a) 1. action potential / depolarisation, reaches presynaptic
membrane ; 2. calcium (ion) channels open / presynaptic membrane
becomes more permeable to Ca2+ ; 3. Ca2+ flood into presynaptic
neurone ; R membrane 4. this causes vesicles of (neuro)transmitter
to move towards presynaptic membrane ; 5. ref. acetylcholine / ACh
; 6. vesicle fuses with presynaptic membrane / exocytosis ; 7. ACh
released into synaptic cleft ; 8. ACh diffuses across (cleft) ; 9.
ACh binds to receptor (proteins) / AW ; 10. on postsynaptic
membrane ; R neurone 11. proteins change shape / channels open ;
12. sodium ions rush into postsynaptic neurone ; R membrane 13.
postsynaptic membrane depolarised ; 14. action potential / nerve
impulse ; 15. AVP ; e.g. action of acetylcholinesterase
(b) Explain the roles of synapses in the nervous system. [6]B)
16. ensure one-way transmission ; 17. receptor (proteins) only in
postsynaptic, membrane / neurone ; ora 18. vesicles only in
presynaptic neurone ; ora 19. ref. adaptation ; 20. increased range
of actions ; 21. due to interconnection of many nerve pathways ;
22. ref. inhibitory synapses ; 23. involved in memory / learning ;
24. due to new synapses being formed ; 25. AVP; e.g. summation /
discrimination
(a)Describe the structure of a chloroplast. [9] (a) 1. biconvex
disc ; 2. 3-10 m diameter ; 3. double, membrane / envelope ; 4.
internal membrane system ; 5. flattened or fluid-filled sacs /
thylakoids ; 6. arranged in stacks / grana ; 7. hold pigments /
named pigment ; 8. ref. clusters of pigments / AW ;
-
9. (membrane of grana) hold ATP synthase ; 10. intergranal
lamellae ; 11. stroma / ground substance ; 12. lipids / starch
grains ;
13. contains enzymes of Calvin cycle ; 14. stroma contains
ribosomes / DNA etc ; 15. AVP ; e.g. variation in shape between
species [9 max
(b) Explain how the palisade mesophyll cells of a leaf are
adapted for photosynthesis. [6(b) 16. closely packed -- to absorb
more incident light / AW ;
17. palisade mesophyll near upper surface of leaf -- to maximize
light interception ;
18. arranged at right angles to leaf surface -- to reduce number
of light absorbing walls ;
19. cylindrical cells -- producing air spaces between cells
;
20. air spaces -- act as reservoir of carbon dioxide ;
21. large surface area -- for gas exchange ;
22. cell walls thin -- so short diffusion pathway ;
23. large vacuole -- pushes chloroplasts to edge of cell ;
24. chloroplasts on periphery -- to absorb light more
efficiently ;
25. large number of chloroplasts -- to maximise light absorption
;
26. chloroplasts can move within cells -- towards light ;
27. chloroplasts can move away from high light intensity -- to
avoid damage ;
(a) Describe the structure of photosystems and explain how a
photosystem functions in
cyclic photophosphorylation. [9]arranged in light harvesting
clusters ; A system
primary pigments / chlorophyll a ;
-
at reaction centre ;
P700 / P1, absorbs at 700(nm) ;
P680 / P11, absorbs at 680(nm) ;
accessory pigments / chlorophyll b / carotenoids ; ignore ref to
chlorophyll a
surround, primary pigment / reaction centre / chlorophyll a
;
absorb light ; linked to 6
pass energy to, primary pigment / reaction centre / ;
chlorophyll a ;
P700 / PI, involved in cyclic photophosphorylation ;
(light absorbed results in) electron excited / AW ;
emitted from chlorophyll ;
chain of electron carriers / ETC ;
ATP synthesis ;
electron returns to, P700 / P1 ;
(b)Explain briefly how reduced NADP is formed in the
light-dependent stage of photosynthesis and is used in the
light-independent stage. [6]photolysis of water ;
releases H+ ; R H / hydrogen atoms by, P680 / PII ; e- released
; by, P700 / PI ; both combine with NADP ; (reduced NADP) reduces,
GP / PGA ; to TP ; ATP used ; NADP, regenerated / oxidized
-
(a)Explain how meiosis and fertilisation can result in genetic
variation amongst offspring.
chiasma / crossing over ; between non-sister chromatids ; of,
homologous chromosomes / bivalent ; in prophase 1 ; linked to 1
exchange of genetic material / AW ; R genes unqualified linkage
groups broken ; new combination of alleles ; independent assortment
; R random assortment metaphase 1 ; linked to 8 detail of
independent assortment ; possible mutation ; random mating ; random
fusion of gametes ; (b)Explain, using examples, how the environment
may affect the phenotype of an organism.phenotypic variation
results from interaction of genotype and environment / VP = VG + VE
; environment may limit expression of gene(s) / AW ; e.g. for size
/ mass / height ; because, food / nutrients / ion, missing /
malnutrition ; named, nutrient / ion / mineral, missing ;
environment may, trigger / switch on, gene ; ref. low temperature
and change in animal colour ; ref. high temperature and, curled
wing in Drosophila / gender in crocodiles ; ref. UV light and
melanin production ; ref. wavelength of light and, flowering /
germination / fruit colour ; other named trigger plus example ;
environment effect usually greater on polygenes / ora ; environment
may induce mutation affecting phenotype ;
-
Q)Describe the structure of a kidney, including its associated
blood vessels.1. (outer) cortex ; 2. medulla ; 3. pelvis ; 4. renal
artery ; 5. renal vein ; 6. nephron / (kidney) tubule ;7. renal
capsule / proximal convoluted tubule (pct) / distal convoluted
tubule (dct), in cortex ; 8. loop of Henle / collecting duct (cd),
in medulla ; 9. glomerulus ;10. afferent & efferent arterioles;
11. capillary network, surrounds tubule / in medulla ;
Q)Describe the mechanisms involved in reabsorption in the
proximal convoluted tubule and describe how the epithelial cells of
the proximal convoluted tubule are adapted to carry out this
process. [9]
mechanisms 12. active transport ; A actively pumped / uses ATP
13. Na+ , out of pct cells / into blood ; 14. (sets up) Na+ ion
gradient ; 15. facilitated diffusion ; 16. using protein carrier ;
A transport protein 17. cotransport (from lumen to pct cell); 18.
of, glucose / amino acids / ions; 19. osmosis ;
-
20. down water potential gradient ; 21. diffusion (in correct
context) ; 22. down a concentration gradient ; max 7adaptations 23.
microvilli ; A brush border 24. many mitochondria ;25. tight
junctions ; 26. folded, basal membrane / described ; 27. many,
transport proteins / cotransporters / pumps;28. AVP ; e.g. many
aquaporins
A)Explain the role of ATP in active transport of ions and in
named anabolic reactions. [7](a) Active transport or anabolic
reactions 1. ATP provides energy (linked to either) ; ignore ref.
to energy currency aloneactive transport2. movement against
concentration gradient ;3. carrier / transport, protein (in
membrane) ; ignore pump 4. binds to (specific) ion ; 5. protein
changes shape ; anabolic reactions 6. synthesis of complex
substances from simpler ones ; 7. starch / cellulose / glycogen,
from, monosaccharides / named monosaccharides / named sugar ; 8.
glycosidic bonds ;9. lipid / triglyceride, from fatty acids and
glycerol ; 10. ester bonds ; 11. polypeptides / proteins, from
amino acids ; 12. peptide bonds ;13. other named polymer from
suitable monomer ; 14. appropriate named bond ;
-
Outline the process of anaerobic respiration in both mammal and
yeast cells. [8]general15. reduced NAD produced in glycolysis ; A
glycolysis described16. small amount of ATP produced in glycolysis
; in yeast cells 17. pyruvate converted to ethanal ;18. carbon
dioxide released / decarboxylation ;19. ethanal, reduced / accepts
H ;20. by reduced NAD ;21. ethanol formed ; in mammalian cells22.
pyruvate converted to lactate ; 23. by reduced NAD ;24. in, liver /
muscle, cells ; 25. AVP ;;26. e.g. reversible in mammal /
irreversible in yeast / single step in mammal / more than 1 in
yeast / reoxidised NAD allows glycolysis to continue / named enzyme
only award either mp19 or mp23 [
(a) Outline, with reference to blood glucose concentration, the
principles of homeostasis in mammals. [6](a) 1. (homeostasis is)
maintenance of, constant / stable, internal environment ;2.
irrespective of changes in external environment ;3. negative
feedback ;4. receptor /appropriate named cell, detects change in,
parameter / blood glucose concentration ; 5. (receptors are) / ,
cells ;
-
6. in, Islets of Langerhans / pancreas ;7. insulin / glucagon,
released ;8. action taken by effector / correct action described
(liver / muscle, cell) ;9. restoration of, norm / set point / AW ;
10. ref. fluctuation around the norm ;
(b) Describe the roles of the endocrine and nervous systems in
control and coordination in mammals.
(b) endocrine 11. hormones ; 12. chemical messengers ; A
chemicals that transfer information 13. ductless glands /
(released) into blood ; 14. target, organs / cells ; 15. ref.
receptors on cell membranes ; 16. example of named hormone and
effect ; nervous17. impulses / action potentials ; R electrical,
signals / current 18. along, neurones ; R nerves 19. synapse (with
target) / neuromuscular junction ; 20. ref. receptor / effector or
sensory / motor, neurones ; differences endocrine21. slow effect /
ora ; 22. long lasting effect / ora ; 23. widespread effect / ora ;
24. AVP ; e.g. extra detail of synapse
(a)Outline the ways in which the endocrine and nervous systems
carry out their roles in control and coordination in animals.
[8]
(a) endocrine1. hormones ; 2. chemical messengers ; A chemicals
that transfer information
-
3. ductless glands / (released) into blood ; 4. target, organs /
cells ; 5. ref. receptors on cell membranes ; 6. example of named
hormone and effect ;nervous 7. impulses/ action potentials ; R
electrical, signals / current 8. along, axon / neurones / nerve
fibres ; R nerves R across 9. synapse (with target) / neuromuscular
junction ; 10. ref. receptor / sensory neurones ; 11. ref. effector
/ motor neurones ; differences endocrine 12. slow effect / ora ;
13. long lasting effect / ora ; 14. widespread effect / ora ; 15.
AVP ; e.g. extra detail of synapse / hormone changes triggered
within cells [8 max]
Describe the part played by auxins in apical dominance in a
plant shoot.[7]
(b) 16. IAA / plant growth regulator ; R plant hormone 17.
synthesised in, growing tips / apical buds / meristems ; R root tip
18. moves by diffusion ; 19. moves by active transport ; 20. from
cell to cell ; 21. also, mass flow / in phloem ; 22. stimulates
cell elongation ; R cell enlargement 23. inhibits, side / lateral,
buds / growth ; A inhibits branching 24. plant grows, upwards /
taller ; A stem elongates 25. auxin not solely responsible or
interaction between auxin and other plant growth regulators ; 26.
AVP ; e.g. role of ABA and lateral bud inhibition 27. AVP ; e.g.
cytokinins antagonistic to IAA / gibberellins enhance IAA [7
max]
-
(a)Describe how non-cyclic photophosphorylation produces ATP and
reduced NADP. [9](a) 1. photosystem I (PI) and photosystem II (PII)
involved ; 2. light harvesting clusters ; 3. light absorbed by
accessory pigments ; 4. primary pigment is chlorophyll a ; 5.
energy passed to, primary pigment / chlorophyll a ; 6. electrons,
excited / raised to higher energy level ; 7. (electrons) taken up
by electron acceptor ; 8. (electrons) pass down electron carrier
chain (to produce ATP) ; 9. PII has (water splitting) enzyme ; 10.
water split into protons, electrons and oxygen ; A equation 11.
photolysis ; 12. electrons from PII pass to PI / electrons from
water pass to PII ; 13. to replace those lost ; give either in
relation to PI or PII 14. protons and electrons combine with NADP
(to produce reduced NADP) ;can award these marking points from a
diagram [9 max]
(b)Outline the steps of the Calvin cycle. [6](b) 15. RuBP
combines with carbon dioxide ; 16. rubisco ; 17. forms unstable 6C
compound ; 18. produces two molecules of, GP / PGA ; 19. GP / PGA,
converted to TP ; 20. by reduced NADP and ATP ; 21. from light
dependent stage ; 22. TP used to regenerate RuBP ; 23. using ATP ;
24. TP can form, hexose / fatty acids / acetyl CoA [6 max]
(a) Describe the photoactivation of chlorophyll and its role in
cyclic photophosphorylation.[8](a) 1. (photosynthetic pigments)
arranged in light harvesting clusters ;
-
2. primary pigments / chlorophyll a ; 3. at reaction centre ; 4.
P700 / Pl, absorbs light at 700nm ; 5. accessory pigments /
chlorophyll b / carotenoids ; 6. surround, primary pigment /
reaction centre / chlorophyll a ; 7. absorb light ; 8. pass energy
to, primary pigment / reaction centre / chlorophyll a ; 9. (light
absorbed results in) electron excited / AW ; 10. emitted from,
chlorophyll / primary pigment / reaction centre ; 11. passes to
electron, acceptor / carrier ; 12. (electron) passes along, chain
of electron carriers / ETC ; 13. ATP (synthesis) ; 14. electron
returns to, P700 / Pl ; [8 max]
(b)Explain briefly how reduced NADP is formed in the
light-dependent stage and how it is used in the light-independent
stage. [7](b) 15. photolysis of water ; 16. releases H+ ; R H /
hydrogen atoms 17. by, P680 / PII ; 18. e released from, P700 / PI
; 19. e (from PI) and H+ combine with NADP ; 20. used in Calvin
cycle ; 21. reduces, GP / PGA ; 22. to TP ; 23. ATP used (during
reduction of GP) ; 24. NADP, regenerated / oxidised ;
-
(a) Describe the role of abscisic acid (ABA) in the closure of a
stoma. [8]
(a) accept ABA for abscisic acid 1. stress hormone ; 2. plant
secretes ABA in, high temperatures / dry conditions ; 3. ABA binds
to receptors ; 4. on plasma membranes of guard cells ; 5. inhibits
proton pump / H+ not pumped out of cell ; 6. high H+ conc /
positive charge, inside cell ; 7. K+ diffuses out of cell ; 8.
water potential of cell increases ; A increase in solute potential
9. water moves out of cell by osmosis ; 10. volume of guard cells
decreases ; 11. guard cells become flaccid ; 12. response very fast
; [8 max]
(b)Describe the role of gibberellins in the germination of
barley seeds. [7]
(b) 13. (barley) seed is, dormant / metabolically inactive ; 14.
seed absorbs water ; 15. embryo produces gibberellin ; 16.
gibberellin stimulates aleurone layer ; 17. to produce amylase ;
18. amylase hydrolyses starch ; 19. in endosperm ; 20. to maltose /
glucose ; 21. embryo uses sugars for respiration ; 22. energy used
for growth ; 23. gibberellins affect, gene / transcription of mRNA,
coding for amylase ; [7 max]
-
(a) Describe how the structure of a chloroplast is related to
its functions. [9](a) 1. ground substance / stroma ;2. for, light
independent stage / Calvin cycle ;3. contains enzymes / named
enzyme e.g. rubisco ;4. also, sugars / lipids / starch / ribosomes
/ DNA ;5. internal membrane system ;6. for, light dependent stage
;7. fluid-filled sacs / thylakoids ;8. grana are stacks of
thylakoids ;9. (grana) hold (photosynthetic) pigments ;10. (grana)
have large surface area for (maximum) light absorption ;11.
(pigments are arranged in), light harvesting clusters /
photosystems ;
12. primary pigment / reaction centre / chlorophyll a,
surrounded by accessory pigments ;13. (accessory pigments) pass
energy to, primary pigment / reaction centre / chlorophyll a ;14.
different photosystems absorb light at different wavelengths ;15.
membranes hold, ATP synthase / electron carriers ;
16 for, photophosphorylation / chemiosmosis ; [9 max]
(b)
Describe how you would separate chloroplast pigments using
chromatography. [6](b) 17. grind leaf with solvent ;18. example of
solvent ; e.g. propanone19. leaf extract contains mixture of
pigments ;20. ref. concentrate extract ;21. further detail ; e.g.
pencil line drawn / extract placed on chromatography paper /
repetitive spotting / drying between spots22. paper placed
(vertically) in jar of (different) solvent ;23. solvent rises up
paper ;24. each pigment travels at different speed ;25. pigments
separated as they ascend ;26. distance moved by each pigment is
unique ;27. Rf value ;28. two dimensional chromatography ;29.
better separation of pigments ; [6 max]
(a) Explain how the palisade mesophyll cells of a leaf are
adapted for photosynthesis. [8]
(b) (a) 1 closely packed to absorb maximum light ;(c) 2
vertical/at right angles to surface of leaf to reduce number of
cross walls ;(d) 3 large vacuole pushes chloroplasts to edge of
cell ;(e) 4 chloroplasts at edge short diffusion path for carbon
dioxide ;(f) 5 chloroplasts at edge to absorb maximum light ;(g) 6
large number of chloroplasts to absorb maximum light ;(h) 7
cylindrical cells or air spaces to circulate gases/provide a
reservoir of CO2 ;(i) 8 large surface area for diffusion of gases
;(j) 9 moist cell surfaces for diffusion of gases ;(k) 10 cell
walls thin for maximum light penetration/diffusion of gases ;(l) 11
chloroplasts can move towards light ;(m)12 chloroplasts can move
away from high light intensity to avoid damage ; [8 max]
-
(c) Outline the light-independent stage of photosynthesis.
[7](d)(b) 13 Calvin cycle/stroma ;(e)14 carbon dioxide fixed by
RuBP ;(f) 15 rubisco ;(g)16 2 molecules of GP formed ; A PGA(h)17
(GP) forms TP ; A GALP/PGAL(i) 18 use of ATP ;(j) 19 use of,
reduced NADP/NADPH ;(k)20 from light dependent stage ;(l) 21 some
TP forms, hexose/sucrose/starch/cellulose/glycerol ;(m)22 some TP
converted to acetyl CoA ;(n)23 some TP used to regenerate RuBP
;(o)24 using ATP ;(p)allow either mp 18 or mp 24(q) marks can be
awarded on a diagram [7 max
(a) Describe the structure of a kidney nephron and its
associated blood vessels. [7](b)(a) 1 renal/Bowmans, capsule ;(c)2
ref. podocytes ;(d)3 (proximal convoluted tubule/distal convoluted
tubule/capsule) in cortex ;(e)4 proximal convoluted tubule ;(f) 5
loop of Henle ;(g)6 (loop) in medulla ;(h)7 distal convoluted
tubule ;(i) 8 afferent arteriole ;(j) 9 glomerulus ;(k)10 efferent
arteriole ;(l) 11 capillary network around/proximal convoluted
tubule/loop/distal convoluted tubule ;(m)12 collecting duct ;(n)
accept points on a labelled diagram [7 max]
Explain how glomerular filtrate is formed. [8](b) 13 endothelium
of, blood capillaries/glomerulus ;14 more/large, gaps between
endothelial cells ;15 podocytes ;16 large gaps between
podocytes/filtration slits ;17 basement membrane, selective
barrier/acts as a filter ;18 prevents, large protein/RMM > 68
000, passing through ;19 no cells pass through ;20 named molecule
which is filtered ; e.g. urea/water/glucose/uric
acid/creatinine/Na+/K+/Cl- ;21 high, blood/hydrostatic, pressure in
glomerulus ;22 afferent arteriole wider than efferent arteriole ;23
lower pressure in, renal/Bowmans, capsule ;24 fluid forced into
capsule/ultrafiltration ; [8 max]
[
(a) Describe the structure of photosystems and explain how a
photosystem functions incyclic photophosphorylation. [8]
-
(a) 1 arranged in light harvesting, clusters/system ;2 primary
pigments/chlorophyll a ;3 at reaction centre ;4 P700/P1, absorbs at
700(nm) ;5 P680/P11, absorbs at 680(nm) ;6 accessory
pigments/chlorophyll b/carotenoids, surround, primary
pigment/reactioncentre/ chlorophyll a ;7 pass energy to, primary
pigment/reaction centre/chlorophyll a ;8 P700 / PI, involved in
cyclic photophosphorylation ;9 (light absorbed results in) electron
excited/AW ;10 emitted from, chlorophyll/photosystem ;11 flows
along, chain of electron carriers/ETC ;12 ATP synthesis ;13
electron returns to, P700/P1 ; [8 max]
(b) Explain briefly how reduced NADP is formed in the
light-dependent stage and how it isused in the light-independent
stage. [7]
(b) 14 photolysis (of water) ;15 releases H+ ; R H/hydrogen
atoms16 by, P680/PII ;17 e- released ;18 by, P700/PI ;19 both
combine with NADP ;(reduced NADP)20 reduces, GP ; A PGA21 to TP ; A
PGAL / GALP22 ATP used ;23 NADP, regenerated/oxidised ; [7 max]
(a) Describe the structure of a myelinated sensory neurone.
[7]
1 nucleus in cell body ;2 (long) dendron ; R plural3 (shorter)
axon ;4 many mitochondria (in cell body) ;5 many RER/nissls
granules, (in cell body) ;6 synaptic knobs ;7 detail of synaptic
knob ;8 (terminal) dendrites ;9 Schwann cells ;10 detail of myelin
sheath ;11 nodes of Ranvier ;accept points on labelled diagram [7
max](b) Explain how an action potential is transmitted along a
sensory neurone. [8]
-
12 Na+ channels open ; A sodium channels13 Na+ enter cell ; R
enter membrane14 inside becomes, less negative/positive/+40mV or
membrane depolarised ;15 Na+ channels close ; A sodium channels16
K+ channels open ; A potassium channels17 K+ move out (of cell) ; R
of membrane18 inside becomes negative or membrane repolarised ; A
negative figuremax 519 local circuits/description ;20 (myelin
sheath/Schwann cells) insulate axon/does not allow movement of ions
;21 action potential/depolarisation, only at nodes (of
Ranvier)/gaps ;22 saltatory conduction/AW ;23 one-way transmission
;24VP ; e.g. hyperpolarisation/refractory period [8 max]
Describe a reflex arc and explain why such reflex arcs are
important. [7]strong stimulus in receptor / AW ;action potential /
impulses, along sensory neurone ;dorsal root of spinal nerve ;into
spinal cord ; synapse with intermediate neurone ;(then) motor
neurone ;action potential / impulses, to effector ;action potential
/ impulses, to brain ;response ; e.g. knee jerk 5 max can be on
diagramfast / immediate ;stops / limits, damage / danger ;automatic
/ no conscious thought ;innate / stereotyped / instinctive ;
[7]
Describe the structure of a myelin sheath and explain its role
in the speed of transmissionof a nerve impulse. [8]
Schwann cells ;wrap around axon ;sheath mainly lipid ;(sheath)
insulates axon (membrane) ;Na+ / K+, cannot pass through sheath /
can only pass throughmembrane at nodes ;depolarisation (of axon
membrane) cannot occur where there issheath / only at nodes of
Ranvier ;local circuits between nodes ;action potentials jump
between nodes ;saltatory conduction ;increases speed / reduces
time, of impulse transmission ;up to 100 ms-1 ;speed in
non-myelinated neurones about 0.5 ms-1 ;
-
(a) Outline the main features of the Krebs cycle. [9]acetyl CoA
combines with oxaloacetate ;to form citrate ;4C to 6C
;decarboxylation / CO2 released ;dehydrogenation / oxidation /
release of hydrogen ;reduced NAD produced / NAD accepts hydrogen
;reduced FAD produced / FAD accepts hydrogen ;ATP produced
;substrate level phosphorylation ;series of, steps / intermediates
; A many named steps off a diagramenzyme catalysed reactions
;oxaloacaetate regenerated ;occurs in mitochondrial matrix ;
Explain the role of NAD in aerobic respiration. [6]
coenzyme ;for dehydrogenase ;reduced ;carries, electrons and
protons / hydrogen / NADfrom Krebs cycle ;and glycolysis ;to ETC /
electron carrier chain / oxidation ;reoxidised / regenerated
hydrogen removed ;ATP produced ; [6 max]
Explain the roles of synapses in the nervous system. [6]
ensure one-way transmission;receptor (proteins) only in
postsynaptic, membrane / neurone ; oravesicles only in presynaptic
neurone ; oraadaptation / ACh amount reduces due to overuse of
synapse ;wide range of responses ;due to interconnection of many
nerve pathways ;inhibitory synapses affect other synapses ;involved
in memory / learning ;due to new synapses being formed ;summation /
discrimination ;
Describe and explain how a stoma is opened.
1 ref. ABA absence ;2 H+ transported out of guard cells,
actively / using ATP ;3 low H+ conc / negative charge, inside cell
;4 K+ channels open / K+ diffuses into cell ;5 water potential of
cell falls ; A decrease in solute potential6 water moves into cell
by osmosis ;7 volume of guard cells increase / turgor increases
;guard cells:8 have hoops of cellulose microfibrils which ensure
increase in length rather thandiameter ;9 have ends that are joined
together ;10 have, thicker inner walls / thinner outer walls ;
-
11 curve apart / bend, (to open stoma) ;
Describe the part played by the proximal convoluted tubules in
the functioning of thekidneys. [8]
1 selective reabsorption ;2 (pct cells have) villi / microvilli
/ large surface area ;3 (pct cells have) many mitochondria ;4 Na+
leave pct cells ;5 by active transport ;6 Na+ concentration falls
in (pct) cells / Na+ concentration gradient ;7 Na+ (diffuse) from
lumen into (pct) cells ;8 through, transporter / carrier, proteins
; ignore channel proteins9 cotransport ;10 of, glucose / amino
acids / vitamins / chloride ions ;11 (from pct cells) into
intercellular fluid ; linked to 1012 (then) diffusion into blood ;
linked to 1013 (normally) all glucose reabsorbed ;14 some water
reabsorbed ;15 some urea reabsorbed ;16 AVP ; e.g. creatinine
secreted into lumen [8 max]accept sodium ions but reject sodium or
Napenalise once only
Explain how the collecting ducts in the kidneys may reduce the
loss of water from thebody. [7]
17 ADH affects collecting duct ;18 binds to receptor on membrane
;19 increase membrane permeability (to water) / more water channels
;20 ref. enzyme controlled reactions ;21 produces (active)
phosphorylase ;22 (which causes) vesicles with, water channels /
aquaporins ; must be linked to 2323 to, move to / fuse with,
(plasma) membrane ;24 more water flows out of collecting duct ;25
down / along, water potential gradient ;26 (then) into blood ;27
urine (more) concentrated / small volume of urine ;28 ref. negative
feedback ;29 AVP ; e.g. role of loop of Henle in creating water
potential gradientmovement of urea increases water potential
gradient
9 (a) Explain how changes in the nucleotide sequence of DNA may
affect the amino acidsequence in a protein. [7]
(a) 1 code is three, bases / nucleotides ; A triplet code2
(gene) mutation ; R chromosome mutation3 base, substitution /
addition / deletion ;4 addition / deletion, large effect (on amino
acid sequence) ;
-
5 frame shift ;6 completely new code after mutation / alters
every 3 base sequence which follows ;7 (substitution) often has no
effect / silent mutation ;8 different triplet but same amino acid /
new amino acid in non-functional part of protein ;9 (substitution)
may have big effect (on amino acid sequence) ;10 could produce stop
codon ;11 sickle cell anaemia / PKU / cystic fibrosis ;12 reference
to transcription or translation in correct context ; A
description12a AVP ; e.g. protein produced, is non-functional / not
produced / incomplete [7 max]
(b) Explain how natural selection may bring about evolution.
[8]
13 individuals in population have great reproductive potential /
AW ;14 numbers in population remain roughly constant ;15 variation
in members of population ;16 environmental factors / named factor
(biotic or abiotic) ; linked to 17 and 1817 (cause) many, fail to
survive / die / do not reproduce ;18 those best adapted survive /
survival of the fittest ;19 (reproduce to) pass on alleles ; R
genes20 genetic variation leads to change in phenotype ;21 ref:
changes in, gene pool / allele frequency ;22 over time produces
evolutionary change ;23 new species arise from existing ones /
speciation ;24 directional / stabilising, selection ; [8 max]
9 (a) Outline the behaviour of chromosomes during meiosis. [9]do
not credit marking points out of sequencedo not credit marking
points out of sequenceprophase 11 idea of condensation of
chromosomes ;2 homologous chromosomes pair up / bivalent formed
;metaphase 13 homologous chromosomes / bivalents, line up on
equator ;4 of spindle ;5 by centromeres ;6 independent assortment /
described ;7 chiasmata / described ;8 crossing over / described
;anaphase 19 chromosomes move to poles ;10 homologous chromosomes /
bivalents, separate ;11 pulled by microtubules ;12 reduction
division ;metaphase 213 chromosomes line up on equator ;14 of
spindle ;
-
anaphase 215 centromeres divide ;16 chromatids move to poles ;17
pulled by microtubules ;9 (a)18 ref. haploid number ;allow 4 or
14allow 11 or 17 [9 max]Describe the ways by which gene mutations
can occur. [6]
19 change in, base / nucleotide, sequence (in DNA) ;20 during
DNA replication ;21 detail of change ; e.g. base, substitution /
addition / deletion22 frame shifts / AW ;23 different / new, allele
;24 random / spontaneous ;
25mutagens ;26ionising radiation ;27UV radiation
11 (a) Explain how changes in the nucleotide sequence of DNA may
affect the amino acidsequence in a protein.
11 (a) 1. (amino acid) code is three, bases / nucleotides ; A
triplet code2. (gene) mutation ; R chromosome mutation3. base /
nucleotide, substitution / addition / deletion4. addition /
deletion, has large effect (on amino acid sequence) ;5. frame shift
;6. completely new code after mutation / alters every 3 base
sequence which follows ;7. substitution may have little or no
effect / silent mutation ;8. different triplet but same amino acid
/ new amino acid in non-functional part of protein ;9. substitution
may have big effect (on amino acid sequence) ;10. could produce
stop codon ;11. sickle cell anaemia / PKU / cystic fibrosis ;
12. reference to transcription or translation in correct context
; A description [8 max
(b) Explain how the allele for haemophilia may be passed from a
man to his grandchildren.You may use genetic diagrams to support
your answer. [7]
(b) 13. (haemophilia) allele on X chromosome ; A gene14.
sex-linked ;15. (haemophilia) allele recessive ;16. man,
homogametic / has one X chromosome ;17. Y chromosome does not have
blood clotting gene ;18. only daughter(s) get his X chromosome ;19.
daughter(s) carrier(s) of (haemophilia) allele ;20. grandson(s) 50%
chance of having, (haemophilia) allele / haemophilia ;21.
granddaughter(s) 50% chance of carrying, (haemophilia) allele
;allow following marks from diagram22. correct symbols ; e.g. XH
and Xh explained23. mans genotype ; e.g. XhY ignore partners
genotype24. F1 (daughters) genotype ; e.g. XHXh ignore her partners
genotype25. F2 (grandsons) genotypes ; e.g. XhY XHY both
required
26. F2 (granddaughters) genotypes ; e.g. XHXH XHXh both required
or XhXh XHXh [7 max]
-
9 (a) Describe how crossing over and independent assortment can
lead to genetic variation.[9]
(a) 1 occur during meiosis I ;crossing over2 between non-sister
chromatids ;3 of, (a pair of) homologous chromosomes / a bivalent
;4 in prophase 1 ;5 at chiasma(ta) ;6 exchange of genetic material
/ AW ;R genes unqualified7 linkage groups broken / AW ;8 new
combination of alleles (within each chromosome) ;independent
assortment9 of homologous chromosomes pairs / bivalents ;10 each
pair lines up independently of others ;11 line up on equator ;12
(during) metaphase 1 ;13 results in gametes that are genetically
unique / AW
(a) Describe the first division of meiosis (meiosis I) in animal
cells. [6]1. reduction division / (to) halve number of chromosomes
/ diploid to haploid / AW ; 2. homologous chromosomes pair up /
bivalents form ; 3. ref. chiasmata / ref. crossing over ; 4.
homologous chromosome pairs / bivalents, line up on equator ; 5.
independent assortment ; 6. spindle / microtubules, attached to
centromeres ; 7. chromosomes of each pair pulled to opposite poles
; 8. by shortening of, spindle / microtubules ; 9. nuclear
envelopes re-form ; 10. cytokinesis / AW ; [6 max]
(b) Discuss the link between the frequency of sickle cell
anaemia and the number of cases
of malaria. [9]accept alternative symbols for alleles throughout
11. frequency of sickle cell anaemia is highest in areas where
malaria is common ; 12. sickle cell anaemia red blood cells cannot
carry oxygen very well / AW ; A sickling blocks capillaries
-
13. homozygous HS / HSHS, have sickle cell anaemia / may die ;
14. homozygous HN / HNHN, have normal, Hb / red blood cells ; 15.
heterozygotes, have sickle cell trait or (sickle cell trait) red
blood cells not (severely) affected ;
16. malaria parasite / Plasmodium, affects red blood cells ; 17.
malaria lethal ; 18. sickle cell trait people / heterozygotes, less
likely to suffer from (severe effects of) malaria ; 19. have
selective advantage ; 20. pass on both HN and HS ; 21. malaria
selects against, homozygous HN / HNHN ; 22. sickle cell anaemia
selects against, homozygous HS / HS HS; 23. idea that sickle cell
allele is maintained within population because of sickle cell trait
individuals ; [9 max]
11 (a) Explain how changes in the nucleotide sequence of DNA may
affect the amino acidsequence in a protein. [8]
1. (amino acid) code is three, bases / nucleotides ; A triplet
code2. (gene) mutation ; R chromosome mutation3. base / nucleotide,
substitution / addition / deletion4. addition / deletion, has large
effect (on amino acid sequence) ;5. frame shift ;6. completely new
code after mutation / alters every 3 base sequence which follows
;7. substitution may have little or no effect / silent mutation ;8.
different triplet but same amino acid / new amino acid in
non-functional part of protein ;9. substitution may have big effect
(on amino acid sequence) ;10. could produce stop codon ;11. sickle
cell anaemia / PKU / cystic fibrosis ;12. reference to
transcription or translation in correct context ; A description [8
max
(b) Explain how the allele for haemophilia may be passed from a
man to his grandchildren.You may use genetic diagrams to support
your answer. [7]
(b) 13. (haemophilia) allele on X chromosome ; A gene
-
14. sex-linked ;15. (haemophilia) allele recessive ;16. man,
homogametic / has one X chromosome ;17. Y chromosome does not have
blood clotting gene ;18. only daughter(s) get his X chromosome ;19.
daughter(s) carrier(s) of (haemophilia) allele ;20. grandson(s) 50%
chance of having, (haemophilia) allele / haemophilia ;21.
granddaughter(s) 50% chance of carrying, (haemophilia) allele
;allow following marks from diagram22. correct symbols ; e.g. XH
and Xh explained23. mans genotype ; e.g. XhY ignore partners
genotype24. F1 (daughters) genotype ; e.g. XHXh ignore her partners
genotype25. F2 (grandsons) genotypes ; e.g. XhY XHY both
required26. F2 (granddaughters) genotypes ; e.g. XHXH XHXh both
required or XhXh XHXh [7 max]
9 (a) Explain the need to maintain biodiversity in an ecosystem
such as a tropical rainforest.[7]
(a) 1. cultural/aesthetic / leisure, reasons;2. moral/ethical,
reasons ; e.g. right to exist/prevent extinction;3. resource
material ; e.g. wood (for building)/fibres for clothes/food
forhumans/(herbal) medicine4. (eco)tourism;5. economic benefits;6.
ref. resource / species, may have use in future/AW;e.g. medical
use7. maintains, food webs / food chains;A description8. nutrient
cycling;9. protection against erosion;10. climate stability;11.
maintains, (large) gene pool/genetic variation;12. scientific
research;
(b) Discuss the advantages and the disadvantages of captive
breeding programmes formammals. [8](b) advantages (max 5)13. can
monitor health of mother;14. can monitor development of foetus;15.
storage of, sperm/eggs/gametes;16. artificial insemination;17.
IVF;18. ref. surrogate mothers;19. international cooperation;20.
genetic records kept;21. can prevent extinction/extend range of a
species/used in restoringecosystem;
-
disadvantages (max 5)22. unnatural environment;23. stress in
captivity;24. behavioural changes;25. reproductive cycles
disrupted;26. may reject selected mate;27. examples of problems
with release ;;28. difficulty in finding foodmay not integrate into
groupsmore susceptible to diseasevery little natural habitat left
to release animals into[max 8][Total: 15]
9 (a) Bacteria are members of the kingdom Prokaryota. Describe
the main features of abacterial cell. [8](a) 1. DNA not surrounded
by nuclear membrane / no nucleus;2. (prokaryote) DNA is circular;3.
DNA not associated with histones; A naked DNA4. plasmids (may) be
present;5. no (double) membrane-bound organelles; A no,
mitochondria / chloroplasts6. no, ER / Golgi; A ribosomes not
attached to membranes7. ribosomes,70S / 18 nm / smaller (than
eukaryotic cells);8. cell wall made of, peptidoglycan / murein /
amino sugars / AW;9. (usually) unicellular;10. 0.5 to 5.0 m
diameter; A any value between 0.5 and 5.0 as long as m is used11.
AVP; (may) have, flagella / pili / capsule / slime layer [8
max]
(b) Outline the use of bacteria in the extraction of metals from
ores. [7](b) 12. ores (may) contain metal sulfides;13. example;
e.g. iron / copper / zinc / cobalt / lead14. insoluble in water so
difficult to extract;15. bacteria oxidise metal sulfide;16. to
soluble sulfate;17. bioleaching;18. example of bacteria; e.g.
A.ferrooxidans19. bacteria need to survive in acidic conditions;20.
mixture of bacteria required (in bioheap);21. (in order to) survive
a wide range of temperatures / range of bacteria with
differenttemperature optima;
22. advantage;23 e.g. low grade ores / spoil heaps, can be
exploitedcan get metal from industrial wastedoes not produce sulfur
dioxidecan be done in situlow energy demandless (heavy)
machinerynot labour intensive
-
relatively cheaper (than other mining methods)24. AVP; e.g. ref.
gold / uranium [7 max]