bio unit 2

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  • Created by: charlie
  • Created on: 17-02-14 15:31

types of variation

1. different species = INTERSPECIFIC VARIATION 

2. same species = INTRASPECIFIC VARIATION 

INTERSPECIFIC 

largely due to differences in DNA : 

  • structure + sequeunce of genes in each organism 
  • way in which genes expressed 

INTRASPECIFIC 

  • GENOTYPE = genetic makeup (collection of alleles inherited from parents) 
  • PHENOTYPE = collection of observabe features (GENOTYPE + ENVIRONMENT) 
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types of intraspecific variation

DISCONTINUOUS 

  • features fall into one category or another 
  • controlled by single alleles (individual either has or doesnt have)
  • e.g. BLOOD GROUPS 

CONTINUOUS 

  • show a whole range of values 
  • most fall into mid range = NORMAL DISTRIBUTION 
  • POLYGENIC = controlled by several genes 
  • influenced by enviro. factors more than discontinuous
  • e.g. height, shoe size... 
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normal distribution, mean + standard deviation

NORMAL DISTRIBUTION =

  • when plotting graph, most individuals in middle + few in extremes 

MEAN =

  • arithemetic average 

STANDARD DEVIATION =

  • spread of data around the mean 
  • shown in width of curve 
  • range on either side of the mean 
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causes of variation

MUTATION IS THE SOURCE OF ALL VARIATION :

  • change in base sequence of DNA --> used in protein synthesis --> change in A.A sequence --> fold + bend into different shaped protein --> new alleles 

OTHER SOURCES OF VARIATION 

  • 1) CROSSOVER in meiosis
  • 2) INDEPENDENT ASSORTEMENT in meiosis 
  • 3) RANDOM FERTILISATION OF GAMETES (all sperm + ova genetically unique) 
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genetic diversity - artificial selection

'take the individual animals with the most desirable features + breed together'

PROBLEMS

  • INBREEDING - reduces genetic variation 
  • closely related individuals share same genes (faulty alleles) that can be paired up if mate 
  • hard to identify faulty genes in heterozygous animals as not expressed 
  • therefore don't know which ones will breed to proudce homozygous offspring 
  • more likely offspring are TT or tt instead of Tt 

ETHICS 

  • higher % of abnormalities = unnecessary suffering 
  • ethical guidelines = animals should be no worse than parent stock had they not been manipulated

can benefit animals = improved resistance to disease / remove characteristics that cause injury 

benefit humans = efficient food production / lower prices 

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genetic diversity - founder effect + population bo

FOUNDER EFFECT 

  • new population established by small number of individuals 
  • carry only small fraction of original populations genetic variation 
  • new population therefore distinctively different from parent population (genotye + phenotype)

GENETIC BOTTLENECKS 

  • large proportion is killed/ prevented from reproducing 
  • then recovers from few individuals 
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cell differentiation

  • early embryo cells are unspecialised - potential to differentiate - (STEM CELLS) 
  • stem cells are TOTIPOTENET = power to turn into any cells type 

each body cell has full set of genes - key to differentiation is SELECTIVE ACTIVATION 

TISSUE = aggregation of similar cells 

  • e.g. nerve, muscle, connective, epithelial 

ORGANS = aggregations of tissues performing specific physiological function 

  • e.g. heart, liver, kidney 

SYSTEMS = groups of organs work together to acheive major physiologcial function 

  • e.g. digestive, repiratory, nervous, circulatory 
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size and surface area

S.A : vol. 

  • affects how quickly substances are exchanged 
  • small organisms have large SA:vol. 
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exchange organs + mass transport systems

  • organism needs supply every cells with substances + remove waste to avoid damage 
  • different sized organisms do this in diff. ways:

SINGLE-CELLED ORGANISMS:

  • substances DIFFUSE directly into/out of cell across cell surface membrane 
  • diffusion rate is QUICK - short diffusion pathway 

MULTICELLULAR ORGANISMS:

  • diffusion across outer membranes too slow:
  • 1)  some cells deep in the body - large diffusion pathway
  • 2)  low S.A:vol ratio - difficult to exchange enough enough substances to large vol. animal 
  • use specialised EXCHANGE ORGANS (e.g lungs)
  • also need efficient system to carry substances (MASS TRANSPORT):
  • e.g. mammals- (CIRCULATORY SYSTEM) uses blood to carry substances 
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heat exchange

  • metabolic activity inside animals creates heat 
  • staying at right temp. is difficult + influenced by size + shape 

BODY SIZE 

  • HEAT LOSS DEPENDS ON S.A:vol ratio 
  • larger SA = easir to lose heat 

BODY SHAPE 

  • compact shape = small SA:vol ratio (MINIMISES heat loss)
  • less compact = large SA:vol ratio (INC. heat loss)

ADAPTIONS FOR HEAT EXCHANGE 

  • animals body shape is ADAPTED to suit ENVIRONMENT 
  • E.G. ARTIC FOX - (cold temp)    small ears + round head (MINIMISE)
  • AFRICAN BAT-EARED FOX - (hot temp)    large ears + pointed nose (INC.)
  • EUROPEAN FOX - (intermediate temp)    fairly pointed/round head + medium ear size 
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heat exchange - behavioural + physiological adapti

ANIMALS WITH HIGH S.A:VOL RATIO LOSE HEAT QUICKLY 

  • evaporates from their surface 
  • problem for animals in hot regions 
  • desert animals have KIDNEY ADAPTIONS - produce less urine 
  • animals in colder regions have HIGH METABOLIC RATES to compensate for heat loss (PHYSIOLOGICAL ADAPTION) 
  • need to eat large amounts of HIGH ENERGY FOODS (nuts)
  • smaller mammals have thick layers of fur to hibernate 

ANIMALS WITH LOW S.A:VOL RATIO LOSE HEAT RELATIVELY SLOWLY

  • in hot regions e.g. elephants have LARGE FLAT EARS (inc. SA)
  • hippos spend much of their day IN THE WATER (BEHAVIOURAL ADAPTION) 
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gas exchange

GAS EXCHANGE SURFACE :

  • where gas exchange takes place (boundary between enviro. + internal)
  • inc. rate of diffusion : LARGE SA + thin SHORT DIFFUSION PATHWAY + STEEP concentration gradient 

GAS EXCHANGE IN SINGLE CELLED ORGANISMS 

  • DIFFUSION through outer surfaces 
  • large SA + thin SHORT PATHWAY so NO NEED for system 
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gas exchange in fish

'SPECIAL AS LOWER CONCEN. OF O2 IN WATER THAN AIR' 

GILLS 

  • GILL FILLAMENTS - large SA for exchange of gases + thin 
  • LAMELLAE - cover gill fillaments - INC. SA even more - lots of capillaries + thin 

COUNTER-CURRENT SYSTEM 

  • 'blood flows through lamellae in one direction + water flows in opposite direction'
  • water with relatively high O2 concen. flows next to blood with low O2 concen. 
  • STEEP CONCEN. GRADIENT = high diffusion rate 
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gas exchange in dicotyledonous plants

  • need CO2 for photo. + rid waste product O2 
  • need O2 for resp. + rid waste product CO2 

main gas exchange surface = MESOPHYLL CELLS (large SA) 

  • gases move in + out through special pores in epidermis (STOMATA/STOMA):

- open to allow exchange of gases 

-close if plant losingtoo much water 

  • GUARD CELLS control opening + closing 

DIAGRAM 

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gas exchange in insects

microscopic air-filled pipes - TRACHEAE (used for gas exchange) 

  • air moves IN through pores on surface (SPIRACLES) 
  • O2 travels DOWN concen. gradient to cells 
  • CO2 from cells moves DOWN own concen. gradient to SPIRACLES to be realease to enviro.
  • TRACHEAE branch to smaller TRACHEOLES - thin permeable walls to individual cells 
  • O2 diffuses directly to respiring cells - insects CIRCULATORY SYSTEM DOESNT TRANSPORT O2 
  • use rhythmic abdominal movement to move AIR IN + OUT  of spiracles 
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control of water loss

EXCHANGE GASES MAKES YOU LOSE WATER 

ADAPTIONS for too much water loss 

INSECTS 

  • close spiracles using muscles 
  • waterproof + waxy cuticle all over body reduces evap 
  • tiny hair around spiracles which reduce evap

PLANTS

guard cells become FLACCID which CLOSES stomata 

XEROPHYTES live in warm/dry/windy conditions: (DIAGRAM)

  • stomata sunk IN PITS to trap water vapour - reduces evap - lower diffusion gradient 
  • CURLED LEAVES with stomata inside protecting from wind 
  • layers of HAIRS on epidermis - trap water vapour - lower diffusion gradient 
  • REDUCE number of stomata + waxy/waterproof cuticle - reduces evap
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circulatory system

FUNCTION 

  • multicellular organisms have low SA:VOL ratio = need system to transport materials 

STRUCTURE 

  • made up of HEART + BLOOD VESSELS (arteries, arterioles, capilaries, veins)
  • blood transports: respiratory gases, products of digestion, metabolic wastes + hormones 
  • pulmonary artery     -          HEART                    LUNGS       
  • pulmonary vein        -         LUNGS                    HEART        
  • aorta                        -          HEART                    BODY 
  • vena cava                -         BODY                       HEART 
  • hepatic artery          -          BODY                      LIVER 
  • hepatic vein            -           LIVER                      VENA CAVA 
  • hepatic portal vein  -          GUT                         LIVER 
  • renal artery              -          BODY                      ARTERIES 
  • renal vein                 -          KIDNEY                   VENA CAVA  
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arteries, arterioles, veins

ARTERIES 

  • from heart (high pressure)
  • walls thick + muscular 
  • have elastic tissue to cope with high pressure 
  • edothelium (inner lining) folded (allow stretch) 
  • only PULMOARY ARTERY carries de-O2 blood 

ARTERIOLES

  • directed to different areas of demand by muscles inside 
  • contract to restrict or relax to control blood flow 

VEINS 

  • back heart (low pressure)
  • wider lumen with little elastic/muscle tissue 
  • VALVES - stop blood flowing backwards 
  • flow is helped by contraction of surrounding body muscles 
  • only PULMONARY VEIN carries O2 blood 
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capillaries + tissue fluid

ARTERIOLES BRANCH TO CAPILLARIES 

  • substances are exchanged 
  • found very near cells in exchange tissues (e.g. alveoli)
  • short diffusion pathway - one cell thick + close to exchange tissues 
  • large number INC. SA 
  • networks of capillaires in tissue - CAPILLARY BEDS 

TISSUE FLUID 

  • 'fluid that surrounds cells in tissues' 
  • made from substances that leave blood - NOT RED BC OR LARGE PROTEINS (too big)
  • cells take in O2 + nutrients from tissue fluid + release metabolic waste 
  • SUBSTANCES MOVE OUT OF BLOOD CAPILLARIES BY PRESSURE FILTRATION: 
  • ARTERIAL END  (high hydrostatic pressure)- pressure inside greater than tissue fluid - substances out 
  • VENOUS END (low hydrostatic pressure) - water potential inside lower thn in tissue fluid - some water in by osmosis 
  • excess tissue fluid drained to LYMPHATIC SYSTEM --> CIRCULATORY SYSTEM 
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water transport in plants + through root

HOW WATER ENTERS PLANT 

  • root hairs (inc SA) --> through cortex --> through endodermis --> into the xylem in the root 
  • always moves from less negative to more negative water potential - 
  • DOWN WATER POTENTIAL GRADIENT - keeps water moving in right direction 

WATER TRANSPORT THROUGH ROOT 

1) SYMPLAST WAY 

  • through cytoplasm 
  • cytoplasm of neighbouring cells connected through PLASMODESMATA (small channels in cell walls)

2) APOPLAST WAY 

  • through cell walls (diffusion or spaces)
  • when gets to ENDODERMIS CELL LAYER - path blocked by waxy strip (CASPARIAN STRIP)
  • now water takes SYMPLAST pathway - through CONTROLLING cell membrane 
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water movement up a plant

AGAINST THE FORCE OF GRAVITY IN 2 WAYS: 

1) COHESION + TENSION 

  • water evap. from leaves at top of xylem --> tension created (suction) --> pulls water --> water molecules cohesive (stick together) --> some are pulled + others follow --> whole column of water through xylem moves UPWARDS --> water enters stem through routes 

2) ROOT PRESSURE 

  • water transported into xylem in roots --> creates pressure 
  • shoves water already in xylem up further 
  • weak pressure (not used in BIGGER plants alone) 
  • helps young small plants where leaves developing 
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transpiration

'EVAPORATION of water from plant's surface (especially leaves)' 

  • water evap. from moist cell walls + accumulates in spaces between cells in leaf 
  • stomata OPEN --> moves OUT down water potential gradient 

FACTORS AFFECTING TRANSPIRATION RATE 

  • LIGHT -     lighter = faster (dark stomata usually closed)
  • TEMP. -     higher = faster (molecules more energy -evap. faster - inc. water potential gradient) 
  • HUMIDITY -     lower = faster (dry air - inc. water potential gradient) 
  • WIND -      windier = faster (air movement blows away outside water molecules - inc. water potential gradent) 

MEASURING TRANSPIRATION - POTOMETERS 

  • measures water uptake by plant - assumes uptake is directly due to water lossed by leaves 
  • make sure that no air enters xylem (due it underwater)
  • increase SA by cutting stem at slant 
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mass transport

  • organs of gas exchange need distribution network 
  • VASCULAR SYSTEMS (plants have phloem + xylem) (animals have circulatory)
  • movement of large vloumes of fluid + dissolved substances within transport system know as MASS FLOW 
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classification systems

'the act of arranging organisms into groups based on their similarities + differences' 

  • science of classification - TAXONOMY 
  • taxonomy makes it easier for indentifying organisms 
  • TAXONOMIC GROUPS - orgerd into hierarchy 
  • HIERARCHY = 'system where smaller groups contained within larger groups - organisms can only belong to one group at each level' 
  • KINGDOM -- PHYLUM -- CLASS -- ORDER -- FAMILY -- GENUS -- SPECIES 
  • as you move DOWN hierarchy MORE GROUPS at each level but FEWER ORGANISMS in each group 
  • e.g. SPECIES ONLY CONTINS ONE ORGANISM - that are able to reproduce to give fertile offspring 
  • scientists constantly UPDATE classification systems because of NEW DISCOVERIES + NEW EVIDENCE about known organisms (DNA sequence) 
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phylogenetics + classification problems

'study of evolutionary history of groups of organisms' 

  • whos related to who + how closely related they are 
  • closely linked to CLASSIFICATION as grouping of organisms needs to reflect on evolutionary relationships 

CLASSIFICATION PROBLEMS 

  • can't always see their REPRODUCTIVE BEHAVIOUR (reproduce to give fertile offspring) because: 
  • they're extinct 
  • reproduce asexually - never together 
  • practical + ethical issues - cant see in the wild (geography) + not in lab (unethical)
  • therefore use other techniques 
  • e.g. compare DNA (more common = more closely related)
  • however no clear cut off to say how much shared DNA used to define species 

naming species (genus+species)- scientists communicate in standard way with no confusion 

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classification - comparing DNA

1) DNA SEQUENCING 

  • looking at orger of bases - closer related have high % similarity of order 
  • led to new classification systems (e.g. in plants) 

2) DNA HYBRIDISATION 

  • DNA from 2 diff. species collected - separated into single strands + mixed 
  • if BASE SEQUENCE is the same H-bonds form between base pairs 
  • more DNA bases that HYBRIDISE together = more alike DNA is 
  • DNA heated to separate strands again 
  • SIMILAR DNA = MORE H-BONDS = HIGHER MP (more energy needed) 
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classification - comparing proteins

1) COMPARING A.A SEQUENCES 

  • sequence of A.A in protein is coded for by base sequence of DNA
  • related species have similar base sequence + therefore SIMILAR A.A SEQUENCES in proteins

2) IMMUNOLOGICAL COMPARISONS 

  • ANTIBODIES to determine how similar two proteins are
  • antibodies bind to proteins in specific manner - SIMILAR PROTEINS bind to same antibodies  
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classification - courtship behaviour

'carried out by orgnisms to attract a mate of the right species. can be simple/complex' 

e.g. simple 

  • releasing a chemical / using a sound / visual displays 

complex 

  • dancing / building (shelters)

CLASSIFY species 

  • SPECIES SPECIFIC - only members of same species will do + respond 
  • prevents interbreeding + makes reproduction more successful 
  • ready to mate - 
  • minimum chance of conception - 
  • recognise own species to produce fertile offspring -
  • no agression triggered -
  • directs to area where mating takes place -
  • identifies who takes control of situation -
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