AQA A2 Biology Unit 4

AQA A2 Biology Unit 4 Populations Specification3.4.1 The dynamic equilibrium of populations is affected by a number of factors.Candidates should be able to: carry out experimental and investigative activities, including appropriate risk management consider ethical issues when carrying out fieldwork, chiefly those relating to the organisms involved and their environment analyse and interpret data relating to the distribution of organisms, recognising correlations and causal relationships appreciate the tentative nature of conclusions that may be drawn from such data. interpret growth curves, survival curves and age-population pyramids calculate population growth rates from data on birth rate and death rate. relate changes in the size and structure of human populations to different stages in demographic transition.DefinitionsAbiotic: Ecological factor that makes up part of the non-biological environmentBiotic: Ecological factor that makes up part of the living environmentEcosystem: More or less self contained functional unit in ecology made up of all interacting biotic and abiotic factors in a specific areaPopulation: A group of individuals of the same species that occupy the same habitat at the same timeSpecies: A group of similar organisms that can breed together to produce fertile offspringCommunity: The organisms of all species that live in the same areaHabitat: The place where an organism normally lives, which is characterised by physical conditions and the species of other organisms presentNiche: All conditions and resources required for an organism to survive, reproduce and maintain viable populationIntraspecific: Competition between organisms of the same speciesInterspecific: Competition between organisms of different speciesPredator: An organism which feeds of another organism known as the prey1.1 Populations and Ecosystems1.2 Investigating PopulationsPopulation = Total number of individuals in the first sample X Individuals in the second sampleNumber of marked individuals recapturedType of TrapMethod of MarkingPitfall trap: Insects, Small MammalsMicrochipElectrofishing : FishPaint or permanent marker onto animalCage set up with food in: Mice, VolesPhoto showing unique markingsRemoval method: blocks of part of environment so can collect fishVisible implant or tag Glue Trap: RodentsToe Clippings: Vertebrates Sweepnet moved through plants: Ground insectsFur RemovalWire funnel trap: Insects in tall vegetation 1.3 Variation in Population Size

1.2.3.Population Size1.4 CompetitionIntraspecific CompetitionInterspecific Competition

1.5 Predation

1.6 Human PopulationsBirth Rate FactorsBirth Rate: number of births per year Total population in the same year X1000Death Rate FactorsDeath Rate: number of deaths per year Total population in the same year X1000

Stable PopulationIncreasing PopulationDecreasing PopulationAQA A2 Biology Unit 4 ATP & PhotosynthesisSpecification3.4.2 ATP provides the immediate source of energy for biological processes.3.4.3 In photosynthesis, energy is transferred to ATP in the light-dependent reaction and the ATP is utilised in the light-independent reaction.Candidates should be able to explain how growers apply a knowledge of limiting factors in enhancing temperature, carbon dioxide concentration and light intensity in commercial glasshouses. They should also be able to evaluate such applications using appropriate data.

DefinitionsATP: An activated nucleotide found in all living cells that acts as an energy carrierEndothermic: Reaction that requires energyActivation Energy: Minimum energy required to bring about a chemical reactionHydrolysis: The breaking of large molecules to small using waterCondensation: Chemical process where two molecules form a larger moleculeElectron carrier molecules: A chain of carrier molecules along which electrons pass, releasing energy in the form of ATPThylakoids: Series of flattened membranous sacs in a chloroplast that contain chlorophyll and the associated molecules needed for the light-dependent reactionNADP: Molecule that carries electrons produced in the light-dependent reactionStomata: Pores surrounded by guard cells that allow gas diffusionStroma: Matrix of chloroplast where the light-independent reaction occurs

2.1 Energy and ATPRoles of ATPAbsorption of Light EnergyLight energy is captured and is transferred to chlorophyll a molecules.Electrons in the outer shell of the chlorophyll a molecule are excited.The electrons are passed through a series of carrier molecules and are used to power,PhotolysisReduction of NADPPhotophosphorylation

223.1 PhotosynthesisThe Light-Dependent ReactionChlorophyllalighte -e -e -e -e -2H2O4H+ + e - + O2 4NADP 4NADPHADP + PPHOTOLYSISPHOTOPHOSPHORYLATIONATP243.2 The Light-Dependent ReactionPhotolysisWater molecules are split using energy from excited electrons in chlorophyll a molecules.

2H2O 4H+ + 4e- + O2

Oxygen is released into the atmosphere.Hydrogen ions and electrons are now available to be used to produce a reducing agent.

26Site of Light-Dependent ReactionReduction of NADPElectrons and Hydrogen ions produced during photolysis are used to reduce NADP to Reduced NADP (NADPH).Excited electrons and hydrogen ions are transferred to NADP.

NADP + H + + e- NADPH

NADPH can donate electrons and hydrogen ions to carbon dioxide and so is a reducing agent.

283.3 The Light-Independent ReactionPhotophosphorylationEnergy from the excited electrons is used to make ATP.A phosphate group is added to ADP.ADP + P --energy from excited electrons ATP

30Products of the Light Dependent StagePhotolysisH+ ionsElectronsOxygenPhotophosphorylationATPUsed to produce NADPH

31The Calvin Cycle

Site of the Light-Independent Reaction

3.4 Factors affecting PhotosynthesisThe Light-Independent ReactionDoes not require light energy.However, requires the products produced in the light-dependent reaction, therefore photosynthesis cannot occur without light energy.Takes place in the stroma.Enzyme controlled, therefore it is affected by temperature.Uses energy from ATP, and the electrons and hydrogen ions from NADPH to reduce CO2 to glucose.35Fixing Carbon DioxideRibulose Biphosphate (RuBP), a 5 carbon molecule, combines with carbon dioxide via the enzyme RuBISCO.This forms 2 molecules of glycerate-3-phosphate (GP), a 3 carbon organic acid.

36Reducing glycerate-3-phosphate (GP)NADPH and ATP from the light-dependent reaction are required for this stage. NADPH transfers electrons and hydrogen ions to GP to form 2 molecules of Triose phosphate.The energy for this is provided by the ATP.The NADPH has now been oxidised back to NADP and can be reused in the light-dependent reaction.The ATP has lost energy and so returns to ADP + P which can also be reused in the light-independent stage.

37Producing Glucose and Regenerating RuBPFor every 6 CO2 molecules entering the cycle, 12 Triose phosphates will be produced.2 of these molecules will be converted into glucose.Of the 12 Triose phosphates that are produced, 10 will be used to regenerate RuBP.Producing GlucoseRegenerating RuBP

38Law of Limiting Factors: The overall rate of the process will be limited by the factor which is at the least favourable value

Factors Affecting the Rate of Photosynthesis39Light IntensityAt low light intensities, the rate of photosynthesis is directly proportional to the light intensity.Because as more light becomes available, more chlorophyll molecules can absorb light so more electrons are excited leading to photolysis and photophosphorylation.More ATP and NADPH are produced so the light-independent reactions can occur at a higher rate so more product is produced.Eventually a maximum rate is reached and so increasing light intensity has no effect so the graph levels off.This can be because all available chlorophyll molecules are absorbing light. Or some other factor is now the limiting factor.

40TemperatureWhen light is not a limiting factor (i.e. high light intensities), increasing the temperature increases the rate of photosynthesis.Above the optimum temperature, any further increase causes the rate to decrease rapidly.Because the Calvin Cycle is enzyme controlled, when the temperature increases both enzymes and substrates gain kinetic energy, so more collisions occur, so more enzyme substrate complexes form, so more product forms.When the temperature exceeds the optimum, the enzymes will denature and the specific shape of the active site will change and no longer be complementary to the substrate so fewer enzyme-substrate complexes can form.

41Carbon Dioxide ConcentrationAt low CO2 levels an increase in concentration causes a directly proportional increase in the rate of photosynthesis. A maximum rate is eventually reached and further increase has no effect and so the graph levels off.This is because atmospheric CO2 levels are lower than the optimum value so when concentration is increased more CO2 is absorbed so more product is made.Eventually, there is no more RuBP available to absorb anymore CO2 so there is no further effect.

42Implications for Commercial Glasshouse Management

43What does glasshouse cultivation allow?Better yields can be achieved because conditions for photosynthesis can be kept at an optimum.Crops can be grown out of season all year providing a better economic return.Crops can be grown in regions where they might not grow well naturally.44Factors to be ConsideredFor maximum yields to be achieved, limiting factors must be kept at an optimum because the faster the plant photosynthesises the more carbohydrates it produces which means the maximum yield will be achieved in the shortest time.Carbon dioxide levelsHigh levels of CO 2 are the optimum however if the levels are too high over a long period of time then the stomata will close resulting in a drop in the rate of photosynthesis. A compromise level must therefore be used.TemperatureAn optimum temperature should be used to ensure that the plants photosynthesise rapidly without any damage to cells.WaterNeed to be well watered to ensure the stomata remain open to absorb CO 2. However the soil must not become waterlogged as it will reduce the uptake of mineral by active transport. The plants must not become to wet either as this will promote fungal disease to spread.LightArtificial lighting is used when natural light intensity falls. Specific wavelengths are chosen so they are absorbed by the plants (i.e. red and blue).MineralsSoil must be supplemented with essential minerals. Potassium is particularly important in stomatal mechanisms and so must be kept at an optimum.45AQA A2 Biology Unit 4 RespirationSpecification3.4.4 In respiration, glycolysis takes place in the cytoplasm and the remaining steps in the mitochondria. ATP synthesis is associated with the electron transfer chain in the membranes of mitochondria.DefinitionsHydrolysis: Breaking down of large molecules into smaller ones by the addition of waterActivation Energy: Energy required to bring about a chemical reactionOxidation: Lose of ElectronsGlycolysis: First part of cellular respiration in which glucose is broken down anaerobically in the cytoplasm to 2 molecules of pyruvateSubstrate-Level Phosphorylation: The formation of ATP by the direct transfer of a phosphate group from a reactive intermediate to ADPAerobic: Connected with the presence of oxygen, aerobic respiration requires oxygen to release energy from glucose and other foodsAdenosine Triphosphate: An activated nucleotide found in all living cells that acts as an energy carrier. Redox: Reaction in which oxidation and reduction take placeKrebs Cycle: Series of aerobic biochemical reactions in the matrix of the mitochondria of most eukaryotic cells by which energy is obtained through the oxidation of acetylcoenzyme A produced in the breakdown of glucoseNAD: (Nicotinamide adenine dinucleotide phosphate) Molecule that carries electrons and hydrogen ions during aerobic respiration4.1 Respiration OverviewGlycolysisGlycolysisGlycolysis takes place in the cytoplasm of the cell.Glucose is first phosphorylated by 2 phosphate groups from 2 molecules of ATP to produce 2 molecules of glyceraldehyde-3-phosphate (GALP).GALP is then oxidised and dephosphorylated into pyruvate.In this process, the phosphate groups are transferred to ADP producing 2 molecules of ATP. A hydrogen is transferred to a molecule of NAD producing NADH.The net yield of glycolysis per glucose is 2ATP2NADH2 pyruvateThe pyruvate produced then diffuses into the mitochondria.1 x Glucose2 x Glyceraldehyde3-phosphate2 x Pyruvate2ATP2ADP + 2P4ATP4ADP + 4P2NAD2NADH514.2 The Link ReactionThe Link ReactionTakes place in the matrix.Pyruvate undergoes oxidative decarboxylation.OxidationElectrons and hydrogen from the pyruvate are transferred to NAD producing NADH.DecarboxylationCarbon dioxide is removed which converts the pyruvate into acetate.The acetate then combines with CoenzymeA to produce Acetyl CoenzymeA.Since 2 molecules of pyruvate were produced in glycolysis, the net yield of the link reaction per glucose is2 Acetyl CoenzymeA2NADH2 Carbon dioxide2 x PyruvateAcetyl CoenzymeANADNADHCarbon dioxideCoenzymeA53The Krebs CycleThe Krebs CycleTakes place in the matrix.Closed cycle of enzyme controlled reactions.Provides a continuous supply of reduced electron carriers for the electron transport chain.AcetylCoA combines with a 4-C compound to produce citric acid, a 6-C compound.The citric acid then undergoesA decarboxylation reaction which removes carbon dioxide.A series of oxidation reactions which remove hydrogen ions and electrons. H + ions and e are picked up by NAD and FAD and they become NADH and FADH.At the end of the cycle the 4-C compound is recycled so the cycle can continue.Since each glucose molecule produced 2 molecules of pyruvate and so 2 molecules of AcetylCoA, the yield per glucose for the Krebs cycle is4 carbon dioxide2FADH6NADH2ATP

ADPATPNADHNADHNADHFADH554.3 Electron Transport ChainElectron Transport ChainFound on the cristae of the mitochondria which provide a large surface area for this to take place.The electron carriers are arranged in descending energy levels.When electrons pass through the carriers, the energy released is used to move hydrogen ions from the matrix into the intermembrane space.This creates a large concentration gradient of H+ ions and so they diffuse back into the mitochondrial membrane by diffusion via ATP synthase.As the H+ ions diffuse through the enzyme, they attach P groups to ADP to produce ATP.At the end of the chain, the electrons are picked up by the terminal electron acceptor, which is oxygen, to produce water.2e - + 2H + + O2 H2OThis process is called oxidative phosphorylation.

574.4 Anaerobic RespirationAnaerobic Respiration1 x Glucose2 x Pyruvate2NAD2NADH2NADH2NAD2 x Lactic Acid2ATP2ADP + 2P60Anaerobic RespirationWhen oxygen isnt available, the electron transport chain cannot operate so the initial supply of NAD run out.To regenerate this, pyruvate produced during glycolysis must be reduced.Pyruvate is converted into lactic acid in animal cells.Pyruvate + NADH Lactic AcidThe net yield from anaerobic respiration is simply the 2ATP produced in glycolysis and is therefore much less energy efficient.In some plants and microbes, pyruvate is converted into ethanol.Pyruvate + NADH Ethanol + Carbon Dioxide + NAD61AQA A2 Biology Unit 4Nutrient CyclesSpecification3.4.6 Chemical elements are recycled in ecosystems. Microorganisms play a key role in recycling these elements.Candidates should be able to analyse, interpret and evaluate data relating to evidence of global warming and its effects on the yield of crop plants, the life-cycles and numbers of insect pests, the distribution and numbers of wild animals and plants.Candidates should be able to analyse, interpret and evaluate data relating to eutrophication.DefinitionsActive Transport: Movement of a substance across a membrane from a region of low concentration to high concentration using ATPAerobic: In the presence of oxygen Anaerobic: Without oxygenBiomass: Total mass of living material in a specific area at a given time, usually measured as dry mass since water value is variableConsumers: Organism that obtains energy by eating another Decomposer: An organism, e.g. fungus that breaks down organic material.Ecosystem: Unit in ecology made up of all interacting biotic and abiotic factors in a specific areaGreenhouse Gas: Such as methane and carbon dioxide, they cause heat to be trapped in the atmosphere raising the Earths temperatureNiches: All conditions and resources required for an organism to survive, reproduce and maintain populationOxidation: Chemical reaction causing the loss of electronsProducers: Organism that synthesises organic molecules from simple inorganic ones Saprobiotic Microorganisms (Saprophyte): Organism that obtains food from dead or decaying remains of other organismsBasic Nutrients CycleThe flow of nutrients such as carbon and nitrogen is cyclic 6.1 The Carbon CycleThe Increase in Carbon DioxideThe Carbon Cycle Diagram

6.2 The Greenhouse Effect and Global Warming

Consequences of Global Warming6.3 The Nitrogen Cycle

The Stages of the Nitrogen Cycle6.4 Use of Natural and Artificial Fertilisers Fertilisers Increasing Productivity6.5 Environmental Consequences of using Nitrogen FertilisersLeaching and Eutrophication78AQA A2 Biology Unit 4 Ecological SuccessionSpecification3.4.7 Ecosystems are dynamic systems usually moving from colonisation to climax communities in the process of succession.DefinitionsEcosystem: More or less a self-contained functional unit in ecology made up of all the biotic and abiotic factors of a specific areaAbiotic: An ecological factor that makes up part of the non-biological environment of an organism e.g. temperatureBiotic: An ecological factor that makes up the living environment e.g. foodCommunities: The organisms of all species that live in the same area Deciduous: Plants that shed their leaves in one seasonHabitats: The place where an organism lives, characterised by physical conditions and the species of other organisms presentClimax Community: The organisms that make up the final stage of ecological successionBiodiversity: The range and variety of living organisms within a particular areaBiomass: The total mass of a living material in a specific area at a given time, usually measured as dry mass as amount of water is variableConservation: The management of the Earths natural resources 7.1 Succession

7.2 Conservation of Habitats