by4 essays

8/10/2019 BY4 Essays

1/32


2/32

b) A Glucose is phosphorylated/ATP is added.

to form Hexose (di)phosphate.

this is split into 2 3C/triose phosphate molecules.

these are converted to pyruvate.

with a net gain of 2 ATP (stated unambiguously).

and 2 reduced NAD.

it occurs in the cytoplasm of all cells/does not require oxygen.in the absence of oxygen, (the Krebs cycle and) ETC cannot

ccur/no oxygen to act as the final electron acceptor at the end of

he ETC.

Pyruvate is converted to lactate/lactic acid in animal cells/humans

(not: ref. to CO2)

or ethanol in plant and/or fungal (cells)/or yeastand carbon dioxide in plant and/or fungal (cells).

using the reduced NAD to reduce the pyruvate/transferring the

ydrogen to pyruvate (in the process).

Anaerobic respiration (only) yields a total of 2 ATP

(i.e. ref. to overall yield)

because a lot of energy is still tied up/contained in the

ctate/ethanol

e. ethanol high in calories)

Maximum 10 marks 10

[10]

June 04


3/32

Write an account outlining the similarities and

differences in the ways that mitochondria and chloroplasts

enerate a proton gradient and synthesise ATP

Diagrams alone are insufficient) (10) (Jun 03)

) ATP Synthesis Mark Scheme

milarities

Both need high energy electrons

Both need stalked particles/ATP synthetase

Both need proton pumps

Both involve a series of carriers/pumps in electron transport

hain

Both need protons which are pumped into a cavityBoth are involved in creating an electrochemical/

hemiosmotic/H-ion/H+/proton gradient

Both involve redox reactions

fferences

Cristae/(folded) inner membrane carries stalked particles in

itochondria Or Intermembrane cavity in mitochondria/ diagramThylakoid membrane in chloroplasts carries stalked particles O

hylakoid cavity in chloroplasts/diagram

3 (types of) proton pumps in mitochondria

1 (type of) proton pump in chloroplasts

Water formed during ATP synthesis in mitochondria/ Protons

erived from glucose breakdown

Water broken down (in non-cyclic photophosphorylation) inhloroplasts/protons derived from water/photolysis produces H ions

High energy electrons are derived from chlorophyll in

hloroplasts

High energy electrons are derived from glucose/reduced

AD/FAD in mitochondria

9 maximum if no comparison


4/32

Give an account of anaerobic respiration in

organisms.

Jan 11

.Glucose is phosphorylated / ATP is added. [1]

. to form hexose (di) phosphate. [1]

. this is split into (two) 3C triose phosphate molecules.

not: abbreviations) [1]

. which are converted to pyruvate. [1]

. and (2) reduced NAD or eq e.g. NADH [1]takes place in the cytoplasm / glycolysis [1]

. in the absence of oxygen, (the Krebs cycle and) ETC cannot

ccur / no oxygen to act as the final electron acceptor at the end

f the ETC. [1]

. Pyruvate is converted to lactate / lactic acid in animal

ells / humans. [1]using the reduced NAD to reduce the pyruvate / transferring the

ydrogen to pyruvate (in the process) [1]

in plants / fungi there is a loss of carbon dioxide /

ecarboxylation [1]

. ethanal / acetaldehyde is produced [1]

ethanal is reduced by NADH to ethanol [1]. anaerobic respiration yields a total of 2 ATP [1]

. (because) a lot of energy is still tied up / contained in the

ctate / ethanol (i.e. ethanol high in calories) [1]


5/32

(a) Describe the light dependent stage of photosynthesis.

[10] (Jan 08)

. (photon of) light strikes chlorophyll / pigment / reaction centre /

hotosystem ; 1

. chlorophyll a (molecule) loses electron ; 1

. in photosystem II / P680 ; 1

. passes down chain of electron carriers ; 1

. converting ADP to ATP ; 1

. reference non-cyclic (photo)phosphorylation in correct context;

. electron passed on to photosystem I / P700 ; 1

. electron lost from photosystem I / P700 ; 1

and then returned to photosystem I / P700 ; 1

reference cyclic photophosphorylation in correct context; 1

. photolysis / splitting of water ; 1

provides electron to replace the one lost from photosystem II /

680 ; 1. produces oxygen ; 1

. electron from photosystem I /P700 with H+ reduce NADP ; 1

. ATP and redNADP available for light independent reaction /

alvin

ycle ; 1

AVP ; e.g. ref to antenna complex / accessory pigments /

equence of

ectron carriers / detail of stalked particles / reaction centres. 1

ny 10 of the 16 available marks

Total : 10]

Points A, B, D, E could be in context of cyclic or non cyclic; K, L,

linked

arks; F, J refer to ATP production and fate of electron)


6/32

ATP, NADPH2from light dependent;

In stroma of chloroplast;

5C acceptor;

ribulose bisphosphate RUBP;

carbon dioxide fixed;Enzyme RuBisco/ref enzyme e.g. sequence of enzyme

controlled reactions;

(breaks down into 2 3C) glycerate 3 phosphate/PGA/GP;

(converted into 2 3C) triose phosphate/TP/GALP;

NADPH H+/reduced NADP;

supplies hydrogen/used for reduction;

ATP broken down into ADP and iP supplies energy.

(not: ATP supplies energy)

RuBP regenerated from TP.

Phosphate from ATP needed for this.

Glucose, lipids, amino acids, chlorophyll, cellulose, starch.

Any 2 products.

Fate of two products qualified, e.g. glucose respired for energy

/amino acid make proteins

AVP e.g. balancing 6 RUBP etc./most TP to RBP some to glucose.

Describe the light-independent stage (Calvin cycle) of

photosynthesis.

Indicate the possible fate of the products of this process.

[10] (June 06)


7/32

Give an account of the light dependent stage of photosynthesis.

(Jun 02)

photophosphorylation; (1)

cyclic and non-cyclic; (1Cyclic

light absorbed by photosystem 1/P700; (1)

electron(s) emittedfrom chlorophyll a molecule; (1)

passed to chain of electron carriers; (1)

ATP Synthesis

energy fuels proton pump; (1)

maintains H+

concentration gradient; (1)protons diffuse and synthesise ATP from ADP and phosphate; (1

Cyclic

electron(s) returns to chlorophyll a/P700/PSI; (1)

Non Cyclic

light absorbed by both photosystems; (1)

electrons emitted from P680 and P700; (1)

both passed to chain of electron carriers and ATP synthesised; (1photosystem 1/P700 receives electrons from photosystem 2/P680;

(1)

photosystem 2/P680 receives electrons from splitting of

ater/photolysis; (1)

NADP accepts hydrogen/H+/protons from splitting of

ater/photolysis; (1)

NADP passes hydrogen to the light independent reaction;(1)specific reference to structure photosystems; (1)

reference to ATP synth(et)ase; (1)


8/32

Give an account of the Calvin cycle in photosynthesis (7)

(A diagram alone is insufficient.)

xplain how the raw materials used in the calvin cycle are obtained (6

(Jan 03)

alvin cycle question

(a) ACarbon dioxide reacts with 5 carbon RuBP

BThe 6C compound formed splits into two 3C

CMolecules of glycerate-3-phosphate (GP)

DWhich react with aTP (mark given for D only if in wrong orde

ith E)

EAnd reduced NADP

FTo form triose phosphate/GALP/Glyceraldaehyde-3

hosphateGMost of these molecules react with ATP

HTo regenerate RuBP

ISome is converted into glucose/carbohydrate/amino acids

Any seven (7)

(b) JATP and reduced NADP are synthesised in the light stage o

hotosynthesis

KATP is synthesised using energy captured in the electro

ansport chain of both photosystems

LATP is also produced by plant cell respiration

MNADPH + H+

is formed in photosystem INWhen (low energy) electrons combine with H and NADP

OCarbon dioxide is absorbed into the leaf/from th

tmosphere

Any three (3)Total 10 marks


9/32

(a) Describe the events of the light dependent stage of

photosynthesis (12) (Jan 04)

A photophosphorylation;

B cyclic and non-cyclic (correct identification);

clicC light absorbed by, photosystem I/P700;

D electron(s) emitted from chlorophyll a molecule; (not:

excited)

E passed to chain of electron carriers/acceptors/transport chain;

ATP Synthesis

F energy fuels proton pump;

G maintains H

+

concentration gradient;H protons/ H+ diffuse and synthesise ATP from ADP and

phosphate;

Cyclic

I electron(s) returns to, chlorophyll a/PSI/P700;

Non-Cyclic

1

1

11

1

1

1

1

1

J light absorbed by both photosystems;

K electrons emitted from P680/PSI and P700/PSII;L both passed to chain of electron carriers and ATP synthesised;

M PSI/P700, receives electrons from, PSII/P680;

N PSII/P680, receives electrons from, splitting of

water/photolysis;

O NADP accepts, hydrogen/H+/protons, from photolysis;

P NADP passes hydrogen to the light independent reaction;

Q specific ref. to structure of photosystems/antenna complex;R ref. to ATP synth(et)ase; (not: ATPase)

(A maximum of 12 marks may be awarded from the 18 available)

1

11

1

1

1

1

1

1[12]


10/32

Describe how energy is trapped by green plants and stored

during the light dependent stage of photosynthesis. (l 0)

(June 05)

energy source is (a photon) of light, pigments / chlorophyll absorb light

energy / light energy changed to chemical energy

1

pigments include chlorophyll a and b, carotene and xanthophylls 1

to absorb different wavelengths / parts of spectrum 1

reference to antennae complex / photosystems (embedded in (thylakoid)

membranes)

1

energy transferred between pigment molecules and to reaction centre

(chlorophyll)

1

emission of electrons by reaction centre (chlorophyll) / P700 /

photosystems

1

electron acceptors 1

electron transfer chain (between PSII and PSI) 1

reference to proton pumps ATPase / chemiosmosis 1

electrons (emitted from PS II) replaced from water photolysis / correct

description of photolysis

1

photolysis takes place inside thylakoid space / mopping up of protons in

stroma by NADP

1

therefore contributes to electrochemical gradient 1

NADP is reduced / NADPH2 end product or final electron acceptor 1

reference to cyclic phosphorylation 1

Energy is stored in the form of ATP 1

ximum 10 marks from available 15.

10


11/32

) A GALP/Triose phosphate/glucose and oxygen.

B GALP/Triose phosphate is converted to glucose.

C Oxygen used by mitochondria/aerobic respiration.

D Glucose used as a respiratory substrate/for ATP synthesis (in

regions of cell division/growth/root/shoot tip).

E may be converted to starch and stored as starch grains

oroplasts

(temporarily)/specialised areas/undergroun

ems/potatoes/seeds/

fruits eq.

(not: food store)

F converted to fructose/fructose combined with glucose to

form sucrose/sucrose is synthesised for transport.

G Glucose is converted to cellulose to form plant cell walls.

H amino acids can be synthesised, providing there is a nitrogen/

nitrate source/using nitrogen

I amino acids from glucose via metabolic pathway can be

used to synthesise protein.

J lipids can be synthesised for storage/phospholipids/ce

embranes.

K with a Magnesium source, chlorophyll can be synthesised.

L/M mention of any other 2 products

Nucleic acids/DNA/RNA/ATP/ADP/Vitamins/

xanthophylls/anthocyanins/carotenes

N all organic materials in the plant must be made from the

intermediates and products of photosynthesis.

(Maximum 10 marks) 10

[10]

June 04


12/32

b) (i) Describe how a batch fermenter is used in the growth

of Pencillium (6)

(ii) Outline the aseptic techniques that are needed for

handling microorganisms in the laboratory. (6) (Jan 04)

(i) A sterilise vessel beforehand;B use (sterile) nutrient medium;

C use filters/aseptic techniques, at vessel openings;

D provide organism with suitable conditions for its

growth;

E nutrients/sugar, depleted/become limiting;

F (may need) forced aeration/sparger;

G mixing, by aeration/stirrer;H temperature control/water jackets remove excess heat;

I pH control;

(A maximum of 6 marks may be awarded from the 9

available)

11

1

1

1

1

1

11

J sterilise apparatus beforehand;

K flame the mouth of culture bottle;

L sterilise loop in Bunsen flame/spreaders by alcohol;M lift lid of petri dish just enough to insert loop/bung etc

held not placed on bench;

N protective clothing;

O safety cabinet/work close to bunsen;

P hand washing before (and after);

Q autoclave/heat equipment at 121C under pressure/use

pressure cooker (to sterilise after use) irradiation;R sterilise work surfaces before/after with

disinfectant/use benchkote; (not: clean)

(A maximum of 6 marks may be awarded from the 9

available)

1

1

11

1

1

1

1

1


13/32

Describe the industrial production of penicillin. [10] (Jan 06)

A. batch culture;

B. all materials added at the start/not during process;C. sterile apparatus/vessel;

D. pure (culture) of Penicillium (notatum);

E. sterile nutrient medium;

F. method of aeration;

G. oxygen for respiration;

H. filters for introduction of sterile oxygen;I. method of mixing

J. temperature control by water jacket;

K. allow growth phase to take place;

L. penicillin produced after growth phase;

M. as glucose is depleted;

N. filtration of culture fluid;

O. antibiotic purified;

P. AVP; e.g. penicillin is produced in free living, possibly to

reduce competition, when food sources are depleted


14/32

(b) Describe the production of penicillin using a batch

culture fermenter. [10] (Jan 08)

. Penicillium notatum / chrysogenum ; 1

. vessel sterilised before use ; 1. (pure) culture introduced ; 1

. nutrients added (at start) ; (mark negated if later additions

ade) 1

. named nutrient ; e.g. glucose / C source / nitrates 1

not : growth factors)

. pH regulated / description of method of regulation / maintain 1

ptimum pH

. monitored by pH probes ; 1

. temperature regulated / reference to cooling jacket to get rid o

xcess

eat 1

temperature monitored e.g. thermometer ; 1

aeration with sterile / filtered air / oxygen ; 1. for respiration ; 1

appropriate method for mixing contents ; 1

. penicillin produced after growth phase / as secondary

etabolite / as

utrients depleted ; 1

. mycelium / penicillium removed by filtration ; 1

. antibiotic / penicillin purified (from remaining liquid); 1

AVP ; e.g. reference to cyclic fed-batch culture 1

not : reference to competition)

ny 10 of the 16 available marks

Total : 10]


15/32


16/32

Give an account of the technique used to monitor the

number of viable cells in a

bacterial population, including aseptic precautions. [10]

(June 08)

Correct name of technique used SERIAL DILUTION;

Any valid sterilising techniques for equipment eg autoclave;Any valid aseptic technique eg flaming bottle neck;

not: flaming loop)

9 cm3 (sterile) deionised / distilled water placed in series of

acteriology / test tubes with lids (correct 9:1 ratio)

1 cm3 bacterial sample placed in first tube (and mixed);

1 cm3 of this transferred to next tube and mixed and repeat foremaining tubes;

Transfer of 0.1 / 0.5 / 1.0 cm3 of each sample onto a (sterile)

utrient

gar plate; (not: loop and streak plate)

only lifting lid slightly to prevent contamination;

Repeat this twice to give a total of 3 plates per dilution;Use of (sterile) spreader to spread sample around plate

Seal plates with tape plus explanation;

Incubate at 25C for 24 hours;

Selection of suitable plates (60-100 / countable colonies) and

ount

olonies

Explanation of working out means of 3 plates and correct

alculation

multiplication to get number of bacteria per cm3 of original

acteria

ample)

Explanation of inaccuracies with clumping/viable cell gives

sibleolony


17/32

) (i) Explain the shape of a typical population growth curve and describe how

numbers are kept constant in a stable population. [6]

(ii) Indicate, with examples, how human activities can cause instability in

populations. [4] Jan 05

. (b) (i) A. (Lag phase) - numbers and therefore rate ofreproduction low. 1

B. (Log/exponential phase) - Abundant resourcesand exponential rate of increase/no limitingfactors/ birth rate exceeds death rate.

1

C. (Stable/stationary phase) - carrying capacityreached or definition.

1

D. Competition for 1E. limiting factor/resource e.g. 1F. Decline phase - depletion of resources,

accumulation of toxins, etc. (not: resources/limiting)

1

G. (In stable population) Birth rate = Death rate 1H. Emigration = Immigration 1

[Six marks can be awarded from the eight available for part(a)]

(ii) I. Human activity increasing birth rate - one

example such as NO2 pollution, algal blooms,eutrophication.

1

J. Mention of two distinct human activities whichincrease death rate (decrease birth rate).Overfishing, hunting, habitat destruction,deforestation, pollution.

1

K. One named example. 1L. Human activities, decreasing death rate -

protection, conservation, predator destruction,game keeping, fish quotas etc.

1

M. Activities affecting immigration - introductionof exotics, garden escapes, biological controlagents.

1

N. One example. 1O. Example of habitat alteration on migrants. 1

[Four marks can be awarded from the seven available, ofwhich one must be either M, N or O.]

[10]


18/32

b) Describe the factors that control the size of a population. [8]

(Jun 05)

(b) A birth rate and death rate;

B population grows if birth rate higher;(ORA)

C immigration and emigration;

D population grows if immigration

exceeds emigration;

(ORA)

E increased predation decreasespopulation;

F disease will reduce size of a

population;

G effect of weather/temperature

qualified;

H availability of food qualified;

I availability of living space qualified;

J human involvement/intervention;

K specific example of human

involvement;

L ref. density dependent/ factors;

M ref. to carrying capacity;

N labelled diagram/description of agrowth curve (3 of 4 phases needed);

O ref. to some factors can cause a

population to crash;


19/32

(b) (i) Explain what is meant by the term population growth

curve. [3]

(ii) Describe the factors that may cause the population of a

species to decrease. [7]

b) (i) A death/decline phase- greater numbers dying than being

roduced;

lag phase where little increase in numbers;

exponential / log phaserapid increase in numbers;

stationary phase, numbers produced equals numbers

ying/maximumarrying capacity reached;

3 max]

accumulation/increase toxic waste;

emigration exceeds immigration;

disease (epidemic);

increase in predators/parasites;

food shortages;

climate change/adverse weather conditions/natural disaster

ualified;

increased competition;

insufficient living space;

reference to human interventions eg deforestation;

reference to density dependent and independent factors;7 max]

otal 10


20/32

a) Define the term population. Give an account of factors that affect

population growth

and population size, distinguishing between density dependent and

density

independent factors. [10]

(Jun 06)

A population is a group of individuals belonging to the

same species. 1

and occupying a defined area. 1

Population numbers are dynamic.

(allow: growth curve / predator prey diagrams labelled)

1

Number / size of population depends on birth rates and

death rates.

1

Number depends on immigration and emigration. 1

Growth occurs if birth rate exceeds death rate. 1

Growth occurs if immigration exceeds emigration. 1

Decline occurs if death rate exceeds birth rate. 1

Environmental factor may slow growth rate or causepopulation to crash. 1

An example of a factor which affects population growth,

weather, predation, disease, food supply, living space,

competition.

1

Density dependent factors have a greater affect on

population numbers if the population size is large. 1Density independent factors have the same affect on

population numbers in small and large populations. 1

An example of a density independent factor, drought, fire,

frost, flood.

(not: pollution)

1

Correct reference to the term carrying capacity.(not: just labelled on graph) 1


21/32

b) Discuss, using examples, the principles of chemical and biologica

control of pests

and their relative advantages and disadvantages. [10]

(Jan 06)

A. Pyrethroids, or other named example;

B. Eradicate quickly;

C. cheap/cost effective;

D. localised/controlled use;

E. disadvantage, non specific

F. eradicate beneficial/other insects/animals/toxic toumans;

G. pests can become resistant;

(not: immune)

H. bioaccumulation;

I. affect on food chains explained;

J. eg. biological control Encarsia/ladybird;(not: cats/foxes etc)

K. specific/less environmental damage/no residues;

L. disadvantage, need pests before can be applied;

M. does not eradicate completely;

N. can lead to superpest/can become pests

hemselves.

O. suitable control agent for pests not always

vailable

P. AVP eg Research/expense biological/need frequen

input/enclosed space; or definition biological

ontrol 10


22/32

Nitrogen gas in the atmosphere is fixed by Nitrogen

Fixing Bacteria 1

which are either free - living in soil 1

or in root nodules of legumes. 1

(Nitrogen in the form of) amino acids and/or proteins 1

Nitrogen is passed to animals during feeding 1

(Nitrogen in form of )urea / ammonia 1

Nitrogen passes to soil during excretion. 1

Dead plants and animals are decayed by bacteria and/or Fungi.

1

Decay releases ammonium (compounds)/ammonia. 1

Ammonium (compounds) are converted to (nitrogen 1

in the form of) nitrates.

Plants (are only able to absorb) nitrogen in the form of

nitrates. 1

Plants fix nitrogen in the form of amino acids and

proteins.( ie inorganic to organic form) 1

Denitrifying bacteria/denitrification break(s) down nitrates and

return nitrogen to the atmosphere.

1

Lightning may cause nitrogen gas to react withoxygen in the air to from nitrates 1

Industrial production of fertiliser(e.g. Haber) 1


23/32

escribe the advantages and disadvantages of

hemical and biological control.

un 10

hemical control

dvantages

Very effective/quick/cheap means of control

Chemicals can be applied on a small area (e.g. Market gardening) /

pplication does not require a high level of skill/knowledge

isadvantages

. Chemicals are not specific/may eradicate useful insects

. Resistance may occur (not: immunity)

Killing of fish/birds/mammals/bioaccumulation;

Risk to human health/contamination of rivers.

ological control

dvantages

. Highly specific to one pest

. Long term control if predator: prey balance / Use in glasshousesMay be inexpensive in long term

No environmental contamination

isadvantages

Slow build up/have to accept some damage to crop/not perfect/pest

ot totally eradicated;

Few successful examples

. Skill and research is expensive/detailed life cycle knowledge iseeded

. Frequent input of predator needed / may only be of use in closed

ystems (greenhouses)

. Predator may become a pest itself/suitable e.g. (cane

ads/hedgehogs on Uist)

ny 10 from the 15 marks available


24/32

itrogen cycle mark scheme(max. 6 for well annotated diagram)

Nitrogen is needed to synthesise amino acids (which are built int

roteins.)

Any sensible e.g. of protein use - antibodies/membrane proteins

nzymes.

Use of nitrogen to synthesise nucleic acids/DNA/RNA/ATPhlorophyll.

[2 max.]

The nitrogen fixing bacteria.

Convert atmospheric nitrogen into nitrogen containin

ompounds/ammonium/amino acids (not: nitrates).

This may be by free living bacteria in the soil.

Or by bacteria living in the root nodulesof

Legumes/peas/beans/clover/lupins.

Decomposers/putrefying/decay bacteria convert organic nitroge

om dead organisms/ nitrogenous excretory products/urea/uric acid.

nto ammonia.

The nitrifying bacteria convert this ammonia into nitrites.

And the nitrites into nitrates, which can be absorbed by plant

quivalent)

The denitrifying bacteria convert nitrates into atmospheric nitrogen

This is a problem in water logged soils since the bacteria ar

naerobic.

Which is why farmers drain wet land in order to increase soil fertility.

[8 max.]

an 02


25/32

i) Describe the role of bacteria in the main processes of the

nitrogen cycle. [7]

(ii) Discuss the various ways in which human activities

influence the nitrogen

cycle. [3]

(Jan 08)

) (i) A Ref. to Putrefaction / putrefying / decomposers

the conversion of (organic) nitrogen from dead organisms /

trogenous excretory products / urea into ammonia

Nitrifying bacteria / nitrification

convert ammonium to nitrite

and nitrite is converted to nitrate, (which can be absorbed by

ants)nitrogen fixing bacteria / nitrogen fixation

convert atmospheric nitrogen into nitrogen containing

ompounds

this may be by free living bacteria in the soil

or by bacteria living in the root nodules of

legumes / peas / beans / clover / lupins

Denitrifying bacteria / dentrificationconvert nitrates into atmospheric nitrogen / nitrogen lost from

cosystems

Any 7 points)

) M Fixing atmospheric nitrogen artificially by chemical processes

at convert it to fertilizers.

Large amount of animal waste from stock rearing is used as

anure.Sewage disposal boosts organic nitrogen supplies

Exploitation if microorganisms e.g. composting, silage etc.

Ploughing improves aeration / draining land and producing

erobic conditions / planting fields of clover / nitrogen removed

hen crops harvested. (not: ref. to eutrophication)

Any 3 points)

Total 10 marks)


26/32

ive an account of how the hormonal control of the kidney enables it

o function in osmoregulation in a mammal.

une 06 -

Kidney Essay

A Antidiuretic hormone

B Is secreted by the (posterior) lobe of the pituitary

C It is carried in the bloodstream to the (distal convoluted tubule and) collecting duct

D When the blood is more concentrated/low /highOP

E Detected by (osmo) receptors in hypothalamus

F ADH levels are higher / ADH released

G Higher ADH levels increase the permeability of the cells lining the DCT/CD

water/explanation of water channels inserted into DCT membrane.

H Water moves out of the DCT/CD by osmosisI Into the interstitial fluid where it is rapidly removed by the capillary network

J This occurs because the medulla of the kidney has a high solute concentration/low

K Due to the countercurrent multiplier system operating in the Loop of Henl

L This conserves water and produces small volumes/

concentrated urine

M When the blood is more dilute/high /lowOP

N ADH levels are lower so less water is reabsorbed

P This allows more water to leave the tubule/collecting duct

Q Resulting in large volumes of dilute urine


27/32

Describe and explain the changes which occur to the glomerular

filtrate as it

passes from the Bowmans capsule to the ureter. June 07

)

A Ref. points B - G in proximal convoluted tubule. If two of

following used in context;B Water absorbed by Osmosis;

C Glucose absorbed by cotransport accept ATP required / active

transport;

D Some substances absorbed by diffusion, e.g. Vit A D K E

chloride ions; (example needed)

E Selective reabsorption / selective absorption;F Water potential of filtrate decreases (not : ref. to surrounding

tissue);

G Pressure drops;

H Ref. to points I - M in (Descending) loop of Henle if two used

in context;

I Na+

levels up/water moves out (by osmosis if not above); (not :salt)

J Water potential down;

K Ascending loop Na+out / chloride out/walls impermeable to

water;

L Water potential up;

M Ref counter current;

N ADH acts on collecting duct/distal convoluted tubule;

O so water absorbed explained/because of increased

permeability;

P AVP e.g. ref urea out from PCT or from collecting duct to

lower WP/Ref. secretion creatinine, penicillin into

PCT/aquaporins.


28/32

Using a labelled diagram show the structure of the spinal cord.

Describe the nerve

pathways involved in the flexion of the arm in response to touching a

hot surface.

June 06nal Cord - Diagram showing and correctly labelled dorsal and

tral roots, grey matter 'butterfly', central canal.

Central canal;

Grey matter/white matter;

Dorsal/ventral roots;

Sensory neurone/motor neurone on same side;

Dorsal root ganglion;

Connector/intermediate/relay neurone;

Meninges/Cerebro/spinal fluid;

Max. 5

Decent quality of diagram

Heat/stimulus detected by receptorin skin;

Impulse/action potentialtravels to CNS via sensory neurone;

Synapses with connector/e.q.neurone;

(not: connects/messages)

Relay of impulse/AP to brain/ascending/descending tracts, i.e. idea of feedback to brain;

And motor neurone;

Terminates at an effector

E.g. of an effectormuscle/gland;

Which brings about a response.


29/32

Describe

(i) how the resting potential is maintained in the axon of a neurone,

(ii) how a nerve impulse is transmitted along a myelinated axon.

une 03

) A inside about -60 to -70mV (compared with outside);

B maintained by sodium (-potassium) pump;

C [K+] higher inside / [Na+] higher outside;

D membrane more permeable to K+ which diffuse /

leak / move out;

E all or nothing / threshold value;

F action potential occurs when membrane becomes

more permeable to Na+and they flood in / sodium

gates;

G depolarisation;

H inside about +40mV (compared with outside);

I K+ then diffuse / move out and repolarise the

membrane;

J refractory period explained;K local currents stimulate next part of neurilemma /

membrane / axon;

L myelin sheath increases distance over which local

currents can act to bring about depolarisation or

speeds up transmission by jumping from node to

node;M depolarisation only at nodes of Ranvier;

(Any 9) 9


30/32

Using a labelled diagram of a synapse, explain

how impulses are transmitted across a synapse.

Jun 10

ecent drawing of a synapse.Na channels

.C.D. With 6 labels (2 correct labels per mark)

. When action potential arrives at axon terminal Ca2+ moves

to synaptic

nob

. Synaptic vesicles fuse with presynaptic membrane. Neurotransmitter/Ach/eq released by exocytosis

. Diffuses over synaptic cleft

ACh binds to receptors on post synaptic membrane

Causing the protein channels to open/Na gates open

. Na+ flows in through channels

So depolarising the post synaptic membrane

. With sufficient depolarisation, an impulse/action potential is

enerated

the post synaptic neurone

. Some comment on the breakdown of ACh by (A)Ch-esterase

. Diffusion back into axon terminal through presynaptic

embrane/Use of

TP for re-synthesis and packagingny 10 from the 15 marks available


31/32

Lag phase, Log phase / exponential- term in correct context;

Induction DNA / gene switching / DNA unzipping;

. Enzyme production/protein synthesis;

. Substrate breakdown / getting used to growth medium;

Slow population growth;

Rapid cell division;

. Abundance of nutrients / oxygen / low levels of waste products / no

nvironmental resistance;

. Cell production exceeds cell death;

ot: ref. birth/immigration/emigration)

Population doubles per unit time;

Population increases then begins to slow;

Lack of nutrients / accumulation waste products / environmental

sistance; (not: ref space)

Stationary phase;

. Cell production = cell death; (not: ref birth, penalise once only)

carrying capacity;

. lack of nutrients / accumulation of waste products if not given as K;

Death phase;

Cell death exceeds cell production;

escribe and explain the shape of the population growth

urve of bacteria cultured in a batch fermenter. [10] (Jan 10)


32/32

. Decomposition / putrefaction;

. Recycling nutrients;

. Breakdown of organic materials into inorganic / suitable e.g.;

. Nitrifying bacteria;. Nitrosomonas, Nitrobacter;

. ammonium compounds to nitrites;

. nitrites to nitrates;

. ammonium compounds to nitrates if no F/G;

Nitrogen fixing bacteria;

atmospheric nitrogen converted into organic nitrogen / e.g.;

. free living azotobacter; rhizobium;

. root nodules of (legumes);

denitrification [Max 8]

. encourage aerobic conditions (to stop denitrifyers) / ploughing

drainage for aerobic conditions to stop denitrifyers;

grow leguminous crops / add organic waste products / manurerea

tc;

Max 2]

he maintenance of soil fertility is mainly determined by

acteria.

) Describe the importance of bacteria in the maintenance of

oil fertility. [8]

i) Suggest how farming practices can encourage the activit

f these bacteria. [2] (Jan 10)

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