Block A

• What is life?


  • Living things consist of cells
  • Living things have different levels of cellular organisation (molecular to tissue/organ)
  • Living things use energy
  • Living things respond to their environment
  • Living things grow
  • Living things reproduce
  • Living things adapt to their environment (short/long-term)
• Origin and history of life has its key features - changes, progression, complexity increase, diversity increase, life strategies reflected in Kingdoms and DNA in genomes are a common feature and correlates with the apparent relatedness
• Entropy


  A measure of disorder. The disorder of things must always increase, and physical systems decay
• Negentropy


  Something not falling into chaos and approaching the 'dangerous state of maximum entropy', death
• Life creates order, biological systems organise and maintain themselves - "life is a contained and set up system that goes against the 2nd Law"
• Life needs to combat entropy. By the sun releasing "hot" photons, the biosphere absorbs it and releases "cold" photons into the universe. Once energy isn't being taken in anymore, decay begins and entropy wins
• Maths, physics and chemistry is universal and governed by rules, laws and theorems that apply anywhere in the universe, they lead to life. So is life an inevitable process or an astronomical coincidence?
• Beginning of life


  Simple organic molecules (chemistry), forming more complex molecules (proteins/lipids/nucleic acids), that organise into cells (biology). The ability to replicate/reproduce, and the development of complex biological pathways
• Earliest evidence of life: australian sealed zircon crystals contain C12 - enriched, C13 - depleted C isotopes - signal of life processes (C12 - preference of enzymes)
• Abiogenesis


  The origin of life from non-living matter
• Abiogenesis


  1. Organic molecules forming in oxygenless world - triggered by UV light

  2. Simple gases mixed in an environment thought to mirror early Earth (>20 a.a formed)
• Chemical (RNA) world came before the biological world
• Drake's equation


  Equation that purports to yield the number of technically advanced civilisations in the Milky Way Galaxy as a function of other astronomical, biological, and psychological factors
• Journey of life


  1. Simple unicellular life - Prokaryotes/Archaea

  2. Eukaryotes

  3. Multicellular organisms
• Asgardian archaea


  • Lokiarchaeota
  • Thorarchaeota
  • Odinarchaeota
  • Heimdallarchaeota
• Asgardian archaea have many genes which were previously thought to be eukaryote-specific
• Wolbachia-like bacteria are common parasitic/mutualistic bacteria
• Both Asgardian archaea and Wolbachia-like bacteria give rise to the "Last Universal Common Ancestor" (LUCA), which gives rise to modern day eukaryotes
• Ediacara biota


  The first multicellular organisms - metazoans. With a bag/disc/mat-like appearance
• Ediacara biota


  600 MYA
• Cambrian explosion


  Hundreds of species in the world have increased to millions. The Ediacaran biota are largely lost. It's a massive burst of evolution (biodiversity) over a very short geological time period
• Cambrian explosion


  540 MYA
• Due to the increase in O2 (increased aerobic respiration), predation was made feasible - prey had to respond
• [Ca2+] increased: shells/skeletons OR just an artefact of good preservation of fossils in rocks
• Evolution


  • Explains diversity of life
  • Explains relatedness of life
  • Explains the complexity of living organisms
  • Explains how life can change over time and hence give rise to diversity/relatedness/complexity
• Charles Darwin's Origins of species

  Travelled to the Galapagos islands in HMS Beagle (22), observed variation in plants and animals in the 5 year voyage
• Human ancestry is complex; while humans aren't descendents of modern apes, we share a common (extinct) ancestor (taxonomy of apes)
• Alfred Russel Wallace's "Wallace Line"


  Exploration of Malaysia had a similar impact on him as Darwin in Galapagos - theory that animals one both sides of the line look different
• Wallace and Darwin published their ideas simultaneously
• Genetic diversity


  Random mutations accumulate over time in every organism's DNA. population thus becomes the "gene pool" (full of heritable variation) which is the fuel of evolution
• Selection pressure


  Increase in species population size is kept in check by the 'struggle for existence' - competition for resources (within species/same species), predation, disease, adverse environmental changes (temperature, O2 levels etc.), competition for a mate
• Survival of the fittest

  Genetic differences between individuals ensure some are better able to cope with a selection pressure in the environment than others
• Survival of the fittest


  Advantageous genetic changes becomes more frequent in the population over many generations
• Based on molecular mechanism, random genotypic mutation causes beneficial phenotype in the face of selection pressure causing increased production of offspring who also inherit the genotype. Mutation and its phenotype increase in the population
• Fossil record


  Remains of organisms preserved in rock (sedimentary), peat and ice. Hard tissue is best preserved (bones and shells), and most soft tissue organisms are lost to time
• Dating of rocks and their fossils

  Carbon dating/potassium-argon dating. It depends on the time-course of decay of K to Ar/radioactive decay of C14
• Different aged rocks contain different fossils. Earlier = deeper layers, a chronology can be constructed and suggest the path of evolution
• In-between types are rare, making connections difficult
• Punctuated equilibrium


  Most species appear suddenly in the geological record and gradual change isn't seen. Periods of evolutionary stasis punctuated by periods of rapid change
• Gradualist theory


  The change happens little by little over time (however the record is incomplete)