Life Science

• Evolution and Adaptation


  • All biological beings must be able to adapt to their environment in order to survive living in their environment
• Adaptation


  Any structure, behavior, or internal process that allows response to a stimulus. It gives better chance of survival for an organism
• Evolution


  Gradual accumulation of adaptations over time
• Adaptations of a polar bear

  • White fur that serves as a camouflage against the ice
  • Thick layer of fat under their skin for thermoregulation
  • Long stiff hair between pads of their feet protects the bear's feet from cold and helps keep the bear from slipping on slippery ice
  • Strong swimmers – enables them to catch prey
  • Hollow fur traps air inside, which makes the bear buoyant in water. The layer of air also provides insulation for the cold Arctic air and water
  • Small rounded ears prevents water from entering the bear's ears and freezing their eardrums
• Natural selection


  Process by which individuals that are better suited to their environment survive and reproduce most successfully; also called survival of the fittest
• Descent with modification


  Each living species has descended, with changes, from other species over time. This is a result of natural selection over a long period of time, which produces organisms that have different structures, establish different niches, or occupy different habitats
• Stimulus


  Any condition in the environment that requires an organism to adjust
• Response


  Reaction to stimulus
• Homeostasis


  Stable level of internal conditions
• Types of organism by cell organization


  • Unicellular – organism is made up of one cell
  • Multicellular – organism is made up of more than one cell
• Differentiated cells


  Different cells in one organism have different functions. Examples are the heart cells and lung cells
• Metabolism


  The chemical process by which a plant or an animal uses food, water, etc., to grow and heal and to make energy
• Categories of living things according to food source

  • Autotrophic – an organism that uses energy from the sun for photosynthesis to make its own food (plants)
  • Heterotrophic – an organism that ingests food to receive energy (animals, fungi, etc.)
• DNA (Deoxyribonucleic acid)


  Contains the hereditary material of a cell; the blueprint of reproduction, growth and development
• Growth


  An increase in the amount of living material
• Development


  All changes that an organism undergoes in its lifetime
• Ecology


  The study of the interaction of organisms with their environment
• Energy flow in an ecosystem

  Energy from the sun is passed from one organism to another; producers (plants) to herbivore (plant eater) to carnivore (meat eater) to decomposers (breakdown dead organisms)
• Factors that determine interdependence, survival, and growth of an organism in an environment


  • Abiotic factors – non-living factors such as air, water, energy, soil, temperature, and minerals are needed for survival
  • Biotic factors – include all living things on earth
• Theories about the Origin of Life


  • Special Creation - Life-forms may have been put on earth by supernatural or divine forces
  • Extraterrestrial Origin - Life may not have originated on earth at all; instead, life may have infected earth from some other planet
  • Spontaneous Origin - Most scientists tentatively accept the spontaneous origin. This theory states that living organisms can originate from inanimate objects
• When life first appeared on earth, the environment was very hot. All of the spontaneous origin hypotheses assume that organic chemicals that were the building blocks of life arose spontaneously at that time
• According to our previous discussions, the earth was formed about 4.5 billion years ago. Most researchers agree that life appeared as the primitive earth cooled and its rocky crust formed, but there is little agreement as to where it occurred
• Theories about where life started


  • At the ocean's edge under the blanket of a reducing atmosphere
  • Under frozen oceans
  • Deep in the earth's crust
  • Within clay
  • At deep-sea vents
• Gunter Wachtershauser's hypothesis


  Life might have formed as a by-product of volcanic activity, with iron and nickel sulfide minerals acting as chemical catalysts to recombine gases spewing from eruptions into the building blocks of life
• Wachtershauser and coworkers were able to use this unusual chemistry to build precursors for amino acids, and to link amino acids together to form peptides
• Critics point out that the concentration of chemicals used in their experiments greatly exceed what is found in nature
• Clay hypothesis


  Life is the result of silicate surface chemistry, with the surface of clays having positive charges to attract organic molecules and exclude water, providing a potential catalytic surface on which life's early chemistry might have occurred
• There is little evidence that the clay hypothesis could actually occur
• Deep-sea vents hypothesis


  Life originated at deep-sea hydrothermal vents, with the necessary prebiotic molecules synthesized on metal sulfides in the vents
• Miller-Urey experiment


  Early attempt to see what kinds of organic molecules might have been produced on the early earth, carried out by Stanley L. Miller and Harold C. Urey
• Miller-Urey experiment


  1. Assembled a reducing atmosphere rich in hydrogen and excluding gaseous oxygen

  2. Placed this atmosphere over liquid water, which would have been present at ocean's edge

  3. Maintained this mixture at a temperature somewhat below 100°C

  4. Simulated lightning by bombarding it with energy in the form of sparks

  
• Within a week they found 15% of carbon originally present as methane gas had converted into other simpler carbon compounds, including formaldehyde, hydrogen cyanide, formic acid, urea, and amino acids glycine and alanine
• Similar experiments were performed later by other scientists and more than 30 different carbon compounds were identified, including the key molecule of life, adenine, which is one of the bases found in DNA and RNA
• Bubble theories


  Theories that the location where life started is at "ocean's edge", with bubbles playing a key role in the evolution of cells
• Alexander Oparin's "primary abiogenesis" theory


  Suggested that life must have arisen from non-living matter under a set of very different environmental circumstances, with cells concentrating materials within themselves by means of a cell membrane in order to evolve, and called the chemical concentrating bubble-like structures protobionts
• Louis Lerman's bubble theory

  Volcanoes erupted under the sea, releasing gases enclosed in bubbles, which concentrated inside the bubbles and reacted to produce simple organic molecules, which were then released into the air, bombarded by energy sources, and fell back into the sea in raindrops to begin the process again
• The earliest evidence of life appears in microfossils (fossilized forms of microscopic life) that are 3.5 billion years old, which were small (1 to 2 micrometers in diameter), single-celled, lacked appendages, and had little evidence of internal structure, resembling present-day bacteria or prokaryotes
• Archaebacteria


  The first major group of bacteria, representing the surviving representatives of the first ages of life on earth, found in oxygen-free depths or high-temperature environments, lacking peptidoglycan in their cell walls, including methanogens and extreme halophiles and thermophiles
• Eubacteria


  The second major group of bacteria, with very strong cell walls and a simpler gene architecture, including cyanobacteria that are photosynthetic and played a role in increasing the concentration of free oxygen in the earth's atmosphere