biology-unit 2 revision powerpoint [autosaved]
TRANSCRIPT
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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
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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