Topic 5

• Ecosystem


  All the organisms living in a particular area, known as the community, as well as all the nonliving elements of that particular environment (e.g. climate, nutrients being cycled etc.)
• Community


  All of the populations of all the organisms living in a particular habitat at a particular time
• Population


  All of the organisms of a particular species living in a particular habitat at a particular time
• Habitat


  The place where an organism lives
• Factors controlling distribution and abundance of organisms in a habitat

  • Biotic (living) factors (e.g. predators, food availability, parasitism or disease)
  • Abiotic (non-living) factors (such as light, oxygen or moisture levels and temperature)
• Ecological niche

  The particular role of a species in its habitat, consisting of its biotic and abiotic interactions with the environment
• The niche concept states that only one organism can occupy each niche in a given habitat at a given time - if two or more species have a niche that overlaps, the best adapted will out-compete the others in surviving to reproduce
• Succession


  The change in species inhabiting an area over time, brought about by changes to the environment made by the organisms colonising it themselves
• Primary succession


  Occurs when an area previously devoid of life is first colonised by communities of organisms
• Secondary succession


  Occurs with existing soil that is clear of vegetation, such as after a forest fire

  
• Pioneer species


  • Adapted to survive in harsh conditions where other species would not survive, e.g. lichens that can penetrate rock surface and break it down, or hold together loose shifting sands
• Humus


  The organic component of soil formed from the decomposition of organisms
• Climax community


  The most productive, self-sustaining and stable community of organisms that the environment can support, usually with only one or two species
• Light-dependent reaction of photosynthesis

  1. Electrons are excited to a higher energy level using the energy trapped by chlorophyll molecules in the thylakoid membranes

  2. Electrons are passed down the electron transport chain from one electron carrier to the next, generating ATP from ADP and inorganic phosphate in a process called photophosphorylation

  3. Photolysis: light energy breaks apart the strong bonds in water molecules, forming hydrogen and hydroxide ions, with the electrons released replacing lost electrons in chlorophyll of PSII
• Cyclic phosphorylation


  1. Photon hits chlorophyll in photosystem I (PSI)

  2. Electrons are excited

  3. Electrons taken up by an electron acceptor

  4. Electrons passed along an electron transport chain, energy released and ATP synthesised

  5. Returns to chlorophyll in PSI
• Non-cyclic phosphorylation


  1. Photon hits chlorophyll in photosystem II (PSII)

  2. Electrons are excited

  3. Electrons taken up by an electron acceptor, passed along an electron transport chain to PSI, energy released and ATP synthesised

  4. Photon hits chlorophyll in Photosystem I, electrons excited

  5. Electrons taken up by an electron acceptor, passed along an electron transport chain to NADP, NADP takes up H+ ion and forms reduced NADP
• Light-independent reaction (Calvin cycle) of photosynthesis

  1. RuBP (5 carbon compound) combined with CO2 in carbon fixation reaction catalysed by RUBISCO

  2. Unstable 6 carbon intermediate splits into two 3-carbon GP molecules

  3. Reduced NADP and ATP used to reduce two GP molecules to GALP

  4. One in six GALP molecules used to make glucose, converted to other organic compounds

  5. Remaining five in six TP molecules used to reform RuBP with ATP
• Chloroplast


  • Contains stacks of thylakoid membranes (grana) with photosynthetic pigments like chlorophyll arranged as photosystems, site of light-dependent stage
  • Contains stroma with enzymes for light-independent stage
  • Chloroplast envelope controls movement of substances in and out, supports endosymbiotic theory
  • Contains starch granules to store photosynthesis products

  
• Net primary productivity (NPP)

  The rate at which energy from the sun is converted into the organic compounds of living organisms
• Chloroplasts


  • Site of photosynthesis
  • Contain stacks of thylakoid membranes (grana) which contain photosynthetic pigments like chlorophyll arranged as photosystems (site of light-dependent stage of photosynthesis)
  • Contain stroma which has enzymes required for light-independent stage of photosynthesis
  • Chloroplast envelope controls movement of substances in and out of the organelle, supports endosymbiotic theory
  • Contain starch granules to store products of photosynthesis

  
• Net primary productivity (NPP)


  The rate at which energy from the sun is converted into the organic molecules that make up new plant biomass
• Gross primary productivity (GPP)


  The energy transferred to primary consumers
• NPP


  GPP - R (respiration)
• Energy losses at each trophic level

  • Undigested matter
  • Respiration (exothermic, transfers thermal energy to surroundings)
  • Metabolic waste products like urea
• Global warming


  Gradual increase in the average temperature of the Earth's atmosphere and surface, believed to lead to permanent climate change
• Evidence for climate change

  • Records of carbon dioxide levels
  • Temperature records
  • Pollen in peat bogs
  • Dendrochronology (study of tree rings)

  
• Extrapolation


  Using data to make predictions
• Models


  Used to predict future climate change, have limitations as they don't include factors like human efforts to reduce greenhouse gas emissions
• Greenhouse effect


  Short-wavelength UV radiation passes through atmosphere, reflected rays of longer wavelength (infrared) are trapped by gases like CO2 and CH4, leading to increased temperature of Earth's surface and atmosphere
• Effects of climate change

  • Changes in distribution of species
  • Changes to development (e.g. sex ratio)
  • Disrupted life cycles
• As temperature increases


  Initially rate of enzyme-catalysed reactions increases, but then decreases above optimum temperature as enzymes become denatured
• Carbon cycle


  Knowledge can help humans make decisions to reduce greenhouse gas levels in atmosphere

  
• Ways to reduce global warming

  • Growing plants for biofuels (carbon neutral)
  • Reforestation
• Climate change is an example of an issue where the scientific consensus reached may depend on who is reaching the conclusions
• Ideas are validated and conclusions are drawn via scientific conferences and publication in peer-reviewed scientific journals
• Evolution


  Change in the heritable traits of biological populations over successive generations, due to change in allele frequency affected by changing selection pressures
• Evolution via natural selection

  1. Variety of phenotypes exist due to random mutation

  2. Environmental change occurs, changing selection pressure

  3. Individuals with advantageous alleles survive and reproduce, passing on those alleles

  4. Allele frequency in population changes over time
• Reproductive isolation


  Reduced or stopped gene flow between two populations, leading to accumulation of genetic differences and formation of new species
• Speciation


  When two populations can no longer interbreed to produce fertile offspring, they are considered separate species
• Types of speciation


  • Allopatric (geographic isolation)
  • Sympatric (non-geographic isolation)