AQA Unit 4 A2 Biology


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AQA Unit 4 A2 Biology

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AQA Unit 4 A2 Biology

  1. 1. Biology Unit 4 AQA
  2. 2. Ecology Definitions Habitat – The place where an organism lives Population – A group of organisms belonging to the same species Community – All the populations of different organisms living and interacting in the same space at the same time Ecosystem – A community of living organisms and the abiotic factors which affect them Abiotic – The physical and chemical features of the environment Biotic – The biological features of the environment (living) Niche – A species role within it’s habitat Adaptation – A feature that members of a species have to increase their chance of survival
  3. 3. Investigating Populations Quadrats: - Set out 2 tape measure at right angles, forming the axes for the chosen area - Generate 2 random numbers (using calculator) to use as co- ordinates - Place quadrat where co-ords meet - Find mean number of species per quadrat - Multiply by size of area being sampled Transects: - It’s a line through an area to be studied to identify changes through an area - Line Transects – a tape measure is placed along the transect and the species that touch the tape measure are recorded - Belt Transects – quadrats are placed next to each other along the transect to work out species frequency & percentage cover along a transect
  4. 4. Measuring Abundance Quadrats: - Have a known dimension - Used to: - Estimate population density - Estimate % cover of an organism - Estimate the frequency of an organism Factors: - Size of quadrat – More small quadrats = more representative results - Number of quadrats – more quadrats = more reliable results - Position of quadrat – must be placed randomly to avoid bias At least 20 samples taken. Eventually a sample size is big enough that the number of species doesn’t increase much more the sample is said to be representative.
  5. 5. Sampling Strategies Random Sampling: • When area is uniformed • Use random co-ordinates Systematic: • When there’s an environmental gradient • Use a transect Stratified: • Compare two areas • Select two areas & sample within them
  6. 6. Mark-Release Recapture A known number of animals are caught and marked. They’re then released back. Later another sample are caught and the number of marked individuals is recorded Assumptions: - No reproduction - No migration - Enough time for both marked & unmarked animals to mix - Marking doesn’t affect behaviour
  7. 7. Variation in Population Size Abiotic Factors: - Affected by factors such as temperature, light, space, water etc… - When conditions are ideal an organism will thrive and vice versa Biotic Factors: - Interspecific Competition: - Competition between different species - Intraspecific Competition: - Competition between the same species - Predation – Predator & Prey populations are linked - Prey increases, more food, so predator increases. - Predator eats prey, prey decreases as they’re eaten - Predator decreases due to lack of food - Predator peaks after prey
  8. 8. Human Populations Population Growth = (BR + Immigration) – (DR + Emigration) % Population Growth Rate = x 100 Demographic Transition Model: - Shows the change in BR, DR & population size over along period of time Population Change Population Start
  9. 9. Survival Curves Show the percentage of all individuals that were born in a population that are still alive at a given age. Life Expectancy – is the age someone is expected to live to - it’s the age at which 50% of the population are still alive e.g. the life expectancy of this example is 81 as that is the age when 50% of the population are still alive
  10. 10. Age-Sex Population Pyramids West Africa: - High BR - Short Life Expectancy - High DR - Developing Country West Europe: - Lower BR - Long Life Expectancy - Lower DR - Developed Country
  11. 11. Ecosystem Definitions Producer – They’re photosynthetic organisms that manufacture organic substances using light energy, water and CO2 Consumer – They’re organisms that obtain their energy by feeding on other organisms Decomposers – When consumers & producers die, the energy can be used by organisms that break down the complex materials into single components again Food Chains – Describes a feeding relationship in which the producer are eaten by the primary consumers. They’re then eaten by secondary consumer Trophic Level – The level between each stage in the food chain Food Web – More than one food chain linked together Grass  Sheep  Human (Producer) (1° Consumer) (2° Consumer) Trophic Level
  12. 12. Energy Transfer Between Trophic Levels Little solar energy converted to chemical energy in PS: - Some is reflected due to wrong wavelength/frequency/colour - Doesn’t hit chlorophyll molecule - Lost as heat during evaporation Energy is lost along a food chain: - Not all the organism is eaten - Not all organism digested – lost in faeces - Urine - Heat in respiration - Movement - Birds & Mammals – energy used to maintain a constant body temperature (homeostasis) Not enough energy to support further trophic levels, so rarely more than 4 trophic levels present in a food chain
  13. 13. Gross Primary Productivity (GPP) – Amount of light energy that plants convert to chemical energy Net Primary Productivity (NPP) – Total amount of energy stored in a plant that is available to the next trophic level NPP = GPP - Respiration Measured in kJ m-2 Year -1 Energy Energy after Transfer Transfer (%) Energy before Transfer Net Primary Productivity = 100X
  14. 14. Ecological Pyramids Pyramids of Numbers: Pyramids of Biomass: • Fresh Biomass less accurate as different amounts of H2O present in organism • Dry Biomass better but organism has to be killed Fox Rabbit Grass Ladybird Aphid Oak Tree Oak Tree Caterpillar Parasite Caterpillar Large Fish Small Fish Zooplankton Phytoplankton This happens as zoo plankton is rapidly reproducing Pyramids of Energy: • Always pyramid shaped • Amount of energy stored in organisms at each trophic level
  15. 15. Agricultural Ecosystems Natural Ecosystem: • Haven’t been changed by human activities Agricultural Ecosystem: • Have changed by controlling abiotic & biotic conditions to make it more favourable for crops or livestock Natural Ecosystem • Solar Energy only • Lower Productivity • More Species & Genetic Diversity • Nutrients Recycled • Populations controlled naturally • Natural Climax Community Agricultural Ecosystem • Solar Energy + Food • Higher Productivity • Less Species & Genetic Diversity • Nutrients Supplemented by Fertilisers • Population Controlled by Pesticides Too • Prevented From Reaching Natural Climax Intensive Rearing Of Livestock: • Increases efficiency of energy conversion – movement restricted & warmth provided to reduce respiration – more energy available for growth • Increase energy input – more energy available for growth (optimum amount/type of food provided) • Animal produces more growth in a shorter period of time earning more money
  16. 16. Biological & Chemical Controls Herbicide: - Chemicals that kill plants Fungicide: - Chemicals that kill fungi Insecticide: - Chemicals that kill insects Pesticide: - Chemicals that kill pests Features of effective chemical pesticide: • Specific – Only toxic to specific organism not to humans • Biodegrade – Breakdown into harmless compounds in soil and chemically stable • Cost Effective – Only useful until pest becomes resistant or needs reapplying • Bioaccumulation – No build up of chemicals in the crop Biological Control Chemical Control Control using organisms that are the pest’s parasite or predator Disadvantages: Not as quick Doesn’t completely remove pest Control organism may become pest Biological Control Chemical Control Specific Always Effect Non-Target Species Control Organism Reproduces Chemicals Must Be Reapplied Pests Don’t Become Pests Develop Resistant Integrated Pest-Control Systems: - Combines Bio & Chem
  17. 17. Carbon Cycle In Carbohydrates, Lipids, Proteins & Nucleic Acids Stages: • Photosynthesis: • CO2 from atmosphere & dissolved in oceans is absorbed by producers • This produces carbon-containing compounds e.g. sugar • Feeding: • Carbon-containing compounds pass along food chain • Death: • Dead remains digested by saprobiotic microorganisms • Decay: • Saprobiotic organisms secrete enzymes that breakdown large carbon-containing compounds into smaller ones • When the microorganisms respire they release CO2 • Respiration: • All organism respire and release CO2 • Fossilisation: • When organisms don’t decay fully due to conditions in the soil • Fossil fuels form (Oil, Coal, Gas) • Combustion: • Fossil fuels are burnt & CO2 is released into the atmosphere
  18. 18. Carbon Cycle Carbon Containing Compounds In Producers Carbon Containing Compounds In Primary Consumers Carbon Containing Compounds In Secondary Consumers Feeding Feeding Carbon Containing Compounds In Dead Remains Death Saprobiotic Microorganism s Decay Death Death Fossil Fuels CO2 In Atmosphere & Dissolved In Oceans Combustion Fossilisation Respiration Photosynthesis Respiration
  19. 19. [CO2] Short-Term Fluctuations: • Day: • Plants respire & photosynthesise • Usually photosynthesis > respiration • More CO2 taken up • [CO2] falls • Night: • Plants respire • More CO2 released • [CO2] rises • Winter: • Cold temp, short days, leaf loss means photosynthesis rate decreases • Less CO2 taken up • [CO2] rises • Summer: • Warm temp, long days means photosynthesis rate increases • More CO2 taken up • [CO2] falls
  20. 20. [CO2] Long-Term Fluctuations: • Burning Fossil Fuels: • Releases CO2 into atmosphere from locked up sources • [CO2] rises • Deforestation: • Trees remove carbon from atmosphere (Carbon Sinks) • Less trees – less PS – less CO2 taken up • Forests cleared by burning – releasing CO2 • Forests cleared by chopping down – leaving the stumps – stumps are decomposed releasing CO2 by respiration
  21. 21. Global Warming Greenhouse Effect: Trapping of the sun’s warmth, increasing the global temperature Main Greenhouse Gases: CO2 Burning FF’s, respiration….. CH4 Livestock, rice farming, landfill….. CFC’s Aerosols, refrigerants….. H2O Consequences: - Rising Sea Levels - Extreme Weather - More Disease - Distribution of Species
  22. 22. Nitrogen Cycle In DNA, RNA, Proteins Nitrogen Fixation: • Lightening • N2(g)  NO3 - • Free-Living Nitrogen Fixing Bacteria (azotobacter) • N2(g)  NH4 + • Symbiotic Nitrogen Fixing Bacteria (rhizobium) • Found in root nodules of legumes (peas, clover…) • N2(g)  NH4 + Nitrification: • Carried out aerobically by nitrifying bacteria • NH4 +  NO2 - (nitrosomonas) • NO2 2-  NO3 - (nitrobacter) Ammonification: • Dead remains/waste  NH3 • Saprobiotic Microorganisms breakdown the nitrogen containing compounds Denitrification: • NO3 -  NO2(g) Anaerobically (waterlogged soil) • Denitrifying bacteria
  23. 23. Nitrogen Cycle N2(g) in Atmospher e Symbiotic N2 fixing bacteria in roots Free-living N2 fixing bacteria in soil NH4 + NO2 - NO3 - N2 in dead remains, waste N2 in Producer s N2 in Primary Consumers N2 in Secondary Consumers Lightening Nitrogen Fixation Nitrification Nitrification Denitrification Absorption DeathDeath Death Ammonification
  24. 24. Nitrogen Fixation in Roots N2(g)  NH4 +  NO3 - Nitrogen to Ammonium ions requires nitrogenase (anaerobic) This requires ATP & rNAD Sugar used by bacteria to produce ATP & rNAD Plants supply bacteria with sugar Symbiotic relationship Plant then gets NO3 - from soil Catalyst
  25. 25. Deforestation & Nitrogen Cycle Trees cut down & burnt: • Ash provides temporary high of N2 • This is rapidly leached from the soil Trees are removed: • More rain hits soil • More leaching • Soil is waterlogged allowing denitrifying bacteria to work • No decomposition so no N2 returned to soil • [NO2] falls
  26. 26. Fertilisers Chemicals that provide crops with minerals for growth More N2 provided  More growth  more PS  more productivity Natural Fertilisers: • Organic • Dead and decaying remains of plants & animals • e.g. manure Artificial Fertilisers: • Inorganic (e.g. NH4NO3) • Mined from rocks • Converted into different forms to provide correct mineral balance for particular crop • More easily leached from soil Artificial fertiliser use can lead to eutrophication & bioaccumulation Build up of chemical in body
  27. 27. Eutrophication • In most water sources nitrate levels are low so it limits algal/plant growth • Added nitrates mean the growth of plants is not limited • Algal blooms appear on water’s surface • This ‘bloom’ absorbs light and prevents it reaching the bottom • Light becomes a limiting factor, so plants at a lower depth die • Lots of dead organisms, saprobiotic organisms grow exponentially • Saprobiotic organisms require O2 • [O2] reduced as more [NO3 -] is released from decaying organisms • O2 is now a limiting factor so aerobic organisms die (e.g. fish) • Less aerobic organisms, so less competition for anaerobic organisms, so there population rises exponentially • Anaerobic organisms further decay dead remains releasing toxic waste, making the water putrid
  28. 28. Leaching • Rain dissolves soluble nutrients (e.g. nitrates) • They’re carried deep into the soil • Dissolved nutrients may find there way into water sources • May cause harm if the water is consumed • Leached nitrates can cause eutrophication Reduces Species Diversity: • N2 rich soils favour growth of grasses etc… • These species out compete other species • Other species die out • Reducing the species diversity
  29. 29. Succession Succession – describes the change of ecosystems over time Seres – various stages of succession Pioneer Species – 1st species to bring about colonisation in an area Climax Community – ultimate stable community that is in equilibrium with the abiotic conditions Primary Succession – when succession starts from bare, previously uncolonised ground or water with no life Secondary Succession – when succession starts again in an area where communities have been destroyed – it occurs more quickly Lithosere/Halosere/Hydrosere – succession from rocks/seawater/freshwater Plagioclimax – when succession is stopped
  30. 30. Succession - 1. Originally hostile – only pioneer species can live here - 2. Pioneer species die – increases organic content of soil e.g. mineral, humus - 3. Gradually environment changes & becomes less hostile - 4. More nutrients present - 5. Other species now grow, with more habitats present - 6. Climax Community eventually reached (usually oak trees)
  31. 31. Conservation Conservation – protection & management of species & habitats Methods: - Seed Banks - Fishing Quotas - Captive Breeding Programmes - Relocation - Protecting Areas/National Parks Conservation Moorland: - Sheep graze & controlled burning prevents climax community from being reached - Preventing loss of habitat for many species
  32. 32. Production of ATP • ATP- Adenine TriPhosphate • Made from ADP + Pi • Energy stored in the phosphate bond • ATPase catalyses the breakdown of ATP into ADP + Pi • ATP synthase catalyses the production of ATP • The ADP + Pi is recycled and the process starts again Properties: • Small compound – easily transported around the cell • Easily broken down (Hydrolysed) • Cell has instant energy supply
  33. 33. Photosynthesis Inner & Outer membrane Granum Contains Chlorophyll Thylakoid Stroma Starch Grain Loop of DNA 2 Photo Systems capture light in a chloroplast PSI (best at 700nm) & PSII (best at 680nm) Lamellae (Membrane joining Thylakoids) 6CO2 + 6H2O + Energy = C6H12O6 + 6O2 Number of Chloroplasts Substomatal Cavity Lower Epidermis Spongy Mesophyll Airy Cells, lots of space Palisade Layer Upper Epidermis Waxy Cuticle Absorption Spectrum Plants absorb red & blue wavelengths only reflecting green. It’s why they’re green
  34. 34. LDS (Non-Cyclic Photophosphorylation) Photolysis Of Water: 2H2O = 4H+ + 4e- + O2 Requires a photon to split water Occurs in the Thylakoids of chloroplasts Thylakoids adapted for their function: • Large SA, large area for attachment of chlorophyll, electron carriers and enzymes • Proteins in grana hold chlorophyll to allow max light intake • Granal membranes contain enzymes that help make ATP • Chloroplast contain DNA & Ribosomes to manufacture proteins for LDS quickly Electron CarrierElectron Acceptor
  35. 35. Cyclic Photophosphorylation Happens when lack of NADP No light wasted Only uses Photo System 1 Only ATP produced
  36. 36. LIS (Calvin Cycle) In Stroma RuBp – Ribulose Bisphosphate TP – Triose Phosphate (GALP) GP – Glycerate 3-Phosphate RUBISCO – Enzyme used in CO2 Fixation ATP and rNADP from LDS 6 Cycles = 1 Glucose Molecule
  37. 37. Respiration C6H12O6 + 6O2 = 6CO2 + 6H2O + Energy 1. Glycolysis: • Makes Pyruvate from Glucose • In cytoplasm • Anaerobic Process • Net Yield of 2ATP Dehydrogenation – Removal of H2 - Using dehydrogenase enzyme Substrate Level Phosphorylation - ADP + Pi  ATP
  38. 38. 2. Link Reaction: • Pyruvate oxidised by removing H • Acetyl CoEnzyme A produced • Per Pyruvate a CO2 molecule produced Pyruvate + NAD + CoA = Acetyl CoA + rNAD + CO2 Decarboxylation – Removal of CO2 - Using Decarboxylase enzyme
  39. 39. 3. Krebs Cycle: • Acetyl CoA + oxaloacetate (4C) = Citrate • Citrate converted to 5C compound ( 2H+ & CO2 removed) • 5C to 4C Produces: • 2 x rNAD • ATP • rFAD • CO2 NAD – Nicotinamide Adenine Dinucleotide FAD – Flavine Adenine Dinucleotide In Mitochondrion
  40. 40. Electron Transfer Chain When rFAD & rNAD are oxidised they release 2H & 2e- Electrons used in transfer chain Energy/ATP produced in ETC is used to power chemiosmosis Hydrogen used in chemiosmosis Oxygen is the last electron acceptor. O2 + 2e- + 2H  H2O
  41. 41. Chemiosmosis In Photosynthesis & Respiration Energy (ATP) from ETC used to power Chemiosmosis Active Transport If ATP synthase not present energy lost in the form of Heat instead of forming ATP Electro – Chemical Gradient
  42. 42. Respiration
  43. 43. Anaerobic Respiration Instead of pyruvate being converted into Acetyl CoA it’s converted into ethanol (in plants and yeast) and lactic acid (in animals and some bacteria)
  44. 44. Genetics Allele: Variant of a gene Phenotype: Characteristics of an organism, often visible, resulting from both it’s genotype and the effects of the environment Genotype: Genetic composition of an organism Poly-genetic Inheritance: More than one gene to produce a characteristic Gene: Section of DNA that codes for a protein Gamete: Reproductive cell that fuses with another gamete during fertilisation Trait: A characteristic Multiple Allele: Many forms of a gene (e.g. Blood group) Heterozygous: One Dominant & One Recessive e.g. Rr Homozygous: Both recessive or dominant e.g. RR or rr Codominant: Both dominant or recessive contribute to final trait
  45. 45. Monohybrid Genetics Red x White RR rr OR OR Or Or R R r Rr Rr r Rr Rr All Rr Red x Red Rr Rr OR OROr Or R r R RR Rr r Rr rr 1RR : 2Rr : 1rr
  46. 46. Sex Linked Diseases Carrier Girl x Well Boy XHXh XHY XH Y XH XHXH XHY Xh XHXh XhY 1 Carrier Girl XHXh 1 Well Girl XHXh 1 Well Boy XHY 1 Ill Boy XhY Male = XY Female = XX
  47. 47. Dihybrid Crosses Yellow Smooth Green Wrinkled YYSS yyss x All YySs Yellow Smooth Yellow Smooth YySs YySs x 9YYSS : 3YySS : 3YYSs : 1yyss F1 Generation F2 Generation
  48. 48. Hardy-Weinberg Equation Assumptions: No mutations No migration/Population Isolated Large populations Random Mating No natural selection P2 + 2PQ + Q2 = 1 P + Q = 1 1RR : 2Rr : 1rr e.g. 1 in 10,000 Albino (Recessive) Population = 10,000 Q2 = 1/10,000 Q = 0.01 P = 1 – Q P = 0.99 (2 x P x Q) x 10,000 = 198 Heterozygotes P2 x 10,000 = 9801 Homozygous Dominants
  49. 49. Speciation • Development of a new species • Population separated – e.g. geographical isolation • Abiotic conditions in each location is different, so there are different selection pressures • In colder climates polar bears with longer fur are more likely to survive, reproduce & pass allele to offspring • Eventually the polar bears become so different that a new species develops – so they’re no longer able to breed with the other group Polar Bears Variation in Fur Length Stabilising Directional