Sorghum is a cereal crop that grows well in very dry (arid) conditions.
(a) Outline two structural features of sorghum that adapt it to survive in arid environments
very extensive root system / roots go very deep ;
small surface area of leaves ; R narrow leaves
leaves roll / presence of hinge cells ; A bulliform
leaves / stalks, have waxy covering / thick cuticle ;
high silica content ;
stomata, reduced in number / in sunken pits ;
idea of supporting tissue ; e.g. sclerenchyma
explain why proteins occur in the blood entering the glomerulus but not in the filtrate
in the renal capsule
) (too) large / MM > 68 000 ;
to pass through basement membrane ;
explain why there is glucose present in the filtrate but not in the urine
reabsorbed ;
in proximal convoluted tubule ;
) explain the difference in the concentration of urea between the filtrate and urine
more urea in urine than in filtrate / ora ; A comparative figs
- water is reabsorbed ;
- in, distal convoluted tubule / collecting duct ;
- most urea stays in urine ; R all urea stays
- other substances are reabsorbed ;
where in the chloroplast the Calvin cycle occurs
) stroma ;
the name of another compound that is produced in the light-dependent stage of
photosynthesis that is used in the Calvin cycle.
ATP / reduced NADP ;
Describe the structure of a motor neurone
nucleus in cell body ;
(short), dendrites / dendrons ;
axon ;
(axon) much longer than, dendrite / dendrons ;
must be stated / not on diagram
cell body contains, mitochondria / RER / golgi / groups of ribosomes ;
many mitochondria at, synaptic knob / terminal branch ;
synaptic vesicles ;
neurotransmitter / named neurotransmitter ; linked to 7
Schwann cells / myelin sheath ;
nucleus in Schwann cell ; R nucleus in myelin sheath
node of Ranvier ;
AVP ; e.g. motor end plate / (dendrites) have receptors (for neurotransmitters)
Explain how an action potential is transmitted along a motor neurone
Na+
channels open ; A sodium channels
Na+
enter cell ; R enter membrane
inside becomes, less negative / positive / +40mV / depolarised ;
Na+
channels close ; A sodium channels
K+
channels open ; A potassium channels
K+
move out (of cell) ; R of membrane
inside becomes, negative / repolarised ; A negative figure
local circuits / description ;
(myelin sheath / Schwann cells) insulate axon / does not allow movement
of ions ;
action potential / depolarisation, only at nodes (of Ranvier) / gaps ;
saltatory conduction / AW ;
one-way transmission ;
AVP ; e.g. hyperpolarisation / refractory period
Explain what is meant by the term endocrine gland.
ductless gland ;
secretes (hormone) into blood ;
Explain briefly what is meant by negative feedback.
a change sets off events that counteract the change / AW / example
described ;
(a) Describe the process of glycolysis 🤓
(glucose) phosphorylated by ATP ;
raises energy level / overcomes activation energy ;
hexose bisphosphate ;
lysis / splitting, of, glucose / hexose ; R sugar splitting
breaks down to two TP ; A GALP / GADP / G3P / PGAL
6C → 2 x 3C ;
dehydrogenation / description ;
2 NAD reduced formed (from each TP to pyruvate formed) ;
4 ATP produced / net gain of 2 ATP ;
pyruvate produced ;
reduced NAD → oxidative phosphorylation / redox ;
accept flow diagram
The optimum temperature for many plants living in temperate regions is approximately
25 °C.
Explain why the rate of photosynthesis in these plants decreases at temperatures above
25 °C
enzymes, denatured / active site changes shape ;
rubisco / enzyme in cyclic photophosphorylation ;
Calvin cycle affected / description ;
less photolysis ;
less ATP produced ;
increased rate of respiration ;
respiration rate faster than photosynthesis rate / ref. compensation
point ;
increased rate of transpiration ;
stomatal closure ;
less CO2 uptake ;
a) Describe a reflex arc and explain why such reflex arcs are important
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 diagram fast / immediate ; stops / limits, damage / danger ; automatic / no conscious thought ; innate / stereotyped / instinctive ;
Describe the structure of a myelin sheath and explain its role in the speed of transmission
of a nerve impulse.
Schwann cells ; wrap around axon ; sheath mainly lipid ; (sheath) insulates axon (membrane) ; Na+ / K+ , cannot pass through sheath / can only pass through membrane at nodes ; depolarisation (of axon membrane) cannot occur where there is sheath / 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 ;
Describe how the liver reduces blood glucose concentration, when insulin is secreted.
binds to receptors (on liver cell membranes) ;
conversion of glucose to glycogen / glycogenesis ;
(because) insulin activates enzyme ; e.g. glucokinase / phosphofructokinase /
glycogen synthase
increased use of glucose in respiration ;
increased uptake of glucose / increased permeability to glucose (of liver
cells) ;
With reference to Figs. 4.2 and 4.3, suggest one advantage and one disadvantage of inhaling insulin rather than injecting it.
advantages:
1 faster response time ;
2 less chance of, infection / contamination ;
3 good for people with needle phobia ; max 1
disadvantages :
4 could cause larger swings in blood glucose concentration ;
5 may need to taken more often / not long lasting ;
6 possible variability of dose / AW ;
The roots of young rice plants are highly tolerant of ethanol. Explain how this helps them to survive when the fields are flooded.
oxygen availability low (when soil is flooded) ;
plants carry out anaerobic respiration ;
ethanol produced ;
roots can continue to respire ;
Outline the role played by accessory pigments in the light-dependent reactions
absorb light ; A harvest light / trap light R collect light
pass energy to, primary pigment / chlorophyll / reaction centre
Outline the differences between cyclic and non-cyclic photophosphorylation
cyclic photophosphorylation
electron emitted returns to, PSI / same photosystem or same chlorophyll
molecule ;
non-cyclic photophosphorylation
electron emitted from PSII absorbed by PSI ;
reduced NADP produced ;
photolysis occurs ; A splitting of water
(photolysis) only involves PSII ;
oxygen produced
A palisade mesophyll cell is adapted to carry out photosynthesis
show how these adaptations help the cell to carry out photosynthesis.
thin cell wall greater light penetration / short diffusion distance
(for gases) ;
cylindrical shape air spaces ;
large vacuole chloroplasts near outside of cell for better light
absorption / maintains turgor ;
chloroplasts can be moved within the cell absorb maximum light / avoid excessive light
intensities ;
Explain the different energy values of carbohydrate, lipid and protein as respiratory substrates.
idea of lipid > protein > carbohydrate / AW ; A lipid has more energy than
either protein or carbohydrate
comparative figures ; e.g. 39.4, 17.0 and 15.8 accept any two
kJ g
1
/ per unit mass ;
more hydrogen atoms in molecule, more energy ;
lipid have more, hydrogen atoms / C-H bonds ;
(most) energy comes from oxidation of hydrogen to water ;
using reduced, NAD / FAD ;
in ETC ;
detail of ETC ;
ATP production
Explain how rice plants are adapted for growth with the roots submerged in water
low oxygen (in water) results in anaerobic respiration ;
2. (anaerobic respiration) produces alcohol ;
3. rice tolerant to alcohol ;
4. (because rice has) high levels of, alcohol dehydrogenase / enzyme that breaks down
alcohol ;
5. presence of, aerenchyma / described ;
6. allows, oxygen / air, to reach roots (from aerial tissues)
Explain why glucose needs to be converted to hexose bisphosphate
provides activation energy / AW ;
for it to split / AW ;
Pyruvate can enter a mitochondrion when oxygen is present.
Describe what happens to pyruvate in a yeast cell when oxygen is not present.
decarboxylated / carbon dioxide given off ;
- ethanal produced ;
- ethanal reduced ;
- by reduced NAD ;
- to ethanol ;
- dehydrogenase ;
State one property of collagen that enables it to carry out its main function in the walls of blood vessels and airways.
high tensile strength / withstands pulling forces / fibrous / insoluble / forms fibrils /
flexible
Describe how the structure of a chloroplast is related to its functions.
ground substance / stroma ;
- for, light independent stage / Calvin cycle ;
- contains enzymes / named enzyme e.g. rubisco ;
- also, sugars / lipids / starch / ribosomes / DNA ;
- internal membrane system ;
- for, light dependent stage ;
- fluid-filled sacs / thylakoids ;
- grana are stacks of thylakoids ;
- (grana) hold (photosynthetic) pigments ;
- (grana) have large surface area for (maximum) light absorption ;
- (pigments are arranged in), light harvesting clusters / photosystems ;
- primary pigment / reaction centre / chlorophyll a, surrounded by accessory pigments ;
- (accessory pigments) pass energy to, primary pigment / reaction centre / chlorophyll a ;
- different photosystems absorb light at different wavelengths ;
- membranes hold, ATP synthase / electron carriers ;
- for, photophosphorylation / chemiosmosis ;
Describe how you would separate chloroplast pigments using chromatography
. grind leaf with solvent ;
18. example of solvent ; e.g. propanone
19. 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 spots
22. 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
Describe how a resting potential is maintained in an axon
axon phospholipid bilayer impermeable to K + / Na
+
;
2. sodium – potassium pump ;
3. detail of sodium-potassium pump ; e.g. transmembrane / globular / ATP binding site
4. active process / ATP used / energy needed ;
5. 3 Na + (pumped) out / 2 K +
(pumped) in ;
6. K + diffuse out / Na
+ diffuse in ;
7. through, protein channels transport proteins ;
8. more K +
channels open than Na +
channels ;
9. therefore, membrane more permeable to K + or more K + leave than Na + enter (axon) ;
10. inside relatively more negative than outside ;
11. –65mV ; A –70mV
12. idea of leaking K +
responsible for resting potential / AW ;
13. electrochemical gradient ;
14. voltage-gated channels closed ; in
Describe, using named examples, how sensory receptors in mammals generate action potentials.
general
15. respond to stimuli / AW ;
16. (some) receptors are the ends of sensory neurones ;
17. (some) receptors are cells ;
18. they are energy transducers ;
19. stimulus causes sodium ion channels to open ;
20. sodium ions enter cell ;
21. depolarisation ;
22. receptor / generator, potential ;
23. if (receptor potential) greater than threshold then action potential generated / all or
nothing principle described ;
24. increased stimulus strength leads to increased frequency of action potentials receptor form of energy detected
rods / cones light ;
taste buds / olfactory cells chemical ;
Pacinian \ Meissner’s, corpuscle pressure / touch ;
Describe the circumstances in which a.a and lactate are used as respiratory substrates
a.a – starvation / lack of fat or carbohydrate ;
lactate – after anaerobic respiration ;
Explain how myelination affects the speed of conduction of impulses
- myelin insulates axon ;
- no myelin at nodes ;
- action potentials / depolarisation, only at nodes (of Ranvier) ;
- local circuits set up between nodes ;
- action potentials ‘jump’ from node to node / saltatory conduction ;
- myelination prevents leakage of ions ; ora
Multiple sclerosis (MS) is an auto-immune condition of humans in which the body’s immune system attacks the myelin sheaths which are then damaged. This leads to a decrease in information reaching the brain from sensory receptors.
(i) Suggest how the myelin sheaths may be attacked.
(ii) Explain why this damage leads to a decrease in information reaching the brain from sensory receptors.
- (sheath) treated as, ‘foreign’ / non-self ;
- ref. role of, antibodies / phagocytes / lymphocytes ;
(ii) 1. less insulation of axon ; - action potentials, slow down / stop
- ref. role of, antibodies / phagocytes / lymphocytes ;
State precisely the location of photosynthetic pigments within a chloroplast.
grana / thylakoid, membrane
summarises the effects of gibberellins on seed germination
When a seed is shed from the parent plant, it is in a state of dormancy,
which means it is metabolically inactive.
When water is absorbed by a seed, it stimulates the production of gibberellin by the
embryo within the seed. The gibberellin stimulates the synthesis of
amylase by cells in the aleurone layer.
Amylase hydrolyses starch molecules in the endosperm converting them
to soluble endosperm molecules. These molecules are converted to
glucose which is transported to the embryo, providing a source of carbohydrate that can be
respired to provide ATP as the embryo begins to grow.
Gibberellin causes these effects by regulating genes that are involved in the synthesis of
amylase. It has been shown that application of gibberellin to seeds can cause an increase in
the transcription of the DNA coding for amylase
Outline the role of insulin in a healthy human
1 causes blood glucose concentration, to decrease
/
return to normal (from
high) ;
2 (target cells are) liver
/
muscle ;
3 increased, absorption of glucose (from blood)
/
permeability of cell
surface membrane to glucose ;
4 increased (rate of) respiration of glucose ;
5 idea of increased conversion of glucose to glycogen ;
6 inhibits secretion of glucagon
/
decreased gluconeogenesis ;
Describe and explain one advantage of treating diabetics with human insulin produced by rDNA technology.
1 identical to that produced by body ; 2 activity the same / fast response / no immune response ;
3 no need for animal insulin
/
AW ;
4 for religious reasons
/
for ethical reasons
/
for e.g. vegetarian ;
5 uncontaminated
/
pure ; 6 so no risk of disease ;
7 production very efficient
/
always available ; 8 extraction from animals, costly / complex / limited by supply of animals ;
In respiration, energy from various substrates is used to synthesise ATP.
(i) Explain why less ATP can be synthesised from the same mass of glucose in anaerobic respiration than in aerobic respiration.
anaerobic – accept ora for aerobic
1 idea that glucose not completely, broken down
/
oxidised
or only glycolysis occurs ;
2 pyruvate
/
lactate
/
ethanol, still contains energy ;
3 ETC stops ;
4 (because) no oxygen to act as (final) electron acceptor ;
5 (so) no, Krebs cycle
/
link reaction
/
oxidative phosphorylation
/ chemiosmosis ;
Explain why more ATP can be synthesised in aerobic respiration from one gram of lipid than from one gram of glucose.
1 lipid contains (relatively) more, hydrogen atoms
/
C-H ;
2 detail ; e.g. molecular formula of glucose and a lipid given
3 more reduced, NAD
/
FAD, produced ;
4 more electrons passed along ETC ;
5 more hydrogen ions pumped across inner mitochondrial membrane
/
more hydrogen ions pumped into intermembrane space
/
steeper proton gradient ;
sensory neurone vs motor neurone
B has many dendrites is myelinated may form a synapse with an intermediate neurone M cell body lies within the CNS S dendron is usually longer than axon cell body lies within spinal nerve
Describe how an action potential arriving at a presynaptic membrane of a neurone can result in the depolarisation of the membrane of a post-synaptic neurone.
1 Ca(2+) channels open (in presynaptic membrane
/
presynaptic knob) ;
2 Ca2+ enter (pre)synaptic knob ;
3 vesicles contain, neurotransmitter
/
ACh ;
4 (vesicles) move towards
/
fuse with, presynaptic membrane ;
5 (ACh
/
neurotransmitter) released
/
exocytosis ;
6 (ACh
/
neurotransmitter) diffuses (across cleft) ;
7 binds to receptors on postsynaptic membrane ;
8 Na(+) channels open ;
9 Na+ enters post-synaptic neurone
Acetylcholinesterase is an enzyme found in the synaptic cleft.
Outline the role of acetylcholinesterase
hydrolyses
/
breaks down, ACh ;
stops continuous production of action potentials (in post-synaptic neurone)
Name precisely the process that produces reduced NADP
non-cyclic photophosphorylation ;
Describe how carbon dioxide reaches the inside of a palisade mesophyll cell from the external atmosphere
1 enters via stoma(ta) ;
2 by diffusion
/
down a concentration gradient ;
3 passes through air spaces ;
4 dissolves in film of water (on cell surface) ;
5 (diffuses) through cell, wall
/
surface membrane (of palisade cells) ;
V The optimum pH for the activity of rubisco is pH8.
Explain why the illumination of chloroplasts leads to optimum pH conditions for rubisco.
1 excited electrons leave, chlorophyll a
/
photosystem ;
2 pass along ETC ;
3 protons present from photolysis ;
4 protons (pumped) into intermembrane space ;
5 rubisco is in stroma ;
6 idea that protons leaving stroma raises pH
) Describe and explain how gibberellins are involved in the germination of wheat or barley seeds.
1 seed is, dormant
/
metabolically inactive ;
2 water enters seed ;
3 embryo, produces
/
releases, gibberellin ;
4 gibberellin stimulates aleurone layer ;
5 (by) affecting, gene coding
/
transcription of mRNA, for amylase ;
6 to produce amylase ;
7 amylase hydrolyses starch ;
8 in endosperm ;
9 to, maltose
/
glucose ;
10 embryo uses sugars for respiration ;
11 energy
/
ATP, used for growth ;
Explain the principles of homeostasis in humans.
1 (homeostasis is) maintenance of, constant
/
stable, internal environment ;
2 irrespective of changes in external environment ;
3 negative feedback ;
4 ref. to input
/
stimulus ;
5 receptor detects change in parameter ;
6 action taken by effector
/
response
/
AW ;
7 restoration of, norm
/
set point
/
AW ;
8 ref. to fluctuation around the norm ;
9 example of homeostasis ;
Outline the effect of ADH on the collecting ducts.
1 ref. to enzyme / phosphorylase / signalling ;
2 ref. to aquaporins ;
3 vesicles (containing aquaporins), move towards / fuse with, (cell surface membrane) ;
4 idea of increased permeability ;
5 water leaves (lumen into cells), by osmosis / down water potential gradient ;
Describe the role of rubisco in the Calvin cycle
1 fixation of carbon (dioxide) ;
2 (catalyses) the reaction between RuBP and CO2 / AW ;
3 to give two GP ;
4 via an unstable intermediate compound ;
Outline how an action potential arriving at this neuromuscular junction can result in depolarisation of the sarcolemma.
1 Ca2+ channels open in, pre-synaptic membrane / (pre)-synaptic knob / motor end plate ;
2 Ca2+ enter, pre-synaptic knob / pre-synaptic neurone / motor end plate ;
3 vesicles contain, neurotransmitter / ACh ;
4 (vesicles) move towards / fuse, with pre-synaptic membrane ;
5 (ACh / neurotransmitter) released / exocytosis, and diffuses (across cleft) ;
6 6. binds to receptors on sarcolemma ; A post-synaptic membrane
7 Na+ channels open and Na+ enters, (muscle fibre / sarcoplasm) ; R sarcolemma
Describe the role of oxygen in aerobic respiration
three from 1 used in, oxidative phosphorylation / ETC ;
2 final electron acceptor ;
3 proton acceptor ;
4 forms water ;
5 allows ETC to continue ;
6 ref. to ATP produced ;
3
Using examples, outline the importance of homeostasis in a mammal
seven from 1 ref. to maintenance of constant internal environment ;
2 blood or tissue fluid as e.g. of internal environment ;
3 ref. to norm / optimum value / set point / within narrow limits ;
4 (low) temperature and consequence ; e.g. slowed metabolism / enzymes less active
5 (high) temperature and consequence ; e.g. enzymes denatured
6 (low) water potential and consequence ; e.g. water leaving cells / cells shrink
7 (high) water potential and consequence ; e.g. water enters cells / cells burst
8 (low) blood glucose and consequence ; e.g. effect on respiration
9 (high) blood glucose and consequence ; e.g. water leaving cells / cells shrink
10 AVP ; e.g. control of pH and consequence
7
Describe the main stages of cell signalling in the control of blood glucose concentration by adrenaline.
1 adrenaline binds to receptors ;
2 in, cell surface membrane / plasma membrane ;
3 receptor changes conformation ;
4 G proteins activated ;
5 adenylyl cyclase activated ; A adenyl cyclase
6 cyclic AMP / cAMP, made ;
7 second messenger ;
8 activates kinase (protein) ;
9 ref. to enzyme cascade / signal amplification ;
10 ref. to phosphorylase ;
11 glycogen broken to glucose / glycogenolysis ;
12 glucose diffuses, out of cells / into blood ;
13 increase in blood glucose concentration ;
8
) Explain the role of auxin in cell elongation in plants.
1 acid-growth (hypothesis) ;
2 auxin stimulates proton pumps ;
3 (in) cell surface membrane ;
4 H+ pumped into cell wall ;
5 using energy / by active transport ;
6 pH of cell wall decreases / cell wall becomes (more) acidic ;
7 pH-dependent enzymes activated ;
8 ref. to expansins ;
9 bonds between cellulose microfibrils broken ;
10 idea that cell wall, ‘loosens’ / becomes more elastic / able to stretch ;
11 (more) water enters cell / turgor pressure increases ;
12 (so) cell (wall) expands
(b) Describe the role of abscisic acid in the closure of stomata
1 plant secretes abscisic acid, in very dry conditions / at times of water stress ; A abscisic acid is a stress hormone
2 abscisic acid binds to receptors ;
3 on cell surface membranes of guard cells ;
4 inhibits proton pump / H+ not pumped out of cell ;
5 high H+ conc inside cell ; A ref. to change in charge
6 (abscisic acid) stimulates Ca2+ influx ;
7 Ca2+ acts as second messenger ;
8 encourages K+ efflux / inhibits K+ influx ; A K+ channels open
9 water potential of cell increases ; A increase in solute potential
10 water moves out of cell by osmosis ;
11 volume of guard cells decreases ;
12 guard cells become flaccid ;
13 response very fast ;
8
State what is meant by the term respiratory quotient (RQ
RQ = volume of carbon dioxide given off; R amount A moles volume of oxygen taken up
Explain why an increase in temperature from 15 oC to 25 oC will increase the rate of oxygen uptake in germinating seeds.
ref. effect of temperature on enzymes in respiration; ref. named effect of temperature e.g. increased collisions/kinetic energy/more substrate molecules with activation energy; ref. to Q10 = 2
State precisely where the Calvin cycle occurs in plant cells
stroma of chloroplast;
b) Describe how carbon dioxide is fixed in the Calvin cycle.
combines with (5C compound) RuBP; to form unstable 6C compound/forms 2 molecules of (3C) GP; ref. enzyme/rubisco;
Explain how the products of photophosphorylation are used in the Calvin cycle.
reduced NADP and ATP; (ATP is) source of energy; (reduced NADP is for) reduction of GP(PGA) to triose phosphate (TP); ref. use of ATP in regeneration of RuBP; ref. to source of phosphate/phosphorylation;
Explain what initially happens to the concentration of RuBP and GP if the supply of carbon dioxide is reduced.
RuBP, accumulates/goes up; due to reduced combination with CO2/AW; in either RuBP or GP, not both GP, goes down/not as much being formed; due to conversion to TP;
Explain how a synapse functions.
1 depolarisation/action potential; 2 of presynaptic membrane/synaptic knob; 3 opening calcium ion channels; 4 calcium ions in; 5 vesicles containing transmitter/acetylcholine; 6 fuse with membrane; 7 contents emptied into synaptic cleft/exocytosis; 8 transmitter/acetylcholine diffuses across synaptic cleft; 9 transmitter/acetychloine binds to receptor; R protein channel 10 on post synaptic membrane; 11 Na+ channels open/NA+ enters; 12 depolarises post synaptic membrane; 13 action potential set up/impulse transmitted 14 breakdown/hydrolysis of transmitter/acetylcholine by enzyme/cholinesterase
Describe the role of glucagon in regulating blood gl
5 when blood glucose levels low; 16 glucagon released from alpha cells (in pancreas); 17 (acts on ) liver (cells); 18 breakdown of glycogen to glucose; 19 use of fatty acides in respiration; R fats 20 production of glucose from other compounds/fats/amino acids/gluconeogenesis; 21 liver releases glucose into blood; 22 glucose levels rise/return to normal; 23 switching off glucagon secretion; 24 antagonistic to insulin;
Name the membrane-bound enzyme responsible for phosphorylating ADP to make ATP.
ATP, synthase / synthetase ; R ATPase
State one use of glucose within the liver cell
(converted to) glycogen / lipid ; (used in) glycolysis / respiration
Suggest why respiration is said to be less effi cient in anaerobic conditions than in aerobic conditions.
anaerobic less ATP / only 2 ATP ; per mol glucose ; lactate still contains energy / only glycolysis involved / stages other than glycolysis not involved ; not sustainable / cannot go on indefi nitely / AW ;
Glucose is phosphorylated at the start of glycolysis in the muscle cell.
Suggest why this phosphorylated glucose does not diffuse out of the cell into the surrounding tissue fl uid
cannot pass through phospholipid bilayer ; too big to fi t through (glucose’s) protein channel ; no specifi c transport protein ; AVP ; e.g. used up as soon as it is made
Additional oxygen is required in the metabolic pathways involved in the conversion of lactate to glucose.
State the term given to this additional oxygen
oxygen debt
Explain how the structure of the glomerular capillaries is adapted for ultrafi ltration
(ii) fl uid can pass through glomerular capillaries because fenestrations in capillary endothelium ; A hole / pores / gaps basement membrane acts as a fi lter ; no substances > 68 000 MM can get through ; no cells can get through ;
Explain why the epithelial cells of the proximal convoluted tubule have many mitochondria in them.
produce ATP / provide energy ; for active transport of Na+ ; out (of cell) ;
Of the 125 cm3 of glomerular fi ltrate that enters the renal capsules each minute, only 45 cm3 reaches the loops of Henle.
Name two substances that are reabsorbed into the blood from the proximal convoluted tubule, apart from water.
mark fi rst two answers any named ion / mineral ions ; vitamins ; amino acids ; glucose ; some urea ;
During stomatal closure:
(i) state precisely where abscisic acid (ABA) binds
receptors) on plasma / cell surface, membrane (of guard cells) ;
During stomatal closure: (ii) identify the ion that diffuses from the guard cells to epidermal cells
K+
During stomatal closure: (iii) compare the relative water potential of the guard cells with that of epidermal cells
(iii) (guard cell has) higher water potential than epidermal cell ; ora
During stomatal closure: describe the change in volume of the guard cells
(iv) decrease
People with insulin-dependent (type 1) diabetes require regular injections of insulin. In the past the insulin used came from animal sources such as pigs. Diabetics now use human insulin that has been manufactured using gene technology.
Describe the advantages of treating diabetics with insulin produced by gene technology
it is identical to human insulin / fits membrane receptor on (target) cells ;
(more) rapid response ;
no / fewer, rejection problems / side effects / allergic reactions ;
ref. to ethical / moral / religious, issues ;
cheaper to produce in large volume / unlimited availability ; R cheap to produce
less risk of, transmitting disease / infection ;
good for people who have developed tolerance to animal insulin
Describe the parts of the pancreas involved in its endocrine function.
islets of Langerhans ;
scattered throughout pancreas / AW ;
alpha and beta cells ;
blood supply (to carry hormones away) ;
Name the hormone that stimulates the breakdown of glycogen in liver cells
glucagon
State under what conditions glycogen would need to be broken down in liver or muscle cells.
low blood glucose concentration / during or after exercise ; R sugar
State what is meant by the term antigen.
foreign / non-self / cell recognition ;
stimulates immune response / AW
) Outline the main features of the Krebs cycle
acetyl CoA combines with oxaloacetate ;
to form citrate ;
4C to 6C ;
decarboxylation / CO2 released ;
dehydrogenation / oxidaextion / 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 diagram
enzyme catalysed reactions ;
oxaloacaetate regenerated ;
occurs in mitochondrial matrix
Explain the role of NAD in aerobic respiration
coenzyme ;
for dehydrogenase ;
reduced ;
carries, electrons and protons / hydrogen / NAD
from Krebs cycle ;
and glycolysis ;
to ETC / electron carrier chain / oxidation ;
reoxidised / regenerated hydrogen removed ;
ATP produced ; ex
Describe how a nerve impulse crosses a cholinergic synapse
action potential / depolarisation, reaches presynaptic membrane ;
(Ca2+) channels open in presynaptic membrane / presynaptic membrane becomes more permeable to (Ca2+) ; R calcium / Ca / Ca+
Ca2+ (flood) into presynaptic, neurone / knob ; R membrane
(this causes) vesicles of, acetylcholine / ACh ;
(to) move towards presynaptic membrane / (to) fuse with presynaptic membrane;
ACh released into synaptic cleft / exocytosis of ACh ;
ACh diffuses across (cleft) ;
ACh binds to receptor (proteins) / AW ;
on postsynaptic membrane ;
proteins change shape / channels open ;
sodium ions (rush) into postsynaptic neurone ; R membrane
postsynaptic membrane depolarised ;
action potential / nerve impulse ;
action of acetylcholinesterase ;
Explain the roles of synapses in the nervous system
ensure one-way transmission;
receptor (proteins) only in postsynaptic, membrane / neurone ; ora
vesicles only in presynaptic neurone ; ora
adaptation / 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 ;
Explain the different energy values of carbohydrate, lipid and protein as respiratory substrates. [6]
idea of lipid > protein > carbohydrate / AW ; A lipid has more energy than
either protein or carbohydrate
comparative figures ; e.g. 39.4, 17.0 and 15.8 accept any two
kJ g
1
/ per unit mass ;
more hydrogen atoms in molecule, more energy ;
lipid have more, hydrogen atoms / C-H bonds ;
(most) energy comes from oxidation of hydrogen to water ;
using reduced, NAD / FAD ;
in ETC ;
detail of ETC ;
ATP production
Explain how synapses ensure one-way transmission of nerve impulses.
vesicles found only in presynaptic neurone / ACh released only from presynaptic neurone or membrane ;
receptor (proteins) found only on postsynaptic membrane ;
For Examiner’s Use
(ii) In a learning activity, it is believed that the number of synapses between brain neurones increases. Suggest the advantages of this increased number of synapses.
allows more interconnection of nerve pathways / AW ; 2. for, memory / AW ; ignore learning 3. allows wider range of responses ; 4. AVP ; e.g summation
explain why ATP is needed at the start of glycolysis
raise chemical PE of glucose / provide activation energy
state the role of NAD in glycolysis
removes hydrogen / hydrogen carrier / coenzyme
state how many molecules of ATP are produced from one molecule of glucose during glycolysis
net 2
name the two types of reaction that occur during the conversion of pyruvate to acetyl CoA in the link reaction
dehydrogenation ; A oxidation decarboxylation ; accept ‘oxidative decarboxylation’ for two marks
describe what happens to the hydrogen released during the link reaction
accepted by NAD ; 2. passed to ETC ; 3. for oxidative phosphorylation ; 4. ref. proton pump / chemiosmosis
Describe the arrangement and location of chloroplast pigments and discuss their effect on absorption spectra.
chlorophyll a is primary pigment ; 2. carotenoids / chlorophyll b, is accessory pigment ; 3. arranged in, light harvesting clusters / photosystems ; A antenna complex 4. on, grana / thylakoids ; 5. ref. PI and PII ; A P700 and P680 6. primary pigment / chlorophyll a, in reaction centre ; 7. accessory pigments / carotenoids / chlorophyll b, surround primary pigment ; 8. light energy absorbed by, accessory pigments / carotenoids / chlorophyll b ; 9. (energy) passed on to, primary pigment / chlorophyll a / reaction centre ; 10. chlorophyll a and b absorb light in red and blue/violet region ; 11. carotenoids absorb light in blue/violet region ; 12. ref. absorption spectrum peaks ; 13. diagram of absorption spectrum ; 14. different combinations of pigments (in different plants) give different spectra
Describe the part played by auxins in apical dominance in a plant shoot
- IAA / plant growth regulator / plant growth substance / plant hormone ; 16. synthesised in, growing tips / apical buds / meristems ; 17. moves by, diffusion / active transport ; 18. from cell to cell ; 19. also, mass flow / in phloem ; 20. stimulates cell elongation ; R cell enlargement 21. inhibits, side / lateral, buds / growth ; A inhibits branching 22. plant grows, upwards / taller or allows stem to grow up to light (instead of sprouting ) ; A stem elongates 23. auxin not solely responsible for apical dominance or there is interaction between auxin and other plant growth regulators ; 24. ref. idea of concentration gradient down shoot so effect of dominance decreases ; 25. AVP ; e.g. role of ABA and lateral bud inhibition / cytokinins antagonistic to IAA / gibberellins enhance IAA also mp 23
Write a balanced equation that summarises photolysis
H2O 2H
+ + 2e
+ ½ O2 ;
A 2H2O 4H
+ + 4e
+ O2
Explain what makes a molecule such as rubisco soluble
hydrophilic / polar / charged, outside / at surface ; hydrophobic / non-polar / non-charged, inside ; globular (protein) ; ref. to polar interactions / hydrogen bonds, with water (molecules)
In the absence of light, rubisco changes shape from an active form to an inactive form. Explain why rubisco does not need to be in an active form in the absence of light.
Calvin cycle / light independent reaction, stops ; no RuBP (for rubisco) ; as no, ATP ; as no reduced NADP ; as no, light dependent reaction / photophosphorylation
The active sites of rubisco accept ribulose bisphosphate (RuBP) and either carbon dioxide or oxygen and can catalyse the two reactions shown below. either RuBP + CO2 unstable intermediate compound 2GP (PGA) or RuBP + 2O2 unstable intermediate compound GP (PGA) + 2CO2 Explain the consequences to the plant of the reaction involving oxygen
two from no (new) CO2 fixed / (previously) fixed carbon lost as CO2 ; photosynthesis decreased ; less, RuBP (re)generated / available ; less, TP / glucose, will be made ; energy / ATP, used in making RuBP wasted
Describe the role of calcium ions (Ca2+ ions) in the shortening of a sarcomere.
1 calcium ions / Ca2+, ions from sarcoplasmic reticulum ; 2 calcium ions / Ca2+, bind to troponin ; 3 troponin changes shape ;
4 tropomyosin moves ; 5 from / exposing, (myosin) binding site on actin ; 6 myosin head binds (to actin) ;
7 myosin head tilts / power stroke occurs ; 8 actin pulled ;
A motor end plate of a neuromuscular junction is part of a modified cholinergic synapse. Explain why mitochondria are present in the motor end plate of a neuromuscular junction.
synthesise / produce, ATP ;
(ATP needed to) synthesise acetylcholine ; (ATP needed for) movement of vesicles / exocytosis ; (ATP needed to) transport calcium ions, out of presynaptic neurone / into sarcoplasmic reticulum ; (ATP needed to) synthesise acetylcholinesterase ; (ATP needed for) Na+(– K+) pumps / pumping / active transport ;
3A
In anaerobic conditions, the pyruvate formed in glycolysis is converted to ethanol in yeast cells and to lactate in mammalian tissue. Compare the pathways by which pyruvate is converted to ethanol or to lactate
1 reduced NAD (used) in both; 2 NAD regenerated / glycolysis can continue, in both;
Differencences yeast / ethanol decarboxylation two steps / pyruvate → ethanal → ethanol ethanol dehydrogenase decarboxylation
mammalian tissue / lactate
no decarboxylation
reversible
one step / pyruvate → lactate pyruvate accepts H lactate dehydrogenase
Explain how glucose is reabsorbed into the blood from a kidney nephron
1 (happens in) proximal convoluted tubule ; 2 all / 100%, glucose (reabsorbed / moves into blood) ; 3 active transport / pumping, of Na+ out of cells into tissue fluid ;
4 Na+ concentration decreases inside cells ; 5 therefore Na+ enters (epithelial / tubule) cells from, lumen / filtrate ; 6 by facilitated diffusion ; 7 this is secondary active transport ; 8 Na+ brings glucose with it ; 9 this is co-transport ; 10 (facilitated) diffusion of glucose out of cells into tissue fluid ; 11 GLUT proteins (on basolateral membranes) ; 12 ref. to microvilli (on lumen side / apical membrane) ; 13 to increase surface area for reabsorption ; 14 tight junctions separate proteins of front and basolateral membranes ;
8A
Describe the role of ADH when the water potential of blood decreases
seven from 1 (low blood water potential) detected by osmoreceptors ; 2 in hypothalamus ; 3 neurosecretory cells (stimulated to) produce ADH ; 4 ADH released by posterior pituitary ; 5 ADH transport in blood ; 6 (ADH) binds to receptors (on cell surface membranes) ; 7 (of) collecting duct / distal convoluted tubule ; 8 aquaporins / water transport proteins, added to membranes ; 9 increases permeability to water (of collecting duct / distal convoluted tubule) ; 10 water moves out of, filtrate / tubule lumen ; 11 by osmosis ; 12 into, interstitial fluid / tissue fluid / blood / capillaries ; 13 small volume of / concentrated, urine produced ; 14 increases water potential of blood (back to norm) ;
7
Describe the response of the Venus fly trap to touch
1 mechanical energy converted to electrical ; 2 ref. to sensory hair cell (is receptor / detects touch) ; 3 cell membrane depolarises ; 4 (if at least) two hairs touched (within 35 seconds) ; 5 action potential occurs ; 6 action potential / depolarisation, spreads over, leaf / lobe ; 7 ref. to hinge / midrib, cells ; 8 H+, pumped out of cells / pumped into cell walls ; 9 cell wall, loosens / cross-links broken ; 10 calcium pectate dissolves (in middle lamella) ; 11 Ca2+ (ions) enter cells ; 12 water, enters / follows, by osmosis ; 13 cells, expand / become turgid ; 14 change from convex to concave ; 15 trap shuts, quickly / in <1s / in 0.3s ; 16 AVP; acid growth hypothesis / expansins / elastic tension
Explain the control of gibberellin synthesis and outline how gibberellin stimulates stem elongation.
control 1 gibberellin synthesis / dwarfism, controlled by gene Le / le ; 2 dominant allele / Le, gives, functional enzyme / active gibberellin ; ora 3 enzyme converts inactive to active gibberellin ;
stem elongation 4 without GA, transcription factor / PIF, attached to DELLA protein ; 5 GA binds to receptor (complex) ; 6 causes DELLA (protein) destruction ; 7 transcription factor / PIF / RNA polymerase, binds to DNA ; 8 (growth) genes, switched on / expressed / transcribed ; 9 causes cell division ; 10 causes cell elongation ; 11 increases internode length ; 12 loosens cell walls / acid growth ; 13 so cells can expand when water enters ; 14 AVP ; e.g. interaction with auxin, ref. to expansins
Explain how aerobic respiration may be affected by a decrease in oxygen availability.
1 less
/
decreased (aerobic respiration) ;
2 oxygen, is the final electron acceptor
/
needed for ETC ;
3 oxidative phosphorylation decreased
/
chemiosmosis decreased ;
4 regeneration of NAD
/
Kreb’s cycle
/
link reaction, decreased ;
5 ATP synthesis decreases
/
ATP synthetase activity decreased
Outline how molecules, such as the compounds from the digestion of asparagus, pass from the blood to become part of the glomerular filtrate.
high blood pressure in glomerulus ;
2 (due to) greater diameter of afferent vessel ; ora
3 molecules pass through holes in (capillary) endothelium ;
4 basement membrane selectively permeable
/
only small molecules pass
through basement membrane
/
large molecules unable to pass through
basement membrane ;
5 less than 69 000 RMM ;
6 molecules pass between gaps in podocytes ;
7 enter renal capsule
Suggest advantages of using monoclonal antibodies for pregnancy testing
can be done at home / easy to use / non-invasive ;
cheap ;
result produced quickly ;
result likely to be accurate ;
can be done early in pregnancy ;
safe to use
monoclonal antibody.
1 identical (antibodies) or produced by cloning ;
2 variable regions / antigen binding sites, all identical
or (antibodies) are specific to one antigen ;
Suggest why membranes in cells lose their normal structure when the water potential is low
1 water leaves mitochondrion ; A other named organelle
2 by osmosis / down water potential gradient ;
3 idea mechanical disruption to membranes ;
4 membranes made of phospholipid (bilayer) ;
5 hydrophilic heads / glycoproteins / glycolipids, form fewer hydrogen
bonds with water ;
6 reduces, stability / fluidity (of membrane) ;
7 ref. (proteins with) hydrophilic channels ;
Define the term excretion
removal / elimination, of waste products ;
of metabolism ;
(which are) toxic ;
(or) substances excess (to requirements
Outline the role of negative feedback in osmoregulation
homeostasis / AW ;
change in water potential ;
detected by (osmo)receptors ;
in hypothalamus ;
response via effector ;
ADH released ;
effect on collecting duct ;
return to, norm / set point
Name two products of the light-dependent stage of photosynthesis that are used in the light-independent stage.
Describe how these two products are used in the light-independent stage of photosynthesis
ATP ;
reduced NADP
1 ATP provides energy ;
2 reduced NADP, is reducing agent / provides hydrogen ;
3 for converting GP to TP ;
4 (ATP used to) regenerate RuBP
Explain what is meant by the term limiting factor.
process / photosynthesis, affected by more than one factor ;
rate is limited by the factor nearest its minimum value /
Carbon dioxide concentration in the atmosphere may be a limiting factor in photosynthesis.
Describe how carbon dioxide reaches the photosynthetic cells in a leaf
enters leaf through (open) stomata ;
by diffusion ;
substomatal air space ;
many air spaces in spongy mesophyll ;
spaces between palisade cells ;
dissolves in moisture on cell (walls) ;
enters through cell walls ;
) Outline anaerobic respiration in mammalian cells and describe how it differs from anaerobic respiration in yeast cells.
Pyruvate, cannot enter mitochondrion / remains in the cytoplasm ;
becomes, hydrogen acceptor / reduced ;
by reduced NAD ;
from glycolysis ;
converted to lactate ;
lactate dehydrogenase ;
allows glycolysis to continue ;
no, decarboxylation / CO2 removed ;
single step ;
reversible reaction / converted back to pyruvate ;
by oxidation ;
ref. oxygen debt ;
ethanol produced ;
Describe how anaerobic respiration in mammalian cells differs from anaerobic respiration in yeast cells.
in mammals
- lactate produced / no ethanol produced ;
- no, decarboxylation / carbon dioxide released ;
- single step ;
- lactate dehydrogenase ;
- reversible ;
Explain why anaerobic respiration results in a small yield of ATP compared with aerobic respiration.
in anaerobic respiration
- only glycolysis occurs / Krebs cycle stops / link reaction stops ;
- glucose, not fully broken down / still contains energy ;
- pyruvate does not enter mitochondrion ;
- (no oxygen) so no final electron acceptor (in ETC) ;
- ETC stops ;
- no oxidative phosphorylation
The concentration of glucose in the blood is controlled by the hormones insulin and glucagon.
Describe the part played by glucagon in the control of glucose in the blood
- affects liver cells ; R muscle cells / liver and muscle cells
- promotes glycogenolysis / AW ;
- promotes use of fatty acids in respiration ;
- promotes gluconeogenesis / AW ;
- results in rise in (blood) glucose concentration ;
- back to, norm / set point
Explain how the structure of a sensory neurone can enable the action potentials to reach the brain very quickly.
- myelin sheath insulates axon ;
- idea of depolarisation / action potentials, only at nodes of Ranvier ;
- ref. saltatory conduction / AW ;
Explain how the palisade mesophyll cells of a leaf are adapted for photosynthesis
- closely packed to absorb (maximum) light ;
- vertical / at right angles to surface of leaf to reduce number of cross walls ;
- large vacuole pushes chloroplasts to edge of cell ;
- chloroplasts at edge short diffusion path for carbon dioxide ;
- chloroplasts at edge to absorb (maximum) light ;
- large number of chloroplasts to absorb (maximum) light ;
- cylindrical cells or air spaces to circulate gases / provide a reservoir of CO2 ;
- moist cell surfaces for diffusion of gases ;
- cell walls thin for (maximum) light penetration / diffusion (of gases) ;
- chloroplasts can move towards light to absorb (maximum) light ;
- chloroplasts can move away from high light intensity to avoid damage
) Describe the structure of photosystems and explain how a photosystem functions in cyclic photophosphorylation
) accept annotated diagram
12. arranged in light harvesting, clusters / system ;
13. primary pigments / chlorophyll a ;
14. at reaction centre ;
15. P700 / PI, absorbs at 700(nm) ;
16. P680 / PII, absorbs at 680(nm) ;
17. accessory pigments / chlorophyll b / carotenoids, surround, primary pigment / reaction
centre / chlorophyll a ;
18. pass energy to, primary pigment / reaction centre / chlorophyll a ;
19. P700 / PI, involved (in cyclic photophosphorylation) ;
20. (light absorbed results in) electron excited / AW ;
21. emitted from, chlorophyll / photosystem ;
22. flows along, chain of electron carriers / ETC ;
23. ATP synthesis ;
24. electron returns to, P700 / PI ;
Explain how the allele for haemophilia may be passed from a man to his grandchildren. You may use genetic diagrams to support your answer.
) 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 diagram
22. correct symbols ; e.g. X H
and X h
explained
23. man’s genotype ; e.g. X h Y ignore partner’s genotype 2 4. F1 (daughter’s) genotype ; e.g. X H X h ignore her partner’s genotype 2 5. F2 (grandson’s) genotypes ; e.g. X h Y X H Y both required 2 6. F2 (granddaughter’s) genotypes ; e.g. X H X H X H X h both required or X h X h X H X h
Outline the role of mitochondria structure in synaptic transmission.
1 produces ATP ; (1) R produces energy any two from 2 (for) ACh production ; 3 (for) vesicle formation ; 4 (for) vesicle movement ; 5 (for) exocytosis / described ; 6 (for) functioning of ion pumps ; R calcium ions (2 max)
Plasmid vectors carrying antibiotic resistance genes are now rarely used in gene technology.
(i) Explain why antibiotic resistance genes are now rarely used.
1 plasmids (easily) transferred between bacteria ; 2 (bacteria of), same species / different species ; 3 bacteria can acquire antibiotic resistance / renders antibiotic useless
explain why, in the absence of oxygen, pyruvate needs to be converted to lactate
1 NAD regenerated ; 2 so glycolysis can continue ; 3 to produce ATP ;
Outline the process of the photolysis of water and describe what happens to the products of photolysis.
1 PII absorbs light ; 2 enzyme (in PII) involved ; 3 to break down water / AW ;
4 2H2O 4H+ + 4e– + O2 ; 5 oxygen is produced ; 6 used by cells for (aerobic) respiration ; 7 or released (out of plant) through stomata ; 8 protons used to reduce NADP ; 9 with electrons from PI ; 10 reduced NADP used in, light independent stage / Calvin cycle ; 11 to convert GP to TP ; 12 electrons also used in ETC ; 13 to release energy for photophosphorylation ; 14 to produce ATP ; 15 electrons (from PII) go to PI ; 16 ref. re-stabilise PI ; [10 max]
) Describe the roles of gibberellins in stem elongation
16 gibberellin is a, plant growth regulator / plant hormone / plant growth substance ; 17 stimulates cell division ; 18 stimulates cell elongation ; 19 detail of cell elongation ; e.g. changes plasticity of cell wall 20 plant grows tall ; 21 apply gibberellin to dwarf plants and they grow taller / gibberellin promotes bolting of some rosette plants ; 22 ref. inactive and active forms ; 23 dwarf plants, lack active form / have inactive form, of gibberellin ; 24 (dominant) allele causes synthesis of enzyme ; 25 (enzyme) catalyses the production of the active form of gibberellin ; 26 recessive allele only inactive form of gibberellin formed / dominant allele results in active form of gibberellins ; 27 AVP ; e.g. ref. to different forms of gibberellins / there is interaction between / gibberellin and other plant growth regulators
The hormone human chorionic gonadotrophin (HCG) is produced by a woman in the early stages of pregnancy. Describe how a pregnancy test kit can detect the presence of HCG.
- (stick / kit) dipped in (early morning) urine sample ;
- hCG / urine, moves up strip ;
- idea that hCG acts as antigen ;
- (mobile) antibody also bound to, indicator / gold ;
- (mobile) antibody in stick binds to hCG ;
- ref. to variable region (of antibody) ;
- ref. to specificity (of antibody) ;
- ref. to monoclonal (antibody) ;
first window or region
9. second antibody is, immobilised / fixed ;
- first antibody and hCG complex binds to second antibody ;
- coloured band indicates pregnancy ;
second window or region
12. immobile antibody binds to mobile antibody-gold complex ;
- second coloured band shows strip is working
Describe the role of the hormone insulin in maintaining a constant blood glucose concentration
- rise in blood glucose concentration detected by β cells ;
- (β cells) in, islets of Langerhans / pancreas ;
- insulin released into blood ;
- binds to receptors in cell surface membrane ;
- ref. to liver / muscle, cells ;
- increase in uptake of glucose (by cells) /
(cell surface) membrane more permeable to glucose ; - increase in use of glucose in respiration ;
- (increase in) conversion of glucose to glycogen ;
- blood glucose concentration falls ;
- inhibits, glycogen / lipid / amino acid, breakdown
The passage below summarises the effects of auxin on the growth of a shoot.
Auxin is synthesised in the growing tips of shoots (apical buds). It is transported from here
down the shoot by active transport / diffusion from cell to cell and also to a lesser extent
by mass flow in the phloem
Auxin seems to be involved in determining whether a plant grows upwards or whether it
branches sideways. When the apical bud is actively growing, it tends to stop lateral buds
from growing. This is called apical dominance. The plant grows upwards
rather than branching out sideways.
However, if the apical bud is cut off, the lateral buds start to grow. It is thought
that removal of the apical bud causes the concentration of auxin in lateral buds to
decrease so the buds can now grow by cell division
and cell elongation / division / mitosis
Describe the roles of the following substances in the light-independent stage of photosynthesis RuBP
(i) 1. carbon dioxide fixation ;
2. production of GP ;
3. ref. to rubisco ;
Describe the roles of the following substances in the light-independent stage of photosynthesis reduced NADP
(ii) 1. reduction (of GP) / donates hydrogen ;
2. GP to TP
Describe the roles of the following substances in the light-independent stage of photosynthesis: ATP
- supplies, energy / phosphate ;
- (to convert) GP to TP ;
- (to) regenerate of RuBP
Describe the role of sodium ion channels in the transmission of a nerve impulse
(ii) 1. ref. to voltage-gated sodium ion channels / ref. ligand gated channels ;
2. channels change shape (when, pd / voltage, changes) ;
- open when, membrane depolarises / action potential arrives / neurotransmitter
binds to receptors ;
4. sodium ions flood in ; 5. diffuses / down concentration gradient ; 6. channels close when membrane, repolarises / potential reaches +30mV ; 7. ref. to sodium-potassium pump ;
Most farmers today grow maize from seeds that have been produced by crossing two different homozygous parents.
Explain why this is done
- to avoid inbreeding depression ;
- hybrids have, higher yields / hybrid vigour ;
- avoids expression of harmful recessive alleles ;
- ref. to genetic uniformity ;
- (which) results in easier, cultivation / harvest / etc
Suggest why more water is produced from the metabolism of lipid than from the other two substrates.
- lipid releases most energy ;
- because it has more, hydrogens / C-H bonds ;
- per unit mass ;
- hydrogens needed for, ATP production / chemiosmosis
Explain the importance of the coronary arteries of the heart.
1 carry blood to, cardiac/heart, muscle/tissue/cells ;
2 supply oxygen ;
3 supply, nutrient/named nutrient ;
4 for, energy release/respiration ; R produce energy
During the cooling period, the ultrastructure of the sorghum chloroplasts changed. The membranes of the thylakoids moved closer together, eliminating the spaces between them. The size and number of grana became reduced.
Explain how these changes could be responsible for the low rate of carbon dioxide uptake by sorghum even when returned to a temperature of 25 °C
1 less surface area ;
2 less absorption of light ;
3 less, photophosphorylation / light dependent reaction ;
4 less chemiosmosis ;
5 (due to) smaller thylakoid space or reduced proton gradient ;
6 less ATP (produced) ;
7 less reduced NADP (produced) ;
8 light-independent reaction / Calvin cycle, slows down ;
9 less carbon dioxide, fixed / combined with PEP ; R uptake
Outline the process of oxidative phosphorylation
1 reduced, NAD/FAD ;
2 dehydrogenase enzymes ;
3 release hydrogen ; A H R H2/H
+
4 hydrogen splits into proton and electron ;
5 electrons flow down, ETC/AW ;
6 energy released ;
7 protons pumped (across inner membrane/from matrix) ;
8 into intermembrane space ;
9 proton gradient ;
10 protons pass through, ATP synthase/stalked particle ;
11 oxygen final, hydrogen/proton, acceptor ;
Explain why carbon dioxide is produced when mitochondria are incubated with pyruvate but not when they are incubated with glucose.
1 glycolysis, does not occur in mitochondrion/only occurs in cytosol or cytoplasm ;
2 pyruvate produced in glycolysis ;
3 pyruvate can enter mitochondrion/glucose cannot enter mitochondrion ;
4 carbon dioxide produced/decarboxylation, in, Krebs/link reaction
Explain how the palisade mesophyll cells of a leaf are adapted for photosynthesis.
1 closely packed to absorb maximum light ;
2 vertical/at right angles to surface of leaf to reduce number of cross walls ;
3 large vacuole pushes chloroplasts to edge of cell ;
4 chloroplasts at edge short diffusion path for carbon dioxide ;
5 chloroplasts at edge to absorb maximum light ;
6 large number of chloroplasts to absorb maximum light ;
7 cylindrical cells or air spaces to circulate gases/provide a reservoir of CO2 ;
8 large surface area for diffusion of gases ;
9 moist cell surfaces for diffusion of gases ;
10 cell walls thin for maximum light penetration/diffusion of gases ;
11 chloroplasts can move towards light ;
12 chloroplasts can move away from high light intensity to avoid damage ;
Outline the light-independent stage of photosynthesis
) 13 Calvin cycle/stroma ;
14 carbon dioxide fixed by RuBP ;
15 rubisco ;
16 2 molecules of GP formed ; A PGA
17 (GP) forms TP ; A GALP/PGAL
18 use of ATP ;
19 use of, reduced NADP /NADPH ;
20 from light dependent stage ;
21 some TP forms, hexose/sucrose/starch/cellulose/glycerol ;
22 some TP converted to acetyl CoA ;
23 some TP used to regenerate RuBP ;
24 using ATP ;
allow either mp 18 or mp 24
marks can be awarded on a diagram
Describe the structure of a kidney nephron and its associated blood vessels.
1 renal/Bowman’s, capsule ;
2 ref. podocytes ;
3 (proximal convoluted tubule/distal convoluted tubule/capsule) in cortex ;
4 proximal convoluted tubule ;
5 loop of Henle ;
6 (loop) in medulla ;
7 distal convoluted tubule ;
8 afferent arteriole ;
9 glomerulus ;
10 efferent arteriole ;
11 capillary network around/proximal convoluted tubule/loop/distal convoluted tubule ;
12 collecting duct ;
Explain how glomerular filtrate is formed.
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/Bowman’s, capsule ;
24 fluid forced into capsule/ultrafiltration
Explain how the destruction of β cells causes diabetes
β cells detect glucose levels or no detection of blood glucose conc. ;
2. β cells secrete insulin or no insulin released ;
3. when blood glucose concentration rises or when blood glucose concentration rises ;
4. (insulin causes) muscle cells / adipose
tissue / liver cells
or muscle cells / adipose tissue / liver cells ;
5. to increase uptake of glucose from blood
/ increased membrane permeability to
glucose
or do not take up excess glucose ;
6. (insulin causes liver cells) to convert
glucose to glycogen
or glucose not converted to glycogen (by
liver cells)
;
7. (insulin causes liver cells) to increase
respiration of glucose
or rate of respiration of glucose does not
increase
;
8. (if no β cells) no control of blood glucose
levels / AW
or no control of blood glucose levels / AW
Explain the importance of the myelin sheath in the functioning of a neurone.
- insulates axon (membrane) ;
- depolarisation occurs only at nodes (of Ranvier) / AW ;
- local circuits ;
- saltatory conduction / AW ;
- speeds transmission of, action potential / impulse ;
- AVP ; e.g. speed increases up to 50 times / 100ms
State one use of glucose within the liver cell.
i) (converted to) glycogen / lipid ;
(used in) glycolysis / respiration
Glucose is phosphorylated at the start of glycolysis in the muscle cell.
Suggest why this phosphorylated glucose does not diffuse out of the cell into the surrounding tissue fluid.
- cannot pass through phospholipid bilayer ;
- too big to fit through (glucose’s) protein channel ;
- no specific transport protein ;
- AVP ; e.g. used up as soon as it is made
Outline the ways in which the endocrine and nervous systems carry out their roles in control and coordination in animals.
endocrine
1. 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
(a) Describe how non-cyclic photophosphorylation produces ATP and reduced NADP
) 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
(b) Outline the steps of the Calvin cycle.
) 15. RuBP combines with carbon dioxide ;
- rubisco ;
- forms unstable 6C compound ;
- produces two molecules of, GP / PGA ;
- GP / PGA, converted to TP ;
- by reduced NADP and ATP ;
- from light dependent stage ;
- TP used to regenerate RuBP ;
- using ATP ;
- TP can form, hexose / fatty acids / acetyl CoA
Suggest and explain why the rate of photosynthesis of the plant decreases to zero just above 40 °C.
- 26
°C optimum temperature for, rubisco / enzyme of Calvin cycle ;
- (at just over 40
°C) enzymes / rubisco, denatured ;
- so less carbon dioxide fixed ;
- reduction in Calvin cycle / AW ;
- increased rate of transpiration / AW ;
- so stomata close ;
- less carbon dioxide uptake ;
- oxygen more likely to combine with rubisco ;
- so increased photorespiration ;
(a) Describe how ATP is synthesised by oxidative phosphorylation.
) 1. reduced, NAD / FAD ;
- passed to ETC ;
- inner membrane / cristae ;
- hydrogen released (from reduced, NAD / FAD) ; R H2
- split into electrons and protons ;
- electrons pass along, carriers / cytochromes ;
- ref. energy gradient ;
- energy released pumps protons into intermembrane space ;
- proton gradient ;
- protons pass through (protein) channels ;
- ATP synthase / stalked particles ;
- (ATP produced from) ADP and inorganic phosphate ;
- electron transferred to oxygen ;
- addition of proton (to oxygen) to form water / (oxygen) reduced to water
(b) 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.
mechanisms
- active transport ; A actively pumped / uses ATP
- Na+ , out of pct cells / into blood ;
- (sets up) Na+ ion gradient ;
- facilitated diffusion ;
- using protein carrier ; A transport protein
- cotransport (from lumen to pct cell);
- of, glucose / amino acids / ions;
- osmosis ;
- down water potential gradient ;
- diffusion (in correct context) ;
- down a concentration gradient ; max 7
adaptations
- microvilli ; A brush border
- many mitochondria ;
PMT
Page 16 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2012 9700 41
© University of Cambridge International Examinations 2012
- tight junctions ;
- folded, basal membrane / described ;
- many, transport proteins / cotransporters / pumps;
- AVP ; e.g. many aquaporins
Describe the structure of a kidney, including its associated blood vessels.
) many of these mps can be given from a labelled diagram
- (outer) cortex ;
- medulla ;
- pelvis ;
- renal artery ;
- renal vein ;
- nephron / (kidney) tubule ;
- renal capsule / proximal convoluted tubule (pct) / distal convoluted tubule (dct), in cortex ;
- loop of Henle / collecting duct (cd), in medulla ;
- glomerulus ;
- afferent & efferent arterioles;
- capillary network, surrounds tubule / in medulla ;
Outline the role of reduced NADP in the light-independent stage
(iii) reduces/donates hydrogen ; A H/hydrogen atoms/H+ AND e– R H+ / H2
GP to TP ; A PGA to PGAL
[
Suggest why this process is called positive feedback.
production of tTA causes production of more tTA/AW
With reference to the events occurring inside a mitochondrion, explain why a faster use of ATP requires a greater rate of oxygen consumption.
- ATP is made, in the electron transport chain/by oxidative phosphorylation;
- oxygen is the final electron acceptor;
- in the, inner membrane of the mitochondrion/cristae;
- transfer of electron (between electron carriers) provides energy;
- energy used to pump hydrogen ions (into intermembrane space);
- creates proton gradient;
- diffusion of hydrogen ions down their electrochemical gradient causes ATP to be synthesised;
- ref. chemiosmosis/ATP synthase/stalked particles;
- idea that if less oxygen (consumed/available) then fewer electrons transferred along the chain;
Suggest what measurements were taken, and how these measurements were used to calculate the oxygen debt
oxygen consumed = oxygen inhaled – oxygen exhaled;
- measure oxygen consumption at rest (x) and after exercise stops (y);
- extra oxygen consumed/oxygen debt = y – x;
- measure mass of lizard;
Describe how, in photosynthesis, light energy is converted into chemical energy, in the form of ATP.
- light energy absorbed by chlorophyll; A photosystems/pigments
- electron, excited/raised to higher energy level;
- (electron) emitted by chlorophyll; A photosystems/pigments
- passes to electron, acceptor/carrier;
- passes along, chain of electron carriers/ETC/Electron Transfer Chain;
- energy released used to pump protons; I ATP production here
- into thylakoid space;
- thylakoid membrane impermeable to protons;
- proton gradient forms;
- protons move down gradient;
- through/using, ATP synthase/ATP synthetase; R ATPase
- enzyme rotates;
- ATP produced from ADP and Pi;
Some parasitic worms, such as tapeworms, live in a mammalian gut where there is no oxygen.
Suggest how a tapeworm produces ATP in this environment.
anaerobic respiration ;
substrate level phosphorylation (in glycolysis);
at triose phosphate pyruvate step ;
(net) gain of 2ATP (per glucose) ; A 2 used and 4 produced
pyruvate, reduced
/
gains hydrogens (from reduced NAD) ;
forming lactate ;
NAD regenerated
/
NADH2 re-oxidised ;
this allows glycolysis to continue
explain why the pancreas is an endocrine gland.
α cells / β cells / islets / B, secrete, hormones / glucagon / insulin ;
into the blood / not into a duct ;
Insulin and glucagon are involved in the control of blood glucose concentration. When blood glucose concentration rises, secretion of insulin increases.
Outline two ways in which insulin affects the activity of cells in the liver.
1 increases permeability of membrane to glucose / increases glucose uptake ;
2 increases respiration of glucose ;
3 (increases), conversion of glucose to glycogen / glycogenesis ;
4 (increases) protein / fat, synthesis ;
explain why plants appear green
they contain chlorophyll ;
green / blue green / yellow green, light reflected ;
Explain why increasing the concentration of carbon dioxide may increase the rate of production of carbohydrates at high light intensities.
1 light not limiting ; 2 much, ATP / reduced NADP, available ; 3 CO2 is the limiting factor ; 4 because low concentration CO2 (in atmosphere) ; 5 more CO2 combines with RuBP ; 6 ref. rubisco ; 7 Calvin cycle / light independent stage ; 8 GP to TP ; 9 more hexose produced ; 10 ref. fate of hexose
) Explain the roles of NAD in anaerobic respiration in both plants and animal
in cytoplasm 19 NAD, becomes reduced / accepts H ;
20 during glycolysis ;
in plants 21 pyruvate converted to ethanal ;
22 ethanal reduced ;
23 by reduced NAD ;
24 ethanol formed ;
in animals 25 pyruvate converted to lactate ;
26 by reduced NAD ;
27 in, liver / muscles ;
28 allows glycolysis to continue ;
Hummingbirds regulate their body temperature whereas butterflies do not regulate their body temperature.
Explain briefly the effect of an increase in temperature on the rate of respiration of a butterfly
1 increase in rate of respiration ;
2 kinetic energy increases / more enzyme-substrate complexes / enzyme activity increases ;
3 effects of too high a rise in temperature ; e.g. denaturation of enzymes
4 AVP ; e.g. Q10 = 2
Suggest the effects on synapses of this irreversible inhibition of acetylcholinesterase
) when acetylcholinesterase is inhibited 1 acetylcholine remains attached to receptors (on post-synaptic membrane) ;
2 sodium channels on post-synaptic (membrane) remain open ;
3 membrane remains depolarised ;
4 action potentials / nerve impulses, continue to be produced ;
Describe how an insecticide could irreversibly inhibit acetycholinesterase
1 permanently ;
2 binds with / blocks, active site ;
3 binds with, another part of enzyme / allosteric site ;
4 change (shape) of active site ;
Gases leave and enter the leaf through pores called stomata.
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 potential
6 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 than diameter ;
9 have ends that are joined together ;
10 have, thicker inner walls / thinner outer walls ;
11 curve apart / bend, (to open stoma) ;
Explain briefly the role of reduced NADP in the light-independent stag
) hydrogen carrier ;
GP, reduced / hydrogen added ; R H2
to, TP / 3 carbon sugar ;
uses ATP ;
Explain how the collecting ducts in the kidneys may reduce the loss of water from the body.
) 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 23
23 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 gradient movement of urea increases water potential gradient [7 max]
Describe the part played by the proximal convoluted tubules in the functioning of the kidneys.
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 proteins
9 cotransport ;
10 of, glucose / amino acids / vitamins / chloride ions ;
11 (from pct cells) into intercellular fluid ; linked to 10
12 (then) diffusion into blood ; linked to 10
13 (normally) all glucose reabsorbed ;
14 some water reabsorbed ;
15 some urea reabsorbed ;
16 AVP ; e.g. creatinine secreted into lumen
For many plants living in temperate regions, the optimum temperature for photosynthesis is approximately 25 °C.
Suggest reasons why the rate of photosynthesis decreases at temperatures above 25 °C
1 rubisco
/
enzymes, denatured
/
AW ;
2 less, photolysis
/
ATP produced
/
light-dependent stage
/
Calvin cycle ;
3 less carbon dioxide fixed ;
4 increase in transpiration ;
5 photorespiration
/
AW ;
6 stomata close ; 7 reduction in carbon dioxide uptake ;
8 loss of turgor
/
wilting ;
[
Describe how the release of calcium ions leads to the contraction of a sarcomere
) 1 (Ca2+) released from sarcoplasmic reticulum ; 2 binds to troponin ; 3 (troponin) changes shape ; 4 tropomyosin is, displaced
/
AW ; 5 (myosin) binding sites exposed ; 6 myosin head now, binds
/
attaches
/
joins, to actin ; 7 AVP ; e.g. ref. myosin pulls actin
Suggest one function for the circular mitochondrial DNA
has genes that code for: mitochondrial proteins ; mitochondrial enzymes ; mitochondrial replication ; rRNA
list three substances that enter the mitochondria and three substances that leave the mitochondria
oxygen
pyruvate
ADP
phosphate
/
Pi
fatty acids
substance that leaves the mitochondria
carbon dioxide
ATP
water
) The poison cyanide binds with cytochrome oxidase, one of the carriers in the electron transport system.
Suggest how ingestion of cyanide by humans leads to death by muscle failure.
max 3 from mp1–mp5 1 ETC / electron transport chain, stops ; 2 Krebs cycle
/
link reaction, stops ; 3 no proton gradient set up ; 4 no proton flow through ATP synthase ; 5 less
/
no, ATP produced ;
6 named muscle fails to contract ; e.g. heart
/
intercostals
compare the structures of ATP and NAD.
) both have ribose (sugars) ; R ribulose ATP has 1, ribose
/
pentose
/
sugar, NAD has 2 ; I ref. to additional hexose both have, adenine
/
purine (base) ; I adenosine NAD has, nicotinamide
/
pyrimidine (base) ; ATP has 3 phosphates, NAD has 2
) Outline the roles of NAD in the cytoplasm of a cell.
d) hydrogen, carrier
/
acceptor ; A gets reduced or gains H
/
H+ and electrons
I donates R H2
/
hydrogen molecules (acts as a) coenzyme ; A enables dehydrogenases to work ref. to glycolysis
/
respiration in anaerobic conditions ; A anaerobic respiration I aerobic
Name the process by which insulin is secreted from β cells.
exocytosis
v Describe the effects of insulin on muscle cells.
causes glucose uptake
/
increases permeability to glucose ; adds transport proteins to cell (surface) membrane ; A in sarcolemma A GLUT(4), proteins / channels / carriers more glucose respired
/
increase in respiration rate ; glucose converted to glycogen
/
glycogenesis
Describe how the effect of adrenaline on liver cells results in an increase in blood glucose concentration.
accept stimulates
/
stimulated, for activates
/
activated throughout 1 (adrenaline) receptor shape change ; 2 G-proteins activated ; A description of G protein releases (α) subunit 3 adenylyl cyclase activated ; A adenyl(ate) cyclase 4 cyclic AMP made ; 5 (cAMP is) second messenger ; 6 activates / phosphorylates, kinase ; 7 ref. to enzyme cascade / cascade of reactions ; 8 glycogenolysis / hydrolysis of glycogen, stimulated / AW ; A break down glycogen 9 AVP ; gluconeogenesis / ref. to glucose transport proteins A description / glucose from, amino acids / lipids A GLUT(2) channels / carriers
, describe the relationship between the strength of the stimulus and the resulting action potential
only, stimulus
/
depolarisation
/
receptor potential
/
potential difference, that reaches threshold produces an action potential ; ora A -50mV for threshold A generator for receptor
idea that the action potential is the same size no matter how strong the stimulus ; ref. to all-or-nothing (law) ; I all-and-nothing
) Describe respiration in yeast cells in anaerobic conditions
1 pyruvate formed by glycolysis ; 2 reduced NAD formed by glycolysis ; 3 pyruvate decarboxylated
/
AW ; 4 ethanal produced ; 5 pyruvate decarboxylase ; 6 ethanal is, hydrogen acceptor
/
reduced ; A gains H or gains H+ and e– 7 from
/
by, reduced NAD ; 8 ethanol formed ; 9 ethanol
/
alcohol, dehydrogenase ; 10 not reversible reaction ; 11 NAD, regenerated
/
can now accept hydrogen atoms ; A reduced NAD oxidised 12 so glycolysis can continue ;
State one structural difference between a guard cell and other lower epidermal cells
(i) have chloroplasts
/
varying thickness of (cell) walls
/
no plasmodesmata
outlines how sensory receptors work.
A sensory receptor cell responds to a stimulus by opening ion chaneels. in
its cell surface membrane. Sodium ions flood into the cell causing the membrane to become
depolarised. This is called the generator potential. If this potential is
large enough to reach a threshold then an action potential is transmitted to the
central nervous system. An increase in the strength of the stimulus will result in an increase in
thefrequency of action potentials transmitted.
Describe how an action potential is transmitted along a sensory neurone in a mammal.
action potential stimulates neighbouring area of membrane ; AW
Na+, moves sideways
/
attracted to areas at resting potential ; A local circuit
causes, Na+ ion channels to open
/
2nd depolarisation ;
(transmission) in one direction due to, hyperpolarisation
/
refractory period ;
myelin sheath
/
Schwann cell ;
sheath insulates, axon
/
dendron
/
neurone ;
depolarisation
/
action potential, only at nodes of Ranvier
/
unmyelinated part ; ora
saltatory conduction
/
action potential ‘jumps’ from node to node ;
With reference to the events occurring inside a mitochondrion, explain why a faster use of ATP requires a greater rate of oxygen consumption.
- ATP is made, in the electron transport chain/by oxidative phosphorylation;
- oxygen is the final electron acceptor;
- in the, inner membrane of the mitochondrion/cristae;
- transfer of electron (between electron carriers) provides energy;
- energy used to pump hydrogen ions (into intermembrane space);
- creates proton gradient;
- diffusion of hydrogen ions down their electrochemical gradient causes ATP to be synthesised;
- ref. chemiosmosis/ATP synthase/stalked particles;
- idea that if less oxygen (consumed/available) then fewer electrons transferred along the chain;
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.
mechanisms
- active transport ; A actively pumped / uses ATP
- Na+ , out of pct cells / into blood ;
- (sets up) Na+ ion gradient ;
- facilitated diffusion ;
- using protein carrier ; A transport protein
- cotransport (from lumen to pct cell);
- of, glucose / amino acids / ions;
- osmosis ;
- down water potential gradient ;
- diffusion (in correct context) ;
- down a concentration gradient ; max 7
adaptations
- microvilli ; A brush border
- many mitochondria ;
PMT 25. tight junctions ; - folded, basal membrane / described ;
- many, transport proteins / cotransporters / pumps;
- AVP ; e.g. many aquaporins
) Describe the structure of a kidney, including its associated blood vessels
- (outer) cortex ;
- medulla ;
- pelvis ;
- renal artery ;
- renal vein ;
- nephron / (kidney) tubule ;
- renal capsule / proximal convoluted tubule (pct) / distal convoluted tubule (dct), in cortex ;
- loop of Henle / collecting duct (cd), in medulla ;
- glomerulus ;
- afferent & efferent arterioles;
- capillary network, surrounds tubule / in medulla ;
Outline the process of oxidative phosphorylation
- hydrogens split into protons and electrons ;
- electrons pass along ETC ;
- energy released used to pump protons ;
- (from matrix) to intermembrane space ;
- inner membrane impermeable to protons ;
- proton gradient forms ;
- protons move down gradient ;
- through ATP, synthase / ATP synthetase ; R ATPase
- enzyme rotates ;
- ATP produced ;
(a) Describe the photoactivation of chlorophyll and its role in cyclic photophosphorylation
- (photosynthetic pigments) arranged in light harvesting clusters ;
- primary pigments / chlorophyll a ;
- at reaction centre ;
- P700 / Pl, absorbs light at 700nm ;
- accessory pigments / chlorophyll b / carotenoids ;
- surround, primary pigment / reaction centre / chlorophyll a ;
- absorb light ;
- pass energy to, primary pigment / reaction centre / chlorophyll a ;
- (light absorbed results in) electron excited / AW ;
- emitted from, chlorophyll / primary pigment / reaction centre ;
- passes to electron, acceptor / carrier ;
- (electron) passes along, chain of electron carriers / ETC ;
- ATP (synthesis) ;
- electron returns to, P700 / Pl ;
Explain briefly how reduced NADP is formed in the light-dependent stage and how it is used in the light-independent stage.
) 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 ; [7 max]
State where the reduced NAD molecules are re-oxidised and describe what happens to the hydrogen atoms.
1 inner mitochondrial membrane/cristae ;
2 dehydrogenase enzymes ;
3 release hydrogen ;
4 hydrogen splits into protons and electrons ;
5 electrons flow down, ETC/Electron Transfer Chain/AW ;
6 energy released ;
7 protons pumped across (inner membrane) ;
8 into intermembrane space ;
9 proton gradient ;
10 protons pass through, ATP synthase/stalked particles ;
11 ATP formed ; linked to 10
12 oxygen (final), hydrogen/proton and electron, acceptor
Describe the role of reduced NAD in respiring yeast cells in the absence of oxygen
1 pyruvate converted to ethanal ;
2 ethanal reduced ;
3 by reduced NAD ;
4 NAD, oxidised/regenerated ;
5 allows glycolysis to continue ;
6 ethanal dehydrogenase ;
7 ethanol formed ;
8 prevents H + from lowering pH
Describe the structure of a myelinated sensory neurone.
1 nucleus in cell body ;
2 (long) dendron ; R plural
3 (shorter) axon ;
4 many mitochondria (in cell body) ;
5 many RER/nissl’s 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
a) Describe the structure of photosystems and explain how a photosystem functions in cyclic photophosphorylation.
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/reaction
centre/ 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 ;
11 (a) Describe the role of abscisic acid (ABA) in the closure of a stoma.
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 ;
(b) Describe the role of gibberellins in the germination of barley seeds.
) 13. (barley) seed is, dormant / metabolically inactive ;
- seed absorbs water ;
- embryo produces gibberellin ;
- gibberellin stimulates aleurone layer ;
- to produce amylase ;
- amylase hydrolyses starch ;
- in endosperm ;
- to maltose / glucose ;
- embryo uses sugars for respiration ;
- energy used for growth ;
- gibberellins affect, gene / transcription of mRNA, coding for amylase ; [7 max]
Outline, with reference to blood glucose concentration, the principles of homeostasis in mammals.
v1. (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) β / α , 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 ; [6 max]
Describe the roles of the endocrine and nervous systems in control and coordination in mammals.
endocrine 11. hormones ;
- chemical messengers ; A chemicals that transfer information
- ductless glands / (released) into blood ;
- target, organs / cells ;
- ref. receptors on cell membranes ;
- example of named hormone and effect ;
nervous 17. impulses / action potentials ; R electrical, signals / current
- along, neurones ; R nerves
- synapse (with target) / neuromuscular junction ;
- ref. receptor / effector or sensory / motor, neurones ;
differences – endocrine 21. slow effect / ora ;
- long lasting effect / ora ;
- widespread effect / ora ;
- AVP ; e.g. extra detail of synapse
(b) Explain how rice is adapted to growing in flooded fields
- ethene (in plant);
- stimulates production of gibberellin;
- gibberellin stimulates, cell division / cell elongation / increase in stem length;
- leaves / flowers, above water;
- (so) photosynthesis can occur;
- (so) sexual reproduction / pollination, can occur;
- aerenchyma / description;
- assists gas diffusion (within plant);
- air can be trapped by specialised underwater leaves;
- (submerged parts of plant) carry out anaerobic respiration;
- produce ethanol;
- can tolerate high concentrations of ethanol;
- produce a lot of ethanol dehydrogenase
(a) Describe the structure of a chloroplast.
- 3 – 10 µm (diameter);
- double membrane;
- ground substance / stroma;
- contains enzymes / named enzyme, e.g. rubisco;
- also, sugars / lipids / starch;
- 70S / AW, ribosomes;
- circular DNA;
- internal membrane system / fluid-filled sacs / thylakoids; A flattened sacs
- grana are stacks of thylakoids;
- (grana) membranes hold, photosynthetic pigments / ATP synthase / ETC
Explain why the epithelial cells of the proximal convoluted tubule have many mitochondria in them.
………………………………………………………………………………………………………………….
- produce ATP / provide energy;
- for active transport of Na+;
- out (of cell);
Name two substances that are reabsorbed into the blood from the proximal convoluted tubule, apart from water.
mark first two answers any named ion / mineral ions;
vitamins;
amino acids;
glucose;
some urea;
v Explain how the structures of the glomerular capillaries and the podocytes are adapted for ultrafiltration
fluid can pass through glomerular capillaries because (max 3) 1. fenestrations in capillary endothelium; A hole / pores / gaps
- basement membrane acts as a filter;
- no substances >68 000 MM can get through;
- no cells can get through;
fluid can pass through podocytes because 5. have, projections / AW;
- gaps (between projections); A filtration slits
Explain why the membrane of the neurone depolarises when the Na+ / K+ pump stops working.
Suggest why calcium ions flood into the neurone when the Na+ / K+ pump stops working.
- (when pump stops working), resting potential not maintained or pump usually maintains the resting potential;
- (during resting potential) membrane polarised or positive charge outside (neurone) / negative charge inside (neurone) / -70mV inside neurone relative to outside / potential difference across membrane;
- (when pump stops working), ions (only) move by diffusion;
- Na+ into the neurone;
- outward diffusion of K+ is limited / K+ stay in neurone;
- ref. non voltage-gated channels;
- (eventually) inside of the neurone, becomes less negative / contains (relatively) more positive ions or there is a reduced potential difference across the membrane;
voltage gated (calcium) channels open;
- (calcium ions move in) by diffusion / move down their concentration gradient; [2]
Describe the role of oxygen in the process of oxidative phosphorylation
- final electron acceptor / accepts electron from last carrier;
- so carrier can be reduced again;
- so electrons can keep flowing (along ETC) / so ETC can continue to work;
- (oxygen) combines with H+ to form water;
Describe briefly where the electrons that are passed along the electron transport chain come from.
- (electron comes from) hydrogen (atom); R H+ / H2
- (from) reduced NAD / reduced FAD;
- (from) dehydrogenation / oxidation, reactions;
- (from substances in) Krebs cycle / link reaction / glycolysis;
- in, matrix of mitochondrion / cytoplasm
State the part of the mitochondrion in which the electron transport chain is found.
inner membrane / crista(e);
Explain why the volume of oxygen released from the plant does not give a true rate of photosynthesis.
(iii) respiration uses oxygen;
Suggest how a tumour on the optic nerve could prevent the transmission of nerve impulses to the brain.
(c) compresses nerve ;
damages, myelin sheaths
/
Schwann cells ;
prevents, setting up of local circuits
/
saltatory conduction ;
stops Na+
/
K+ pumps from working ;
blocks blood supply;
qualified ; e.g. effect on, oxygen supply
/
glucose supply
/
ATP production
AVP ; e.g. may stop ion channels opening
Describe the action of ADH on the kidney.
Diabetes insipidus is a condition caused by an inability to produce ADH or by the kidneys being unable to respond to ADH.
Suggest symptoms that may be experienced by a person who has diabetes insipidus.
…………………………………………………………………………………………………………………………………
affects collecting duct, (cells
/
wall) ; A distal convoluted tubule cells
binds to receptors on cell surface membranes ;
activates series of enzyme controlled reactions ;
(phosphorylase causes), vesicles
/
aquaporins, to move to cell surface membrane
(on lumen side) ;
vesicles
/
aquaporins, fuse with cell surface membrane ;
cells
/
wall, more permeable to water ;
water moves out of lumen (of collecting duct) ;
down water potential gradient ; [max 5]
produce, a lot of urine
/
dilute urine ;
dehydration
/
thirsty ;
cramps
/
loss of salts ;
The decrease in the water potential of the blood is sometimes due to the loss of water from the body of a mammal.
List two ways by which water may be lost from the body
for one mark ; any 2 from urine sweat water vapour (from exhaled air) faeces bleeding tears [max 1]
State precisely where ADH is released into the blood
posterior pituitary
) A chloroplast also contains DNA.
Suggest the functions of DNA in chloroplast
DNA codes for, proteins
/
polypeptides
/
enzymes ;
one example of protein or enzyme ; e.g. rubisco
/
electron acceptor
/
ATP synthase
/
transport
ref. transcription
/
mRNA ;
Explain why lipids have a higher energy value than carbohydrates.
lipids 1 more C-H bonds
/
more reduced
/
more hydrogen ;
2 produces more reduced NAD ;
3 produces more ATP per, gram
/
unit mass ;
4 more, aerobic respiration
/
oxidative phosphorylation
/
chemiosmosis ;
5 fats only broken down aerobically ;
Explain why maintaining a resting potential requires energy.
1 active transport ;
2 ref. to sodium potassium pump ;
3 sodium ions out and potassium ions in ;
4 against their, concentration
/
electrochemical, gradient ;
5 ref. to, ion diffusion
/
ion leakage ; [max 3]
Rubisco is involved in the fixation of ……………………………………………… by RuBP (ribulose
bisphosphate) in the Calvin cycle. The resulting six carbon compound immediately
splits to give two molecules of glycerate-3-phosphate (GP). GP is converted to triose
phosphate (TP) using ……………………………………………… and
……………………………………………… produced in the light-dependent stage. Some of the
TP produced is used to regenerate ribulose bisphosphate so that the Calvin cycle
can continue. The remaining TP may be used to synthesise other compounds
including ……………………………………………… which can directly enter the Krebs cycle
1 carbon dioxide ; A CO2
2 ATP ;
3 reduced NADP ; mp 2 and mp3 in either order
4 acetyl CoA ; [4]
Chloroplasts can move within palisade cells.
Suggest two advantages of chloroplast movement within palisade cells.
to absorb, more
/
maximum, light ;
to avoid damage by high light intensities ; [2]
) Describe the series of reactions that make up the Krebs cycle.
1 oxaloacetate accepts, acetate
/
acetyl group
/
2C fragment ;
2 to form citrate ; 3 4C to 6C ; 4 decarboxylation ; 5 CO2 released ; 6 dehydrogenation
/
oxidation ; 7 reduced NAD produced ; 8 reduced FAD produced ; 9 ATP produced ; 10 substrate-linked
/
substrate-level, phosphorylation ; 11 ref. to intermediate compounds ; 12 enzyme-catalysed reactions ; 13 oxaloacetate regenerated ;
(a) Outline the process of glycolysis.
1 lysis
/
splitting
/
break down, of glucose ; R sugar splitting 2 (glucose) phosphorylated by ATP ; 3 raises energy level / to activate the reaction / reduces activation energy /
to make it reactive ; 4 fructose (1,6) bisphosphate ; 5 (breaks down to) two, triose phosphate
/
TP ; 6 hydrogen removed by NAD ; A triose phosphate oxidised by NAD 7 reduced NAD formed ; 8 pyruvate produced ; 9 small yield of ATP ;
(ii) Describe the role of coenzyme A in respiration
) combines with, acetyl group
/
acetate ;
ref. to link reaction ; (delivers, acetyl group
/
acetate) to the Krebs cycle ;
(acetyl group
/
acetate) combines with oxaloacetate ; R Acetyl CoA combines with oxaloacetate
With reference to Fig. 2.1, describe and explain the effect of temperature on the rate of photosynthesis.
describe 1 increased temperature increases the rate of photosynthesis at high light intensities ; 2 increased temperature has little effect at low light intensity ;
explain 3 increased kinetic energy ; 4 (leads to) increased, no. of collisions
/
(rate of) enzyme activity
/
ESCs
/
enzyme-subtrate
complexes ; 5 (high light intensity) temperature is the limiting factor ; 6 (low light intensity) light intensity is the limiting factor ;
Describe the role in photosynthesis of an accessory pigment, such as carotene
passes energy to, chlorophyll a
/
primary pigment
/
reaction centre ;
may absorb light wavelengths that, chlorophyll a
/
primary pigment
/
reaction centre, does not
absorb ; forms part of, light-harvesting cluster of pigments
/
photosystem
/
antenna complex ;
In mammals, excess amino acids cannot be stored in the body.
Outline the formation of urea from excess amino acids by liver cells
deamination
/
amine group removed ; A amino
/
NH2
ammonia
/
NH3, formed ; combined with carbon dioxide ; urea cycle ; A ornithine cycle
The mammalian kidney is composed of many nephrons.
Describe the process of ultrafiltration in the nephron.
1 (diameter of lumen of) afferent arteriole wider than efferent arteriole ; 2 (leads to) high, blood / hydrostatic, pressure ; 3 plasma / fluid, passes through, gaps / fenestrations, between endothelial cells (of capillaries) ; 4 ref. to basement membrane acts as a, filter / selective barrier ; 5 red cells / large proteins / molecules greater than 68 000(MM), cannot pass through ; 6 podocytes qualified ; 7 (filtrate) passes into (renal) capsule ;
(passes through the medulla)
loop of collecting duct
Henle ;
(ADH acts on its walls)/
collecting duct
distal convoluted tubule
(most of the water is reabsorbed into the blood)
PCT ;
(glucose is reabsorbed into the blood)
PCT ;
Outline the roles of synapses in the nervous system.
ensure one-way transmission ; allow interconnection of nerve pathways / AW ; involved in, memory / learning ; idea of filtering out, less frequent impulses / low level stimuli / AW
