a2 revision notesfinished

8/12/2019 A2 Revision Notesfinished

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'rokaryotes

icroscopic prokaryotic cells ( * &m long rather than +*+m) -ack of a nucleus (/A in cytoplasm) and possibly plasmids

-ack of membrane*bound organelles 'resence of 0s ribosomes /o cytoskeleton

Protoctists

1ukaryotic cell structure Simple body form, either unicellular, filamentous (chains), colonial (ball) or

macroscopic (large and isible)

The 'roctoctist2s kingdom tends to be full of organisms that do not fit into anyother 3ingdom e.g. algae and yeast

Fungi

4eterotrophic nutrition (get food from eating, unlike plants) ade of a network of *yphae, which form a 5 structure called a +ycelium.

(look up odule + notes) 6all walls containing chitin

Plants

The distinguishing features of the 'lants are7

ulticellular with eukaryotic structure 6ell walls containing cellulose 6omple$ body form 'hotoautotrophic nutrition (make food themseles through '8S) 'resence of photosynthetic cells with chloroplasts

stages in the life cycle: a diploid spore*producing stage and a haploidgamete*producing stage.

&nimals

The distinguishing features of the Animals are7

ulticellular with eukaryotic cell structure 6ells without cell walls 4eterotrophic nutrition

4ighly organised organs and tissues including nerous co*ordination The only haploid cells they hae are gametes

2

,istinguishing Characteristics o) the Kingdoms


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4.5.%

!ndiiduals in the same species look different (hae differentphenotypes). This is called $ariation

9ariation is caused by7

+. The genotypeof the indiidual (i.e. which alleles they hae). The enironment

enetic di$ersity describes the range of different genotypeswithin a species. !f there are few genotypes the genetic diersity is

small. !f there are lots of genotypes the genetic diersity is large.

6auses of enetic iersity:

+. !ndependent Assortment. utation

5. ;andom fusion


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-ndependent &ssortment> which allele of each pair goes intowhich gamete. This is caused by the orientation of homologouspairs of chromosomes during metaphase of meiosis

6hanges in the se?uence of bases in codons (mutation) causegenetic ariation. This usually occurs by /A being improperlycopied or damaged. 6hemicals (mutagens) and radiation can dothis.

1ach gamete is different. Therefore, by combining differentgametes new ariation occurs (random )usion).

uring meiosis sections of /A are swapped between homologouschromosomes (pairs of chromosomes). This creates moreariation by creating new combinations of alleles (crossing o$er)

4

,ihyrid Cross4.5./


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ihybrid 6rosses are for crosses inoling two different genes( loci).

A > 'urple stem, a > reen Stem, > "ig -eaes, d > little

leaes

5

Parents Phenotype: Purple stem & Purple Stem &Big Leaves Big Leaves

Parents enotype: !a"# !a"#

ametes:

$1 enotype:

$1 Phenotype: % : 3 : 3 : 1 !B : !'' : aaB : aa''

Purple & Big : Purple & Little : reen & Big : reen & Little

!#

a"

!" !#

a"

!"

a# a#

!"

!"

!#

!#

a"

a"

a#

a#

! ! " "

! ! " # ! ! # #

! ! " #

! a " " ! a " #

! a " "

! a " #

a a " "

! a " #

! a # #

a a " #

a a # #a a " #! a # #! a " #

0cological !ampling Techniues4.5.4


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#iotic Factor: A liing ariable within the ecosystem, which affects the surialof organisms. 1$amples include predation, competition, and pollution frome$creted waste.

&iotic Factor: A non*liing ariable within the ecosystem, which affects thesurial of organisms. 1$amples include temperature, light, and water.

2andom !ampling(?uadrats placed at randomly generated interals) %sed where habitat is uniform ;emoes obserer bias %sed in a large area %sed if time is limited

!ystematic !ampling(?uadrats placed at regular interals)

%sed to show 3onation %sed where there is continuous ariation %sed to sample linear habitats (e.g. a roadside)

types of systematic sampling techni?ue7

-ine Transect: %sed where time is limited %sed to isually illustrate how species change along a line

"elt Transect: 'roduces more data, gies detail about species abundance down the line

as well as range Shows species dominance down the line

hat inter$al should e used

Transects can either be continuous with the whole length of the line beingsampled, or samples can be taken at particular points along the line

#or both line and belt transects, the interal at which samples are taken willdepend on the indiidual habitat, as well as on the time and effort which can beallocated to the surey.

Too great an interal may mean that many species actually present arenot noted, as well as obscuring @onation patterns for lack of obserations.

Too small an interal can make the sampling time consuming, as well asyielding more data than is needed.

(

4.5.5An e$ample of a 6amed 0n$ironment

!s the "ritish 2ocky !eashore


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&iotic #actors include7 dessication, salinity, wae action, temperature, wateraailability, substrate, aspect, p4 etc

#iotic #actors include7 interspecific competition, intraspecific competition,predation, food aailability, presence of e$creted wastes

Species liing in the ;ocky Sea shore

Splash one: 7ichenB can surie dessication = temp ariation, re?uires littlenutrient

%pper Shore: #lack Tar 7ichenB can surie long periods without water, growsslowly, but is less tolerant to dessication than lichen.

iddle Shore: 0ggwrackB ore water aailability, less temp range, but morepredation from herbiores and carniores

-ower Shore: Kelp B constant enironment, usually submerged, lower light leels,intense competition from same and other species

on2t learn this case study if your teacher gae you noteson a different habitat. -earn this study if you2re desperate

Adaptations of Species in trophic leels

)

&iotic Factorshae moreeffect going up the beach

#iotic Factorshae moreeffect going down the beach

4.5.8

icro*algae (#ladderwrack):

+. 4as bladders of /that allow it to float (toreach light)

. Tolerates fresh water5. 4as specialised gonads (resceptacles) which

release lots of sperm into the sea


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on2t learn this case study if your teacher gae you noteson a different habitat. -earn this study if you2re desperate

*

4.5.9

7ight ,ependent !tep o) Photosynthesis


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-ight ependent Step:

+. 6hlorophyll absorbs light (remember chlorophyll is the trap in the

bottom of the photosystem)

%


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. 6hlorophyll emits electrons

5. 1lectrons are receied by electron carrier proteins in the thylakoidmembrane (electron transport chain)


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. ;eduction : !n a series of reactions ' reacts with AT' and /A'4reduced ' to form A-' (by reducing ' the /A4'4 itself iso$idised, reerting to /A')

5. ;egeneration : Some A-' is conerted back into ;u"' so the 6alin6ycle can continue. The rest of A-' is conerted into glucose in aseries of reactions.

A glucose molecule is generated eery 8turns of the 6alin 6ycle

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4.5. location of photosystems = electron transport chainStroma > site of 6alin 6ycle = photolysis of water

rana proide large surface area for absorbtion of light

4.5.1=


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Of the +I sunlight energy that reaches plants, J5I is conerted into/''. 1nergy is lost in the following ways7 reflected light, light ofwaelengths not useful to plants, passes through leaes, lost inrespiration, lost as heat etc

0$olution: the idea that one species changes into another oer time

6atural !election: arwin2s suggestion for the process by which eolutionmight occur

0$olution y 6atural !election(arwinian 1olution)

+. There is ariation in a species

. ore indiiduals are born than the enironment can sustain, sosome indiiduals must die.

5. The indiiduals that surie tend to be those that hae alleleswhich gie them a selecti$e ad$antage in their enironment (i.e.they are the best adapted to their enironment, e.g. camouflaged).These are the GfittestH


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This process is speeded up by isolation (see


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alleles and speeds the accumulation of new mutations (which is what leadsto speciation)

The different types of isolation.

1olution is a theory, not a fact. any people beliee that species werecreated (creationism). Other people beliee in eolution, but bymechanisms other than /atural Selection. Dou should respect the opinionsof other people, een if you do not necessarily agree with them.

Primary successionis the first stage of the ecological successionof plant

life from abioticland with no soilto fully support plantecosystems(e.g., aforest). !n primary succession, pioneer plants like mosses and lichen,start to Pnormali@eP the habitat, creating rudimentary soil from theirdead matter. These pioneer plants create conditions for the start ofplant growth and so more comple$ plants like grassesand shrubsbegin tocolonise the area.

Oer time the grass area is colonised by small woody plants, which gieway to small trees and finally, after a few hundred years, large trees

take oer. The large trees represent the clima" community becausesuccession stops at this point.

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+ethod o) isolation ,escription

1cological isolation The species occupy different parts of thehabitat

Temporal isolation The species e$ist in the same area, butreproduce at different times

"ehaioural isolation The species e$ist in the same area, but do notrespond to each other2s courtship behaiour

'hysical incompatibility Species coe$ist, but there are physical reasonswhich stop them from copulating4ybrid iniability !n some species, hybrids are produces but they

do not surie long enough to breed4ybrid sterility 4ybrids surie to reproductie age, but cannot

reproduce

4.5.15

4.5.18
http://www.answers.com/topic/ecological-succession-1http://www.answers.com/topic/abiotic-1http://www.answers.com/topic/soilhttp://www.answers.com/topic/planthttp://www.answers.com/topic/ecosystemhttp://www.answers.com/topic/foresthttp://www.answers.com/topic/pioneer-planthttp://www.answers.com/topic/moss-2http://www.answers.com/topic/lichenhttp://www.answers.com/topic/habitat-ecologyhttp://www.answers.com/topic/grasshttp://www.answers.com/topic/shrubhttp://www.answers.com/topic/ecological-succession-1http://www.answers.com/topic/abiotic-1http://www.answers.com/topic/soilhttp://www.answers.com/topic/planthttp://www.answers.com/topic/ecosystemhttp://www.answers.com/topic/foresthttp://www.answers.com/topic/pioneer-planthttp://www.answers.com/topic/moss-2http://www.answers.com/topic/lichenhttp://www.answers.com/topic/habitat-ecologyhttp://www.answers.com/topic/grasshttp://www.answers.com/topic/shrub


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A good e$ample of primary succession takes place after a olcano haserupted. The barren land is first colonised by simple pioneer plants whichpae the way for more comple$ plants, such as hardwood trees by

creating soils and other necessities. %nlike secondary succession, whichrefers to succession after an enironmental disaster (such as a forestfire) primary succession occurs on the geologic timescale, oer thousandsof years

oos can play a large role in consering endangered species by7

+. 6onducting research

. ;unning captie breeding programmes

5. ;eintroducing species into the wild


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Unit 4: Environment and Survival

Topic 8: -n)ection' -mmunity @ Forensics

4.8.1

Time of death can be measured using the following factors7

o "ody temperature

o 1$tent of rigor mortis

o -eel of decomposition

o #orensic entomology

"ody temperature:

The rate of cooling depends on the situation the body is found in e.g.

6lothing B slows cooling

1*

SNAB A2 Revision Notes

A body cools following an S*shaped(sigmoid) cure. The initial plateau at50Q6 lasts 5 B K min, then the bodycools ?uickly to ambient temperature.

After


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#ound in water B speeds cooling#ound indoors B slows coolingAir moements B speed cooling1$tent of rigor mortis:

;igor mortis is the stiffening of Coints and muscles. Small muscles stiffenfirst and unstiffen last.

uscles stiffen because they run out of AT', causing the actin andmyosin muscle fibres to stick permanently to each other. usclesunstiffen because the muscle fibres begin to break down.

On page L of your te$t book is a little more detail about the se?uence ofeents that causes muscles to run out of AT'.

-eel of decomposition:

&utolysisis the break down of body tissues using the body2s own en@ymesfrom the digestie system and from lysosomes

After this, bacteria from the gut inade tissues and release moreen@ymes. This tends to happen in anaerobic conditions, which faours thegrowth of anaerobic bacteria

1%

Temperature o) ody !ti))ness o) ody &ppro" time since death

Farm /ot stiff /o more than 5 hrsFarm Stiff 5 B Lhrs6old Stiff L B 5Khrs6old /ot stiff R 5K B


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Autolysis is increased by mild heat and slowed by intense heat. 4umidityhas a big inolement as well B dry conditions slow autolysis and, in somecases (e.g. mummies) stop it completely.

The presence of wounds, the clothing the person was wearing and thecombination of gases released during decomposition also hae an effect.

#orensic entomology:

The insects found in a dead body can help identify time of death in 5ways7

+. !f the temperature of the body has remained relatiely constant

the age of the maggots growing in it can be determined by theirstarting length and the temperature of the part of the body theygrew in.

6orpse succession:

e.g. a maggot 5mm long found growing at LQ6 will be roughly .5 days (Lhrs old)

. %sing the life*cycle of the maggot to identify age

5. !f maggots are taken from the body, allowed to grow and the timetaken to pupate is recorded7 it is sometimes possible to workbackwards from the pupation date and work out hold the maggotsmust hae been when they were taken from the body. This worksbecause maggots of different species usually take a fi$ed numberof days to pupate.

2+


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4.8.%

The identity of a dead person can be ascertained by7

+. !dentity papers

. #ingerprints

5. ental records


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&. /A is labeled using a /A probe specific to the satellite

K. An *ray is taken to reeal the location of the bands of /A

The fingerprint is the pattern of bands on the electrophoresis gel.

Assuming the original /A sample has not been contaminated (by e.g. ahair from the pathologist) the fingerprint will be e$act.

4.8./

Succession on corpses:

The idea that as each organism or group of organisms feeds on a body, it

changes the body. This change in turn makes the body attractie toanother group of organisms, which changes the body for the ne$t group,and so on until the body has been reduced to a skeleton. This is apredictable process, with different groups of organisms occupying thedecomposing body at different times. This techni?ue allows you to tell, bythe age and specific species liing on a corpse, how old the corpse is.

Succession and forensic entomology also show if the body has beenmoed.

4.8.4

& typical prokaryote

22


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2iosomes. Same function as eukaryotic cells (protein synthesis),

but are smaller (0s rather than Ls).

6uclear Bone. The region of the cytoplasm that contains /A.There is no nuclear membrane.

,6&. Always circular, and not in chromosome form.

Plasmid. 9ery small circles of /A, containing non*esential genes.

6an be e$changed between different bacterial cells.

Cell memrane. made of phospholipids and proteins, like eukaryoticmembranes.

+esosome. Tightly*folded region of the cell membrane containing allthe proteins re?uired for respiration and photosynthesis.

Cell all. !##1;1/T from plant cell wall. ade of murein (aprotein). There are two kinds of cell wall, which can be distinguishedby a ram stain:

A: ram positie bacteria hae a thick cell wall and stainpurple": ram negatie bacteria hae a thin cell wall with an outerlipid layer and stain pink.

Capsule(or !lime 7ayer). Thick polysaccharide layer outside of thecell wall. %sed for7

+. Sticking cells together. As a food resere5. As protection against desiccation (drying out) and chemicals, and

as protection against phagocytosis (being broken down by a white

blood cell).

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Flagellum. A rotating tail used for propulsion.

& typical $irus

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Prokaryotic Cells 0ukaryotic cells

Small cells ( & mm) -arger cells (R + mm)Always unicellular Often multicellular

/o nucleus or any membrane*boundorganelles

Always hae nucleus and othermembrane*bound organelles

/A is circular, without proteins/A is linear and associated with

proteins to form chromatin

;ibosomes are small (0S) ;ibosomes are large (LS)

/o cytoskeleton Always has a cytoskeleton

6ell diision is by binary fission 6ell diision is by mitosis or meiosis

;eproduction is always ase$ual ;eproduction is ase$ual or se$ual


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9iruses hae a wide range of different structures. Some iruses areabout +nm in diameter, whilst others can range from B5nm.

All iruses hae a protein coat (the capsid), which contains geneticmaterial. The genetic material is either /A or ;/A, and can besingle or double*stranded.

The irus genetic material (the iral genome) contains only a fewgenes, from about in the polio irus to more than in theherpes irus (human genome contains JL, genes). The iralgenome codes for the proteins re?uired to manufacture the irus.

The protein capsid is made from identical subunits (calledcapsomeres). The capsomeres can be arranged into an icosahedralshape (e.g. polio = herpes), or a cylindrical shape (e.g. T9 =rabies) or a loose containment structure (e.g. measles =influen@a).

!n addition, some iruses also hae an outer membrane enelope, whichallows the irus to penetrate the host cell membrane byendocytosis. !nfluen@a, 4!9 and measles irus all hae membraneenelopes.

9iral amage B Fhat do 9iruses actually do to us

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ligandsD


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-ike bacteria, iruses hae protein ligands on their capsid thatattach to ligand receptors on eukaryotic cells. After a irus ligandattaches to a host cell ligand receptor it becomes anchored to thehost cell. The irus attempts to get its iral genome into the host

cell, usually through endocytosis using its lipid membrane. 9iruseswithout lipid membranes may hae specialised proteins designed tohelp inCect the iral genome into the cell cytoplasm.

(i) 9irus ;/A enters host cell(ii) 9irus may also inCect ;/A 'olymerase into host cell as well.(iii) 9iral ;/A and ;/A 'olymerase enter host cell nucleus ia

nuclear pores

(i) 9iral ;/A is copied in nucleus() 9iral ;/A is transcribed using iral ;/A 'olymerase(i) 9iral m;/A is translated in the cytoplasm(ii) /ew 9irus proteins formed(iii) 9iral proteins associate with copied ;/A forming new

complete iruses(i$) /ew iruses leae host cell to infect other cells

9iruses that hae a /A code instead of an ;/A code often inserttheir iral /A into the host cell2s /A. Other ;/A iruses inCectthe en@yme ;eerse Transcriptase, which makes a c/A copy ofthe iral ;/A. The c/A copy is then inserted into the host cell2s/A. Other iruses (e.g. 4!9) also inCect the en@yme integrase,which helps insert the iral c/A into the host2s /A

"e sure you can recall what the 5 iral en@ymes do7

/A 'olymerase:;/A Transcriptase:!ntegrase:

Some iruses target specific tissues (e.g. 'oliomyelitis irus targetsmotor neurones, 4!9 targets helper T cells, !nfluen@a targetsepithelial cells = rabies irus targets specific brain cells). !f lots ofnew irus is being made, these host cell may lyse(burst) and die.

2(


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*- is the 4uman immunodeficiency 9irus, which eentually leads toAc?uired !mmunodeficiency Syndrome (&-,!)

4!9 is spread by direct contact i.e. through se$ual intercourse,blood*to blood transfer (tattoos, needle sharing, piercing = cut*to*cut transfer).

Once inside the bloodstream an 4!9 infection occurs in 5 distinctphases7

+. The acute phase. 4!9 irus has a ligand ('+), which

attaches to a receptor (6


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3iller T cells. Fith low numbers of 4elper T cell, the immune systemcannot communicate effectiely and this increases the ability of4!9 to surie in the body.

4.8.9

/on*specific immune responses:

-n)lammation: damaged white blood cells and mast cells releasehistamineat the site of infection. 4istamine causes local arteriolesto asodilate, increasing the blood supply to the area. !t also causesholes to open between endothelial cells in capillary walls. This causes

local oedema (the swelling associated with inflammation). !t allowsmonocytes and neutrophils into the infected area, which engulf anddestroy foreign bodies and pathogens. 1entually phagocytes arrieand complete the Cob. ead monocytes and pathogen form pus.

7yso3yme:an en@yme that breaks down bacterial cell walls, causingthem to lyse and die. -yso@yme is made in lysosomes insidephagoctyes and is responsible for digesting engulfed bacteria.

-yso@yme is also made by the skin, epithelial cells, and is present intears

-nter)eron:a protein made by irus*infected cells. !t blocks ;/Asynthesis and therefore stops irus replication

Phagocytosis: the process in which a pathogen is engulfed anddestroyed. acrophages engulf pathogens using pseudopodia (Gfake

feetH). The bacterium is taken into the macrophage by endocytosisand enters the macrophage inside a acuole. -ysosomes containinglyso@yme fuse with the acuole and digest the bacterium inside.

2%


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4.8.

Pathogens hae proteins on their surface that our immune systemhas learned to recognise as foreign. These proteins are called

antigens. T cells, " cells = acrophages all hae the ability torecognise an antigen and once this has happened, they will trigger animmune response.!n addition to this, macrophages hae the ability to present foreignantigens to T and " cells. Once a pathogen has been engulfed anddestroyed +*C proteins inside the acrophage stick to thepathogenic antigen. They are then incorporated into the cellmembrane of the acrophage, so it can present the foreign antigen

and actiate the T and " cells responses.

Antibodies (also called -mmunogloulins) are proteins produced by "cellls. They are found in blood plasma, lymph, tissue fluid, tears,mucus and milk.

3+

!ntigen-'in#ing site


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1ach " cell produces a different immunoglobulin molecule whichrecognises and binds to a specific antigen. There are oer a milliondifferent " cells in your body, therefore you hae the ability torecognise and react to a million different antigens.

The $ariale region of the immunoglobulin protein is whatrecognises = binds to the antigen. 1ach ariable region is different,

hence the name.

There are & different families of immunoglobulin molecule in thehuman body (, , A, = 1. !g * also known as *globulin). Thefamilies can be distinguished from each other by slight differencesin the constant regionof the protein

1ach antobody molecule contains two pairs of proteins7

* Two heay chains* Two light chains

1ach pair of chains is held together by disulphide bridges (hydrogenbonds would be too weak).

1ach immunoglobulin molecule has antigen binding sites and can,therefore, bind antigens at one time. This means that a singleantibody molecule can bind to pathogens at the same time, which

31

.onstant,egion

/aria'le,egion

"isulph#eBri#ges


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causes pathogens to clump together and form the &ntiodyA&ntigenComple".

The formation of the Antibody*Antigen 6omple$ is importantbecause it7

* !solates pathogens so they cannot infect other host cells

* akes it easier for macrophages to engulf = destroy thepathogens.

* Stops the pathogen from entering a host cell* akes it easier for T cell actiation as more antigens are

presented in one area

4.8.

a2 revision notesfinished

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