SNAB topic 5

• 5.1 Understand the terms ecosystem, community, population and habitat.

  Ecosystem: Allthe organisms, bioticand abiotic elementsof an environment

  Population- All of the organisms ofONE speciesliving in a habitat at one time

  Community:All populationsof organisms living in a habitat

  Habitat-the place where an organism lives
• 5.2 Understand that the numbers and distribution of organisms in a habitat are controlled by biotic and abiotic factors.

  The numbers and distribution of organisms in a habitat arecontrolled by biotic and abiotic factors.
• 5.3 Understand how the concept of niche accounts for distribution and abundance of organisms in a habitat.


  Niche-the role a species takes in its habitat

  Niche concept: Only one organism can occupy each niche in a habitat at one time. If there is an overlap, thebest adapted organism will outcompetethe other organism.

  Distribution and abundance willdepend on the number and type of niches availablewithin the habitat
• CORE PRACTICAL 10:

  Carry out a study on the ecology of a habitat, such as using quadrats and

  transects to determine distribution and abundance of organisms, and

  measuring abiotic factors appropriate to the habitat.


  EquipmentQuadrat (Open, 10x10)Transect (50m)ClipboardEquipment for chosen abiotic variable (lux meter for light intensity; barometer for wind pressure; densiometer for shade/cover; hygrometer for humidity)

  MethodChoose a site where there is a clear gradient in an abiotic variableLay out transectPlace quadrat at set intervals with bottom left corner on the mark at each sampling point

  Record percentage cover at each sampling point for chosen species at each interval, by counting how many squares are mostly covered by the selected species.

  Measure and record the abiotic variable at each sampling point. Take multiple recordings at each sample point for a mean value.

  GraphPlot a graph of percentage cover against the chosen independent, abiotic variable.

  StatisticsCalculate means for the repeats of abiotic factors at each sampling point-UseT-testtocompare meansbetween two groups-UseSpearman'sto assesscorrelationbetween variables-UseChi-squared testto evaluate if there is asignificant difference/associationbetween two variables.
• 5.4 Understand the stages of succession from colonisation to a climax community.

  Primary succession:Coloniser species, establishes habitable soil

  Secondary succession- takes over barren soil

  Organic matter is added to the groundthrough plant death.

  [Rock is penetrated by roots. Sands are held together by roots]

  Soil conditions improve.

  More complex /varied/productive plants such as shrubs can survive, followed by shade intolerant trees and shade tolerant trees. Eventually, aclimax communityforms.
• 5.5 Understand the overall reaction of photosynthesis as requiring energy from light to split apart the strong bonds in water molecules, storing the hydrogen in a fuel (glucose) by combining it with carbon dioxide and releasing oxygen into the atmosphere.


  Overall equation:

  6H2O + 6CO2 --> C6H12O6 + 6O2

  
• 5.6 Understand how phosphorylation of ADP requires energy and that hydrolysis of ATP provides an immediate supply of energy for biological processes.

  ADP + Pi --(energy)--> ATP

  ATP-----> ADP + Pi + energy

  ATP provides an immediate supply of energy

  energy is released from: the exothermic reaction of hydrogen bonds being made between the released Pi + water molecules.
• 5.7 Understand the light-dependent reactions of photosynthesis including how light energy is trapped by exciting electrons in chlorophyll and the role of these electrons in generating ATP, reducing NADP in photophosphorylation and producing oxygen through photolysis of water.


  PSI absorbs light energy of 700nm. PSII absorbs at 680.

  Light excites electrons in chlorophyll in the thylakoid membrane, within the chloroplast.Light also splits water byphotolysis, releasing 1/2O2 , 2 electrons and protons

  The electrons leave chlorophyll, travel down electron carriers, releasing energy.This energy is used to generate ATP

  In cyclic photophosphorylation, the electrons lost by PSII are regained from the ones released from photolysis of water.

  In non cyclic photophosphorylation,PSI loses electrons, that go down the ETC and reduce NADP (with protons), making NADPH. PSI only regains electrons from accepting the ones from PSII through the last electron carrier in the ETC.
• 5.7 (PART B) The light dependent reaction

  
• 5.8 i) Understand the light-independent reactions as reduction of carbon dioxide using the products of the light-dependent reactions (carbon fixation in the Calvin cycle, the role of GP, GALP, RuBP and RUBISCO).


  -CO2 isfixatedwithRuBP, a 5 carbon compound, by theRUBISCO enzyme

  -The unstable 6 carbon intermediate splits into 2GP.

  -The GP is reduced by NAPH using energy from ATP, to form GALP

  1/6 GALP--> glucose--> polysaccharides, lipids, amino acids, nucleic acids

  5/6 GALP--> regenerate RuBP using energy from ATP
• 5.8 i) (PART B) Calvin cycle

  
• 5.8 ii) Know that the products are simple sugars that are used by plants, animals and other organisms in respiration and the synthesis of new biological molecules (polysaccharides, amino acids, lipids and nucleic acids).

  Glucose--> polysaccharides, lipids, amino acids, nucleic acids
• CORE PRACTICAL 11:

  Investigate photosynthesis using isolated chloroplasts (the Hill reaction).


  Equipment•Leaf sample•scissors•mortar and pestle•Centrifuge & tubes•Ice-water-salt bath•Glass rod•Measuring cylinder•Beaker•Pipettes•Lamp•Isolation medium (sucrose solution)•Buffer•DCPIP solution•Colorimeter

  Method1) Cut and crush leaf sample2) Place in cold isolation solution3) Filter/strain sample into beaker using funnel and muslin cloth•Place beaker in a cold water bath4) Centrifuge a sample in a tube at high speed for 10 minutes•Once chloroplasts are separated, discard the supernatant5) Add ice cold isolation medium to pellet/sediment•Add buffer solution, mix6) Pour 5cm3 of the solution into 5 test tubes7) Place test tube rack with one of the test tubes a determined distance away from the lamp8) Add 10cm3 DCPIP to the test tube9) Immediately take a sample and place it in a colorimeter, measure the absorbance under ared filter10) Vary the distances from the lamp

  •Take a sample every two minutes for 10 minutes

  ControlPlace one of the tubes in a dark cupboard, covered with tin foil. Measure the absorbance for this and compare the results with this value.

  GraphPlot a graph of absorbance against time for each distance from the light

  Explanation/conclusionAs light intensity decreases, the rate of photosynthesis decreasesThis means less electrons are released by chlorophyllThis means DCPIP is decolourised less

  
• 5.9 Understand the structure of chloroplasts in relation to their role in

  photosynthesis.

  
• 5.10 i) Be able to calculate net primary productivity.

  NPP=GPP-R
• 5.10 ii) Understand the relationship between gross primary productivity, net primary productivity and plant respiration.


  •GPP=Total input of energy (e.g. from sun or from energy available in carbohydrates in plants)•R=energy used plant respiration•NPP=energy stored as biomass available to herbivores

  NPP=GPP-R

  GPP is higher than NPPIn animals:•Inefficient digestion (<100% absorbed), egestion•Respiration

  In plants:•Some light passes through leaves (translucent)•Not all light hits leaves•Not all wavelengths of light absorbed•Some light reflected
• 5.11 Know how to calculate the efficiency of biomass and energy transfers between trophic levels.


  (percentage increase/decrease calculations)Energy efficiency = (net productivity energy received) x 100
• 5.12 Understand the different types of evidence for climate change and its causes, recognising correlations and causal relationships.

  Evidence•Records of CO2 levels•Temperature records

  Pollen found in peat bogs-•pollen is preserved in peat bogs•a plant species can be identified from its pollen•climate affects the type of plants growing•depth of peat correlates with period of time since pollen was produced•changes in pollen over time indicate changes in climate

  Dendrochonology- the study of tree rings;•Size/width of rings is affected by the temperature in each year•tree rings arewider in warm/wet years•tree rings arethinner when it is cold/dry.•Very thin rings may indicatedroughts.•Changes in width of rings over time (from centre) indicate a changing climate
• 5.12 sorry i forgot to include ice cores


  Ice cores are another way of analysing climate change:

  •ice from deeper below is older

  •ice has bubbles

  •bubbles have different levels of CO2 going up the ice core

  •this indicates climate change over time
• 5.13 Understand the causes of anthropogenic climate change, including the role of greenhouse gases (carbon dioxide and methane) in the greenhouse effect.

  Greenhouse gases are released byfossil fuel burningandlivestock.

  Thesetrap infrared radiationwithin the atmosphere, leading to an increase in Earth's surface temperature
• 5.14 i) Understand that data can be extrapolated to make predictions and that these are used in models of future climate change.


  Data can be extrapolated to make predictions and that these are used in models of future climate change.
• 5.14ii) Understand that models for climate change have limitations.

  Limitations of models-They do not include factors such ashuman effort to reduce greenhouse gas emissions.-Limited power of computers/equipment-Models' inability to reproduce atmospheric phenomena
• 5.15 Understand the effects of climate change on plants and animals (distribution of species, development and life cycles).

  Effects of climate change•Changing rainfall patterns•Changes in seasonal cycles

  Effects on plants/animalsChange in distributionof species, i.e. migration.Migration may causeextinctionof species due to competitionChanges in developmentof species. e.g. sex determination of some reptiles is dependent on temperatureDisrupted life cyclesof species
• 5.16 Understand the effect of temperature on the rate of enzyme activity and its impact on plants, animals and microorganisms.

  As temperature increases, enzyme activity initially increases too.However, past the optimum temperature, enzymes becomedenaturedand the activity slows down because the shape of theactive site has changed.

  Increased temperature may meandevelopment of animals could be sped up, shortening the life cycle. Sex determination of reptiles may be affected.

  Increasing temperature may mean thatmicroorganisms will multiply fasteras cellular activity speeds up. It may also be past the optimum temperature for some microorganisms so they could die off. Hotter temperatures are more welcoming to pathogens (37degreesC)
• 5.17 Understand how evolution (a change in the allele frequency) can come about through gene mutation and natural selection.

  •Variation of phenotypes/genotypes from random mutations.

  
  

  •Environmental change poses as a Selection pressure

  
  

  •Some individuals have advantageous alleles

  ->Selective advantage for these individuals

  -->Can survive and reproduce

  --->Passes on alleles to their offspring

  
  

  ----->Over time, the frequency of certain alleles within a population changes.

  
  

  (This can lead to sympatric speciation between populations, when new species are developed)
• 5.18 Understand the role of the scientific community (scientific journals, the peer review process, scientific conferences) in validating new evidence, including proteomics and genomics, that supports the accepted scientific theory of evolution.

  Scientific community role•Scientific journals•The peer review process•Scientific conferences

  Proteomics/Genomics are thestudies of proteins and genomes.

  •By comparing genomesbetween species, scientists can construct phylogenetic trees,linking multiple species to common ancestors. (This is done by seeing the degree of similarity between the genetic sequence in both species.)

  By studying proteins•An organism'sadaptation to its environmentthrough the proteins can be understood.

  •A phylogenetic tree can be made bycomparing primary sequences of amino acids in the proteins of similar species.The more similar the sequences are, the more similar the DNA is.
• 5.19 Understand how isolation reduces gene flow between populations, leading to allopatric or sympatric speciation.

  Allopatric isolation: geographic isolation of two populations

  Sympatric isolation: non-geographic isolation e.g. temporal, behavioural, gametic, anatomic

  Isolation reduces gene flow between the population and accumulation of genetic differences can causespeciation.

  This means that they canno longer breed to produce fertile offspring
• CORE PRACTICAL 12: Investigate the effect of temperature on the initial rate of an enzyme-catalysed reaction, to include Q10.


  EquipmentWater bathBoiling tubeH2O2 solutionSoaked peasGas syringeMortar and pestleStopwatchDelivery tube/bung

  Method1) Measure set mass of peas2) Grind and place in boiling tube3) Set up delivery tube and gas syringe4) Add 5cm3 H2O25)Immediately attach bung/delivery tube to boiling tube6) Time reaction for a controlled time7) Measure volume of gas produced at regular time intervals8) Repeat experiment at different temperatures

  Control variables•Concentration of H2O2 solution•Mass of peas•Time of reaction

  GraphPlot graph of temp against concentration

  CalculationRate=Volume of gas/timeQ10=(Second rate/First rate) ^(10/second temp-first temp).

  Q10 being larger means that temperature increase affects the reaction more (typically around 2-3)

  
• CORE PRACTICAL 13: Investigate the effects of temperature on the development of organisms (such as seedling growth rate, brine shrimp hatch rates).


  Equipment5 water bathsBeakerSea saltEgg cystsMagnifying glass

  Method1)Measure 2g sea salt, add to 100cm3 water in beaker2)Take a pinch of egg cysts, count 40 with magnifying glass3)Place 40 in 5 separate beakers4)Place separate beakers in separate water baths (at 10°C, 15°C, 20°C, 25°C and 30°C)5)Count number of hatches larvae each day6) Repeats can be made for each temperature

  GraphPlot number of larvae against time

  StatisticsSpearman's rank to determinestatistical relationship.
• 5.20 Understand the way in which scientific conclusions about controversial issues, such as what actions should be taken to reduce climate change or the degree to which humans are affecting climate change, can sometimes depend on who is reaching the conclusions.


  The conclusions of decisions regarding climate change may lie in their own best interests

  
  

  E.g. An oil company would likely not vouch for sanctions on fossil fuels
• 5.21 Understand how knowledge of the carbon cycle can be applied to methods to reduce atmospheric levels of carbon dioxide.

  -Reducing combustion of fuels

  -Reducing livestock numbers

  -Reforestation to increase photosynthesis

  
  

  (Carbon cycle image attached)

  
• 5.22 Understand how reforestation and the use of sustainable resources, including biofuels, are examples of the effective management of the conflict between human needs and conservation.


  Examples of the effective management-Reforestation-Use of sustainable resources