edexcel bio 2 notes (1)

8/18/2019 Edexcel Bio 2 Notes (1)

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Organelle Structure and function

Nucleus • enclosed in double membrane with pores

• contains chromosomes with genes made of DNA to control protein

synthesis

Ribosomes • made of RNA and protein

• free in cytoplasm or attached to RER

• site of protein synthesis

Rough endoplasmicreticulum

•

interconnected sacs with ribosomes attached• transport proteins to other parts of cell

Smooth endoplasmic

reticulum

• synthesis of lipids and steroids

Mitochondria • double membrane – inner folded into cristae

• site of later stages of aerobic respiration

Centrioles • one pair found in animal cells

• made of protein microtubules

• involved in spindle formation and cellular transport

ysosomes • digestive en!ymes wrapped in membrane

• brea"down of unwanted structures or old cells

Nucleolus • dense body in nucleus

• synthesis of ribosomes

#esicle • Small fluid$filled sac in the cytoplasm% surrounded by membrane

• &ransports substances in out of the cell via the cell membrane and

between the organelles

• Some are formed by the 'olgi apparatus (e)ocytosis* and some

by the plasma membrane (endocytosis*


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CellsEukaryotes (such as human liver

cell)

Prokaryotes (such as a bacterium)

Larger cells (2-200 um diameter) Very small cells (


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Cell cycle:

i n t e r p h a s e

G1 (first gap phase) synthesis of cellular proteins and organelles

S (synthesis phase) replication of DNA

G2 (second gap phase) synthesis of spindle proteins

d i v i s i o n

mitosis (nuclear

division)

separation of the 2 DNA helices making up the

chromosome

cytoplasmic division cleavage of a single cell into two daughter cells

Mitosis phases:

Prophase:• idea that during prophase +chromosomes , chromatids- (becoming* visible .

• idea of centrioles move to opposite poles .

• reference to formation of +spindle ,spindle$fibres , microtubules- .

• disappearance of nucleolus , nucleoli .

brea"ing down of nuclear +envelope , membrane- (in prophase* .

Metaphase:

• nuclear envelope is bro"en down by metaphase , e/ .

• (at metaphase* +chromosomes , centromeres- attached to spindle (fibres* .

• idea of +chromosomes , chromatids- lined up at e/uator .

Anaphase:

• centromeres divide , split , separate , pulled apart.

• +spindle fibres , microtubules- become +shorter , contract , condense-.

• chromatids +separate , pulled apart-.

• chromosomes , chromatids move towards (opposite* +poles , ends , sides ,

centrioles-.

Telophase:

• +spindle fibres , microtubules- have now +vanished , bro"en down , e/-.

• chromosomes +unravel , uncoil , e/- (and become invisible* .


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• reference to reformation of +nuclear membrane , envelope , e/- , +nucleolus ,

nucleoli-.

Diagrammatic representation of mitosis

Order: A D C ! " note that A #interphase$ is sometimes referred to as part of mitosis %utmost of the time it&s listed as separate.

Difference et!een mitosis and meiosis

Meiosis Mitosis

(3omologous* chromosomes associate inpairs

(3omologues* independent,do not pair(4'N2RE ref1 separation

Crossing$over,chiasmata formation No crossing$over

&wo,(nuclear stages* divisions, 5 6 offspringcells

2ne,(nuclear stage* division, 5 7 offspringcells.

'enetically different (product* 'enetically identical (product*.

Cyto"inesis

&he cytoplasmic division of a cell at the end of mitosis% bringing about the separation

into two daughter cells1

#unction$importance of spindle

• Attachment of centromeres.

• Separation of (daughter* chromatids.


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Plants

%ylem tissue structure Centre of the stem'

• long cells , tubes with no end walls.

• continuous water columns.

• no cytoplasm , no organelles,named organelle.

• to impede,obstruct flow , allows easier water flow.

• thic"ening,lignin.

• support , withstand tension , waterproof , "eeps water in cells.

• pits in walls.

allow lateral movement , get round bloc"ed vessels.

Sclerenchyma fires structure Outer edge particularly'

• 8undles of dead cells running vertically.

• 3ollow lumen.

• No end walls.

• &hic"ening,lignin.

• support , withstand tension.

• More cellulose than other plant cells.

Structure of function of starch

• Contains amylose and amylopectin.

• Amylose not a mar"' :

• ong and unbranched chains.

• 9$6 glycosidic bonds.

• coiled structure.

• (so* compact.

•

(so* can fit more in a small space.

Amylopectin not a mar"' :

• (long*% branched chains.

• (has* 9$6 and 9$: glycosidic bonds.

• side branches which can be bro"en down /uic"ly.

• 4nsoluble.

• so water doesn;t cause it swell via osmosis

Structure of cellulose


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• (cellulose* contains beta glucose , e/ .

• (glucose molecules*


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Organelle Diagram Description Function

Cell !all• Rigid structure

surrounding

plant cells.• Cellulose.

• Supports plant cells

Middle lamella • 2utermost

layer.

• Adhesive.

• Stability

Plasmodesmata • Channels in cell

wall that lin"ad


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Amyloplast • Small organelle

enclosed bymembrane.

• Starch

granules.

• Storage of starch.

• Converts starch bac" t

glucose.

(acuole & Tonoplast • #acuole is a

compartmentsurrounded bya membranecalled thetonoplast

• #acuole contains cell

(water% en!ymes%

minerals% waste produ

• &urgidity to prevent

wilting

• 8rea"down and isolati

of unwanted chemical

• &onoplast controls wh

enters and leaves the

Cell !all structure

• Ref to cellulose .

• Cellulose arranged into microfibrils .

• Embedded into a matri) .

• Named component of matri) e1g1 pectin , hemicellulose .

• Ref to +primary and secondary cell walls , several layers of microfibrils- .

• Ref to plasmodesmata .

Plant fires• cellulose microfibrils (in cell wall* .

• reference to net$li"e arrangement (of microfibrils* .

• secondary cell wall .

• reference to secondary cell wall being thic"er .

• idea that these features ma"e them the plant fibres strong .

Sustainaility

• #O3 A 4A05 ) Oil)%ased plastics and fuels are not sustaina%le as$:

• Release carbon dio)ide , ref1 to global warming , pollution .

• plastic is from oil .

• oil is a non$renewable resource .

• 'eneration of non$biodegradable waste .

• (however* +plants , starch- are renewable .

• plants can be re$grown , e/ .

• (fibres often biodegradable so* doesn;t accumulate , doesn;t ta"e up landfill space ,

e/ .


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Disad)antages

• &he ropes made from plant fibres aren;t as strong.

• 8ags made out of paper are less strong than plastic bags and disintegrate when wet.

• Degradation of waste re/uires aerobic organisms% so little happens in deep landfill

sites.

• Closer to the surface% methane (a greenhouse gas* is often produced.

Tissues of a leaf

• ower epidermis – contains stomata to let air in and out for gas e)change

• Spongy mesophyll – full of spaces to let gases circulate

•

=alisade mesophyll – most photosynthesis occurs here• >ylem – carries water to the leaf ? transports mineral ions

• =hloem – carries sugars away from the leaf

• @pper epidermis – covered in a waterproof wa)y cuticle

Plants re*uirements of !ater + mineral ions

• ater.

• =hotosynthesis.

• Structural rigidity , transport minerals , temperature regulation.

• Magnesium ions.

• Chlorophyll.• Nitrate ions.

• DNA , protein , chlorophyll production.

• Re/uired for plant growth , fruit production , seed production.

• Calcium ions.

• =lant growth.

Digitalis

• Bo)glove e)tract.

• &reated dropsy.

• reference to digitalis as active drug.• idea of e)tracting drug (from the plant , soup* , tested on patients ,

Starch Plant fibres

• ound in all plants

• !ioplastics " less fossil fuel used up

# crops can $e regrown%

• &ehicle fuel " such as $ioethanol%

Same reasoning as a$ove%

• 'ther uses include glues plaster

hair mousses and antiperspirants%

• opes and fa$rics " less fossil fuel

used up # crops can $e regrown tomaintain supply

• *roducts are $iodegrada$le " this

means less accumulates and fills uplandfills%

• +asier to grow and process "

cheaper and easier for developingcountries


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• idea of try to find suitable dose , trial and error .

Modern day drug testing

• idea that only contemporary testing will use animals , e/ .

• idea that only contemporary testing will +test on healthy people , have phase 9- .

• idea that +phase 9 , e/- is to +detect side effects , find safe dosage- .

• idea that only contemporary testing will pay volunteers .

• idea that only contemporary testing may involve double$blind trials .

• idea that after phase 9% phase 7 occurs – drugs are tested on a larger group of

people .

• idea that this chec"s how effective the drug actually is .

• idea that only contemporary testing will +use statistical analysis , reference to phase 0

, use large number , comparison to e)isting treatments - .

• idea of more regulation .

• idea of controlling +factors ,variables , e/- in tested cohort e1g1 age% lifestyle .

Placeo

• idea of two groups .

• idea that group 9 is given +placebo , inactive substance , sugar pill , e/- .

• reference to placebo effect .

• idea that other group is given the drug .

• idea that this chec"s the effectiveness of the drug , e/ .

Doule,lind trial

• idea that neither doctors nor patients "now placebo,drug group.

• idea that this reduces bias.

• reference to phase 7 , 0.

-eaf cross,section


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#6hloem 7 ,'lem in 8ascular %undle$

Stem cross,section

P =hloem. . Sclerenchyma fibres. R >ylem. S Corte). T Epidermis. / Cambium

Adaptations in different' %erophytes relating to !ater

• shallow roots enable rapid upta"e of rainfall.

• widespread,shallow roots allow collection of larger volume water,over a larger

area,rapid upta"e of water.

• swollen stem for water storage.

deep roots for accessing deep groundwater.

small, no leaves so little transpiration.

Structure of lea)es of %erophytes to "eep !ater in

• Reduce number of stomata. reduce surface area

• &hic" wa)y cuticle. increases diffusion distance

• eaves reduced to spines. reduces surface area

• Epidermal hairs. reduced diffusion gradient

• Sun"en stomata. reduced concentration difference

• Curled leaves. reduced concentration gradient

0n)ironmental factors the influence !ater loss in a leaf

• temperature .

• increase gives more ("inetic* energy , movement to water molecules .

• on surface of spongy mesophyll cells .

• greater evaporation (into air spaces* .

• increases diffusion gradient , rate (of water vapour through stomata* .

• wind , air movement .

• increases , speeds removal of water vapour , humid air .


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• from (leaf* surface, stomata .

• increases diffusion gradient (of water vapour through stomata* .

• decreases boundary layer .

• humidity .

• increase means more water vapour around leaf , stomata .• reduces diffusion gradient (of water vapour through stomata* .

• light intensity .

• increase causes stomata to open , widen .

• so more diffusion of water vapour .

• from air spaces (in spongy mesophyll* .

• water stress , e)tremely high temperature , high winds .

• stomata close .

• less diffusion .

1o! to find surface area of a leaf

• draw round leaf on graph , s/uared paper , grid .

• count s/uares

02planation of !ater path!ays as it tra)els from the epidermis of a root to a %ylem)essel3

• apoplast pathway described .

• e1g1 water moves through the cell walls;

•or water moves through the spaces between cells;

• symplast pathway described .

• e1g1 water moves through the cytoplasm;

• reference to the vacuolar pathway.

• e1g1 water moves through the vacuoles;

• reference to the endodermis and +Casparian strip , layer of suberin , wa)y layer- .

• function of the Casparian strip .

• e1g the Casparian strip is waterproof; or stops movement of water in the apoplast

pathway

Role of the epidermis

• endodermal cells have Casparian strip .

• reference to +suberin , e/- .

• which is waterproof , e/ .

• stops movement of water in apoplast pathway , description .

• water directed into symplast pathway , description .

• reference to +control of upta"e , active transport of ions (into )ylem*- .

1o! AT of mineral ions into 2ylem )essels in the roots results in !ater entering)essels and then eing mo)ed up the 2ylem tissue


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• ater potential in )ylem reduced (by entry of ions*.

• ater potential gradient established between )ylem and surrounding cells.

• =lasma membranes of surrounding cells are partially permeable.

• ater enters )ylem by osmosis.

• #olume of water in )ylem increases.• Cannot move bac" due to gradient.

=ressure in )ylem increases (and forces water upwards*.

Cohesion,tension theory

• Evaporation from leaves , transpiration.

• ater in )ylem under tension,negative pressure,pulled up.

• ater molecules cohere,stic" together,form hydrogen bonds. F1gnore: references to

adhesionG

So water a single column.

Another mar" scheme for cohesion,tension theory• water evaporates,transpires.

• reduces water potential , creates water potential gradient , increases

osmotic gradient .

• moves via apoplast pathway.

• water drawn out of )ylem.

• creates tension,pulling effect , creates negative pressure (in conte)t*.

• cohesive forces or 3 bonding between water molecules , water moves as a column

/ses of !ater in a plant

• photosynthesis .

• +component , e/- of +cytoplasm , sap- .

• water as a solvent ,e/ .

• water as a transport medium ,e/ .

• involved in thermoregulation , e/ .

• reference to role in structural support .

• reference to involvement in hydrolysis .

• reference to turgor changes .

Transpiration

• oss of water vapour from the surface of the plant% mainly from the leaves .

Root pressure in relation to !ater mo)ing through the 2ylem

• 4nvolves active transport.

• Secretion , movement of salts into )ylem.

• Reference to role of endodermis .

• ater moves along water potential gradient .

4hy less !ater is lost at upper surface of lea)es

• more stomata on the lower surface.

• (thic"er* wa)y cuticle on the upper surface .


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Molecular phylogeny

• Study of evolutionary history of organism groups

• Measures relation between species.

• DNA and proteins e)amined – the more closely related the more similar the

molecules

Domains

• 8acteria% Achaea and Eu"arya .

• =ro"aryotae in Archaea and 8acteria .

• 2ther "ingdoms (organisms with a nucleus* in Eu"arya .

• Archaea and bacteria distantly related% so classified into two domains .

567GDOM 0%AMP-0S #0AT/R0S

Pro"aryotae 8acteria• =ro"aryotes

• Single$celled

• No nucleus

• ess than I Jm

Protocista Algae% proto!oa • Eu"aryotic

• 'enerally water

inhabitants

• Single$celled or

simple multi$cellular

#ungi Mould% yeast% mushrooms• Eu"aryotic

• Chitin cell wall

• Saprotrophic (absorb

substances fromdecaying organisms*

Plantae Mosses% ferns% floweringplants

• Eu"aryotic

• Multicellular

• Celluse cell walls

• Contain chlorophyll

• =hotosynthesis ability

• Autotrophic (produceown food*

Animalia 4nsects% fish% reptiles% birds%mammals% molluscs%nematodes

• Eu"aryotic

• Multi$cellular

• No cell walls

• 3eterotrophic

(consume plants K

animals*

Comparison of species

• Bossil records• 3omologous features


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• Evolutionary history

• DNA 8ase se/uence

• Ecological Niches

(ariation of genotype to )ariation of phenotype• 4ndividuals of a species have different genotypes.

• &his means a variation in phenotype , e/.

• 4dea that some characteristics are monogenic (controlled by one gene*.

• Reference to discontinuous variation , e)ample.

• 4dea that most characteristics are polygenic at different loci (controlled by many

genes*.

• Reference to continuous variation , e)ample .

0n)ironmental influences to phenotypes

• 3eight – polygenic.

• (by* nutrition , e)ample e1g1 malnutrition limiting child;s ma)imum height.

• Monoamine 2)idase A (MA2A* – monogenic.

• En!yme that +brea"s down , e/- monoamines.

• Reference to low levels of MA2A to mental health problems.

• Reference to antidepressants , tobacco reducing MA2A levels.

• Cancer.

• (by* diet.

• Animal hair colour.

• Seasonal , temperature influences , e)ample e1g dar" hair in summer but white hair

in winter.

• 'enes re/uired to trigger the change .

7iche

• Role of the species within its habitat.

• 4nteractions with other living organism , e)ample e1g1 prey and predators.

• 4nteractions with non$living environment , e)ample e1g1 gas e)change.

• reference to niche being uni/ue to species.

• reference to competition if two species occupy the same niche.

A d a p t a t i o n s

!ehavioural ,he way an organism acts to increase its chance of

survival and reproduction

*hysiological *rocesses inside an organisms $ody that increase chance

of survival

Anatomical ,hese are structural features of an organism-s $ody that

increase its chance of survival


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Adaptations

• idea of selection pressure , change in environment.

• reference to competition , predation .

• mutation #in conte,t$ .

• idea of advantageous allele.• idea that individuals with advantageous + alleles , characteristics , e/ - survive and

breed .

• idea of (advantageous* + allele , mutation - being passed on (to future generations* .

• idea of more individuals with this adaptation in the population , increased fre/uency

of advantageous alleles in the population

Biodiversity and endemism

8iodi)ersity

• #ariety of living organisms in an area

Species di)ersity

• Number of different species (in an area*

• Abundance of each species (in an area*

Genetic di)ersity

• #ariation of alleles within a species

Species richness

• the number of species .

• in +an area ,one location ,habitat- .

0ndemic

• idea that the ( species , e/ * is restricted in its distribution , species only found in one

specific + location , area , e/ -

1aitat

• &he area in which an organism lives

Measurement of species di)ersity

• Count the number of different species .

• &he higher the number of species% the greater the species richness .

• imitation – no indication of the abundance of each species .

• (so* Count the number of different species and number of individuals .

• @sage of biodiversity inde) , e/ .

Practical measurements of species di)ersity

•choose an area within the habitat to sample .

• idea that the sample is random .


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• idea of reduction of bias .

• count the number of individual species .

• aysL plants – /uadrat. airborne insects – sweepnet. ground insects – pitfall trap.

a/uatic animals – net .

• reference to repeats .

• Estimate total number of individuals or total number of different species .• idea of sampling techni/ue being the same .

Measurement of genetic di)ersity

• 'enetic diversity is the variety of alleles in the gene pool of a species.• &he gene pool is the complete set of alleles in a species

• &he greater the variety of alleles% the greater the genetic diversity

• Measured by phenotype.

• idea that different alleles code for different versions of the same characteristics.

• arger the number of phenotypes% the greater the diversity.

• Measured by genotype.

• Se/uence of 8ase pairs in DNA analysed.

• 2rder of bases in alleles is different.

• 8y se/uencing DNA% similarities and differences are observed.

• arger the number of alleles% the greater the genetic diversity

Reduction of genetic di)ersity

• Reduced variety,number of different alleles,DNA , reduced gene pool (in new

population*.

• Bounder effect.

• A few individuals from a population become isolated,form colonies

• ('enetic* bottlenec"s.

• (Significant* fall in si!e of population

• Selective breeding , artificial selection.

@sing organisms with particular alleles,traits,phenotypes,characteristics.

6mportance of storing seeds rather than plants

• ta"e +less , smaller- space , e/ .

• can have more individuals , e/ .

• reference to +greater , more- genetic variety .

• idea of less +maintenance , cost- .

• li"ely to survive longer , e/ .


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• can free!e seeds , e/ .

6mportance of storing seeds from different plants

• idea of +greater , maintain- genetic variety

• e1g1 wider gene pool% different alleles .

• idea of less chance of inbreeding .• idea of reducing chance of storing seeds with

• +low viability , disease , e/- .

Seeds of different si9es

• idea of maintaining or increasing +genetic diversity , si!e of gene pool , genetic

variation- .• idea of more chance of having beneficial alleles ,e/ .

• increases chance of future survival +if environment changes , due to higher

adaptability - , e/ .

• less chance of all being susceptible to a disease , e/ .

1o! 9oos maintain the genetic di)ersity of endangered species

• breeding programme , e/ .

• careful selection of mate , e/ .

• allowing only to mate with a different individual to previous mating , e/ .

• only allowing those with different genes to mate , e/ .

• use of genetic testing , e/ .

• record "eeping (studboo"s* .

• reason for outbreeding .

• reintroduction to the wild , e/ .

Seedan" conser)ation

•

details of assessment of seed viability e1g1 only select seeds with a living embryo%use of > ray (to detect embryo presence* , e/ .

• idea of +cleaning seeds , surface sterilisation , e/- .

• idea of drying (of the seed* .

• idea of storing at low temperatures .

• idea of regularly testing viability (during storage of seed* .

• idea of what to do if viability decreases% e1g1 if less than I germinate collect fresh

seed for storage

Prolems !ith re,introduction and capti)e reeding

• idea that conditions are difficult to re$create in captivity , li!ards won;t breed , e/ .


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• ethical issues /ualified e1g1 cruelty , immorality .

• reintroduced species could bring disease .

• idea that the reintroduced species may not retain their natural behaviours in the wild .

Sexual reproduction

4ays in !hich a human sperm cell is specialised for its function

• shape /ualified e1g1 hydrodynamic% streamlined .

• idea of reduced resistance .

• +acrosome , 8esicle- containing +en9'me , acrosin-.

• involved in +digestion , brea" down- of the +9ona pellucida ,


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Role of digesti)e en9ymes for the style

• idea of +brea"down , digestion , e/- of style .

• (brea"s down* protein , pectin , middle lamella .

• reference to hydrolysis , e/ .

• easier for pollen tube to grow , reduced resistance , e/ .

• supplies +nutrients , named nutrient , energy-• for (pollen tube* growth , e/ .

Crossing o)er

• (before 9st meiotic division* homologous pairs of chromosomes pair up

• chromatids +twist , tie , e/- around each other .

• +bits , parts , e/- of the chromatid brea" off and


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• tube nucleus +disintegrates , brea"s down , e/-and tip of pollen tube bursts to release

7 male nuclei .

• one nucleus fuses with egg nucleus to form a !ygote.

• division by mitosis to form embryo.

• other male nucleus fuses with two other polar nuclei at the centre of the embryonic

sac to form triploid nucleus.• large nucleus forms to become a food store called endosperm .

• reference to double fertilisation

Stem Cells

Totipotent stem cell

• totipotent (stem cells* can give rise to +all , any , 79:- cell types , e/ . 1

• (stem cells* are +undifferentiated , unspecialised- , e/ .

• can "eep dividing , e/ .

•

only present in early life of embryo .• no genes switched off .

Pluripotent stem cell

• =luripotent (stem cells* can give rise to +all , any- cell types , e/ .

• E>CE=& e)traembyronic cells .

ote " first point must %e linked with second to earn marks

Differentiation

• &he process by which a cell becomes specialised .

-ocation of stem cells

• Embryo – differentiate into all cells needed to form a fetus .

• Adult tissues e1g1 bone marrow .

Differential gene e2pression , enaling cells to ha)e different structures andfunctions3

• different genes active in different cells , different genes

• active at different times , some genes +active , inactive- , e/ .

• active genes ma"e mRNA , e/ .

• active genes ma"e proteins , polypeptides ,e/ .

• (proteins* control cell +processes , e/- .

• idea of permanent change (to cell* , e/

8enefits

• Replace damaged tissues (in diseases* .

• credit e)ample e1g1 nerve tissue for spinal cord or heart tissue for heart$related

diseases .

• idea of saving many lives e1g1 growth of organs for those waiting for transplants .


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• idea of /uality of live being improved e1g1 replacing damaged cells in eyes in blind

people .

Adult stem cells multipotent'

•

body tissues of an adult e1g bone marrow .• simple operation but discomfort to patient .

• needle into centre of a bone .

• small /uanity of bone marrow removed .

• idea that adult stem cells +are not fle)ible , are limited in use , e/- .

0mryonic stem cells

• 2btained from early embryos

• Embyros created in 4#B lab , e)plained

• Stem cells removed after 6$I days

• Embryos destroyed .

• idea that embryonic stem cells can develop into +all , any , 79: , e/- cell types .

• more li"ely to cause immune re


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• 'uidelines , codes of practice to ensure scientists are wor"ing in a similar manner .

• Monitoring developments in research to ensure any changes are regulated and

guidelines are up$to$date.

• =roviding advice,information to the government and professionals to promote the

science involved in the research% and aid society in understanding the benefits

Experiment-based questions

Oser)ing mitosis

• Cut OImm tip from a growing root.

• =lace root on a watch glass% then add hydrochloric acid.

•

Add drops of stain to dar"en chromosomes and ma"e them more visible undermicroscope (credit e)ample. e1g1 toluidine blue*.

• arm watch glass using a 8unsen burner.

• =lace root tip on a microscope slide.

• @se a mounted needled to brea" the tip open and spread it evenly.

• Add more drops of stain and place a cover slip over it.

• S/uash the cover slip.

• arm slide to intensify stain.

• Repeat e)periment to increase reliability.

Totipotency & Tissue Culture

• Single cell ta"en from a growing area (credit e)ample – e1g1 root*

• idea that cell is placed in a sterile growth medium.

• idea that the growth medium contains nutrients and growth hormones.

• plant cell will +grow , divide , e/- into unspecialised cells .

• idea that unspecialised cells will differentiate into specialised cells if the conditions

are optimum

• Cells will grow and differentiate into an entire plant

Plant tensile strength

• Attach each of the four fibres to a clamp stand at one end.

• 3ang weights from other end.

• Add one weight at a time to the fibres until they brea"

• Record the mass ta"en to brea" each fibre.

• More mass greater tensile strength.

• Repeat e)periment to increase reliability.

• Heep variables constant – such as length of fibres% temperature% and humidity.• =rotective gear must be worn.


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6n)estigating plant mineral deficiencies ;anuary ?'

•

4dea of genetically similar plants e1g1 clones% cuttings% e)plants or seedlings fromsame parent plant .

• plants all of same + age ,si!e - (at start* .

• reference to at least five nutrient broths with different (nitrate* concentrations .

• sensible range of different nitrate concentrations either side of and including 7PP

(ppm* .

• correct reference to any t!o abiotic variables that need to be "ept constant (volume

of mineral solution , si!e of container , amount of light* .

• idea of sensible measure of growth e1g1 mass , number of leaves , length of roots

,height of plant .• time allowed for growth + wee"s , months -.

• appropriate reference to repeats% e1g1 replication at each concentration or repeating

the whole e)periment

Anti,microial properties of plants

• &a"e plant e)tract by drying and grinding.

• Soa" in ethanol.

• Bilter li/uid bit.• Evenly spread bacteria on +agar , nutrient plate , e/-.

• Dip disc of absorbent paper in plant e)tract.

• Soa" a disc in ethanol to act as a control.

• =lace discs on plate% widely apart.

• 4ncubate plate to allow bacterial growth.

• idea that an +inhibition !one , clear patch , e/- (on the lawn of the bacteria* will be

present if plant has antimicrobial properties.

• no inhibition !one should be present on control disc.

edexcel bio 2 notes (1)

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