bio unit 2

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) 

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... 

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 

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) 

'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 

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 

• 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 

S.A : vol. 

• affects how quickly substances are exchanged 
• small organisms have large SA:vol. 

• 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 

• 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 

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) 

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 

'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 

• 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 

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 

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

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  

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 

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 

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 ***** (CASPARIAN *****)
• now water takes SYMPLAST pathway - through CONTROLLING cell membrane 

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 

'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 

• 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 

'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) 

'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 

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) 

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  

'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 -