Introduction Notes


All Materials © Cmassengale

Study of Life  

  • First life forms arose on Earth more than 3.5 billion years ago  
  • Single-celled, microscopic organisms (living thing) appeared first & floated alone in seas  
  • Over 40 million species (types of organisms) exist with only about 2 million identified 
  • Many organisms are unidentified & new species are still discovered  
  • Biology is the study of all living things and how they interact with each other & their environment  
  • Over long periods of time, species changed or evolved so that new species arose from earlier organisms & came to inhabit almost every part of the earth (bacteria living in thermal vents, parasites living inside another organism, etc.)  
  • Organisms must adapt to their specific environment to survive & reproduce


Unifying Themes of Biology 

 The six unifying themes include:  

  1. Cell Structure & Function
  2. Stability & Homeostasis
  3. Reproduction & Inheritance
  4. Evolution
  5. Interdependence of Organisms
  6. Matter, Energy, & Organization

Cell Structure & Function  

  • Cell is the basic unit of structure & function  
  • All organisms are made of one or more cells; Unicellular (one celled) or Multicellular (Composed of more than one cell)  


  • Cells are small but highly organized; they contain specialized structures that carry out the jobs of a cell called organelles  


  • There are many different kinds of cells, but all cells have similarities
  • All cells are surrounded by a cell membrane, contain cytoplasm, and have DNA (the genetic information for making new cells or cell structures)  
  • New cells made by unicellular organisms are identical (clones) to the parent cell that produced them – asexual reproduction  
  • Multicellular organisms begin life as one fertilized cell (sexual reproduction), but the cells multiplied and underwent differentiation (changed structure & function) to become many different kinds of cells  

Stability & Homeostasis  

  • All organisms maintain stable internal conditions such as body temperature & water content
  • Stable level of internal conditions called homeostasis  

Reproduction & Inheritance  

  • All organisms reproduce new organisms like themselves by transmitting hereditary material to their offspring  
  • DNA (Deoxyribonucleic acid) is a large molecule containing the hereditary material of the cell


  • In unicellular organisms like bacteria, DNA exists as a single loop or chromosome in the cytoplasm  


  • In multicellular organisms, DNA is enclosed in a membrane known as the nucleus 
  • Genes are short segments of DNA the carry the instructions for a single trait of an organism  
  • DNA of a cell contains all of the genes (instructions) it will ever need  
  •  All body cells have a complete set of DNA (genome), but different types of cells use certain genes from the set; example: Muscle cells have the genes to make thyroxine, but they don’t use these genes  
  • In sexual reproduction, an egg (ovum) is fertilized by a sperm to form a zygote so the new organism is made of cells with hereditary information from both parents  
  • In asexual reproduction, cells copy their DNA & split so all new cells are identical  


  • Populations of organisms change over time or evolve (Theory of Evolution)  


  • Natural selection or “survival of the fittest” is the process that drives evolution  
  • Organisms with favorable traits are better able to survive & reproduce  
  • The survival of organisms with favorable traits causes a gradual change in populations of organisms over many generations  
  • Evolution by natural selection is driven by competition for resources such as food, habitat, mates  

Interdependence of Organisms  

  • Ecology is the study of the interaction of organisms with each other and their environment  
  • Sunlight is the ultimate energy for all organisms  
  • Energy from the sun is passed from one organism to another; producers (plants) to herbivore (plant eater) to carnivore (meat eater) to decomposers (break down dead organisms)  


  • Abiotic (nonliving factors) such as air, water, energy, soil, temperature, & minerals are also needed for survival  
  • Biotic factors include all living things on earth (plants, animals, fungi, microorganisms)  
  • Biosphere supports life & includes the biotic (all organisms) & the abiotic (all nonliving factors) on earth  
  • Organisms respond to their environment by:
    * Fleeing
    * Adapting
    * Dying
  • Most organisms can survive a temporary change, but permanent change can lead to extinction (dinosaurs)  
  • Thousands of species are listed endangered (population so small could become extinct)  
  • Human interference is the main cause for endangerment & extinction
    * Pollution of land, air, and water
    *Hunting for sport, food, and commercial products also threatens the survival of many organisms
    * Clear-cutting rain forests
    * Diverting rivers & lakes
    * Draining wetlands (everglades)
    *Global Warming  
  •   Endangered organisms can be protected & returned to larger population size (American Bison almost wiped out –60 million to 250 in 90 years- now several thousand herds)  


  • Species is a group of organisms so similar to one another that they can interbreed & produce fertile offspring  
  •  Extinction of any species upsets the balance of nature (Almost extinct Pacific Yew tree found to contain chemical used to treat cancer)  


Matter, Energy, & Organization  

  • Organisms are highly organized, maintain internal order, & require a constant energy supply
  • Plants & unicellular organisms with chlorophyll capture sunlight through photosynthesis & store it in food to be used by other organisms  
  • Autotrophs or producers use sunlight, water, & carbon dioxide to make glucose (energy rich sugar) & oxygen – photosynthesis  

  • Heterotrophs (consumers) feed on producers or other consumers to get energy & release carbon dioxide  

   Biology affects life in many ways  

  • Biotechnology uses organisms to make products needed by people (human insulin made by bacteria)
  •   Fossils fuels (coal, oil, & natural gas) provide energy & materials such as nylon & polyester  


  • Animal products such as wool, silk, and leather make clothing  
  •  Wood provides energy & shelter for us, but endangers other animals (spotted owl) when forests are cut  
  • New medicines, better water treatment & garbage disposal improves our health