MCAS: Grade 8 (II)
April 21, 2015
Natural Selection: Question 19 – Session 2 – 2014
1. Natural Selection
Genetically, all species are not created equal and neither are the individuals within a species. Differences in the DNA of any single individual are created by a variety of mechanisms including the recombination of entire tracks of DNA as well as single “point” mutations. On the face of things, these changes may not result in variations which are immediately apparent. Only under conditions of environmental stress or “selective pressure” might responses differ within a population. The following animation depicts the reaction of a random bacterial culture to a chemical change in the environment.
While 99% of the population is wiped out, mutations in select individuals convey a resistance to the toxic effect of the bactericidal chemical. These mutants begin to expand within the environment until a new challenge is presented.
The bactericide-antibiotic resistant strain is now free to proliferate and expand. The key elements of natural selection are, therefore, an internal genetic preparedness for meeting the challenges of changing conditions coupled with the ability to reproduce within the confines of these new environments. Thus, answer D for Question 19 makes the most sense.
Fun Reading from My Library:
What on Earth Evolved? 100 Species that Changed the World (2009)
Christopher Lloyd (Author), Andy Forshaw (Illustrator)
Bloomsbury Publishing London, UK W1D 3QY
Evolution: The Story of Life on Earth (2011)
Jay Hosler (Author), Kevin Cannon (Illustrator), Zander Cannon (Illustrator)
Farrar, Straus, and Giroux NY, NY 10011