Unit 4 A2 Biology Notes AQA


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Unit 4 A2 Biology Notes AQA

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Unit 4 A2 Biology Notes AQA

  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 coordinates - 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. 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
  6. 6. 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
  7. 7. Human Populations Population Growth = (BR + Immigration) – (DR + Emigration) % Population Growth Rate = Population Change Population Start x 100 Demographic Transition Model: - Shows the change in BR, DR & population size over along period of time
  8. 8. 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
  9. 9. Age-Sex Population Pyramids West Europe: - West Africa: - High BR Short Life Expectancy High DR Developing Country Lower BR Long Life Expectancy Lower DR Developed Country
  10. 10. 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 Trophic Level Grass  Sheep  Human (Producer) (1° Consumer) (2° Consumer)
  11. 11. 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
  12. 12. Net Primary Productivity 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 Energy = Transfer (%) kJ m-2 Year -1 Energy after Transfer X 100 Energy before Transfer
  13. 13. 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
  14. 14. Photosynthesis 2 Photo Systems capture light in a chloroplast PSI (best at 700nm) & PSII (best at 680nm) Thylakoid Stroma Starch Grain 6CO2 + 6H2O + Energy = C6H12O6 + 6O2 Granum Contains Chlorophyll Substomatal Cavity Inner & Outer membrane Waxy Cuticle Loop of DNA Lamellae (Membrane joining Thylakoids) Absorption Spectrum Number of Chloroplasts Upper Epidermis Airy Cells, lots of space Palisade Layer Spongy Mesophyll Lower Epidermis Plants absorb red & blue wavelengths only reflecting green. It’s why they’re green
  15. 15. LDS (Non-Cyclic Photophosphorylation) Electron Acceptor Electron Carrier 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
  16. 16. Cyclic Photophosphorylation Happens when lack of NADP No light wasted Only uses Photo System 1 Only ATP produced
  17. 17. 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
  18. 18. 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
  19. 19. 2. Link Reaction: • • • Pyruvate oxidised by removing H Acetyl CoEnzyme A produced Per Pyruvate a CO2 molecule produced Decarboxylation – Removal of CO2 - Using Decarboxylase enzyme Pyruvate + NAD + CoA = Acetyl CoA + rNAD + CO2
  20. 20. 3. Krebs Cycle: • • • Acetyl CoA + oxaloacetate (4C) = Citrate Citrate converted to 5C compound ( 2H+ & CO2 removed) 5C to 4C Produces: • 2 x rNAD • ATP NAD – Nicotinamide Adenine Dinucleotide • rFAD FAD – Flavine Adenine Dinucleotide • CO2
  21. 21. Electron Transfer Chain When rFAD & rNAD are oxidised they release 2H & 2eElectrons used in transfer chain Hydrogen used in chemiosmosis Energy/ATP produced in ETC is used to power chemiosmosis Oxygen is the last electron acceptor. O2 + 2e- + 2H  H2O
  22. 22. Chemiosmosis In Photosynthesis & Respiration Energy (ATP) from ETC used to power Chemiosmosis If ATP synthase not present energy lost in the form of Heat instead of forming ATP Electro – Chemical Gradient Active Transport
  23. 23. Respiration
  24. 24. 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)