biol 2 aqa, aqa, biology

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  • Created by: Alice
  • Created on: 06-05-11 15:31


Sampling; random sampling

sampling bias


using a large sample size

Causes of variation:

  • Mutations; random changes to genes
  • Meiosis; nuclear division forms gametes
  • Fusion of gametes; in sexual reproduction offspring inherit from parents

Environmental Influences- plants in poor light

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Types of Variation

Variation due to genetic factors:

  • A character displaying variation usually controlled by a gene.

Variation due to environmental influences:

  • normal distribution curve
  • Diet

Mean and Standard Deviation

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CT- single rings                                                           (

AG- double rings                                                                         

3 hydrogen bonds link CG

2 hydrogen bonds link AT

Function of DNA- hereditary material responsible for passsing genetic info form cell to cell

Adaptations: Stable, pass without change, can carry large amount of genetic information.

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The Triplet Code

What is a gene?

Genes are sections of DNA that code for specific polypeptides.

The Triplet Code

Each amino acid has own code of bases on DNA

As code has 3 bases its called triplet code


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Allele- form of a gene


                           DNA combines

                      w/ proteins, which is coiled,

                    then into loops, which pack

                  together to form chromosome

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Homologous chromosomes

  • Occur in pairs
  • homologous pairs= diploid number, in humans=46
  • 2 chromosomes that determines same genetic characteristics but not identical
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Process of Meiosis

1) homologous chromosomes pair up and chromatids wrap round each other, these may be exchanged by crossing over, by the end of this homologous pairs have been separated into different cells.

2) Chromatids move appart, 4 cells have been formed

Locus- the position of a gene on a chromosome of DNA molecule

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Independant segregation of Homologous Chromosomes

  • chromosomes line up alongside homologous partner
  • lying side by side organised randomly
  • one of each will go to daughter cell
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Genetic combinations

Genetic recombination by crossing over

  • Chromatids twist round each other
  • portions of chromatids break off
  • these portions rejoin with homologous chromatids

New combinations are produced

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Genetic Diversity

Genetic diversity- variation in a species due to difference in alleles

Genetic Bottleneck- when a population suffers a dramatic loss in numbers. The new population will show much less variation to the fall in the number of alleles

  Founder effect- When a few individuals from a population colonize a new area. The new population will not have all of the alleles of the original population and shoe much less variation.

Artificial selection, choosing those with desired characteristics- selective breeding

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Taxonomic Definitions

Hierarchy- groups arranged on different levels

Analogous structures- structures with same function, but not based on phylogenetic relationships

Phylogenetic-  related through evolution.

 Artificial classification-grouping based on analogous structures

Natural classification- grouping things together based on homologous structure, and phylogenetic relationships.

  •  Species- Similar to one another but different to members of other species, capable of breeding to produce living, fertile offspring. 
  • Binomial system- Two names, Genus, Species

Homologous structures- based on phylogenetic relationships

Taxonomy- the classification w/ groups in a hierarchical order.

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( 4 polypeptide chains-Q' structure

Role of haemoglobin:

  • Readily associate w/ O2 at gas-exchange surface
  • Readily dissociate from O2 at tissues requiring it
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Why have different haemoglobin?

Haemoglobin with a high affinity for O2; take up O2 more easily but release it less readily

Haemoglobin with low affinity for O2; take up O2 less easily but release more readily

Different haemoglobin have different affinities for O2 due to differing amino acid sequence and tertiary structure

loading/associating- haemoglobin +O2

unloading dissociating- haemoglobin -O2

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Oxygen dissociation curves

(   further to the right in pressure= lungs

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Effects of Carbon Dioxide concentration

The Bohr effect- haemoglobin has a reduced affinity for oxygen, higher concentration of CO2, the more readily haemoglobin releases its O2.

( higher partial pressure- at the lungs

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Loading, transport and unloading of oxygen

The higher the rate of respiration -> the more CO2 the tissues produce -> the lower the pH -> the greater the haemoglobin shape change -> the more readily O2 is unloaded -> the more oxygen available for respiration

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Surface are to volume ratio

small animals= large surface area to volume ratio, lose heat rapidly, so have a high metabolic rate

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joined by condensation reactions linked by glycosidic bonds 

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Role of Starch

  • Energy storage
  • as its insoluble in water, doesn't diffuse out of cells easily
  • compact, stored in small space
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  • shorter chains than starch
  • more highly branched than starch 
  • animal starch, as mainly stored in small granules in the liver of animals
  • as made of smaller chains; more readily hydrolysed to a-glucose
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  • made of B-glucose!
  • Different structure- OH group reversed
  • forms straight unbranched chains, running parallel 
  • Weak H bonds, but as so many of them overall is fairly strong
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Plant Cell Structure

Leaf palisade cell

  • long thin cells-> continuous layer to absorb sunlight
  • numerous chloroplasts 
  • large vacuole pushing chloroplasts to the edge
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  • Transport Water
  • Thick cell walls
  • As they mature they walls incorporate a substance called lignin and the cells die
  • the end walls break down, allows cells to form a continuous tube to form
  • like a straw as its hollow
  • the lignin often forms rings or spirals arounf the vessel
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Replication of DNA

Semi-conservative replication

  • DNA helicase separates strands
  • free nucleotides match up to complimentary bases
  • DNA polymerase continues to attract complimentary nucleotides
  • Two identical strands of DNA are formed
  • Each strand retains half the original DNA, so is semi-conservative
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Evidence of semi-conservative


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Interphase- proteins synthesised, DNA replication, organelles grow and divide

Metaphase- chromosomes arrange themselves at the centre (equator) of the cells

Anaphase-- spindle pulls appart, chromatids move to pole of spindle

Telophase- chromatids become indistinct, nuclear envelope reforms

Cytokinesis - the cell division

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Treatment- preventing DNA from replicating; interphase

or inhibiting the metaphase stage, interfering with spindle formation

Cancer cells have fast rate of division

Treatment of chemo in doses , to not kill of healthy body cells

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Cell differentiation and organisation

cell-differentiation=process in which a cell becomes more specialised

Tissue- group of same type of cell working together to perform specific function

Organ- Tissues coordinated to perform variety of functions

Organ systems-digestive, respiratory, circulatory

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Exchange between organisms

Features of specialised exchange surfaces:

large SA:V

very thin- short diffusion pathway

partially permeable, to allow selected materials across

movement of internal/environmental medium, to maintain a diffusion gradient

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Gas-Exchange Insects

Waterproof coverings- over body surfaces

Small SA:V

Spiracle- air pore

Trachea- strengthened by rings 

Tracheoles- smaller tubes into body tissues, atmospheric air brought straight to respiring tissues

Along a diffusion gradient

Ventilation- movement of muscles to create mass movements of air in and out of tracheae 

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Gas-Exchange Fish


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Gas Exchange leaf


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Leaf Tissues


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Circulatory system of a mammal


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Blood Vessels


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ARTERY-carry blood away from heart- O2, to arterioles

Vein= carry blood to heart, de- O2, to capillaries

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Artery structure related to function-

thick muscle layer- to constrict/dialate

thick elastic layer- high blood pressure

thick wall- resists vessel bursting under pressure

Vein structure related to function-

thin muscle-carry blood away from tissues

thin elastic layer- low pressure

Valves- to prevent backflow

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( one cell thick, short diffusion path,highly branched, large surface area for diffusion, spaces between lining, white blood cells can escape

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Arterioles carry blood under lower pressure than arteries

Thicker muscle layer than arteries- controls blood flow, movement into capillaries

thinner elastic layer than arteries- blood is under lower pressure

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Return of Tissue fluid to the circulatory system

  • loss of tissue fluid from capillaries reduces hydrostatic pressure inside them
  • at venous end , has lower hydrostatic pressure than outside it in tissue fluid
  • tissue fluid is forced back into capillaries by the higher hydrostatic pressure inside them
  • osmotic forces from proteins in blood plasma pull water back into capillaries
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Movement of water through roots


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symplastic pathway- as result of osmosis, through cytoplasm

apoplastic pathway- through cell wall

uptake of water by root hairs

long, thin maximum surface area

thin surface layer- shorter diffusion path

water moves in by osmosis as root has lower water potential than soil as has solutes eg amino acids etc

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Movement of water up stems

out through stomata when humid, stomata are open, H2o moves out

across a leaf:

mesophyll cells lose water to the air spaces

(replaced by xylem by apoplastic/symplastic pathway)

these cells now have a lower water potential,  they in turn take up water by osmosis


Water molecules-cohesive (stick together) by H bonds as H2o evaporates out of leaf by transpiration

water forms continuous pathway across mesophyll cells and down the xylem

water drawn up when evaporated

this is process is called the TRANSPIRATION PULL

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Factors that affect transpiration:

  • Light-stomata open in daylight, water moves out of stomata (evaporate)
  • Temperature-how much air can hold- hotter more, water potential of air, speed at which molecules move
  • Air movement-water vapour builds on underside of leaf, if breezy it carries the water vapour, changes water potential gradient by altering rate of water vapour removed
  • Humidity-affects water potential between air spaces in the leaf and the atmosphere
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( capillary tube w/bubble in

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  • shoot cut under water to prevent air being drawn into stem up through xylem which would stop transport of water
  • Potomer filled with water trying to avoid bubbles
  • joints sealed with agar jelly
  • millimetre scale used
  • potometer set up under water
  • air bubble introduced into capillary tube

to measure water lost, calculate volume of capillary tube, then treat it as a prism to measure volume of water lost in millimetres cubed per however long

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  • thick cuticle- forms waterproof barrier, less water can escape
  • hairy leaves- trap moist air near to leaf surface
  • stomata in pits/grooves- to trap moist air next to leaf and reduce water potential gradient
  • spines for leaves, reduce surface area, slower rate of diffusion
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Artificial classification- dividing organisms up by eg, if they had wings

natural classification- based on evolutionary relationships, based on shared features,groups in a hierarchy in which groups are contained within larger groups on different levels, with no overlaps

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Evidence for relationships between organisms

Comparison of DNA base sequences- due to mutations the sequences of bases of DNA of new species will change, similarity in bases-close related species

DNA hybridisation:

  • DNA from 2 species extracted & cut
  • DNA from one is labelled
  • mix both sets, DNA heated to break hydrogen bonds
  • mixture cooled to allow combination
  • non-complimentary bases don't join
  • more heat required to break strands, more closely related
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Courtship behaviour

recognise members of same species- to produce fertile offspring

identify fit mate- fertile

form a pair bond-lead to successful mating and raising of offspring

Synchronise mating- so it takes place when maximum chance of the sperm and egg meeting

can see how closely related animals are by comparing similarities/differences in courtship behaviour

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Genetic Variation in bacteria

Mutations- random

Conjugation, bacterial cell transfers plasmid                          linear strand forms                                                                                                           new plasmid


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Gene transmission

Horizontal gene transmission- Conjugation, passing DNA to another bacterial cell, can go between other species, resistance spreading to other pathogens if present at the same time

Vertical gene transmission- a mutation, bacteria becomes resistant to antibiotic, high proportion of resistant bacteria, they then grow and divide

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How antibiotics work: 

  • by preventing bacteria from making normal cell walls
  • By inhibiting the synthesis and assembly of important peptide cross-linkages in bacterial cell walls
  • Weakened walls, so when water moves in by osmosis, cell bursts by osmotic lysis
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Biodiversity- Species diversity

Ecosystem diversity- refers to range of different habitats within a particular area

Measure of species diversity, 2 components;

  • the no. different species in a given area
  • the proportion of the community that is made up of an individual species

Species diversity equation:

d = N (N-1)               d= species diversity index    N=total no organisms all species

     En (n-1)               n=total no organisms each species  E= the sum of

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Species diversity and human activities

Impact of agriculture:

  • reduced genetic diversity, reduced alleles

Impact of deforestation:

  • deforestation- loss of biodiversity
  • loss of species
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These are really good. The only problem is that some of the cards are blank, which I found a bit troublesome when I tried to print it. But these are brilliant, thank you!

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