CIE paper 4

Question 1

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

Answer 1

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

Question 2

explain why proteins occur in the blood entering the glomerulus but not in the filtrate
in the renal capsule

Answer 2

) (too) large / MM > 68 000 ;

to pass through basement membrane ;

Question 3

explain why there is glucose present in the filtrate but not in the urine

Answer 3

reabsorbed ;

in proximal convoluted tubule ;

Question 4

) explain the difference in the concentration of urea between the filtrate and urine

Answer 4

more urea in urine than in filtrate / ora ; A comparative figs

2. water is reabsorbed ;
3. in, distal convoluted tubule / collecting duct ;
4. most urea stays in urine ; R all urea stays
5. other substances are reabsorbed ;

Question 5

where in the chloroplast the Calvin cycle occurs

Answer 5

) stroma ;

Question 6

the name of another compound that is produced in the light-dependent stage of
photosynthesis that is used in the Calvin cycle.

Answer 6

ATP / reduced NADP ;

Question 7

Describe the structure of a motor neurone

Answer 7

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)

Question 8

Explain how an action potential is transmitted along a motor neurone

Answer 8

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

Question 9

Explain what is meant by the term endocrine gland.

Answer 9

ductless gland ;

secretes (hormone) into blood ;

Question 10

Explain briefly what is meant by negative feedback.

Answer 10

a change sets off events that counteract the change / AW / example
described ;

Question 11

(a) Describe the process of glycolysis 🤓

Answer 11

(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

Question 12

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

Answer 12

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 ;

Question 13

a) Describe a reflex arc and explain why such reflex arcs are important

Answer 13

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 ;

Question 14

Describe the structure of a myelin sheath and explain its role in the speed of transmission
of a nerve impulse.

Answer 14

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 ;

Question 15

Describe how the liver reduces blood glucose concentration, when insulin is secreted.

Answer 15

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) ;

Question 16

With reference to Figs. 4.2 and 4.3, suggest one advantage and one disadvantage of inhaling insulin rather than injecting it.

Answer 16

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 ;

Question 17

The roots of young rice plants are highly tolerant of ethanol. Explain how this helps them to survive when the fields are flooded.

Answer 17

oxygen availability low (when soil is flooded) ;

plants carry out anaerobic respiration ;

ethanol produced ;

roots can continue to respire ;

Question 18

Outline the role played by accessory pigments in the light-dependent reactions

Answer 18

absorb light ; A harvest light / trap light R collect light

pass energy to, primary pigment / chlorophyll / reaction centre

Question 19

Outline the differences between cyclic and non-cyclic photophosphorylation

Answer 19

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

Question 20

A palisade mesophyll cell is adapted to carry out photosynthesis

Answer 20

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 ;

Question 21

Explain the different energy values of carbohydrate, lipid and protein as respiratory substrates.

Answer 21

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

Question 22

Explain how rice plants are adapted for growth with the roots submerged in water

Answer 22

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)

Question 23

Explain why glucose needs to be converted to hexose bisphosphate

Answer 23

provides activation energy / AW ;

for it to split / AW ;

Question 24

Pyruvate can enter a mitochondrion when oxygen is present.

Describe what happens to pyruvate in a yeast cell when oxygen is not present.

Answer 24

decarboxylated / carbon dioxide given off ;

2. ethanal produced ;
3. ethanal reduced ;
4. by reduced NAD ;
5. to ethanol ;
6. dehydrogenase ;

Question 25

State one property of collagen that enables it to carry out its main function in the walls of blood vessels and airways.

Answer 25

high tensile strength / withstands pulling forces / fibrous / insoluble / forms fibrils / flexible

Question 26

Describe how the structure of a chloroplast is related to its functions.

Answer 26

ground substance / stroma ; 2. for, light independent stage / Calvin cycle ; 3. contains enzymes / named enzyme e.g. rubisco ; 4. also, sugars / lipids / starch / ribosomes / DNA ; 5. internal membrane system ; 6. for, light dependent stage ; 7. fluid-filled sacs / thylakoids ; 8. grana are stacks of thylakoids ; 9. (grana) hold (photosynthetic) pigments ; 10. (grana) have large surface area for (maximum) light absorption ; 11. (pigments are arranged in), light harvesting clusters / photosystems ; 12. primary pigment / reaction centre / chlorophyll a, surrounded by accessory pigments ; 13. (accessory pigments) pass energy to, primary pigment / reaction centre / chlorophyll a ; 14. different photosystems absorb light at different wavelengths ; 15. membranes hold, ATP synthase / electron carriers ; 16. for, photophosphorylation / chemiosmosis ;

Question 27

Describe how you would separate chloroplast pigments using chromatography

Answer 27

. 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

Question 28

Describe how a resting potential is maintained in an axon

Answer 28

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

Question 29

Describe, using named examples, how sensory receptors in mammals generate action potentials.

Answer 29

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 ;

Question 30

Describe the circumstances in which a.a and lactate are used as respiratory substrates

Answer 30

a.a – starvation / lack of fat or carbohydrate ; lactate – after anaerobic respiration ;

Question 31

Explain how myelination affects the speed of conduction of impulses

Answer 31

1. myelin insulates axon ; 2. no myelin at nodes ; 3. action potentials / depolarisation, only at nodes (of Ranvier) ; 4. local circuits set up between nodes ; 5. action potentials ‘jump’ from node to node / saltatory conduction ; 6. myelination prevents leakage of ions ; ora

Question 32

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.

Answer 32

1. (sheath) treated as, ‘foreign’ / non-self ; 2. ref. role of, antibodies / phagocytes / lymphocytes ; (ii) 1. less insulation of axon ; 2. action potentials, slow down / stop

Question 33

State precisely the location of photosynthetic pigments within a chloroplast.

Answer 33

grana / thylakoid, membrane

Question 34

summarises the effects of gibberellins on seed germination

Answer 34

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

Question 35

Outline the role of insulin in a healthy human

Answer 35

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 ;

Question 36

Describe and explain one advantage of treating diabetics with human insulin produced by rDNA technology.

Answer 36

``` 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 ; ```

Question 37

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.

Answer 37

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 ;

Question 38

Explain why more ATP can be synthesised in aerobic respiration from one gram of lipid than from one gram of glucose.

Answer 38

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 ;

Question 39

sensory neurone vs motor neurone

Answer 39

``` 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 ```

Question 40

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.

Answer 40

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

Question 41

Acetylcholinesterase is an enzyme found in the synaptic cleft. Outline the role of acetylcholinesterase

Answer 41

hydrolyses / breaks down, ACh ; stops continuous production of action potentials (in post-synaptic neurone)

Question 42

Name precisely the process that produces reduced NADP

Answer 42

non-cyclic photophosphorylation ;

Question 43

Describe how carbon dioxide reaches the inside of a palisade mesophyll cell from the external atmosphere

Answer 43

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) ;

Question 44

V The optimum pH for the activity of rubisco is pH8. | Explain why the illumination of chloroplasts leads to optimum pH conditions for rubisco.

Answer 44

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

Question 45

) Describe and explain how gibberellins are involved in the germination of wheat or barley seeds.

Answer 45

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 ;

Question 46

Explain the principles of homeostasis in humans.

Answer 46

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 ;

Question 47

Outline the effect of ADH on the collecting ducts.

Answer 47

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 ;

Question 48

Describe the role of rubisco in the Calvin cycle

Answer 48

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 ;

Question 49

Outline how an action potential arriving at this neuromuscular junction can result in depolarisation of the sarcolemma.

Answer 49

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

Question 50

Describe the role of oxygen in aerobic respiration

Answer 50

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

Question 51

Using examples, outline the importance of homeostasis in a mammal

Answer 51

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

Question 52

Describe the main stages of cell signalling in the control of blood glucose concentration by adrenaline.

Answer 52

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

Question 53

) Explain the role of auxin in cell elongation in plants.

Answer 53

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

Question 54

(b) Describe the role of abscisic acid in the closure of stomata

Answer 54

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

Question 55

State what is meant by the term respiratory quotient (RQ

Answer 55

RQ = volume of carbon dioxide given off; R amount A moles volume of oxygen taken up

Question 56

Explain why an increase in temperature from 15 oC to 25 oC will increase the rate of oxygen uptake in germinating seeds.

Answer 56

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

Question 57

State precisely where the Calvin cycle occurs in plant cells

Answer 57

stroma of chloroplast;

Question 58

b) Describe how carbon dioxide is fixed in the Calvin cycle.

Answer 58

combines with (5C compound) RuBP; to form unstable 6C compound/forms 2 molecules of (3C) GP; ref. enzyme/rubisco;

Question 59

Explain how the products of photophosphorylation are used in the Calvin cycle.

Answer 59

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;

Question 60

Explain what initially happens to the concentration of RuBP and GP if the supply of carbon dioxide is reduced.

Answer 60

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;

Question 61

Explain how a synapse functions.

Answer 61

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

Question 62

Describe the role of glucagon in regulating blood gl

Answer 62

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;

Question 63

Name the membrane-bound enzyme responsible for phosphorylating ADP to make ATP.

Answer 63

ATP, synthase / synthetase ; R ATPase

Question 64

State one use of glucose within the liver cell

Answer 64

(converted to) glycogen / lipid ; (used in) glycolysis / respiration

Question 65

Suggest why respiration is said to be less effi cient in anaerobic conditions than in aerobic conditions.

Answer 65

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 ;

Question 66

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

Answer 66

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

Question 67

Additional oxygen is required in the metabolic pathways involved in the conversion of lactate to glucose. State the term given to this additional oxygen

Answer 67

oxygen debt

Question 68

Explain how the structure of the glomerular capillaries is adapted for ultrafi ltration

Answer 68

(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 ;

Question 69

Explain why the epithelial cells of the proximal convoluted tubule have many mitochondria in them.

Answer 69

produce ATP / provide energy ; for active transport of Na+ ; out (of cell) ;

Question 70

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.

Answer 70

mark fi rst two answers any named ion / mineral ions ; vitamins ; amino acids ; glucose ; some urea ;

Question 71

During stomatal closure: | (i) state precisely where abscisic acid (ABA) binds

Answer 71

receptors) on plasma / cell surface, membrane (of guard cells) ;

Question 72

During stomatal closure: (ii) identify the ion that diffuses from the guard cells to epidermal cells

Answer 72

K+

Question 73

During stomatal closure: (iii) compare the relative water potential of the guard cells with that of epidermal cells

Answer 73

(iii) (guard cell has) higher water potential than epidermal cell ; ora

Question 74

During stomatal closure: describe the change in volume of the guard cells

Answer 74

(iv) decrease

Question 75

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

Answer 75

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

Question 76

Describe the parts of the pancreas involved in its endocrine function.

Answer 76

islets of Langerhans ; scattered throughout pancreas / AW ; alpha and beta cells ; blood supply (to carry hormones away) ;

Question 77

Name the hormone that stimulates the breakdown of glycogen in liver cells

Answer 77

glucagon

Question 78

State under what conditions glycogen would need to be broken down in liver or muscle cells.

Answer 78

low blood glucose concentration / during or after exercise ; R sugar

Question 79

State what is meant by the term antigen.

Answer 79

foreign / non-self / cell recognition ; stimulates immune response / AW

Question 80

) Outline the main features of the Krebs cycle

Answer 80

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

Question 81

Explain the role of NAD in aerobic respiration

Answer 81

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

Question 82

Describe how a nerve impulse crosses a cholinergic synapse

Answer 82

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 ;

Question 83

Explain the roles of synapses in the nervous system

Answer 83

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 ;

Question 84

Explain the different energy values of carbohydrate, lipid and protein as respiratory substrates. [6]

Answer 84

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

Question 85

Explain how synapses ensure one-way transmission of nerve impulses.

Answer 85

vesicles found only in presynaptic neurone / ACh released only from presynaptic neurone or membrane ; receptor (proteins) found only on postsynaptic membrane ;

Question 86

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.

Answer 86

allows more interconnection of nerve pathways / AW ; 2. for, memory / AW ; ignore learning 3. allows wider range of responses ; 4. AVP ; e.g summation

Question 87

explain why ATP is needed at the start of glycolysis

Answer 87

raise chemical PE of glucose / provide activation energy

Question 88

state the role of NAD in glycolysis

Answer 88

removes hydrogen / hydrogen carrier / coenzyme

Question 89

state how many molecules of ATP are produced from one molecule of glucose during glycolysis

Answer 89

net 2

Question 90

name the two types of reaction that occur during the conversion of pyruvate to acetyl CoA in the link reaction

Answer 90

dehydrogenation ; A oxidation decarboxylation ; accept ‘oxidative decarboxylation’ for two marks

Question 91

describe what happens to the hydrogen released during the link reaction

Answer 91

accepted by NAD ; 2. passed to ETC ; 3. for oxidative phosphorylation ; 4. ref. proton pump / chemiosmosis

Question 92

Describe the arrangement and location of chloroplast pigments and discuss their effect on absorption spectra.

Answer 92

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

Question 93

Describe the part played by auxins in apical dominance in a plant shoot

Answer 93

15. 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

Question 94

Write a balanced equation that summarises photolysis

Answer 94

H2O 2H + + 2e + ½ O2 ; A 2H2O 4H + + 4e + O2

Question 95

Explain what makes a molecule such as rubisco soluble

Answer 95

hydrophilic / polar / charged, outside / at surface ; hydrophobic / non-polar / non-charged, inside ; globular (protein) ; ref. to polar interactions / hydrogen bonds, with water (molecules)

Question 96

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.

Answer 96

Calvin cycle / light independent reaction, stops ; no RuBP (for rubisco) ; as no, ATP ; as no reduced NADP ; as no, light dependent reaction / photophosphorylation

Question 97

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

Answer 97

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

Question 98

Describe the role of calcium ions (Ca2+ ions) in the shortening of a sarcomere.

Answer 98

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 ;

Question 99

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.

Answer 99

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

Question 100

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

Answer 100

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

Question 101

Explain how glucose is reabsorbed into the blood from a kidney nephron

Answer 101

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

Question 102

Describe the role of ADH when the water potential of blood decreases

Answer 102

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

Question 103

Describe the response of the Venus fly trap to touch

Answer 103

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

Question 104

Explain the control of gibberellin synthesis and outline how gibberellin stimulates stem elongation.

Answer 104

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

Question 105

Explain how aerobic respiration may be affected by a decrease in oxygen availability.

Answer 105

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

Question 106

Outline how molecules, such as the compounds from the digestion of asparagus, pass from the blood to become part of the glomerular filtrate.

Answer 106

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

Question 107

Suggest advantages of using monoclonal antibodies for pregnancy testing

Answer 107

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

Question 108

monoclonal antibody.

Answer 108

1 identical (antibodies) or produced by cloning ; 2 variable regions / antigen binding sites, all identical or (antibodies) are specific to one antigen ;

Question 109

Suggest why membranes in cells lose their normal structure when the water potential is low

Answer 109

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 ;

Question 110

Define the term excretion

Answer 110

removal / elimination, of waste products ; of metabolism ; (which are) toxic ; (or) substances excess (to requirements

Question 111

Outline the role of negative feedback in osmoregulation

Answer 111

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

Question 112

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

Answer 112

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

Question 113

Explain what is meant by the term limiting factor.

Answer 113

process / photosynthesis, affected by more than one factor ; rate is limited by the factor nearest its minimum value /

Question 114

Carbon dioxide concentration in the atmosphere may be a limiting factor in photosynthesis. Describe how carbon dioxide reaches the photosynthetic cells in a leaf

Answer 114

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 ;

Question 115

) Outline anaerobic respiration in mammalian cells and describe how it differs from anaerobic respiration in yeast cells.

Answer 115

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 ;

Question 116

Describe how anaerobic respiration in mammalian cells differs from anaerobic respiration in yeast cells.

Answer 116

in mammals 1. lactate produced / no ethanol produced ; 2. no, decarboxylation / carbon dioxide released ; 3. single step ; 4. lactate dehydrogenase ; 5. reversible ;

Question 117

Explain why anaerobic respiration results in a small yield of ATP compared with aerobic respiration.

Answer 117

in anaerobic respiration 1. only glycolysis occurs / Krebs cycle stops / link reaction stops ; 2. glucose, not fully broken down / still contains energy ; 3. pyruvate does not enter mitochondrion ; 4. (no oxygen) so no final electron acceptor (in ETC) ; 5. ETC stops ; 6. no oxidative phosphorylation

Question 118

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

Answer 118

1. affects liver cells ; R muscle cells / liver and muscle cells 2. promotes glycogenolysis / AW ; 3. promotes use of fatty acids in respiration ; 4. promotes gluconeogenesis / AW ; 5. results in rise in (blood) glucose concentration ; 6. back to, norm / set point

Question 119

Explain how the structure of a sensory neurone can enable the action potentials to reach the brain very quickly.

Answer 119

1. myelin sheath insulates axon ; 2. idea of depolarisation / action potentials, only at nodes of Ranvier ; 3. ref. saltatory conduction / AW ;

Question 120

Explain how the palisade mesophyll cells of a leaf are adapted for photosynthesis

Answer 120

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. moist cell surfaces for diffusion of gases ; 9. cell walls thin for (maximum) light penetration / diffusion (of gases) ; 10. chloroplasts can move towards light to absorb (maximum) light ; 11. chloroplasts can move away from high light intensity to avoid damage

Question 121

) Describe the structure of photosystems and explain how a photosystem functions in cyclic photophosphorylation

Answer 121

) 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 ;

Question 122

Explain how the allele for haemophilia may be passed from a man to his grandchildren. You may use genetic diagrams to support your answer.

Answer 122

) 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 ```

Question 123

Outline the role of mitochondria structure in synaptic transmission.

Answer 123

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)

Question 124

Plasmid vectors carrying antibiotic resistance genes are now rarely used in gene technology. (i) Explain why antibiotic resistance genes are now rarely used.

Answer 124

1 plasmids (easily) transferred between bacteria ; 2 (bacteria of), same species / different species ; 3 bacteria can acquire antibiotic resistance / renders antibiotic useless

Question 125

explain why, in the absence of oxygen, pyruvate needs to be converted to lactate

Answer 125

1 NAD regenerated ; 2 so glycolysis can continue ; 3 to produce ATP ;

Question 126

Outline the process of the photolysis of water and describe what happens to the products of photolysis.

Answer 126

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]

Question 127

) Describe the roles of gibberellins in stem elongation

Answer 127

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

Question 128

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.

Answer 128

1. (stick / kit) dipped in (early morning) urine sample ; 2. hCG / urine, moves up strip ; 3. idea that hCG acts as antigen ; 4. (mobile) antibody also bound to, indicator / gold ; 5. (mobile) antibody in stick binds to hCG ; 6. ref. to variable region (of antibody) ; 7. ref. to specificity (of antibody) ; 8. ref. to monoclonal (antibody) ; first window or region 9. second antibody is, immobilised / fixed ; 10. first antibody and hCG complex binds to second antibody ; 11. coloured band indicates pregnancy ; second window or region 12. immobile antibody binds to mobile antibody-gold complex ; 13. second coloured band shows strip is working

Question 129

Describe the role of the hormone insulin in maintaining a constant blood glucose concentration

Answer 129

1. rise in blood glucose concentration detected by β cells ; 2. (β cells) in, islets of Langerhans / pancreas ; 3. insulin released into blood ; 4. binds to receptors in cell surface membrane ; 5. ref. to liver / muscle, cells ; 6. increase in uptake of glucose (by cells) / (cell surface) membrane more permeable to glucose ; 7. increase in use of glucose in respiration ; 8. (increase in) conversion of glucose to glycogen ; 9. blood glucose concentration falls ; 10. inhibits, glycogen / lipid / amino acid, breakdown

Question 130

The passage below summarises the effects of auxin on the growth of a shoot.

Answer 130

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

Question 131

Describe the roles of the following substances in the light-independent stage of photosynthesis RuBP

Answer 131

(i) 1. carbon dioxide fixation ; 2. production of GP ; 3. ref. to rubisco ;

Question 132

Describe the roles of the following substances in the light-independent stage of photosynthesis reduced NADP

Answer 132

(ii) 1. reduction (of GP) / donates hydrogen ; | 2. GP to TP

Question 133

Describe the roles of the following substances in the light-independent stage of photosynthesis: ATP

Answer 133

1. supplies, energy / phosphate ; 2. (to convert) GP to TP ; 3. (to) regenerate of RuBP

Question 134

Describe the role of sodium ion channels in the transmission of a nerve impulse

Answer 134

(ii) 1. ref. to voltage-gated sodium ion channels / ref. ligand gated channels ; 2. channels change shape (when, pd / voltage, changes) ; 3. 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 ;

Question 135

Most farmers today grow maize from seeds that have been produced by crossing two different homozygous parents. Explain why this is done

Answer 135

1. to avoid inbreeding depression ; 2. hybrids have, higher yields / hybrid vigour ; 3. avoids expression of harmful recessive alleles ; 4. ref. to genetic uniformity ; 5. (which) results in easier, cultivation / harvest / etc

Question 136

Suggest why more water is produced from the metabolism of lipid than from the other two substrates.

Answer 136

1. lipid releases most energy ; 2. because it has more, hydrogens / C-H bonds ; 3. per unit mass ; 4. hydrogens needed for, ATP production / chemiosmosis

Question 137

Explain the importance of the coronary arteries of the heart.

Answer 137

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

Question 138

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

Answer 138

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

Question 139

Outline the process of oxidative phosphorylation

Answer 139

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 ;

Question 140

Explain why carbon dioxide is produced when mitochondria are incubated with pyruvate but not when they are incubated with glucose.

Answer 140

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

Question 141

Explain how the palisade mesophyll cells of a leaf are adapted for photosynthesis.

Answer 141

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 ;

Question 142

Outline the light-independent stage of photosynthesis

Answer 142

) 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

Question 143

Describe the structure of a kidney nephron and its associated blood vessels.

Answer 143

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 ;

Question 144

Explain how glomerular filtrate is formed.

Answer 144

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

Question 145

Explain how the destruction of β cells causes diabetes

Answer 145

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

Question 146

Explain the importance of the myelin sheath in the functioning of a neurone.

Answer 146

1. insulates axon (membrane) ; 2. depolarisation occurs only at nodes (of Ranvier) / AW ; 3. local circuits ; 4. saltatory conduction / AW ; 5. speeds transmission of, action potential / impulse ; 6. AVP ; e.g. speed increases up to 50 times / 100ms

Question 147

State one use of glucose within the liver cell.

Answer 147

i) (converted to) glycogen / lipid ; | (used in) glycolysis / respiration

Question 148

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.

Answer 148

1. cannot pass through phospholipid bilayer ; 2. too big to fit through (glucose’s) protein channel ; 3. no specific transport protein ; 4. AVP ; e.g. used up as soon as it is made

Question 149

Outline the ways in which the endocrine and nervous systems carry out their roles in control and coordination in animals.

Answer 149

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

Question 150

(a) Describe how non-cyclic photophosphorylation produces ATP and reduced NADP

Answer 150

) 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

Question 151

(b) Outline the steps of the Calvin cycle.

Answer 151

) 15. RuBP combines with carbon dioxide ; 16. rubisco ; 17. forms unstable 6C compound ; 18. produces two molecules of, GP / PGA ; 19. GP / PGA, converted to TP ; 20. by reduced NADP and ATP ; 21. from light dependent stage ; 22. TP used to regenerate RuBP ; 23. using ATP ; 24. TP can form, hexose / fatty acids / acetyl CoA

Question 152

Suggest and explain why the rate of photosynthesis of the plant decreases to zero just above 40 °C.

Answer 152

1. 26 °C optimum temperature for, rubisco / enzyme of Calvin cycle ; 2. (at just over 40 °C) enzymes / rubisco, denatured ; 3. so less carbon dioxide fixed ; 4. reduction in Calvin cycle / AW ; 5. increased rate of transpiration / AW ; 6. so stomata close ; 7. less carbon dioxide uptake ; 8. oxygen more likely to combine with rubisco ; 9. so increased photorespiration ;

Question 153

(a) Describe how ATP is synthesised by oxidative phosphorylation.

Answer 153

) 1. reduced, NAD / FAD ; 2. passed to ETC ; 3. inner membrane / cristae ; 4. hydrogen released (from reduced, NAD / FAD) ; R H2 5. split into electrons and protons ; 6. electrons pass along, carriers / cytochromes ; 7. ref. energy gradient ; 8. energy released pumps protons into intermembrane space ; 9. proton gradient ; 10. protons pass through (protein) channels ; 11. ATP synthase / stalked particles ; 12. (ATP produced from) ADP and inorganic phosphate ; 13. electron transferred to oxygen ; 14. addition of proton (to oxygen) to form water / (oxygen) reduced to water

Question 154

(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.

Answer 154

mechanisms 12. active transport ; A actively pumped / uses ATP 13. Na+ , out of pct cells / into blood ; 14. (sets up) Na+ ion gradient ; 15. facilitated diffusion ; 16. using protein carrier ; A transport protein 17. cotransport (from lumen to pct cell); 18. of, glucose / amino acids / ions; 19. osmosis ; 20. down water potential gradient ; 21. diffusion (in correct context) ; 22. down a concentration gradient ; max 7 adaptations 23. microvilli ; A brush border 24. 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 25. tight junctions ; 26. folded, basal membrane / described ; 27. many, transport proteins / cotransporters / pumps; 28. AVP ; e.g. many aquaporins

Question 155

Describe the structure of a kidney, including its associated blood vessels.

Answer 155

) many of these mps can be given from a labelled diagram 1. (outer) cortex ; 2. medulla ; 3. pelvis ; 4. renal artery ; 5. renal vein ; 6. nephron / (kidney) tubule ; 7. renal capsule / proximal convoluted tubule (pct) / distal convoluted tubule (dct), in cortex ; 8. loop of Henle / collecting duct (cd), in medulla ; 9. glomerulus ; 10. afferent & efferent arterioles; 11. capillary network, surrounds tubule / in medulla ;

Question 156

Outline the role of reduced NADP in the light-independent stage

Answer 156

(iii) reduces/donates hydrogen ; A H/hydrogen atoms/H+ AND e– R H+ / H2 GP to TP ; A PGA to PGAL [

Question 157

Suggest why this process is called positive feedback.

Answer 157

production of tTA causes production of more tTA/AW

Question 158

With reference to the events occurring inside a mitochondrion, explain why a faster use of ATP requires a greater rate of oxygen consumption.

Answer 158

1. ATP is made, in the electron transport chain/by oxidative phosphorylation; 2. oxygen is the final electron acceptor; 3. in the, inner membrane of the mitochondrion/cristae; 4. transfer of electron (between electron carriers) provides energy; 5. energy used to pump hydrogen ions (into intermembrane space); 6. creates proton gradient; 7. diffusion of hydrogen ions down their electrochemical gradient causes ATP to be synthesised; 8. ref. chemiosmosis/ATP synthase/stalked particles; 9. idea that if less oxygen (consumed/available) then fewer electrons transferred along the chain;

Question 159

Suggest what measurements were taken, and how these measurements were used to calculate the oxygen debt

Answer 159

oxygen consumed = oxygen inhaled – oxygen exhaled; 2. measure oxygen consumption at rest (x) and after exercise stops (y); 3. extra oxygen consumed/oxygen debt = y – x; 4. measure mass of lizard;

Question 160

Describe how, in photosynthesis, light energy is converted into chemical energy, in the form of ATP.

Answer 160

12. light energy absorbed by chlorophyll; A photosystems/pigments 13. electron, excited/raised to higher energy level; 14. (electron) emitted by chlorophyll; A photosystems/pigments 15. passes to electron, acceptor/carrier; 16. passes along, chain of electron carriers/ETC/Electron Transfer Chain; 17. energy released used to pump protons; I ATP production here 18. into thylakoid space; 19. thylakoid membrane impermeable to protons; 20. proton gradient forms; 21. protons move down gradient; 22. through/using, ATP synthase/ATP synthetase; R ATPase 23. enzyme rotates; 24. ATP produced from ADP and Pi;

Question 161

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.

Answer 161

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

Question 162

explain why the pancreas is an endocrine gland.

Answer 162

α cells / β cells / islets / B, secrete, hormones / glucagon / insulin ; into the blood / not into a duct ;

Question 163

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.

Answer 163

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 ;

Question 164

explain why plants appear green

Answer 164

they contain chlorophyll ; green / blue green / yellow green, light reflected ;

Question 165

Explain why increasing the concentration of carbon dioxide may increase the rate of production of carbohydrates at high light intensities.

Answer 165

``` 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 ```

Question 166

) Explain the roles of NAD in anaerobic respiration in both plants and animal

Answer 166

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 ;

Question 167

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

Answer 167

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

Question 168

Suggest the effects on synapses of this irreversible inhibition of acetylcholinesterase

Answer 168

) 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 ;

Question 169

Describe how an insecticide could irreversibly inhibit acetycholinesterase

Answer 169

1 permanently ; 2 binds with / blocks, active site ; 3 binds with, another part of enzyme / allosteric site ; 4 change (shape) of active site ;

Question 170

Gases leave and enter the leaf through pores called stomata. | Describe and explain how a stoma is opened

Answer 170

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) ;

Question 171

Explain briefly the role of reduced NADP in the light-independent stag

Answer 171

) hydrogen carrier ; GP, reduced / hydrogen added ; R H2 to, TP / 3 carbon sugar ; uses ATP ;

Question 172

Explain how the collecting ducts in the kidneys may reduce the loss of water from the body.

Answer 172

) 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]

Question 173

Describe the part played by the proximal convoluted tubules in the functioning of the kidneys.

Answer 173

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

Question 174

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

Answer 174

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 ; [

Question 175

Describe how the release of calcium ions leads to the contraction of a sarcomere

Answer 175

) 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

Question 176

Suggest one function for the circular mitochondrial DNA

Answer 176

has genes that code for: mitochondrial proteins ; mitochondrial enzymes ; mitochondrial replication ; rRNA

Question 177

list three substances that enter the mitochondria and three substances that leave the mitochondria

Answer 177

oxygen pyruvate ADP phosphate / Pi fatty acids

Question 178

substance that leaves the mitochondria

Answer 178

carbon dioxide ATP water

Question 179

) 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.

Answer 179

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

Question 180

compare the structures of ATP and NAD.

Answer 180

) 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

Question 181

) Outline the roles of NAD in the cytoplasm of a cell.

Answer 181

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

Question 182

Name the process by which insulin is secreted from β cells.

Answer 182

exocytosis

Question 183

v Describe the effects of insulin on muscle cells.

Answer 183

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

Question 184

Describe how the effect of adrenaline on liver cells results in an increase in blood glucose concentration.

Answer 184

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 ```

Question 185

, describe the relationship between the strength of the stimulus and the resulting action potential

Answer 185

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

Question 186

) Describe respiration in yeast cells in anaerobic conditions

Answer 186

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 ;

Question 187

State one structural difference between a guard cell and other lower epidermal cells

Answer 187

(i) have chloroplasts / varying thickness of (cell) walls / no plasmodesmata

Question 188

outlines how sensory receptors work.

Answer 188

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.

Question 189

Describe how an action potential is transmitted along a sensory neurone in a mammal.

Answer 189

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 ;

Question 190

With reference to the events occurring inside a mitochondrion, explain why a faster use of ATP requires a greater rate of oxygen consumption.

Answer 190

1. ATP is made, in the electron transport chain/by oxidative phosphorylation; 2. oxygen is the final electron acceptor; 3. in the, inner membrane of the mitochondrion/cristae; 4. transfer of electron (between electron carriers) provides energy; 5. energy used to pump hydrogen ions (into intermembrane space); 6. creates proton gradient; 7. diffusion of hydrogen ions down their electrochemical gradient causes ATP to be synthesised; 8. ref. chemiosmosis/ATP synthase/stalked particles; 9. idea that if less oxygen (consumed/available) then fewer electrons transferred along the chain;

Question 191

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.

Answer 191

mechanisms 12. active transport ; A actively pumped / uses ATP 13. Na+ , out of pct cells / into blood ; 14. (sets up) Na+ ion gradient ; 15. facilitated diffusion ; 16. using protein carrier ; A transport protein 17. cotransport (from lumen to pct cell); 18. of, glucose / amino acids / ions; 19. osmosis ; 20. down water potential gradient ; 21. diffusion (in correct context) ; 22. down a concentration gradient ; max 7 adaptations 23. microvilli ; A brush border 24. many mitochondria ; PMT 25. tight junctions ; 26. folded, basal membrane / described ; 27. many, transport proteins / cotransporters / pumps; 28. AVP ; e.g. many aquaporins

Question 192

) Describe the structure of a kidney, including its associated blood vessels

Answer 192

1. (outer) cortex ; 2. medulla ; 3. pelvis ; 4. renal artery ; 5. renal vein ; 6. nephron / (kidney) tubule ; 7. renal capsule / proximal convoluted tubule (pct) / distal convoluted tubule (dct), in cortex ; 8. loop of Henle / collecting duct (cd), in medulla ; 9. glomerulus ; 10. afferent & efferent arterioles; 11. capillary network, surrounds tubule / in medulla ;

Question 193

Outline the process of oxidative phosphorylation

Answer 193

1. hydrogens split into protons and electrons ; 2. electrons pass along ETC ; 3. energy released used to pump protons ; 4. (from matrix) to intermembrane space ; 5. inner membrane impermeable to protons ; 6. proton gradient forms ; 7. protons move down gradient ; 8. through ATP, synthase / ATP synthetase ; R ATPase 9. enzyme rotates ; 10. ATP produced ;

Question 194

(a) Describe the photoactivation of chlorophyll and its role in cyclic photophosphorylation

Answer 194

1. (photosynthetic pigments) arranged in light harvesting clusters ; 2. primary pigments / chlorophyll a ; 3. at reaction centre ; 4. P700 / Pl, absorbs light at 700nm ; 5. accessory pigments / chlorophyll b / carotenoids ; 6. surround, primary pigment / reaction centre / chlorophyll a ; 7. absorb light ; 8. pass energy to, primary pigment / reaction centre / chlorophyll a ; 9. (light absorbed results in) electron excited / AW ; 10. emitted from, chlorophyll / primary pigment / reaction centre ; 11. passes to electron, acceptor / carrier ; 12. (electron) passes along, chain of electron carriers / ETC ; 13. ATP (synthesis) ; 14. electron returns to, P700 / Pl ;

Question 195

Explain briefly how reduced NADP is formed in the light-dependent stage and how it is used in the light-independent stage.

Answer 195

) 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]

Question 196

State where the reduced NAD molecules are re-oxidised and describe what happens to the hydrogen atoms.

Answer 196

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

Question 197

Describe the role of reduced NAD in respiring yeast cells in the absence of oxygen

Answer 197

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

Question 198

Describe the structure of a myelinated sensory neurone.

Answer 198

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

Question 199

a) Describe the structure of photosystems and explain how a photosystem functions in cyclic photophosphorylation.

Answer 199

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 ;

Question 200

11 (a) Describe the role of abscisic acid (ABA) in the closure of a stoma.

Answer 200

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 ;

Question 201

(b) Describe the role of gibberellins in the germination of barley seeds.

Answer 201

) 13. (barley) seed is, dormant / metabolically inactive ; 14. seed absorbs water ; 15. embryo produces gibberellin ; 16. gibberellin stimulates aleurone layer ; 17. to produce amylase ; 18. amylase hydrolyses starch ; 19. in endosperm ; 20. to maltose / glucose ; 21. embryo uses sugars for respiration ; 22. energy used for growth ; 23. gibberellins affect, gene / transcription of mRNA, coding for amylase ; [7 max]

Question 202

Outline, with reference to blood glucose concentration, the principles of homeostasis in mammals.

Answer 202

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]

Question 203

Describe the roles of the endocrine and nervous systems in control and coordination in mammals.

Answer 203

endocrine 11. hormones ; 12. chemical messengers ; A chemicals that transfer information 13. ductless glands / (released) into blood ; 14. target, organs / cells ; 15. ref. receptors on cell membranes ; 16. example of named hormone and effect ; nervous 17. impulses / action potentials ; R electrical, signals / current 18. along, neurones ; R nerves 19. synapse (with target) / neuromuscular junction ; 20. ref. receptor / effector or sensory / motor, neurones ; differences – endocrine 21. slow effect / ora ; 22. long lasting effect / ora ; 23. widespread effect / ora ; 24. AVP ; e.g. extra detail of synapse

Question 204

(b) Explain how rice is adapted to growing in flooded fields

Answer 204

11. ethene (in plant); 12. stimulates production of gibberellin; 13. gibberellin stimulates, cell division / cell elongation / increase in stem length; 14. leaves / flowers, above water; 15. (so) photosynthesis can occur; 16. (so) sexual reproduction / pollination, can occur; 17. aerenchyma / description; 18. assists gas diffusion (within plant); 19. air can be trapped by specialised underwater leaves; 20. (submerged parts of plant) carry out anaerobic respiration; 21. produce ethanol; 22. can tolerate high concentrations of ethanol; 23. produce a lot of ethanol dehydrogenase

Question 205

(a) Describe the structure of a chloroplast.

Answer 205

1. 3 – 10 µm (diameter); 2. double membrane; 3. ground substance / stroma; 4. contains enzymes / named enzyme, e.g. rubisco; 5. also, sugars / lipids / starch; 6. 70S / AW, ribosomes; 7. circular DNA; 8. internal membrane system / fluid-filled sacs / thylakoids; A flattened sacs 9. grana are stacks of thylakoids; 10. (grana) membranes hold, photosynthetic pigments / ATP synthase / ETC

Question 206

Explain why the epithelial cells of the proximal convoluted tubule have many mitochondria in them. ..................................................................................................................................

Answer 206

1. produce ATP / provide energy; 2. for active transport of Na+; 3. out (of cell);

Question 207

Name two substances that are reabsorbed into the blood from the proximal convoluted tubule, apart from water.

Answer 207

mark first two answers any named ion / mineral ions; vitamins; amino acids; glucose; some urea;

Question 208

v Explain how the structures of the glomerular capillaries and the podocytes are adapted for ultrafiltration

Answer 208

fluid can pass through glomerular capillaries because (max 3) 1. fenestrations in capillary endothelium; A hole / pores / gaps 2. basement membrane acts as a filter; 3. no substances >68 000 MM can get through; 4. no cells can get through; fluid can pass through podocytes because 5. have, projections / AW; 6. gaps (between projections); A filtration slits

Question 209

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.

Answer 209

1. (when pump stops working), resting potential not maintained or pump usually maintains the resting potential; 2. (during resting potential) membrane polarised or positive charge outside (neurone) / negative charge inside (neurone) / -70mV inside neurone relative to outside / potential difference across membrane; 3. (when pump stops working), ions (only) move by diffusion; 4. Na+ into the neurone; 5. outward diffusion of K+ is limited / K+ stay in neurone; 6. ref. non voltage-gated channels; 7. (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; 2. (calcium ions move in) by diffusion / move down their concentration gradient; [2]

Question 210

Describe the role of oxygen in the process of oxidative phosphorylation

Answer 210

1. final electron acceptor / accepts electron from last carrier; 2. so carrier can be reduced again; 3. so electrons can keep flowing (along ETC) / so ETC can continue to work; 4. (oxygen) combines with H+ to form water;

Question 211

Describe briefly where the electrons that are passed along the electron transport chain come from.

Answer 211

1. (electron comes from) hydrogen (atom); R H+ / H2 2. (from) reduced NAD / reduced FAD; 3. (from) dehydrogenation / oxidation, reactions; 4. (from substances in) Krebs cycle / link reaction / glycolysis; 5. in, matrix of mitochondrion / cytoplasm

Question 212

State the part of the mitochondrion in which the electron transport chain is found.

Answer 212

inner membrane / crista(e);

Question 213

Explain why the volume of oxygen released from the plant does not give a true rate of photosynthesis.

Answer 213

(iii) respiration uses oxygen;

Question 214

Suggest how a tumour on the optic nerve could prevent the transmission of nerve impulses to the brain.

Answer 214

(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

Question 215

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. ...................................................................................................................................................

Answer 215

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 ;

Question 216

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

Answer 216

for one mark ; any 2 from urine sweat water vapour (from exhaled air) faeces bleeding tears [max 1]

Question 217

State precisely where ADH is released into the blood

Answer 217

posterior pituitary

Question 218

) A chloroplast also contains DNA. | Suggest the functions of DNA in chloroplast

Answer 218

DNA codes for, proteins / polypeptides / enzymes ; one example of protein or enzyme ; e.g. rubisco / electron acceptor / ATP synthase / transport ref. transcription / mRNA ;

Question 219

Explain why lipids have a higher energy value than carbohydrates.

Answer 219

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 ;

Question 220

Explain why maintaining a resting potential requires energy.

Answer 220

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]

Question 221

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

Answer 221

1 carbon dioxide ; A CO2 2 ATP ; 3 reduced NADP ; mp 2 and mp3 in either order 4 acetyl CoA ; [4]

Question 222

Chloroplasts can move within palisade cells. | Suggest two advantages of chloroplast movement within palisade cells.

Answer 222

to absorb, more / maximum, light ; to avoid damage by high light intensities ; [2]

Question 223

) Describe the series of reactions that make up the Krebs cycle.

Answer 223

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 ;

Question 224

(a) Outline the process of glycolysis.

Answer 224

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 ;

Question 225

(ii) Describe the role of coenzyme A in respiration

Answer 225

) 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

Question 226

With reference to Fig. 2.1, describe and explain the effect of temperature on the rate of photosynthesis.

Answer 226

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 ;

Question 227

Describe the role in photosynthesis of an accessory pigment, such as carotene

Answer 227

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 ;

Question 228

In mammals, excess amino acids cannot be stored in the body. | Outline the formation of urea from excess amino acids by liver cells

Answer 228

deamination / amine group removed ; A amino / NH2 ammonia / NH3, formed ; combined with carbon dioxide ; urea cycle ; A ornithine cycle

Question 229

The mammalian kidney is composed of many nephrons. | Describe the process of ultrafiltration in the nephron.

Answer 229

``` 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 ; ```

Question 230

(passes through the medulla)

Answer 230

loop of collecting duct | Henle ;

Question 231

(ADH acts on its walls)/

Answer 231

collecting duct distal convoluted tubule

Question 232

(most of the water is reabsorbed into the blood)

Answer 232

PCT ;

Question 233

(glucose is reabsorbed into the blood)

Answer 233

PCT ;

Question 234

Outline the roles of synapses in the nervous system.

Answer 234

``` 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 ```