Biology Unit 2

• Emergence


  Properties or behaviors that emerge only when parts interact as a whole
• Fitness


  A measure of survival and reproduction of a trait or genotype
• Phenotype


  Observable characteristics or trait
• Anthropocentrism


  A human-centered perspective
• Fixation


  Permanent establishment of trait, gene, or genotype
• Convergent Evolution


  Appearance of similar traits NOT due to a common ancestor
• Microbial Mats are the earliest evidence of life on Earth (that most scientists agree on)
• Microbial Mats


  • Multilayered sheets of prokaryotic cells
  • Each layer is dominated by specific types of microorganisms
  • Creates food chain in the mat
  • Possible birthplace of eukaryotes and multicellularity
• Hypothermal Vents


  • Chemical energy to form large molecules from smaller ones
  • Nothing is in equilibrium; lots of chemical energy
  • Constrains to where life can live
• Anoxygenic Photosynthesis

  • Enabled movement to new environments
  • Do not produce oxygen
  • Need chemical energy from the environment to make their energy
• Oxygenic Photosynthesis


  Necessary for the evolution of complex life
• Bacteria and archaea can be multicellular, usually under special environmental conditions, but not exactly the same as "complex" multicellularity in eukaryotes
• Requirements for Multicellularity


  • Cell-cell adhesion by forming a matrix membranes
  • Intercellular communications (i.e. it's hot, there's danger, etc.)
• 3 Classes of Multicellularity in Bacteria


  • Filaments
  • Aggregates
  • Multicellular Magnetotactic Prokaryotes (MMP)
• Filaments


  • Formation of long chains of cells, some of which elongate but do not divide
  • Linear or brance
  • Single or multiple layers
  • Many clonal in origin
  • Not a necessary to be in multicellular form to survive
• Aggregates


  • Cells embedded in self-produced extracellular matrix
  • Biofilm or swarms
  • Cells have distinct morphologies
  • Can be colonel or non-colonal
  • Not a necessary to be in multicellular form to survive
• Multicellular Magnetotactic Prokaryotes (MMP)


  • Magnetotactic: orient themselves to Earth's magnetic field
  • Joined at tight intercellular junctions
  • Division by fission of entire structures
  • Only OBLIGATE multicellular bacteria
  • Can be a colonel or not
• Multicellularity is a major evolutionary transition and a key step in the evolution of life
• Multicellularity evolved several times and is not a homology
• Fitness


  An organism's ability to pass on its genetic material to the next generation
• All matter is subject to the physical laws of the universe, and life has additional constraints from fitness and ancestors
• Advantages of Multicellularity


  • Resistance to Stress: temperature, pH, osmotic pressure, and more
  • Resistance to Predidators: bigger = easier to resist engulfment
  • Improved Nutrient Acquisition: better at catching and consuming prey
  • Division of Labor: leads to cell specialization
• Disadvantages of Multicellularity


  • Energetic costs: need to make adhesive and communication molecules
  • Physical Limitations: less freedom of movement
  • Need to Resolve Conflicts Between Cells: what to do with "cheater" cells?
• Multicellularity enables new possibilities like cell differentiation, development of structures, and implications to intelligence and consciousness
• Theories of Multicellularity


  • Symbiotic Theory: cooperations of single-celled organisms from different species, each with a different role
  • Colonial Theory: cooperations of single-celled organisms from the same species
  • Cellularization Theory: a single cell with multiple nuclei
• Cell

  Basic structural and functional unit of life
• Tissue

  An ensemble of similar cells that together carry out a specific function
• Differentiation


  Cell or tissue specialization
• Adhesion


  Cells interact and adhere with neighboring cells
• Morphology


  Form and structure of organisms
• Simple Multicellularity


  • Reproductive and somatic cells
  • Adhesive molecules to maintain a unified structure
  • Limited signaling and sharing of resources between cells
• Complex Multicellularity


  • Reproductive, somatic, and other complex cell differentiation
  • Adhesive molecules to maintain unified structures
  • Organized signaling and resource-sharing
  • Tissue differentiation (specialized tissues) and programmed cell death (apoptosis)
• Diffusion


  • Things will flow from high concentration to low (equilibrium) concentration
  • Unicellular organisms can exchange gasses through diffusion (passive) through channels
  • Limited in size by ambient pressure of O2 (only a few mm thick)
• Bulk Transport


  • How complex multicellular organisms transport oxygen
  • Cells -> tissues -> organs -> organ systems
  • Interactions are very important; parts do not make the system
  • Bilaterian animals mostly have well-developed circulatory and respiratory systems
  • Vascular plants transport with xylem and phloem
• The Eukaryotic Cell


  • Lots of genes needed for complex multicellularity
  • Eukaryotic DNA is highly condensed
  • Dynamic cytoskeleton and membrane systems
  • Cell differentiation and programmed cell death (apoptosis)
• All living organisms (mostly) must take in oxygen and repel carbon dioxide
• Unicellular life and simpler animals can directly exchange with the environment through diffusion, while complex body plans require cell adhesion, communication, and differentiation
• Complex multicellular organisms must also process complex genetic and signaling pathways only possible in eukaryotic cells
• Evolution cannot predict the future, but traits with immediate benefits will remain in a population
• Sexual reproduction is nearly universal across eukaryotes