biology-unit 2 revision powerpoint [autosaved]

7/28/2019 Biology-Unit 2 Revision Powerpoint [Autosaved]

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Topic 3- Voice of the Genome


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Electron microscope (EM) Beam of electrons used to produce

magnified image

Electron beam generated by electrongun, focused by electromagnets

Membranes and other structuresstained by heavy ions, stand out as

dark areas EM better than optical microscope

laser beam short than light rays


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Cell

In multicellular organisms, cells are specialised for aparticular function

E.g. Epithelial cells, muscle cells


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Tissue

Similarcell types from the same originworkingtogether for the same function


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Organ

Severalcell types working together for many functions

Made up of tissues


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Organ system

A group of organs working together to carry out a

particular function.

E.g. The circulatory system


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Nucleus

Largest in Eukaryotic cell (10-20 micrometres in

diameter)

Double membrane with pores

Contains chromosomes


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Nucleus

Nucleolus

Pore

Outermembrane

Innermembrane

Nuclearenvelope

Nucleoplasm

Chromatin


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Histone

Highly alkaline, positively-charged proteins in the

nucleus of eukaryotic cells. Package and order DNA into structural units called

nucleosomes.

Main component of chromatin


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Nucleolus

Site of ribosome synthesis

Consists of protein and RNA


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Mitochondria Rod shaped/cylindrical organelles

Large (0.5-1.5 micrometres wide, 3-10 micrometres long)

Found in all cells, large numbers in metabolically active

cells (e.g. muscle fibres, hormone secreting cells.)

Surrounded by a double membrane


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Mitochondria


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Endoplasmic reticulum (ER)

Outer membrane of nucleus

Rough Endoplasmic reticulum (RER)

Smooth Endoplasmic reticulum (SER)


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Endoplasmic reticulum


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RER Ribosomes attached to outer surface

Vesicles formed from swellings at margins thatbecome pinched off

Site of synthesis of proteins that are packaged invesicles and exit the cell (e.g. digestive enzymes)


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SER

No ribosomes

Site of synthesis of proteins needed by cells (e.g.lipids)


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Golgi apparatus Stack-like collection of flattened membranous sacs

Smooth (no ribosomes), curved cisternae

One side formed by fusion of membranes of vesicles

from ER, other side vesicles are formed from swellingsat margins that become pinched off

Modifies proteins by addition of carbohydrates


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Golgi apparatus

Proteinmaterialmoves fromconvex side toconcave

Cisternae


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RER and Golgi apparatus Protein produced by ribosome

Ribosomes attached to RER

Proteins stored within RER Proteins folded with RER lumen

RER produces vesicles, packages proteins

Vesicles fuse with Golgi

Golgi modifies protein, carbohydrate added

Water removed to concentrate

Golgi produces lysosomes/ secretory vesicles


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Lysosomes Small spherical organelles, single membrane

Contain concentrated mixture of hydrolytic enzymeswhich are produced in Golgi apparatus or RER

Breakdown contents of imported food vacuoles

Then broken down into products of digestion which

escape into cytoplasmAlso fuse and digest broken-down organelles in

cytoplasm


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Lysosomes


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Microtubules Straight, unbranched, hollow cylinders (25nm wide)

In the cytoplasm of Eukaryotic cells

Consists of tubulin (a globular protein)

Built up/broken down when needed


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Microtubules


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Centrioles Centrosome= 2 perpendicular centrioles

Single centriole consists of 9 triplets of microtubules

Before nuclear division they separate, moving to the

poles of the cell


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Centrioles


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Eukaryotes Eukaryotic cells = good nucleus

True nucleus present

Plant and animal cells

Large 80s ribosomes present

RNA polymerase made up of 14 subunits


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Origin- mitochondria and

chloroplasts

Prokaryotes taken up into food vacuoles of eukaryotes

for digestion

Useful, integrated into host cell

Explains why mitochondria and chloroplasts have aDNA double helix like bacteria and ribosomes likeprokaryotes


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Animal Cells


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Plant Cells


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Plant Cell Wall Rigid

Consists of cellulose fibres which run through otherpolysaccharides (e.g. pectin, hemicelluloses)

Sticky middle lamella holds neighbouring cellstogether

Lignin makes wall strong and impermeable


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Chloroplasts Part of group of organelles known as the plastids

(which are only found in plant cells)

Large, green, biconvex

Site of photosynthesis

Double membrane


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Chloroplasts


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VacuoleA fluid-filled space in the cytoplasm surrounded by a

membrane called the tonoplast

Contains a solution of sugars and salts called the cellsap.


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Prokaryotes

Cells containing no true nucleus

Before the nucleus

Bacteria and cyanobacteria (photosynthetic bacteria)

Small 70s ribosomes present


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Mitosis


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Interphase G1 = First growth phase. New organelles synthesized in

the cytoplasm, intense biochemical activity andaccumulation of stored energy

S = DNA synthesis, each chromosome copies itselfby replication, forms chromatids

G2 = Second growth phase. Intense biochemicalactivity and increase in the amount of cytoplasm


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Prophase Chromatids condense , forming bivalents

Nuclear envelope breaks down

Nucleolus breaks down

Spindle fibre begins to form

Centrioles migrate to opposite poles


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Metaphase Centrioles move to opposite ends of the cell

Microtubules of the cytoplasm start to form spindle

Microtubules attach to centromeres of chromatids Chromatids line up on equator


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Anaphase Spindle fibres contract

Chromatids separate

Centromere leads

Spindle fibres attached to Kinetochores

Move to opposite poles of the cell


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Telophase Chromosomes are in the process of decondensing and

are becoming visible

Nucleus visible

Nucleolus present

Spindle broken down

2 separate nuclei visible Chromatin visible

Evidence of cell plate formation


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Cytokinesis Cell organelles (e.g. mitochondria, chloroplasts) are

evenly distributed between the cells

In-tucking of plasma membrane at equator, pinchingcytoplasm in half

Two cells form


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Chromatids Daughter strands of a duplicated chromosome joined

by a centromere


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KinetochoreA protein structure on chromatids where the spindle

fibres attach during cell division to pull sisterchromatids apart


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Cell cycle Mitosis

Used for growth and asexual reproduction


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Meiosis Gamete formation

2 stages: Meiosis I and Meiosis II

Prophase I, Metaphase I, Anaphase I, Telophase I,Cytokinesis, Prophase II, Metaphase II, Anaphase II,Telophase II, Cytokinesis

Four daughter cells produced, haploid

Same as mitosis, repeats (no interphase on second cycle)


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Genetic variation in Meiosis

Crossing over

Independent assortment


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Crossing over Pairs of homologous chromosomes (bivalent)

Bivalent coils and shortens continuously, chromatidsbreak

Broken ends re-join at corresponding sites, chiasmaforms

Lengths of genes exchanged

New gene combinations produced


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Independent assortment Bivalents line up randomly on equator during meiosis I

Orientation at the equator of the spindle is random

Possible gene combinations= 223


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Gene locus

The location of a gene on achromosome


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Sexual Reproduction Fusion of two gametes (fertilisation) = zygote

Meiosis halves the normal chromosome number

Gametes= haploid (contains half of the normalchromosome number)

Diploid= cells that contain the full number ofchromosomes


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Asexual Reproduction Single organism produces offspring, clones

No gamete formation, cells of new offspring produced by

mitosis

Advantage = a large number of individuals canbe quickly produced by a single

organism Disadvantages = no variation in offspring, genetic

mutations will be passed on,exponential growth


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Fertilisation in mammals Occurs in upper part of oviduct

Erect penis into vagina, ejaculation

Vagina acidic, semen alkaline to neutralise so sperm can survive Waves of contractions by muscles in uterus walls to draw semen

into oviduct

Sperm reaches ovum, enzymes break acrosome

Digests through zona pellucida

Contents of cortical granules released by exocytosis to hardenmembrane and prevent other sperms entering (polyspermy)

Meiosis II is completed

Nuclei fuse


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Haploid cells Cells with half of the total number of chromosomes , n

In humans, n= 23

Gametes

When fertilisation occurs, zygote will have the full numberof chromosomes

Enables mixing of alleles


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Sperm cell Formed in seminiferous tubules in the testes

Acrosome contains hydrolytic enzymes to

digest through ovum wall Large no. of

mitochondria respiration, energy (ATP)forsperm

Flagellum

mobility so sperm can swim downfallopian tubes to egg

Streamlined less resistance to motion

Receptors bind to egg cell surface membrane


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Enzyme release Sperm comes into contact with zona pellucida

Acrosome swells

Vesicle/ acrosome fuses with sperm cell surface

membrane

Enzymes (e.g. acrotin) are released by exocytosis


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Egg cell


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Structure of a flowering plant

(angiosperm)


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Fertilisation in Flowering plants Pollen grain germinates on the style, pollen tube grows

down towards ovary (growth controlled by tubenucleus)

Pollen grain contains tube nucleus and generativenucleus

Pollen germinates, division of generative nucleus, twohaploid gamete nuclei form and move down pollentube and enter embryo sac

One fuses with egg cell (zygote) other with 2 nuclei (triploid cell-seeds storage tissue, endosperm)


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Stem Cells Undifferentiated cell

Can give rise to other types of cell

Can proliferate

Totipotent = can differentiate into any cell type

Pluripotent = can differentiate into almost any celltype

Multipotent= is restricted into what type of cell it canbecome (e.g. bone marrow cell)


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Stem Cell Sources Umbilical cord blood

Blastocyst

Bone marrow

Brain/skin/liver cells

Addition of adult nucleus to enucleated egg cell


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Reasons for stem cells research Creates use for spare embryos from IVF, which

otherwise would be destroyed

Can obtain embryonic stem cells at eight-cell stagewithout causing embryo death

Increases understanding of infertility, miscarriagesand diseases


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Reasons against stem cell research

Potential life

Embryo should be considered full human status fromthe moment of its creation

Not natural

Stem cell research is expensive


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IVF In vitro fertilisation

Drug injected to block normal menstrual cycle steps

Synthetic FSH injected superovulation

Male provides semen sample, processed to concentratehealthiest sperms

Laparoscope with ultrasound used to remove some egg

cells from ovaries Mixed with sperms in dish and incubated

Up to three embryos transferred back into uterus


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Reasons for IVF Enables couples with fertility problems to have

children

Enables cancer survivors to have children usinggametes harvested prior to treatment

Can avoid inherited diseases

Children will be much longed and cared for


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Reasons against IVF Not natural

May result in multiple births

Excess of unwanted children in orphanages and foster

homes

Excess embryos are potential human lives


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Blastocyst

A hollow ball of cells that forms five days afterconception

Outer blastocyst cell layer goes on to form the placenta

Inner cell mass goes on to form tissues of developing

embryo, pluripotent stem cells


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Cloning Produces genetically identical offspring

Somatic cell taken from donor sheep, egg cell takenfrom second donor sheep

Somatic cell nucleus placed inside egg cell nucleus

Electric shock given to start mitosis, grown in culture

Placed in surrogate, clone produced that is identical to

somatic cell donor


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Problems with cloning Many attempts to produce live-born offspring has been

unsuccessful

High proportion of offspring produced by cloning havehealth problems (Dolly the sheep developed arthritis

at a fairly young age, had to be put down)


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Gene Expression

Some genes are switched on (expressed), producingactive mRNA which is translated into proteins withinthe cell

However, others arent


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- galactosidase

Enzyme

Produced by the prokaryote Escherichia coli

Breaks down the carbohydrate lactose into glucose andgalactose


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When lactose is absent Lactose repressor molecule binds to operator gene in

the DNA

RNA polymerase cannot bind

No mRNA produced

Prevents transcription of- galactosidase gene


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When lactose is present Lactose molecule reacts with the regulator protein

Prevents it from binding with the operator gene

Lactose-metabolising enzyme is transcribed, lactosemetabolised

Once lactose is used up, repressor molecule blockstranscription again


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Regulator gene

A gene that is involved in the turning on or off thetranscription of structural genes


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Operator gene

A sequence of bases when a repressor binds to it


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Structural geneA gene whose product is an enzyme, or protein that is

involved in structural functions

E.g. The gene which codes for -galactosidase


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When gene expression goes wrong FOP fibro dysplasia ossifcans progressiva

Inherited, caused by gene mutation

Genes that produce proteins needed to become aspecialised bone cell not switched off in white blood cells

Tissue damage wbcs produce protein, diffuses intosurrounding muscle cells, causes muscles to express othergenes which turn them into bone cells


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Master genes E.g. Fruit flies Drosophila

Control the development of each segment of the body

Master genes discovered when mutations causing segmentsnot to develop properly were looked at

Produce mRNA which is translated into signal proteins

Signal proteins switch on genes that produce proteinsneeded for cell specialisation in each segment


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Genes active in flower formationWhen a plant starts to flower, cells in meristem

become specialised, forms organs that make up flower

Gene expression across meristem determines whichstructures will form

Three genes (A, B and C) determine which organ typewill be produced in each area of meristem


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A B

C

Sepals

Carpels

Petals

Stamens


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Apoptosis

Cell death

When suicide genes are expressed, nucleus andcytoplasm fragments


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Polygenic inheritance

The inheritance of phenotypes that are determined bythe collective effect ofseveralgenes

These genes are often located at loci on different

chromosomes


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Multifactorial

Phenotypes that are determined by several genes andenvironmental factors

E.g. Skin colour


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Discontinuous variation


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Continuous variation


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Height Multifactorial

Continuous variation

Humanheight increasingevidence that taller men have morechildren, greater movements ofpeople (less inbreeding), better

nutrition, improved health, end ofchild labour (more energy intogrowth), better heating of housesand quality of clothes (more energyinto growth)


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Melanin Dark pigment in skin and hair (more melanin = darker)

Made in melanocytes found in skin and hair follicle root

Melanocyte activated by melanocyte-stimulating hormone(MSH)

Receptors for MSH on surface of melanocyte cells

Melanocytes place melanin on melanosomes which are

transferred to surrounding skin and hair cells

Surround nucleus, protect DNA from harmful UV


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Effect of UV on melanin Increases amount of MSH on MSH receptors

Melanocytes more active, skin darkens

Hair not darker, UV light causes chemical and physicalchanges to melanin and surrounding proteins in hair

cells

Hair lightens as melanin is destroyed


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MAOA Monoamine oxidase A, gene that occurs on Xchromosome

Catalyses breakdown of neurotransmitter in brainresponsible for regulation of behaviour and stress

Mutation, no enzyme produced

Studies suggest link between mutation and violentbehaviour


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Cancer Rate of cell division > rate of cell death

Causes growth of a tumour, often in tissue with highmitosis rate (e.g. lung, bowel)

Caused by DNA damage (mutation) (e.g. UV light,asbestos, carcinogens, in gametes)


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Oncogenes

Code for proteins that stimulate transition from onecell stage to the next

Continually active tumour


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Tumour suppressor genes

Produce suppressor proteins, stop cycle

Mutationcycle doesnt stop


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Topic 4- Biodiversity and Natural

Resources


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Xylem Water transport: Lumen enables vertical movement

of water

Waterproof prevents water loss

Pores enables sideways movement ofwater

Support: Lignin strength

Rings/spirals strength and flexibility


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Xylem


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Water transportation in xylem

Water evaporates from all surfaces of plant, mostly fromleaves

Water diffuses through stomata, down diffusion gradient(transpiration)

Water that leaves is replaced by water from roots

Water evaporation in substomatal cavities provide forceneeded to draw water up the plant by capillary action

(surface tension) Transpiration stream stream of water passing through

plant (continuous)


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Phloem Translocationmovement of sugars up and down the plant,

requires energy

Sieve tube elementsliving, tubular cells, connected end toend, cytoplasm is present but in small amounts, lacks a nucleusand most organelles for more space for solutes to move, cell

walls made of cellulose so solutes can move laterally a well asvertically

Sieve plates formed by perforations in cell walls

Companion cellscontrols the movement of solutes andprovides ATP for active transport in the sieve tube element.


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Phloem


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Sclerenchyma tissue

Dead cells

Form outer cap to vascular bundle

Impregnated with lignin

Strength

Sclerenchyma


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Vascular bundle

Phloem

Vascular

bundle

Stem


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Parenchyma

Plant cells turgid, vacuoles filled with cell sap

Contents push hard against walls which push againstsurrounding cells

Rigidity


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Lignin

Polymer produced by plant cells to strengthen the cell wall

Lignin impregnates cell wall, cells become lignified

Entry of water and solutes into them become restricted

Tonoplast breaks down, autolysis of cell contents (cellcontents broken down by enzymes and are lost)

Leaves an empty tube


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Water

Solvent

Thermal properties

High surface tension and cohesion Density and freezing properties


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Water - solvent

Many chemicals dissolve easily in water

Enables vital chemical reactions to occur in cytoplasm

E.g. NaCl Cl- ions attracted to +ve part of water

molecule whereas Na+ attracted to ive part

Polar molecules dissolve easily , hydrophilic


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Water thermal properties

Specific heat capacity is very high

Large amount of energy needed to break hydrogenbonds

Therefore, water heats up and cools slowly

Avoids rapid temp. changes in organisms

Water surface tension and


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Water- surface tension and

cohesion Hydrogen bonding strong cohesive forces

Cohesive forces between molecules surface tension(useful, pond skaters)

Adhesion hydrogen bonds between watermolecules and cell wall

W t d it d f i


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Water density and freezing

propertiesWater expands when it freezes

As it cools, molecules slow down, enables for max. no.of hydrogen bonds to form

Hydrogen bonds hold molecules further apart than inliquid ice less dense than water


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Transpiration

Process in which water vapour is lost from the leaf

Diffuses through stomata, evaporates off of leafsurface

Increase of rate of transpiration Increase windspeed, increase temperature, increase CO2concentration, decrease humidity


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Starch

Branched chain of single glucose units

1,6 and 1,4 glucose linkages formed by condensationreactions

Composed of more than one type of molecule(amylopectin and amylose)

All monomers have the same orientation


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Structure and function of starch

Consists of many glucose monomers glucose is therespiratory substrate

Large unreactive, in soluble, no osmotic effect

Compact can be stored

Branched increased mobilisation of glucose units


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Cellulose Straight chain of single glucose units

-1,4- glycosidic linkages formed by condensationreactions

Held together by hydrogen bonds between OHgroups (micro fibrils)

Alternate glucose units rotated by 180

Insoluble, tough, slightly elastic


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Cellulose micro fibrils

Flexible, inelastic, tensile strength

Hydrogen bonding between OH- groups

Several layers

Criss-cross arrangement


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Plasmodesmata

Microscopic channels that link adjacent cells, enabling

for transport and communication to occur betweenthem

Cytoplasm continuous between the cells
http://localhost/var/www/apps/conversion/tmp/scratch_2//upload.wikimedia.org/wikipedia/commons/2/29/Apoplast_and_symplast_pathways.svg


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Middle lamella

Pectin layer which cementstwo adjacent cells together

Dark line that is theboundary between one celland the next


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Pits

The main channels by which water may enter and

leave the plant cell

Forms where only a single cellulose layer is deposited

in the cell wall


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Pectin

Polymers of single galactose units

Soluble dietary fibre, daily intake = five grams

Become bound together by calcium ions, forming calciumpectate (present in middle lamella, glues adjacent cellstogether)

During fruit ripening, pectin broken down bypectinesterase and pectinase enzymes, fruit becomes softer

as middle lamella breaks down Gelling agent, thickening agent and stabiliser in foods (e.g.

in jam)


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Hemicelluloses

Short, branched polysaccharide

With pectin, acts as the glue

Binds to surface of cellulose and each other

Joins cellulose microfibrils together


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SeedsAdapted to protect embryo, aid dispersal and provide

nutrition for plant

Endosperm(storage)


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Seed banks

Only seeds with a living embryo are taken, detected usingX-ray

Seeds are cleaned, dried

Stored at low temperatures

Viability regularly tested

If viability decreases, collect fresh seed for storage


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Sustainability

Sustainability = resources that meet human needswhile preserving the environment

Starch is sustainable plant fibres can be regrown,renewable, CO2 release is equal to CO2 removed whencrop was grown

Oil isnt sustainable fossil fuel, non-renewable,releases CO2 into atmosphere, non-biodegradable


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Clinical trials

Animal testing (e.g. rats) legal requirement, to lookfor toxicity, well known metabolism, no harm to humans

Phase 1 Small dose of drug tested on a small no. ofhealthy individuals, check for side-effects

Phase 2 Tested on small no. of patients to measurementeffectiveness of drug

Phase 3 Double blind trial, testing on larger group ofpatients


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Double-blind trial

Some patients are given the new drug whilst others aregiven a placebo (e.g. sugar-coated dummy pill or old

drug) Doctors and patients do not know which one is the

new drug

Reduces bias

Can see if new drug works better than the placebo/ olddrug


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Three domains

Archaea

Eukaryote/ Eukarya

Bacteria


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Taxonomy The science of classification

Kingdom

Phylum

Class

Order

Family

Genus Species

Remember: King Peter Called OutForGenuine Scientists

Used in theBinomial system


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Species

A group of organisms with similar morphology,

physiology and behaviour, which can interbreed andproduce fertile offspring and are reproductivelyisolated from other species


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Habitat

A place where an organism lives


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Ecosystem

A community of organisms and their surroundings


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Community

The total of all populations living together in a

particular habitat


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Population

A group of organisms, all of the same species, and all

of whom live together in a particular habitat


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Adaptation

A process in which an organism becomes fitted to its

environment

Depends on: strength of selection pressure, size ofgene pool, reproductive rate of organism


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Types of adaptation

Anatomical (e.g. ears of African elephants largerthan Asian elephant due to environment)

Behavioural (e.g. sheep ignoring sounds which arenot important to them)

Physiological (e.g. formation of sun tan when skinis exposed to sunlight)


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Genetic Diversity

The number of different alleles in a population

Allele frequency


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Niche

The role of a species within a community


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Evolution

A change is allele frequency in a population overtime


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Process of evolution

A population has some naturally occurring genetic variation with new allelescreated through mutations.

A change in the environment causes a change in the selection pressures actingon the population.

An allele which was previously of no particular advantage now becomesfavourable

Organisms with the allele are more likely to survive, reproduce and so produceoffspring.

Their offspring are more likely to have the allele, so it becomes more commonin the population.


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Species richness

The total number of different species within a givenarea or community

Calculated using Simpson Diversity Index:

diversity = N(N-1)n(n-1)

Where

N = total no. of organisms ofall species found

n = no. of individuals of eachspecies


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Allele

Different forms of a gene

Dominant the gene that is expressed, masks thegenotype of the recessive allele

Recessive causes a phenotype only seen in ahomozygous genotype


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Punnet square

Shows the probability of an offspring having aparticular genotype


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Homozygous

When identical alleles of the gene are present on bothhomologous chromosomes


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Heterozygous

When an organisms cells contain two different allelesof a gene at a gene locus


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Phenotype

The appearance of a cell or organism

Caused by a contribution of genotype

Can be affected by environmental factors


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Abiotic factors

A non-biological factor that is part of the environment

of an organism (e.g. temperature)


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Biotic factors

Associated with competition within a single

population or between the members of differentpopulations.


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Endemism

When an organism is exclusive to one geographicallocation


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Zoos

Maintain endangered species

Education

Captive breeding programmes

Scientific research

Reintroduction into the wild Studbooks

d f


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Genetic drift

Genetic drift = change in allele frequency overtime

In a small population, some alleles may not get passedon by chance

Reduction in genetic variation

b d d


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Inbreeding depression

In a small population, likelihood of closely individualsmating increases

Frequency of homozygous genotypes rises, heterozygoteslost

Offspring inherits recessive alleles from both parents

Harmful effects, offspring less able to survive an reproduce,smaller, not live as long, females produce less eggs


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Experiments

i h


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Root tip squash 5mm of root tip cut, transferred to watch glass

Add 30 drops of aceto-orecin stain, 3 drops HCL

Heated 3-5 minutes (steam bath/Bunsen burner)

Tissues transferred onto microscope slide, root tipgently pulled apart (mounted needles)

More stain added, cover slip, tissue firmly squashed bythumb pressure

Examined under high power microscope Safety precautions: Cut away from oneself, wear a lab

coat

Mi l d fi i i l


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Mineral deficiency in plants 9 petri dishes (complete culture solution, minus

phosphorus, minus magnesium, minus nitrogen,minus potassium, minus iron, minus sulphur, minus

calcium, distilled water) 15cm3 of water in each

5 healthyLemna plants into each, add lids andincubate together for several weeks, examining twice a

week Record no. of live plants, green leaves, dead leaves,

length of longest root


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Antimicrobial properties in plants Crush extract (e.g. garlic or mint) in pestle with mortar,

10cm3 ethanol

Filter off ethanol

Add bacteria stain Bacteria need to be evenly distributed on sterile agar plate

Incubate to encourage bacteria growth

Measure diameter

Safety: Dont incubate at 37C (pathogens will grow),aseptic technique (prevent contamination of pathogens)

T il h f l fib


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Tensile strength of plant fibres Soak stem (with no leaves or flowers)

Extract bundles of fibres from stem anddry them

Add same masses each time until fibrebreaks, recording the mass required

Repeat experiment, using same length,diameter and fibre from same source

Safety precaution: Wear goggles in

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