A2 Biology - Part 1

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  • Created by: Rosa
  • Created on: 29-09-13 12:40

Mrs Millard - Productivity- Topic 5

PRODUCTIVITY = It is the amount of energy input into a TROPHIC level (level in a food chain) that is converted into biomass (amount of material in all of the organisms in that level/material in all organisms e.g. proteins , lipids) . Rest of energy is lost , mainly heat.  Along the food chain less energy is transferred from one trophic level to the next approx 10% transferred 90% LOST

  • PYRAMIDS - numbers = misleading no. of organisms in a trophic level at 1 time. 
  •   - biomass = always like a pyramid shape , realistic but kills organisms 
  •  - exception in sea with phytoplankton and zoo plankton (on top but more) as they have a high produtivty rate and reproduce rapidly 
  • -pyramid of energy - amount of energy in trophic level over a period of time always pyr.shape
  • light energy is reflected or is the wrong wavelength (plants- green light not good) 
  • PRODUCERS LOSSES - heat due to metabolic rate 
  • PRIMARY CONSUMERS LOSSES - egestion (getting rid of undigested food) , excretion (getting rid of waste products made by body), heat loss from respiration- CO2 breathing (metabolic proccess) , muscle contraction - SAME FOR SECONDARY CONSUMERS
  • Active transport (movement of molecules against conc.gradient) inefficent photosynethesis
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Mrs Millard - Productivity (2)- Topic 5

  • 10% RULE - only 10% energy transferred from one trophic level to the next 
  • mammals and birds are endothermic , so maintain a constant body temp. which is best for reactions . On a cold day lose more heat use more energy to keep warm- reduce 10% rule 
  • SA:vol - small SA:vol it will keep more heat - 10% rule increase - more transferred to biomass
  • Carnivores - have efficent digestion system , less faeces produced as less roughage eaten than herbivores so more energy into biomass , higher then 10%. But 3rd in trophic level - 90% eneregy loss between traophic levels 1 & 2 and another 90% between 2 & 3- more links in food chain less efficent 
  • PRODUCTIVITY MEASURED = energy in trophic level converted in to biomass , for a period of time , for an area ---- kJ m-2 yr-1 
  • GPP (gross primary productivity) - all biomass produced by a plant per m2 per year - proteins , lipids - Sugar cane has high GPP as no limiting factors for photosynthesis e.g high light intensity and grows straight to intercept more light , weeds killed no interspecific competition , added fertilisers. 
  • Some GPP used by plant for making organic molecules ,growth , storage - losses=respiration
  • NPP =GPP - R ... biomas potentially avaliable for the primary consumer. 
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Mrs Millard - Agricultural Ecosystems - Topic 5

AIM = to reduce loss so increase productivity 

  • Rearing Animals (livestock)- keep food chain short , reduce no. of stages where energy is lost, much energy from sun is transferred to humans.  We can restirct their movement , resuce heat loss , feed a controlled diet so not malnourished and use hormone supplements such as growth hormone 
  • Growing plants (crops) - keep NPP as high as poss - need GPP to be big and losses small. Need PS efficency of crop as high as possible such as high light intensity , lots of CO2 + water , and optimum temp - reducing effect of limiting factors 



  • cheap,large amount of food. - control conditons for max.yield- welfare for animal considered - takes up less space then free range


  • does not consider 5 freedoms e.g, freedom from hunger + thirst- welbeing of animals sacrifced for human gain - use of antibitotics , hormones may harm humans health- use of fossil fuels for keeping sheds warm
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Mrs Millard - Pest Control - Topic 5

  • PESTS = any organism that lowers the productivity of crops 
  • WEEDS = interspecific competition - outcompete crop plants 
  • INSECT PESTS = feed directly on crop plant - they decrease area for PS , some damage roots and disrupt flow of sugar e.g. **** the phloem (this can also spread disease) 

PESTICIDES - they are specific to a pest and does not damage the plant , its quick to react and long lasting , cheap and easy to use. 

  • CONTACT PESTICIDES - can also kill BENEFICIAL predators, it is sprayed on the crop , it must contact pest e.g. insect- enters  through spiracles - easy but needs frequent top up 
  • SYSTEMIC PESTICIDE- absorbed by crop into tissues , affects pests feeding on crops but wont affect beneficial insects , normally sprayed on leaves and absorbed - or can reach roots of weed and kills whole weed
  • RESIDUAL PESTICIDES - longlasting onto soil , kills insects eggs,fungles & spores
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Mrs Millard - Resistance to Pesticides - Topic 5

When the use of the pesticide no longer kills enough of the pest population. The pest has become resistant to the pesticide. 

Development of Resistance : 

  • In pest population there is variation due to a mutation occuring 
  • The mutant allele codes for the protein that makes the pest resistant 
  • Pesticide kills the pest except the one with the mutant allele 
  • these survive & reproduce and pass on the mutant allele to their offspring - so more of pest population is resistant 

PEST RESURGENCE = recovery of pest population - goes higher than before 

BIOLOGICAL CONTROL - intro. of a natural predator in the area to reduce pop. of pest

  • not all pests are eaten but this is ok if no. of pest remains well below the level where economic damage occurs - not all pests eaten becuase they hide from predators - eggs may have been born by time prey eats. 
  • Advanatges - works reducing pest nos. without harming benefical organism, long lasting use INTERGRATED CROP MANAGEMENT -e.g. rostating crops , using fertilisers - max. productivity 
  • Problems - pest not completley irradicated so could come back if predator dies out - take too long to work
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Mrs Millard - DDT - Topic 5

DDT was used in 1950s

DDT is stored in fat tissue but is not broken down. Each organism in food chain eats many organisms in the trophic levels below so takes in lots of small doses of DDT which builds up.

DDT effects many birds shells as it means there is not enough calcium in adult birds so when they lay eggs the shell breaks under mothers weight while she incubates the shells 

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Mrs Millard - Fertilisers and Productivity - Topic

  • Fertilisers increase productivity and yield aswell as providing minerals such as Nitrates (N) - to make amino acids - proteins and growth, Potassium (K) - need to activate some enzymes ,Phosphate (P) - to make ATP and phospholipids 

Eutrophication - is the proccess by which nutrients build up in bodies of water - it occurs mainly in freshwater lakes - Proccess: 

  • most lakes and rivers there is little nitrates and so nitrate is a limiting factor for plant and algal growth 
  • due to leaching nitrate conc. increases it ceases to be a limiting factor and plants and algae grow exponentially 
  • as algae grow mostly at the surface , upper water becomes densley populated with algae - ALGAE BLOOM - it absorbs light and prevents light reaching lower depths 
  • light becomes limiting factor for growth of plants and alage at lower depths so they die
  • sapribiotic algae uses the dead plants and algae as food so grow exponentially - they need oxygen for their respiration so increase demand for o2 - conc of o2 in water decreases and nitrates are released from dying organisms 
  • oxygen then is limiting factor for pop. of aerobic organisms e.g. fish - so die - now little competition for anerobic organisms so they grow exponetially- they decompose material releasing nitrates & toxic waste e.g. hydrogen sulphide - water becomes putrid 
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Miss Smith - Human Populations - Topic 1

  • IMMIGRATION = influx of individuals from another country
  • EMMIGRATION = out flow of individuals from the country
  • CRUDE BIRTH RATE = no.of births in a year / total pop. that year X 1000
  • CRUDE DEATH RATE = no.of deaths in a year / total pop. that year X1000
  • POP. GROWTH RATE = crude birth rate - crude death rate

Population limited by - abiotic factors , minerals , ions , light , temp. , water , space and biotic factors such as competition , disease , reproductive potenital , food supply 

Birth rate affected by economic conditions , religious backgorunds, social pressures and conditions , birth control and political factors 

Death rate affected by , age profile (more old people) , life expectantcy at birth , food supply , safe drinking water , medical care, war, natural disasters


  • STAGE 1 - stable population , high birth and death rate
  • STAGE 2 - increasing population , high birth rate and reducing death rate 
  • STAGE 3 - increasing population , falling birth and death rate
  • STAGE 4 - stable population , low birth and death rate
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Miss Smith - Human Populations - Topic 1 - (2)


  • wide base = high birth rate 
  • narrow base = low birth rate 
  • sides are vertical and many people over age of 65 = low death rate 
  • large base and sides go in v.quickly = high death rate 
  • barrel shaped = falling birth rate & rising life expectancy 

SURVIVAL CURVE - shows the percentage of people still alive at different ages - used to calculate average life expectancy - go to 50% on y axis and draw line across until S curve then draw down - S-CURVE IS BELOW!

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Miss Smith - Competition- Topic 1

  • Intrespecific competition = one species may become extinct as competiton between different species but both population may drop in size - it is competitive extinction where no two species can occupy the same niche 
  • Intraspecific competition = competition between members of the same species , which leads to natural selection , it can reduce population growth and lower general carrying capacity
  • Competition may include for food , light , space , water, breeding sites and mates
  • Predation = the pressure of a predator (the herbivore in the case of plants) - reduce numbers
  • Community = defined as all the populations of different organisms living and interacting in a particular place at the same time - e.g. oak woodland , oak trees , nettles , bluebells , fungi
  • Habitat = place where a community of organisms live , within an ecosystem there are many habitats. For example in an oak woodland the leaf canopy of the trees is habitat for blue **** but a decaying log is a habitat for woodlice
  • Niche = how an organism fits into the environment - it refers to where an organism lives and what it does there - includes all abiotic and biotic factors required for an organism to survive, reproduce and maintain a viable population - species may be similar but aspects of their behaviour maybe different - no two species occupy the exact same niche
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Miss Smith - The Carbon Cycle - Topic 6

Carbon is in the nutrient cycle. 

  • main source of carbon for organisms is from the CO2 in atmospherehigh turnover of carbon:
  • photosynthetic organisms remove it from air to build up macromolecules e.g fats and proteins 
  • all organisms return carbon to atmosphere by respiration 
  • conc. of carbon in atmoshere differs as at night no light so no PS can take place.- though respiration still happens at night , it is less as temp. is lower - in summer more PS so less CO2 in air 

Levels of CO2 in atmosphere have increased as: 

  • combustion of fossil fuels - e.g. coal and oil - release co2 preciously locked up in fuels
  • deforestation- removed large amounts of photosynthesising biomass so less CO2 removed from atmosphere 

CO2 is a greenhouse gas so is contributing to global warming. Much CO2 stored in oceans dissolves excess carbon , aquatic photosynhesisng organisms PHYTOPLANKTON use dissolved carbon to form macro molecules in their bodies.

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Miss Smith - The Carbon Cycle - Topic 6 - 2

  • Carbon passed along food chains  - when died both plants and animals broken down by SAPROBIOTIC mircorganisms , DECOMPOSERS -  they secrete the enzymes , enzymes then break down complex molecules to smaller and soluble that then the SAPROBIOTIC microogranisms absorb by diffusion - carbon from dead organism is then released by respiration of decomposer 
  • if decay is prevented then they are fossilised , bottom of ocean and form sedimentary rocks - carbon eventually returns to atmosphere as these rocks are weathered 
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Miss Smith - Nitrogen Cycle- Topic 6

All living organisms require nitrogen , however very few can use nitrogen gas directly. Plants mainly take up nitrogen in the form of nitrate ions from soil , they are absorbed using active transport. Animals obtain nitrogen by eating and digesting these plants. There are 4 main stages in the nitrogen cycle. 

  • AMMONIFICATION - production of ammonia from organic ammonium containing compounds e.g. urea , protein and nucleic acid (found in faeces). Saprobiotic mircroorganisms including fungiand bacteria feed off this material releasing ammonia which forms ammonium ions in the soil - here nitrigen returns to the non-living component of the eco-system
  • NITRIFICATION- oxidiation reaction happens in 2 stages - 1) oxidation of ammonium ions to NITRITE ions . 2) oxidation of nitrite ions to NITRATE ions - requires oxygen so soil with many air spaces needed.
  • NITROGEN FIXATION - nitrogen gas is converted into nitrogen containing compounds - most important form of nitrogen fixation is carrid out by microogranisms of which there are 2 types- 1) free-living nitrogen-fixing bacteria - bacteria reduce gaseous niitrogen to ammonia which then used to manufacture amino acids, nirtogen rich compounds released when they die   2) mutulastic nitrogen-fixing bacteria - bacteria live in nodules of roots of plants (pea) - obtain carbohydrates from plants and plant aquires aminio acids from bacteria 
  • DENITRIFICATION - soils become waterlogged and have lack of oxygen , type of mircroogransm present changes - increase in anaerobic denitrifying bacteria which convert soil nitrates into gaseous nitrogen, therefore reduces avalibility of nirogen containing componds for plants - land to be productive need to prevent de-nitrifying bacteria 
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Mrs Millard - Photosynthesis - Topic 3





WATER + CO2 -------sunlight/chlorophyll----------> GLUCOSE + O2 

6H20 + 6CO2 -----------------------------------------------> C6H12O6 + 6O2 

Important as it makes glucose for respiratory substrate , also converted to make amino acids for growth and enzymes. Converts insouluble starch to stored glucose and into lipids and cellulose for cell walls , production of glucose important as eaten in food chains.

Important as can convert into light energy into chemical energy. Simple organic molecules e.g. H20 built up into organic molecules such as glucose- also makes 02. There are 2 stage -- 1) LIGHT DEPENDENT STAGE --2) LIGHT INDEPENDENT STAGE

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Mrs Millard - Photosynthesis - Topic 3 -- (2)


  • light intensity - used for energy to excite the electron in chlorophyll to make ATP for light independent reaction 
  • CO2 conc - needed for providing catbon to make carbohydrate aswell as O2. Hydrogen is added to reduce the CO2 
  • temperature - optimum temp. needed for enzyme reactions to occur so there are enough collisions and E-S complexes formed , enough product made prevents denaturation if at optimum
  • (water avalibility) - photolysis for light dependent reaction   

                              - e-  to replace e- lost from chlorophyll 

                              - H+ to reduce NADP ---> LIR 

                              -  chorophyll needed to absorb the light energy +  provide for excited e- 

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Mrs Millard / Miss Smith - What Statistical Test??

  • Will your investigation involve finding the no. of individuals in particular categories? 

YES - use X2 test!! - it gives a measure of the deviation between the observed + expected results 

X2 = SUM OF (O-E)2 / E                   O=observed value    E= expected values 

Degrees of freedom = no.of samples - 1 

Chi 2 value must be greater than value in table (0.05) column if you are to reject null hypthesis 

Null hypothesis = there is no difference between the observed and expected results 

  • Will your investiagtion involve looking for associations between measurments from the same sample ? 

YES - use Spearmans Rank Correlation - LOOK AT SHEET 

  • Will your investigation involve looking for differences between mean values? 

YES - use standard error and 95% confidence limits

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Miss Smith - Respiration- Topic 4

2 different forms of cellular respiration: 

  • AEROBIC respiration = requires O2 and produces CO2, water and ATP
  • ANAEROBIC respiration = takes place without O2 and produces lactate in animals or ethanol and CO2 in plants - but only little ATP

AEROBIC respiration is split into 4 parts : 

  • GLYCOLISIS - splitting of 6-carbon glucose molecules into 3-carbon pyruvate molecules 
  • LINK REACTION - conversion of 3-carbon pyruvate into molecule into CO2 and 2-carbon molecule called ACETYLCOENZYME A 
  • KREBS CYCLE - intro. of acetylcoenzyme A into a cycle of oxidation-reduction reactions that yield some ATP and a large no, of electrons 
  • ELECTRON TRANSPORT CHAIN - use of electrons produced by Krebs Cycle to synthesise ATP - water producd as by-product 
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Miss Smith - Respiration, Glycolysis- Topic 4

  • occurs in cytoplasm of all living cells 
  • a hexose (6-carbon) sugar (glucose) split into 2 molecules of 3-carbon pyruvate molecules

Can be split into 4 stages: 

  • ACTIVATION OF GLUCOSE BY PHOSPHORYLATION - glucose made more reactive by addition of 2 phosphate molecules. Phosphate molecules from hydrolysis of 2 ATP to ADP , provides energy to activate glucose (lowers activation energy) 
  • SPLITTING OF PHOSPHORYLATED GLUCOSE - each glucose molecule split into X2 3-carbon molecules known as triose phosphate
  • OXIDATION OF TRIOSE PHOSPHATE - Hydrogen removed from triose phosphate molecules and transferred to a hydrogen-carrier molecule , known as NAD to form REDUCED NAD
  • PRODUCTION OF ATP - enzyme-controlled reactions convert triose-phosphate into 3-carbon molecule PYRUVATE - in proccess 2 molecules of ATP are regenerted from ADP 


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Miss Smith - Respiration, Link & Kreb Cycle- Topic


  • occurs in matrix of mitchondria 
  • its aim is to create acetyl co-enzyme A for the Krebs Cycle
  • Pyruvate is oxidised by removing hydrogen , hydrogen accepted by NAD to form reduced NAD, later used to form ATP 
  • 2 carbon molecule (acetyl group) combines with molecule called co-enzyme A to produce acetylcoenzyme A .
  • CO2 molecule for each pyruvate is produced 
  • EQUATION = pyruvate+NAD+coA--------------> acetyl CoA + reduced NAD + CO2 

KREBS CYCLE - X2 for every glucose

  • happens in matrix of mitochondria , produce hydrogen for electron transport chain
  • 2 carbon acetylcoenzyme A from link reaction combines with a 4 carbon molecule = 6 carbon molecule 
  • 6-carbon molecule loses CO2 and hydrogens to ive 4-carbon molecule and ATP as a result of substrate-level phosphorylation - now can combine with acetylcoenzyme A , cycle repeat.
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Miss Smith - Respiration, Electron Transport Chain

  • Where? It happens in cristae of mitochondria (inner membrane) 
  • Why? large SA for co-enzyme + enzyme to attach to 
  • Purpose - to use energy from the electrons within the hydrogen atoms to convert ADP+Pi into ATP


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