Textbook Notes (362,755)
Canada (158,052)
York University (12,350)
Biology (939)
BIOL 1500 (49)
all (6)
Chapter 10


4 Pages
Unlock Document

York University
BIOL 1500

10.1 Life: ability to replicate and by the presence of some sort of metabolic activity Atmosphere contained large amounts of CO , ni2rogen, methane, ammonia, hydrogen, and hydrogen sulfidethis environment might have served as the cradle of life, warm little pond Urey-Miller Experiment (Phate 1): Formation of small molecules containing carbon and hydrogen 1) Created model of warm little pond a. Flask of water with H 2 CH 4methane), and NH (Am3onia) 2) Subjected warm little pond to sparks to simulate lightening 3) Cooled atmosphere so any compounds in it would rain back down into water 4) Waited to examine contents of water Within days organic molecules (including amino acids) in their primordial sea Under conditions similar to those on early earth, small organic molecules form, and these molecules have some chemical properties of life 10.2 RNA World (Phase 2): Formation of self-replicating, information-containing molecules  Researchers discovered a molecule that could function as an enzyme that links together nucleic acids  RNA world hypothesis: proposes that the world may have been filled with RNA based life before it became filled with the DNA based life we see today  RNA molecules are on the border o Replicate-first condition for life o Don’t carry out metabolism-second condition for life Microspheres (Phase 3): The development of a membrane, enabling metabolism and creating the first cells  Critical phase in the generation of life from non-life: the development of a membrane that separated these self-replicating small molecules from their surroundings, compartmentalizing them into cells and making metabolic activity possible  Evidence supports the idea that self-replicating molecules-possibly RNAs may have formed in earth’s early environment and later acquired or developed membranes, enabling them to replicate and making metabolism possible, the two conditions that define life 10.3  Biologists use the word species to label different kinds of organisms  According to the biological species concept species are populations of organisms that interbreed, or could possibly interbreed, with each other under natural conditions, and that cannot interbreed with organisms outside their own group. Important clarifications 1) Members of a species are either actually or could possibly interbreed a. Just because two individuals are physically separated they aren’t necessarily in different species b. The definition refers to natural conditions, not concerning itself with breeding in captivity  The concept is only concerned with reproductive isolation o The inability of individuals from two populations to produce fertile offspring with each other, thereby making it impossible for gene exchange between the populations to occur Prezygotic barrier  Impossible for individuals to mate with each other and/or make it impossible for the male’s reproductive cell to fertilize the female’s reproductive cell o Different courtship rituals o Sufficient physical differences they are unable to mate o Physical or biochemical factors prevent the male gamete from fertilizing the female gamete Postzygotic barrier  Occur after fertilization and generally prevent the production of fertile offspring from individuals o Mules: hybrid offspring of horses and donkeys and although they can survive, they cannot breed with each other or produce offspring 10.5 The biological species concept is remarkably useful when describing most plants and animals, it falls short of representing a universal and definitive way of distinguishing many life forms  Difficulties in classifying a sexual species: useless distinction for the asexual species  Difficulties in classifying fossil species: difference in size and shape of fossil bones can never reveal whether a reproductive isolation existed  Difficulties in determining when one species has changed into another: may not be possible to identify the exact point at which the change occurred from one species evolving to an other  Difficulties in classifying ring species: sufficient differences physically and behaviorally in so far that they become reproductively incompatible within their species. Because the two non-interbreeding populations in the north are connected by gene flow through other populations farther south, there is no exact point at which one species stops and the other begins  Difficulties in classifying hybridizing species: hybridization has been observed among plant species and among animal species. This phenomenon fits with the biological species concept, but what about when hybrids have high survival rates and are fertile whether interbreeding with other hybrids or with individuals from either of the parental species. These shortcomings have prompted the development of several alternative approaches to defining what a species is. The most commonly used alternative, morphological species concept  Characterizes species based on physical features such as body size and shape.  Can be used effectively to classify asexual species  Does
More Less

Related notes for BIOL 1500

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.