POPULATIONS AND ENVIRONMENTSPopulation: a group of interbreeding organisms of one species in a habitatCommunity: all the populations of different organisms living and interacting in a particular place at the same time; group of different species form a communityHabitat: where a community of organisms liveEcosystem: Made up of all the interacting Biotic and Abiotic factors Therefore two species which have different niches will provide a maximum yield as each will exploit the environment more effectively.Abiotic Factors: non- living factors that affect an ecosystem and its organisms such as temperature and rainfallBiotic Factors: living factors that affect an ecosystem and its organisms such as competition and predationEcosystem: made up of all the interacting biotic and Abiotic features in a specific areaEcological Niche: the role of a species in an ecosystem; it is governed by the adaptation of the animal to biotic and abiotic factors. INTERSPECIFIC COMPETITION TAKES PLACE WHEN TWO SPECIES HAVE OVERLAPPING NICHES (this is because no two species can coexist in the same habitat if they have the same niche). Therefore if two species are observed to compete then they must have the same niche.Species: a group of interbreeding individuals which do not normally breed with other species to produce fertile offspringFood Chain: a sequence of organisms in an ecosystem in which each is the food of the next organism in the sequenceFood Web: all the interconnected food chains in an ecosystemTrophic Level: a feeding level in a food wed, it shows energy transfers away from the producerThe primary consumer gains the most energy; therefore herbivores gain more energy than carnivoresPyramid of energy: a representation of energy at each trophic level, it is a triangular shape as energy is lost BETWEEN trophic levelsWhy ecosystems rarely have more than five trophic levels:Not enough energy left as there are energy loses between trophic levelsProducer: The first organism in a food chain, it is an autotroph; capable of manufacturing food by photosynthesisHow Producer converts energy to biomass:1) Uses energy for photosynthesis2) Materials are synthesised to be used for growth3) The chemical energy is storedWhy dry biomass of animals to dry biomass of plants is always a lot less than one:1) Plants are producers and animals are consumers2) Energy is lost between trophic levels due to loss of energy through respiration, heat, etc.Primary Consumer: The second organism in a food chain, obtains energy from the producer; herbivoreSecondary Consumer: obtains energy from the primary consumer; carnivoreDecomposers: Organisms that break down producers and consumers when they die and thus release minerals and elements which can be used by plantsHow Decomposers may work on dead matter to make the contents available to a plant:1) Secrete enzymes for digestion of dead matter, usually it is starch2) Digestion produces sugars and nitrogenous waste3) The nitrate (nitrogenous waste) is taken up by plants4) Decomposers absorb the sugars (glucose) produced from digestion and use them for aerobic respiration5) As decomposers respire they produce Carbon Dioxide may be used by the plant leaves in photosynthesis6) However they also use up Oxygen as they respire, therefore reducing diversity of oxygen dependant organisms7) Decomposers will also change subject to temperature and pHDifference between decomposers and detritivores: 1) Decomposers secret enzymes for extracellular breakdown of organic matter2) Detritivores ingest organic matterDetritivores usually increase the activity of microbial decomposers by:1) Breaking down larger pieces of organic matter2) Increase oxygen content for respiration of decomposersPyramid of Numbers: Representation of the number of organisms in each trophic level in an ecosystemLimitations of Pyramid of Numbers: 1) No accounts is taken of size2) Numbers of certain organisms can be so great that they cannot be represented using the same scale as other speciesPyramid of Biomass: A representation of the mass of each trophic level in an ecosystem = ALWAYS pyramid shaped (except one case where Zooplankton and Phytoplankton are involved).Carrying Capacity: The maximum population that a particular environment can hold

Abiotic Factors:1) Temperature; measured using a thermometerIn cold blooded animals: 1) Too high temperature; enzymes denature; growth stops. 2) Too low temperature; enzymes slow down; stop growthIn warm blooded animals: 1) Too high temperature; more energy spent lowering body temperature to optimum2) Too low temperature; more energy spent raising body temperature to optimumIn plants, when a plant is larger than another plant, it not only takes away the outcompeted plants sunlight, but also provides it with shade, therefore keeping the temperature constant; this can be a good and a bad thing.2) Light; energy source for plants, if it increases, then there is increase in rate of photosynthesis and therefore an increase in the population growth. It is measured using a light meter or light sensor.3) Water and Humidity; if water is scarce, then less organisms present. Humidity affects transpiration rate of plants and evaporation rate in animals. It is measured using a hygrometer.4) Wind Speed; Increases transpiration rate as it moves away the humidity bubbles at the stomata causing a more desirable diffusion gradient for water vapour5) pH; Influences enzyme activity. It is measured using a pH meter.6) Oxygen; It is an oxidiser which allows cellular respiration which is to allow continued release of energy from food. Oxygen also affects photosynthesis. It is measured using an oxygen-sensitive electrode.7) Wave Action; It may erode soil and rocks as well as moving any living organisms. It is measured using an anemometer8) Carbon Dioxide; It can be a limiting factor to photosynthesis. It is used in forming permanent plant tissues. It is measured using a gas analysis.9) Nitrogen; it is used by plants to make PROTEINAny abiotic measurement will be repeated several times at a site and then averaged. The measurements may be repeated over a course of a year, or day, etc.Some plants are more greatly affected by competition than others.From the above factors, the following can be limiting factors of photosynthesis (basically this is any factor that affects the rate of photosynthesis):1) Temperature- usually when this increases respiration and photosynthesis both increase2) Light (believe it or not some plants grow better when light intensity is LOW, they therefore can survive latter stages of succession)3) Oxygen4) Carbon DioxideA plant which has a higher rate of photosynthesis will outcompete other plant species.REMEMBER: Photosynthesis is the main route by which energy enters an ecosystem Ways in which larger plants affect smaller plants:1) Reduce light2) Reduce water3) Reduce mineral ions4) Reduce wind5) Increase humidity6) Reduce temperatureIt is best to carry out studies on animals in their natural habitats as this allows you to see the effect of biotic and Abiotic factors.Measurement used in order to find rate of photosynthesis: Oxygen produce per unit timeOut of the above, organisms would compete for light, water, carbon dioxide, nitrogen.

GREENHOUSESWhy you should not increase temperature in a greenhouse on a dull day:1) Temperature increases rate of respiration too, therefore the rate of photosynthesis will be too low to replace respiratory losses2) Not cost effectiveHow Carbon Dioxide is enriched in a greenhouse:1) Dry ice in the environment2) Combustion3) ManureCarbon Dioxide is not enriched above 0.1% in the greenhouse because:Not cost effective as other factors could then limit photosynthesisWhy Carbon Dioxide in a greenhouse is done in the winter:Cost of enrichment covered by extra cash gained from sale of crops as crops sell for more in the winter

Why yield of crop grown in greenhouse in winter is lower than in summer when enhancing conditions not applied:1) Lower light intensity limits photosynthesis2) Lower light duration limits photosynthesis3) Lower temperature limits photosynthesisHow conditions are enhanced:1) Carbon Dioxide enhanced by burning oil2) Heat enhanced by using heater3) Light enhanced by light left on for extra hours4) Fertilisers (contain nitrogen) enhanced by regularly applicationFarming Practises which increase the productivity of crops:1) Fertilisers added to soil2) Pesticides applied3) Selective breeding used4) Genetic modification5) Ploughing aerates soil and allows nitrification6) Crop rotation increases soil nutrients7) Irrigation removes the limiting factor of water8) Covers and netting protects against birdsWhy artificial fertilisers are applied to crops:1) Increases yields2) Replaces ions taken in by cropWhy extra artificial fertilisers are not applied:Increased application of fertiliser does not increase yields; uneconomical, known as the law of diminishing returnsA high concentration of fertiliser in soil can reduce plant growth:1) Fertiliser lowers soil water potential 2) Decreases potential gradient between plant and soil therefore water cannot diffuse from soil into plant via osmosisAdvantages of Inorganic/Artificial fertilisers than Organic/Natural fertilisers such as manure:1) Ions in readily available form2) Effects relatively rapid3) Easy to applyDisadvantages of Inorganic/Artificial fertilisers than Organic/Natural fertilisers such as manure:1) Quickly leached2) More likely to cause pollution3) Relatively expensive4) Production is energy consuming5) Natural fertilisers contain a wide range of elements6) Natural fertilisers aerate the soilHow features of a greenhouse control the physical environment:1) GLASS: allows light and heat through limits air movements2) BLINDS: controls light and heat entering glass3) VENTILATOR: 1) Allows entry of CO2, 2) Prevents excess humidity and 3) Limits spread of diseaseWhy water is needed in soil for plants:To allow stomata to open which then allows CO2 absorption

PESTICIDESParasites: Organisms that live on or in, host organisms.CHEMICAL CONTROL (sometimes called insecticide):Advantages:1) In pests such as weed, removal of weed actually leads to less competition2) If it is very low toxicity, it will not affect humans3) Acts quickly4) Can be applied to specific area5) Kills greater variety of pests

Disadvantages:1) Not all plants may be sprayed2) Some spray may wash of plants3) Pest may become resistant (grow immune to pesticide)4) Bioaccumulation 5) Kills beneficial organisms6) Enters food chain7) Residue is left on cropHow a pest becomes resistant: 1) There is variation in the pest population2) Mutation occurs3) This produces the allele giving resistance4) There is a selection pressure for this gene5) Therefore pests with this gene breed6) This leads to an increased frequency of surviving alleleAlthough pest plants are not wanted, they do increase the diversity of the environment as they attract new speciesPlants with large surface area to volume ratio are easily affected by pesticides as there is a shorter diffusion pathwaySYSTEMIC INSECTICIDE: Insecticides absorbed by plants allowing plant tissues to kill insects feeding on themAdvantages of Systemic Insecticide:1) Only affects an insect that eats plant (specific)2) Insecticide is not diluted which reduces the amount needed3) Insecticide does not cause eutrophicationSome plants can be made as a pesticide by incorporating the pesticide into genome of plant to allow plant to produce toxin, this called genetically modifying crops.Advantages of making Genetically Modified Crops against pests:1) More effective than other methods2) Poisons may harm other3) Prevent spread of disease4) Economic benefit to farmerDisadvantages of making Genetically Modified Crops against pests:1) Plasmid may enter another species2) May sterilise other species3) Disruption of food chainWhy there may be Chemical Pesticides in bodies of other organisms other than the pest:1) Insect may eat a high number of pests which have been affected by the Chemical Pesticide2) The insect cannot break down the chemical, therefore it remains in the insects bodyWhy resistant pests increase in number:They can survive the chemical; they then reproduce to allow the genes to be passed onBIOLOGICAL CONTROL (using a predator to control pest organism/ sometimes you can release sterile males of the pest):Advantages:1) If well trained, it will only attack the pests, i.e. specific2) Only one application is required and is therefore cheaper3) Safer as it does leave chemical residue4) Pests do not become resistant5) Application linked to life cycle of pest6) Maintains low level of pest7) Can be used in organic farmingDisadvantages:1) You do not completely remove pest2) Can only be used for glasshouse crops3) There is a cost of researching 4) It may become a pest itself5) May attack non-target species6) It is slower than chemical control7) It is more subject to environmental factors8) Difficulty in maintaining population of predator9) Cost of predatorIn Biological Control you must:1) Look for predator of same origin as pest; predator can survive in similar climate2) Study effect of predator on other organisms in laboratory; may outcompete native species or may attack them3) Release large number of predators; increases chance of successful introduction so that damage to crops is little 4) Ensure stable coexistence of predator and pest at low population densities; no further introduction requiredIn Biological Control, the pests cannot be completely wiped out because:1) Predator may die out2) Predator may become a pest itselfLethal Concentration: concentration which kills 50%Benefits of an Integrated Pest Management Scheme:1) If one method fails, the other is still partially effective2) Reduced amounts of pesticides needed3) Increases yield4) Less chance of resistance5) Less effect on food webs6) Chemical controls initial surges in pest numbers whilst biological gives longer term control of pestsHow you would know that a pesticide was working:Pest numbers decrease and REMAIN low

INVESTIGATIONIn all these investigations, we will be measuring the BIOTIC factors as biotic factors are living organisms.We can measure the biotic factors in 5 ways:1) Abundance of population: counting the number of organisms in the sample2) Richness of population: number of different species found in a sample3) Diversity of population: Simpson Diversity index which takes into account the richness and abundance4) Growth of population: comparison of growth with between species5) Biomass of population: used when studying productivity of an organismAbundance of the population:1) Frequency: the likelihood of the species occurring in a quadrat2) Percentage Cover: Estimate of the area within a quadrat that a species coversHow Percentage Cover of an organism of an area may be measured:1) Use of quadrats that are randomly placed2) Use a large number of quadrats so as to reduce sampling error3) Estimate percentage of area covered by organism (by counting all the squares occupies by the species)Why Percentage Cover is better to use than Frequency:1) Frequency is too large2) Plants are too smallSometimes, you may even lay quadrats every 10 metres rather than use random sampling, this is because:1) It is systematic sampling2) To establish a patternHow to place quadrats at random:1) Split area into squares and number them2) Draw numbers from a hatWhy quadrats must be placed at random:To avoid bias, generally whenever you collect animals/plants, whatever method it may be, randomness is most importantHow you would decide the number of quadrats to use:1) Take enough to carry out a statistical test 2) Take into consideration the amount of time you have to carry out the investigation3) Take a large enough number to make results reliable4) Ensure unnecessary extra quadrats are not placedWhat size the quadrat should be:1) Depends on size of animal2) If a species occurs in a series of groups in an area, then use a large number of small quadrats to give representative dataTwo methods of sampling a population:1) Systematic sampling2) Random SamplingSYSTEMATIC SAMPLING:

Transect: lines that allow us to sample along a changing habitat (usually used to measure distribution of a species from one habitat to another)Interrupted-Belt Transect: Quadrats are placed at intervals along the lineContinuous-Belt Transect: Quadrats are place along the entire lineA Point Transect: You record plants touching certain points along the line Line Transect: You record all plants touching the linePoint Transects and Line Transects are done without quadratsCharacteristics of a Line Transect: it is quick but can be unrepresentativeCharacteristics of a Belt Transect: it involves more work but can generate more complete data Transects are usually used in environments such as down a rocky shore, into a forest or down a mountain side.Purpose of a Chi-Squared test:To compare different numbers collected from the two sites and show whether the differences are significant enough to confirm or reject the null hypothesisRANDOM SAMPLING:1) Divide study area into grid of numbered line2) Using random numbers, from a table or generated by computer, obtain a series of coordinates3) Take samples at the intersection of each coordinates of number of individuals and number of species4) Repeat many times and take a meanReasons why sample may not represent of whole population:1) Sampling Bias: investigators may make unrepresentative choices2) Chance: Even if sampling bias has been avoided you may still get a bias sample by chanceHow Mark-Release-Recapture can be used to estimate the number of a population that is MOBILE:1) Capture sample, mark and release2) The harming must not harm the animal, (mention method of marking)3) Take second sample and count marked organisms4) Use the LINCOLN INDEX which is (Number in sample 1 x Number in sample 2) Number marked in sample 2Things to ensure when using Mark-Release-Recapture:1) Animals are not harmed2) Animals must not be made less mobile or more visible to predators due to the mark; one way to do this is to mark the animal using an ultra-violet marking pen which can only be seen under ultra-violet light 3) Leave enough time for the marked individuals to redistribute themselves and mix with the population4) Ensure it is not breeding season of the animal, as breeding season increases the population size5) The mark must not be rubbed of or lost during investigation6) The population has a definite boundary so there is no migration7) The proportion of marked to unmarked in second sample is the same as the proportion of this in whole population8) Sampling method is the sameVERY IMPORTANT: sometimes, instead of marking the animal, they take the animals DNA, this is fine because finding the animals base sequence is like marking the animal, therefore finding the same base sequence again would show that the animal has been recorded before.Along with measuring the population size, the scientists are also recommended to measure the biotic and abiotic factors.Why population size may change during a year:1) Breeding2) Availability of food source3) Predator presence4) Variation in disease5) Temperature variation6) Availability of water

Precautions and ethical considerations when doing field work:1) Only work in places where risk of falling in water is small2) Only work in places where risk of pollution is small3) Ensure cuts and broken skin are covered4) Ensure all participants wash hands afterwards5) Ensure not to disrupt the food chain of the environmentPopulation size may vary as a result of:1) The effect of Abiotic factors2) Interspecific and Intraspecific competition as well as predationInterspecific Competition: competition between members of different species (it takes place when two species have overlapping niches)Therefore if two species have very different niches, then they will have very little Interspecific competition between themselves.If species A has a predator called Z, and species B has a predator called Y, and both species A and B eat from the same plants, then if size of predator Z decreases, the size of species B will also decrease, why:1) If predator z decreases, species A will increase (survive more)2) Therefore there will be more competition between species A and B for the plant3) Competition will result in species B size decreasingPredation can help other species:1) Predator eats a specific species2) The other species has less competition and therefore can now increase percentage survival rateIntraspecific Competition: competition between members of the same species Intraspecific competition tends to have a stabilising influence on population size because it is density-dependent.Although predators reduce population size of prey, they actually increase mean mass of prey:1) Predators kill prey therefore reducing prey population size2) Therefore less competition between prey population 3) More food available4) Therefore more food eaten by a single prey than would be eaten before presence of predator5) Therefore preys may be small in number but each one will be fatter than usualREMEMBER: species that are better camouflaged will survive against predators; this is a form of Directional SelectionAnimals that use snow as a camouflage against predators will be affected by global warming as global warming melts snowPopulation Growth:1) Lag Phase; small number of individuals reproduce slowly2) Rapid Growth Phase; increasing number of individuals reproducing3) Stable Phase; population GROWTH declines and population size remains stable4) Carrying Capacity is establishedPopulation Growth: (Births + Immigration)-(deaths + emigration), to work out just GROWTH RATE, you need birth rate and death rate, If a population stays the same size, then B + I = D + E, if a population is increasing in size, B + I > D + E If a population is decreasing in size, B + I < D + E(Immigration increases genetic variability as migrants bring in new alleles, therefore small populations have small genetic variability as their gene pool is small)Percentage Growth Rate: (Population change during period x 100) Population at start of periodBirth Rate: (Number of births per year x 1000) Total population that yearDeath Rate: (Number of deaths per year x 1000) Total population that yearIncrease in population size: (Birth Rate Death Rate) x current population, therefore overall population after increase will be:Increase in population + current populationAverage Life Expectancy: age at which 50% of the population in the sample used are still aliveHow to work out average life expectancy from a graph of number of survivors against age as a % of maximum:1) Divide the maximum number of survivors by 22) Go across this value and see what age it produces on the x-axis3) Divide the produced age by the maximum age, then multiply by 100A womans life expectancy can be longer than a mans because:1) Men have a higher risk of cardiovascular disease2) Men drink more and smoke more3) Men are involved in warDemographic Transition: Change in the population structure Examples of demographic transition: Increase in average life expectancy, lower death rates, higher birth rates

Analysing population pyramids:1) The wider the base of the pyramid, the faster the population growth2) If the base of the pyramid is narrow, this indicates a falling population 3) An age pyramid with a wide base that declines quickly and has a narrow tip indicates high infant mortality and short life expectancy

Survivorship Curves:Type I curve: long life expectancy, low infant mortality Type II curve: intermediate life expectancyType III curve: short life expectancy, high infant mortality

How a sample may be used as a control: Shows results without adding the element being experimentedFactors which could to decrease in death rate: 1) Improved medical care2) Improved nutrition and more food3) Improved sanitation4) Less disease5) Improved living conditions6) Improved economy7) War endsAverage Life Expectancy may increase:1) Improved medical care2) Improved nutrition3) Improved sanitation4) Lower infection rates5) Less disease6) Vaccination and heath education

ENERGYHow and why the efficiency of energy transfer is different at different stages in the energy transfer through an ecosystem:1) Over 90% of the suns energy is reflected into space by clouds and dust2) Not all wavelengths of light can be absorbed and used for photosynthesis3) The light might not fall on the chlorophyll molecule4) Efficiency of photosynthesis in plants is low approximately 2% efficient5) Some of the energy is lost by the consumers through release of heat, or by restoring heat depending on the environmental temperature6) Some of the energy is lost by the consumers through faeces7) Consumers may not eat all of their food/prey8) Food consumed may not be fully absorbed and digested9) Efficiency of energy transfer to consumers is greater than the efficiency of energy transfer to the producers10) Efficiency of energy is lower in older animals11) Carnivores use more of their food than herbivoresPercentage Efficiency of energy transfer:(Energy given out Energy provided) X 100

REMEMBER: When producers that are single celled, less energy will be lost between producers and primary consumers because:1) Single-celled producers are more digestible, therefore less energy lost in faeces2) All of the single-celled producer will be eatenHow energy from the sun may ultimately end up in dead plant matter:1) Photosynthesis will produce carbon containing substance2) When plants die out, these substances remainIntensive Rearing of livestock:1) Faster rate of growth2) Slaughtered while young so more energy transferred to biomass3) Fed on concentrated diets so higher proportion of food absorbed from gut i.e. higher proportion of food digested4) Heating so that no energy wasted maintaining body temperature (mammals are Endotherms-have high body temp) 5) Reduced movement, therefore less respiratory losses6) Plentiful food supply7) High survival rate as no predators8) Selective breedingHowever many of these methods require energy input usually in the form of burning fossil fuels.REMEMBER: Animals can lose energy (have a high energy expenditure) maintaining their body temperature if the environmental temperature is too high/too low by increasing respiration/metabolism (to increase body temperature if environmental temperature too low) or allowing heat to escape from the body (to lower body temperature if environmental temperature too high).This energy they have lost in maintaining temperature could leave them too weak to grow or breed.Residual Food Intake (RFI): difference between the amount of food an animal actually eats and its expected food intakeHaving animals with low RFI is better as it is more cost effective and allows more growth rate with the same amount of foodAny animal that eats more than what is required for it to fulfil its daily requirements will use the extra food for storage or growth.Indirect energy input: Energy required for producing things required in crop productionEnergy Efficiency: Energy in harvest crop total energy input, energy efficiency will be lower in well developed as they have more machines, therefore higher energy inputGross Production: Total quantity of energy that the plants in a community convert to organic matterNet Production (Plant): Gross Production Respiratory losses

ATP IN PHOTOSYNTHESISPhotosynthesis: 6CO2 + 6H2O C6H12O6 + 6O2; carbon dioxide reduced (gains electrons) to form glucoseRespiration: Glucose + Oxygen Carbon Dioxide + water + energy; oxidation takes place, electrons and energy lostATP:1) Provides energy in small, usable amounts for the wide variety of energy-requiring reactions2) Is relatively small molecule that can diffuse around the cell quickly3) It is soluble4) Mainly found in mitochondria5) Is extremely unstable and is constantly broken down and re-synthesised to and by ADP and Pi (free organic phosphate)Therefore it cannot be stored

Reasons why ATP is a suitable source of energy:1) Energy released in small amounts2) Soluble3) Involves a simple reaction4) Makes energy available rapidly5) Lowers activation energy6) It is reformedWhy it is important to synthesise large amounts of ATP:1) ATP is unstable2) ATP cannot be stored3) ATP is needed for processes such as active transport, etc.4) ATP only releases small amounts of energy

The reaction for ATP is: ATP + H2O ADP + Pi + Energy; this is a hydrolysis reaction

Why organisms need ATP:1) Metabolism such as polysaccharide synthesis from monosaccahrides, polypeptide synthesis from amino acids and DNA synthesis from nucleotides2) Movement3) Active Transport; provides the energy to change the shape of carrier proteins in a plasma membrane4) Maintenance, Repair and Division5) Secretion; ATP is needed to form the lysosomes necessary for the secretion of cell products6) Production of substances such as enzymes and hormones7) Maintenance of body temperature8) Activation of moleculesThe Light Dependent Reaction: Takes place in Thylakoids (membranes within the chloroplast that contain chlorophyll) Light energy hits chlorophyll which then excites and emits 2 high energy electrons These electrons pass down an electron transport system RELEASING ENERGY that is used by phosphorylation to make ATP from ADP and used to reduce NADP to become NADPH Energy is also used to split water via the process of PHOTOLYSIS, which produces electrons to replace chlorophyll electrons. Photolysis also produces protons and Oxygen (2H2O 4H+ + 4e- + O2) The electrons are used to make reduced NADPH (NADP) The Oxygen is released into atmosphere DOES NOT depend on temperature as no enzymes involvedREMEMBER: Thylakoids are a part of the GRANA in the chloroplast; therefore ATP and NADH are made in the thylakoids of the granaHow ATP is made in the Light Dependent Reaction:1) Light energy excites electrons in chlorophyll2) Electrons pass down electron transfer chain3) Electrons reduce carriers4) This electron transfer chain takes place in the chloroplast membranes5) Energy is released when electrons pass along the electron transfer chain6) Energy released is used to generate ATP from ADP and Phosphate (phosphorylation)Producers such as plants have an advantage if they have a large surface area to volume ratio, this is because:1) There is a larger area to absorb light2) There is a larger area to absorb CO23) Shorter diffusion pathway for gases4) Light able to penetrate all cells

The Light Independent Reaction: Takes place in the Stroma of Chloroplast It involves the REDUCTION of Carbon Dioxide using ATP and NADPH DOES depend on temperature as enzymes involved, therefore if temperature is too high, enzymes denature, ending photosynthesisLight Independent Reaction: Stages of Calvin Cycle: 1) CO2 combines with 5-carbon RuBP (Ribulose Bisphosphate) with the enzyme Rubisco as a catalyst, Oxygen acts a competitive inhibitor with CO2 for the active site of Rubisco2) This produces 2 MOLECULES of 3 carbon compound GP (Glycerate 3-Phosphate)3) ATP (provides energy) and NADPH used to reduce GP into 3 carbon compound TP (Triose Phosphate) this process will not work in the dark, this is because ATP and NADPH cannot be made without light4) Some of the TP is used to make carbohydrates like GLUCOSE, but MOST of it is used to make more RuBP for the next cycleTherefore, if the light dependent reaction ids stopped, the Calvin Cycle will stop, therefore less RuBP will be formed and thus there will be less CO2 uptake.The Light Independent Reaction depends on the ATP and NADPH made in the Light Dependent ReactionWhy more CO2 means higher rate of photosynthesis:1) More CO2 to convert RuBP to GP2) Therefore more GP available to use with ATP and NADPHWhen plants are submerged in water the rate of photosynthesis would decrease because:The water would absorb light, therefore less light absorbed by plants, leading to a decreased rate of photosynthesis.How the concentration of CO2 would fluctuate over 24 hours above ground level:1) Higher CO2 concentration at night as photosynthesis in plants which removes CO2 only takes place in the light2) Respiration takes place throughout the 24 hours, therefore high CO2 at night3) However, even in the dark plants DO take up CO2, but it is just significantly less than the amount they take up during the day4) In light, the rate of photosynthesis will be higher than the rate of respiration5) The higher you go above ground level, the lower the concentration of CO2 this is because the higher you go above ground level, the more leaves there will be, which will be carrying out photosynthesis which removes CO2Why it is important for plants to produce ATP during respiration as well as photosynthesis:1) In the dark, there is not ATP production with photosynthesis, therefore we need respiration as ATP cannot be stored2) Some tissues are unable to photosynthesise3) Plants use more ATP than produce in photosynthesis4) ATP is needed for active transport

RESPIRATIONAerobic Respiration is 4 processes: 1) Glycolysis

one molecule of glucose oxidised to produce 2 molecules of Pyruvate (3 carbon ion) The reaction YIELDS two molecules of ATP and two molecules of NADH Takes place in the CYTOPLASM of cell as glucose is too large to enter the mitochondria The process does NOT require Oxygen Glycolysis is an oxidation reaction as it involves the removal of Hydrogen to form Pyruvate ATP is necessary for Glycolysis as it activates the glucose to become phosphorylated glucose

2) Link Reaction Also called Pyruvate Oxidation Pyruvate used to produce Acetate and Carbon Dioxide, the Acetate is picked up by co-enzyme A forming Acetyl Co-enzyme A No ATP is produced in the Link Reaction but 2 NADH molecules are formed as well as CO2 and Acetyl Co-enzyme A Takes place in the Matrix of MITOCHONDRIA

3) Krebs Cycle

Electrons stripped from the Acetate, creating large amounts of electron carriers in the form of NADH and FADH2 Takes place in the Matrix of MITOCHONDRIA Each cycle produces 1 ATP, 3 NADH, 1 FADH2 and 2 CO2 The cycle turns TWICE per molecule of glucose, therefore it produces 2 ATP, 6 NADH, 2 FADH2 and 4 CO2 The Krebs Cycle is a series of Oxidation and Reduction reactions

4) The Electron Transport Chain

Takes place on the Cristae (large surface area) in the MITOCHONDRIA Electrons released from NADH and FADH2 Electrons pass from one protein to another in oxidation/reduction reactions The energy from these reaction used to pump H+ ions from the matrix into outer-membrane using Active Transport This creates a diffusion gradient of H+ ions (called THE PROTON GRADIENT), which diffuse back into the matrix through the centre of the ATPase enzyme, as they do, the ATPase enzyme synthesises a molecule of ATP from ADP and Pi using some of the energy from the oxidation/reduction reactions By-products are low energy electrons and protons which combine with Oxygen to form Water We are breathing now due to Electron Transport Chain, we need to provide Oxygen to convert the electrons into water as OXYGEN IS THE FINAL ELECTRON ACCEPTOR Role of Oxygen in Aerobic Respiration:It is the final acceptor for an electron and hydrogen to form water Importance of the Proton GRADIENT:Without it, H+ would not be able to move into the membrane, therefore no ATP produced, the energy being made from the oxidation/reduction reactions would then be released as heat instead of being used to turn ADP and Pi into ATPThe mitochondria in muscle cells contain many Cristae because:1) Provides large surface area for the Electron Transport Chain2) This allows for more ATP to be made which is needed for muscle contraction

Difference between how ATP is produced in Electron Transport Chain and Photosynthesis:1) In Electron Transport Chain, the energy comes from a chemical reaction whereas in Photosynthesis it comes from light2) In Electron Transport Chain, it is made in the dark as well as light whereas in Photosynthesis it is only made in the lightImportance of inner membrane (middle membrane) of mitochondria in the production of ATP:1) Allows electrons to be transferred down electron transport chain by carrying out oxidation/reduction reactions with proteins2) Provides energy to take H+ into space between the matrix and outer-membrane3) Allows H+ back into matrix through ATPase4) Provides energy gained from the oxidation/reduction reactions to combine ADP and Pi to make ATPIn Respiration, you will get NAD and NADH, in Photosynthesis; you will get NADP and NADPHOverall each glucose molecule produces 38 molecules of ATPOnly Link Reaction and Krebs Cycle produce CO2A body cell will know it needs to respire more if the levels of ADP in it are very high as this shows that less ATP is presentA manometer which measures volume may be used to in an experiment to measure respiration.Substances which would have a net movement into the MITOCHONDRIA:1) Pyruvate2) ADP3) Phosphate (Pi)4) Oxygen5) NADHSubstances which would have a net movement out of the MITOCHONDRIA:1) CO22) Water3) ATP4) NADWhy ATP is better than glucose for cell metabolism:1) Energy available more rapidly2) Energy released in small quantitiesAdvantages of ATP as an energy-storage molecule and why it is useful in many biological processes:1) Cannot pass out of cell2) Easily broken down as it takes place in one step: ATP ADP + Pi, this is why ATP is called an immediate source of energy3) Releases energy in small amounts4) Lowers activation energy5) It is reformedOVERALL, HOW ATP IS MADE IN THE MITOCHONDRIA (TRICK QUESTION: DONT MENTION GLYCOLYSIS):1) ATP produced in krebs cycle2) Krebs cycle produces FADH and NADH3) Electrons released from FADH and NADH4) Electrons pass along proteins of the electron transport chain in a series of oxidation/reduction reactions5) Energy is released which is used to allow H+ (protons) to enter 6) As H+ leave through ATPase, energy is used to combine ADP with Pi to make ATPALWAYS REMEMBER: All respiration reactions depend on temperature as they involve enzymes, therefore if temperatures are low, respiration rates will be low as the enzymes will have less kinetic energy

MEASURING AEROBIC RESPIRATIONThis experiment is carried out by measuring Oxygen consumptionPROCESS:1) Organism respires, it takes in O2 and gives out CO22) Normally this will not change volume of gas in apparatus as CO2 made would replace O2 lost3) But when we add Sodium Hydroxide, Sodium Hydroxide absorbs CO2 (so its as though the organism is not making CO2)4) Therefore volume of air in apparatus decreases as the organism uses O25) This change in volume causes a change in pressure which causes the coloured liquid to move along the tube allowing the RATE OF OXYGEN USED PER UNIT TIME to be measured6) Units of rate of aerobic respiration: mm3O2g-1h-1

Measurements taken in this experiment:1) Distance the coloured liquid moves and time2) Mass of organism3) Diameter of tubeAnaerobic Respiration: it is simply Glycolysis that does not go any further, therefore net yield of ATP is 2 molecules Takes place when oxygen is limited, most organisms start with Aerobic Respiration, then Oxygen runs out (or cannot be taken in) so they use Anaerobic Respiration Produces less ATP (2), therefore a lot less efficient, therefore a lot more CO2 produced (in plants and fungi) as more anaerobic respiration must take place to produce same amounts of ATP as Aerobic Respiration Takes place in the cytoplasm (this means it does not take place in an organelle like Photosynthesis and Aerobic Respiration) Only takes a short time to complete Animals and bacteria convert Pyruvate into Lactate Plants and fungi convert Pyruvate into Carbon Dioxide and Ethanol, therefore Lactate and Ethanol production INCREASES as Oxygen levels DECREASE but eventually stop when glucose is used up completely. The conversion of Pyruvate to Ethanol/Lactate is assisted by NADH reducing (by providing H+) Pyruvate to Ethanol/Lactate and NAD+

The conversion of Pyruvate to Lactate/Ethanol by giving Pyruvate a hydrogen from NADH is essential as it re-synthesises NAD+ from NADH, therefore allowing NAD+ to accept a Hydrogen and allowing Glycolysis to continueBOTH aerobic respiration and anaerobic respiration are affected by temperature as they BOTH involve enzymes.Why Aerobic Respiration yields more ATP than Anaerobic Respiration:1) Oxygen is the final electron acceptor and oxygen is not present in anaerobic respiration2) Electron Transport Chain produces most ATP which is not present in anaerobic respirationThere is no Oxygen uptake in anaerobic respiration; therefore Oxygen levels remain constant whilst an organism respires anaerobically.FLOODING can also cause anaerobic conditions as water prevents Oxygen from being used.Anaerobic respiration has to start with glucose, if it is not glucose, then you will have to apply enzymes to break the substance down into glucose.So overall, there are only 3 reactions which PRODUCE ATP:1) Light Dependent Reaction in Photosynthesis, (however the ATP made in Photosynthesis is used up in the Light Independent Reaction)2) Glycolysis in Respiration3) Electron Transport Chain in Respiration(HINT: The ATP made in Krebs Cycle is the same ATP originally made in Glycolysis)

CYCLESCarbon Cycle: Involved CO2 from atmosphere or HCO3- in water - being fixed into organic molecules by photosynthesis and then released back into the atmosphere by respiration and other systems.Why global warming is taking place:MethaneSource: Fermentation of waste, Natural gas, Flatulent cows, Coal mining, Storage of manure on farms, Anaerobic soilThese are all anthropogenic sources (caused by humans); however 76% of methane comes naturally.How producing and using biofuels results in a negative percentage change in CO2 production:1) CO2 taken up in photosynthesis2) More taken up than produced when using biofuels

Carbon Source: Ecosystem that releases more carbon dioxide than it accumulates in biomass over the long term, e.g. deforestationCarbon Neutral: Ecosystem is one where carbon fixation and carbon release are balanced over the long termCarbon Sink: Ecosystem is one that accumulates more carbon in biomass than it releases as carbon dioxide over the long termNitrogen Cycle:

1) Plants absorb Nitrate (NO3-) using active transport which REQUIRES ATP: Some of the Nitrate is lost to the atmosphere as Nitrogen through denitrifying bacteria which are anaerobes and therefore thrive waterlogged soil, Some of the Nitrate has been gained from Nitrogen in the atmosphere using Nitrogen-fixing bacteria which breaks the triple bond in Nitrogen to convert it to AMMONIA using the enzyme Nitrogenase as a catalyst, (to do this nitrogen-fixing bacteria use ATP and organic compounds gained from soil) lightning can also convert Nitrogen to AMMONIA, ammonia helps in amino acid production, otherwise ammonia is gained through decay of organic material2) Plants combine Nitrate with carbohydrates to make PROTEINS3) Plants are eaten and Nitrogen is passed along food chain4) When the Nitrogen-rich matter dies, it is broken down by saprobionts using diffusion,( as saprobionts respire aerobically, they release CO2 which can also be used by the plant), and converted to Ammonium ions(NH4+)5) Nitrifying bacteria convert the Ammonium ions (NH4+) into Nitrite (NO2-) and then Nitrite (NO2-) into Nitrate (NO3-) in a process called nitrification which is exothermic, thus releasing that is used by nitrifying bacteria to make ATPRemember that Nitrifying bacteria, Nitrogen-Fixing bacteria and Saprobionts are aerobic, therefore they will require oxygenDifference between Saprobionts and Detritivores: Detritivores use ingestion and Saprobionts use extracellular digestionHow Detritivores help Saprobionts:1) Break plant tissue into smaller pieces giving a larger surface area for Saprobionts to work2) Aerate the soil which helps the Saprobionts to respire aerobically3) Excrete useful minerals such as urea, which Saprobionts can metaboliseIn summarisation, the way soil bacteria improves crop yield and provides plants with nitrogen is:1) Detritivores break up larger pieces of organic material to increase surface area available to the saprobionts2) Saprobionts (sometimes called Putrefying bacteria) break down organic material using enzymes using EXTRACELLULAR DIGESTION, into ammonium compounds which are converted into nitrite and then into nitrate by Nitrifying bacteria3) Nitrogen-Fixing bacteria fix nitrogen from atmosphere into ammonium which is converted into nitrite and then into nitrate by Nitrifying bacteria4) Nitrate is taken up by plants, which is needed by plants for protein synthesis5) As the saprobionts respire aerobically, they release CO2 which can be used by plants for photosynthesisRemember: denitrification takes place under anaerobic conditions.Remember: Sewage contains urea which can be decomposed by bacteriaAdvantage of growing leguminous plants:1) They contain nitrogen-fixing bacteria in their root nodules, which convert nitrogen to ammonium2) This ammonium is released on decomposition and converted to nitrates by nitrifying bacteria 3) Therefore there is a less need for fertilisersThe more ammonia there is in the soil, the better it is for crops, and this is because:1) The ammonia can be converted to nitrate 2) This can be used by crops to produce protein

Role of Nitrogen Fixing bacteria in the Nitrogen Cycle:1) Convert nitrogen into ammonia2) Add usable nitrogen to an ecosystemNitrogen-Fixation requires a lot of ATP which is obtained from respiration of products of photosynthesis.Nitrogen-Fixing bacteria respire aerobically, therefore providing lots of ATP, however the nitrogen-fixing bacteria uses NITROGENASE as a catalyst which only respires anaerobically. The aerobic respiration helps remove O2 for nitrogenise to workVERY IMPORTANT POINT: enzymes which work in anaerobic conditions require that the environment is kept cool; this is because anaerobic respiration would increase the temperature of the environment which could lead to the enzyme becoming denaturedDifference between plants that use Nitrogen-Fixing bacteria to get nitrogen and plants that get nitrogen through a fertiliser:Plants using nitrogen-fixation will grow more slowly as nitrogen-fixation required ATP, therefore less ATP used for growthEutrophication:1) Fertilisers drain into rivers and lakes increasing levels of nitrate and other nutrients (LEECHING)2) Algae absorbs this nitrate and uses it for protein synthesis eventually causing an algal bloom, this blocks sunlight for other plants which eventually die3) Nutrients run out and algae die too4) Bacteria decompose the dead matter and as they respire aerobically they consume Oxygen5) Lack of Oxygen begins to kill aquatic life (deoxygenation)6) Bacteria decompose the dead matter into ammonium compounds which is converted to nitrate by nitrifying bacteria7) This could lead to an increased nitrate in drinking water which could cause human illnessNitrate concentrations in rivers and lakes can be reduced by increase rainfall as it dilutes nitrate which in turn stops eutrophication.Eutrophication will be faster in warmer weathers as more heat means that bacteria will have higher kinetic energyIn essence, there are two ways in which nitrate can be lost from the soil:1) Leeching (eutrophication)2) Denitrification

DEFORESTATION & CONSERVATIONDeforestation: 1) Creates CO2 as trees absorb CO2 which is released when burnt2) Reduces diversity due to loss of habitats, niches, ecosystems, food, soil erosion and by changing the climate3) Causes soil erosion as there are no trees to protect soil from rain4) Causes changed rainfall patterns and droughts as there is less transpiration from leavesHow deforestation increases CO2 concentration:1) Less trees means less photosynthesis2) Less photosynthesis means less CO2 absorbed from the atmosphere3) Burning of the trees involves combustion which produces CO2Logging: Removal of mature trees from a forestSustainable Logging: Logging sectors of a forest in a sequence, ensures there is always tree to be cut. It is the opposite of clear cutting

Advantages of Sustainable Logging:1) Recolonisation possible from adjacent areas2) There is sufficient time for recoveryReasons for conservation of the forest ecosystem:1) Trees available as a sustainable resource2) Maintain habitats3) Maintain diversity and protect endangered species4) Maintain stability of ecosystem5) Maintain food chains6) Reduced loss of soil7) Reduced flood8) Reduce greenhouse effect and therefore global warming9) The forest ecosystem is also a source for medicinesCoppicing: Cutting down some trees in a wood to leave stumps, new shoots grow from the stumps

SUCCESSIONSuccession: Change in a community over time due to change in environmentSuccession is of two types:1) Primary Succession: starts with bare rock usually after a volcanic eruption 2) Secondary Succession: starts with soil usually after a forest clearingHow Succession occurs:1) Colonisation by pioneer species2) As pioneer species increase in number, they die and are broken down by saprobionts which increase humus content 3) Change in environment as there is an increase in organic matter and nutrients, the humus helps maintain moisture4) This enables other species to colonise5) This causes a change in biodiversity6) The environment becomes less hostile7) New species better competitors and eventually one species outcompetes other species8) This species is called the climax community What the pioneer species does: Change environment via nutrients to make it less hostileWhy pioneer plants having seeds that grow in fluctuating temperatures is an advantage:1) At the start of succession, there is only bare soil2) Temperature in bare soil always fluctuatesThe environment before succession is extremely hostile; therefore very few species are able to tolerate the conditions.Climax Community: Stable community after which no more succession takes placeTrees that are usually the tallest and bulkiest will be the best as they will block light, needed by other plants for photosynthesis, therefore the climax community usually reduces plant diversity as those plants survive which can photosynthesise with less lightWhy species change during succession:1) Pioneer species add humus to the soil making the environment less hostile2) This allows a new species to develop which is a better competitorWhy nitrate in the soil increases during succession:1) Increase in dead organisms2) Leading to an increase in nitrification3) Also nitrogen-fixation could also be taking place making ammonia, which then turns into nitrateOn bare rock, the pioneer species will usually be moss caused by the soil particles of a rock gathering in cracks as the rock weathers.Ecosystems develop by the process of colonisation and succession until the climax community is reached.Grazing stops succession at the grassland stage.Sometimes, the plant/forest is burnt, and succession begins on the burnt land, this is beneficial because:1) Younger plants have more shoots, therefore provide more food2) Younger plants provide more cover3) Unproductive plants are removedWhy diversity of animals increases:1) Greater variety of food2) Higher variety of habitats3) More detritusIn sand-dune ecosystem, minerals enter the ecosystem by:1) Shells2) Flooding by seawater3) Weathering of underlying rock4) Nitrogen fixation5) Excretory productsIn a sand dune system, the climax community will be the furthest away from the sea and the pioneer species will be widespread.CONSERVATION OF HABITATS FREQUENTLY INVOLVES MANAGEMENT OF SUCCESSION.

INHERITANCEGenotype: Genetic constitution of an organism/combination of alleles he individual posses, Example of Genotype: IAIOPhenotype: Expression of the genotype and its interaction with the environmentExample for Phenotype: if there is a genotype IAIO in which A is dominant, then the phenotype is: AGene: A length of DNA that codes for a particular proteinGene Pool: All the alleles in a populationChromosome: One long DNA molecules which contains genesLocus: The position of a gene on a chromosomeAllele: Alternative version of a gene, (there may be multiple alleles of a single gene)Dominant Allele: The allele always expressed in the phenotypeRecessive Allele: The allele that is only expressed in the phenotype in the absence of the dominant alleleHomozygous: When both the alleles are the same: BB or bbHeterozygous: When both alleles are different: BbAA

AAAAA

aAaAa

When seeing the possible genotype the children of two individuals may have, we draw a genetic cross, separating the alleles of the parents: E.g. if the parents had genotype: Aa and AA, then we do the following:Therefore there is a 50% chance the child has Aa and 50% chance the child has AA.

Co-dominance: When both alleles are being expressed in the phenotypeExample of Co-dominance: if the genotype is IAIB in which A and B are co-dominant, then the phenotype will be: ABMonohybrid Inheritance: Inheritance of a single gene with two allelesWhy Monohybrid Cross ratios may not take place in reality: 1) fusion of gametes is random2) Mating is related to chance3) Differential mortalityCo-Dominance: when alleles are co-dominant, so if they are present they are both expressed in the phenotype, takes place usually when a gene has more than 2 allelesSex Linkage: concerns genes found on the sex chromosomes, X and Y, (X gene will contain the disease)Males have only one X chromosome (XY) therefore can never be carriers. Females have two X chromosomes (XX) therefore can be carriers. The gametes will be each chromosome, i.e. men have genotype XY, separating them gives you two gametes, X and Y.Sex Linked diseases that kill children will become extinct as children who are affected will not be able to pass on the disease.VERY rarely there may be a gene that is existent on the Y chromosome, however this would mean that all males would be affected and no females.Males are more likely to have a sex-linked disease that is recessive:1) Males have only one alleles, therefore it could be the recessive one2) Females need two recessive alleles to have the diseaseIn question where they ask you to prove why a certain condition is recessive/dominant, just write EVERYONES genotypes and try to figure out an answer.How to prove that a certain condition is on the recessive allele:1) Affected child produced from unaffected parents2) Therefore parents are heterozygousHow to prove that a certain condition is on the dominant allele:1) Affected parents produce unaffected child2) Therefore parent are heterozygous (and still affected, therefore allele causing condition is dominant)If a certain condition was recessive, but scientists wanted to make a person with the condition, then this would be difficult because:1) The parents would have to heterozygous: Bb and Bb would make bb2) There is no way of knowing which parents are heterozygous (i.e. no way of differentiating between Bb and BB)How to prove a condition is not sex-linked:1) The condition is on the dominant alleleXrXr

XRXRXrXRXr

YXrYXrY

1) Affected male (XRY) and unaffected female (XrXr) are producing an affected male (XRY) which is not possible, look at diagram:

How to prove a condition in on the x-chromosome:Affected male children from unaffected fatherSerious diseases caused by dominant alleles are uncommon compared with serious diseases caused by recessive alleles:1) If it is on the dominant allele, then all individuals with allele of the disease develop the disease, i.e. they become aware of the disease and therefore decided not to have children2) If the serious disease is on recessive allele, it may not affect individual, therefore individual will not be aware of the disease and may have childrenSome diseases are fatal, yet they are passed on, this may be due to the fact that the disease takes effect in old age, by which time offspring have already been produced.

If a recessive allele is causing a hindrance to a species ability to compete, then the frequency of the recessive allele will decrease over time, because:1) Due to directional selection2) The dominant allele has an advantage over the recessive allele, therefore more likely to survive.Dominant Allele frequency + Recessive Allele frequency = 1; p + q = 1 (this is as long as the two alleles are for the same gene)Homozygous Recessive frequency + Heterozygous frequency + Homozygous Dominant frequency = 1; p2 + 2pq + q2 = 1Hardy-Weinberg principle: The frequency of alleles will remain constant from one generation to the next providing no mutation, geographical isolation, selection, migration etc. takes place. (The Hardy-Weinberg Principle is actually more of a PREDICTION than a principle)We cannot do an investigation on the frequency of certain alleles in a group of organisms if one of the organisms is deaf, blind, etc. This is because this organism will not survive and therefore will not pass on allele Assumptions made when using the Hardy-Weinberg equation:1) No selection2) Random mating3) Large gene pool4) No migration5) No mutation6) Equally fertile genotypes7) Generations do not overlapWhen studying genetic crosses, you use an animal which:1) Gives large number of offspring; low sampling error2) Short life cycle; results obtained quickly3) Male and female easily distinguished for mating4) Small size; easy to handle and less space requiredHow there is genetic variation in a sexually reproducing animal:1) Independent alignment of chromosomes which gives a new arrangement of alleles2) Random fertilisation which gives a chance combinations of gametes3) Mutations create new alleles

SELECTION PRESSURENatural Selection: process in which those organisms whose alleles give them a selective advantage are more likely to survive, reproduce and pass on their alleles to the next generation (Intraspecific competition is important for it)

Stabilising Selection: few organisms survive at extremes which means that is selects for the mean which remains unchanged, it occurs in non-changing environment and is repeated over many generationsExample: Very big animal is too slow but very small animal is too weak, therefore middle pathway is bestDirectional Selection: Organisms with a particular extreme of phenotype have a selective advantageExample: Bacteria which gain resistanceDisruptive Selection: Selection against middle, selection for one extremeExample: Bird species called finches, smaller beaks helped catching insect, larger beaks helped opening seed, middle sized beaks were uselessAnimals that are large have a small surface area to volume ratio, therefore they lose less heat.In the exam, you will only get questions regarding directional and stabilising selection.

SPECIATIONProcess of Speciation: 1) Isolation between two populations (if the isolation has been due to separation of lands, then write GEOGRAPHICAL ISOLATION between two populations)2) No gene flow i.e. interbreeding between populations3) Variation 4) There are different environmental factors which allow a certain characteristic to survive5) Mutation6) Some organisms have allele to adapt and therefore survive , for example mutation allele may produce camouflage 7) Adaptive organisms survive and reproduce8) There is an increase in the frequency of the surviving allele9) Gene pool differs from original species, therefore no interbreeding can occur10) This occurs over a long period of timeReproductive Isolation: Organisms cannot breed with another group

When a species is isolated: 1) Less competition2) Less predators Speciation is a lot less frequent these days:1) Similar biotic and Abiotic pressures2) Similar selection pressures3) No isolationREMEMBER: The larger a species, the smaller the surface area to volume ratio, therefore less heat is lost by these species.

In Graph Analysis and Drug Trials:1) When describing a graph, mention peak points, increase and decrease in graph and overall increase/decrease in graph2) Sometimes the evidence from the graph may not be enough to draw a certain conclusion. WHY: Any correlation does not mean there is a causal relationship There may some other factor producing a rise/fall in both factors Sometimes, there is no relation between both factors further along the graph Also if a control group was not used, then effectiveness cannot be measured Fluctuations in a graph are a clear sign that conclusions cannot be drawn from it In graphs, where conclusions are being drawn regarding a disease, check if it says reported cases, if it does you can mention about how we dont know the full amount of disease cases as many were not reported and THEREFORE we cant draw conclusions.3) Objective of a control: show effect of the thing you are investigating without the thing you are investigating it with4) Dependent Variable (the variable that we measure) must only be affected by the Independent Variable (the variable we change)5) Sometimes, data is given in a logarithmic form; this exaggerates the numbers and allows the effect of low numbers to be seen, therefore it increases the range of values. Sometimes, data is given in a ratio; this allows comparison as it shows proportional change.6) In some graphs, medical cases are presented for the prevalence of a certain disease; however, the number presented may not be the actual number of people with that disease as many people do not go the doctors.7) When an investigation involves metabolism, scientists may experiment on people of different ages as metabolism rate differs on age.8) When it asks you to describe a graph, be sure to mention a peak point if there is one, if not, describe the correlation, i.e. whether it is negative or positive.9) Sometimes data on a graph is given in a percentage, the advantage of this is:1) Allows comparison2) Shows proportional Change as sometimes the initial weight/size/volume etc. of substances is different.10) Experiments are repeated for the following reasons:1) Allows anomalies to be identified2) Makes the average more reliable3) Allows more concordant results4) Allows the mean to be calculated5) To make the line of best fit and intercept on a graph more precise11) Difference between accuracy and reliability:1) Accurate: without error2) Reliable: that figure can be reproduced when measurement repeated12) Why it is important to check the repeatability of measurements:1) Increases reliability of measurements2) If measurements are repeatable, then anomalies are unlikely13) If you wanted to see if two results are similar:Plot scatter diagram of one set of results against the other and you should see a positive correlation14) Any questions in which data is regarding cancer, it would be important to remember that cancer takes many years to develop; therefore this restricts conclusions drawn regarding it.15) When asked to give an evaluation on a claim or statement, mention all the points that indicate the claim or statement to be true, and then mention how it could be false.16) Why it is best to have a large sample: reduces sampling error17) Advantages of collecting large number of results: 1) Allows anomalies to be identified2) Allows use of statistical test18) If it asks you why a drug may not be perfect: Unknown Long-Term side effects Study should be carried out on humans and the study should be repeated19) Before carrying drug trials, scientists should consider the following regarding the drug: Dose to be given No serious side effects How effective Cost of drug

20) When taking drug trial, scientists should consider the following of volunteers: Age Health Gender Ethnicity Genetic Factors Lifestyle Body Mass21) When scientists wish to use an animal in a test, before deciding the number of animals to use they must consider: Ethical Consideration Take a large number to improve reliability Consider cost and space available22) When experiment involves volunteers, they must be healthy as they will have normally functioning bodies. Also when dividing volunteers into groups, it should be done randomly to avoid bias. 23) If scientists use two drugs/vaccines and both combined have higher effect, then both must be similar i.e. they must have the same antibodies, etc.24) How mean can be found from a graph: Draw line of best fit Then find the gradient and divide it by the distance moved25) Any experiment wherein the words water and mention of the word partially permeable come together, you should automatically realise that water potential will be involved somehow.26) Sometimes, in an experiment, they experiment on people of all the same age: this is so that a comparison can be made.27) When in an experiment, people are assigned to different groups RANDOMLY; it means everyone has an equal chance of being assigned to either group. They do this by using a random number generator. 28) Also remember your basics such as when you evaporate water from a substance, it becomes more concentrated.29) When scientists measure something per unit of another thing it is so as to a comparison between the two different things.30) If scientists wish to know the most common volume or concentration of a substance, they take a large random sample.31) In a medical study, the information is useful to scientists because It allows scientists to: Determine the most effective dose Determine the most length of treatment Investigate long-term effect Find most cost-effective treatment 32) Double Blind trials are trials wherein neither the volunteers nor the doctors know which treatment a particular volunteer is receiving, this improves reliability because: Prevents bias Prevents positive/negative psychological effects33) When in a graph, the points are joined with straight lines rather than curves, it is because: the intermediate values between points are unknown34) When something is normally distributed, it means median = mode, this is known as continuous variation and has a bell-shaped graph35) In genetic research, scientists need to ensure that the environment is the same36) When it says the ratio of x to y was z, it means z = x y37) In Spearmans Rank Correlation test, positive values mean positive correlation between x and y and negative values mean negative correlation between x and y38) Even if an investigation was failure, it is important for scientists to report their results because:1) Saves money and time for others2) Ensures same work is not repeated

IN MOST INVESTIGATIONS INVOLVING DATA, SCIENTISTS WILL ALSO WORK OUT THE STANDARD ERROR OF THE MEAN

When working out percentage increase: (big number-small number small number) x 100When working out percentage decrease: (small number-big number big number) x 100

When working out volume of a chemical after dilution:Initial volume x concentration of chemical = volume of chemical that is in that initial volume, the rest is basically water.

Be wary of questions in which the investigator recorded results of an investigation every couple of seconds, then he displayed the investigation on a graph and the graph increases and then levels off. If you think about it, after the graph has levelled off, if the investigator recorded results, he would begin to observe same results, and therefore zero changes. Examiners could ask what did he observe when the graph levelled off? The answer is nothing, zero.

STANDARD DEVIATION: Degree of variation from the mean. The smaller the Standard Deviation is the better.When Standard Deviations overlap, conclusions cannot be made as effectively as results may be due to CHANCE, if standard deviations do not overlap, we say the difference is REAL.Why at times Standard Deviation is better than the mean:1) Range only shows highest and lowest values2) Also it is possible to have two very different data sets with the same range3) Also range is affected by a single outlier4) Standard Deviation shows spread about the mean and allows statistical useWhy a statistical test is necessary for analysis:1) A statistical test determines the probability of results being due to chance2) This enables us to reject or accept the null hypothesisPurpose of a Chi-Squared Test: to compare different numbers collected from two sites and show whether differences are significantIf it says: explain the meaning of p < 0.05 using the words probability and chance, you will write:There is a probability of less than 5% that the results are due to chance