" The Big Picture!" by Mr C

VSB Science Blog

Chapter Two Notes

Chapter Two Notes


Big Ideas in Biology: Change with Time


What is the significance of a change with time? How do we define evolution? What are some patterns of evolution and how can we prove that a change actually occurred. How are species formed or changed with time? These are the primary questions in chapter two.


Evolution is:

  • an explanation for the increase in biological diversity.


  • a theory that describes how current species are descendants of species of previous generations.


  • is a process by which populations show change (gradual or punctual) over several generations.


  • a basic definition of evolution is a gradual change of species with time.


First of all, a change within a species of organisms can be noted by a change in structure, habitat or even behaviour. This change can be refered to as an adaption.


When is a population of organisms considered to be adapted to it’s environment?

( this is a great question to remember..)


  • Even though the environment may change to a small degree, successive generations of offspring thrive.


  • The most desirable adaptations are those which give an organism a advantage to survive.


A way of showing a longer duration of change with time is to examine remnants of previous generations. These remnants can be actual bones or imprints of organisms. This preserved bits of structural or imprinted information are refered to as fossils.

Ø  Fossil records provide the most direct evidence of evolution

  • Most fossils are found in sandstone and limestone.
  • Problems with fossils:

There are gaps in fossil records

  • due to movement of the earth
  • no know record of organism in that time period
  • one organism eating another at one location and then depositing the remnant at another location


Some specimens are not complete organisms


The process of fossilization requires a specific type of soil


Some specimens are too soft to make a fossil

  • for example a shelled organism would make a better imprint than a worm)


With the advent of genetic research and cell biology, there are now new ways to establish indirect proof of a change with time:


  1. Embryology:
  • Examining the stages of development of an embryo in a variety of species, there appears to be some similarities. This similarity was noted by …who said “     “. Basically, the development of an embryo shows the species phylogenic or family history.


  1. Examining structures

There are three terms relative to structures that are useful for comparing species.


This table may be helpful for comparing homologous to analogous structures.

Structure type and example Structure Function
Homologous similar different
Analogous different similar
Vestigial present no function


  1. Physiology


  1. Biochemistry


Pattern of Evolutions:



If an organisms develops similar structures due to living in similar environments but they are separated due to being geographically isolated, this is an example of convergent evolution. Basically two distinct species show a similarity, although they are not genetically link. The term converge means to come together.



If an organism is separated by geographic barriers, then it will not be able to reproduce with other species. This population will diverge from the original species that it was separated from.


Sources of change


The concept of speciation


The term “speciation” refers to the formation of new species. New species are formed when one population of the same species is separated from another and there is no exhange of genetic information between the two populations.


what can cause speciation?


Isolating mechanisms that may lead to speciation

( remember diagram in class about sea snails)

  • geographic
  • ecological
  • behavioral
  • morphology
  • genetic


While many of these isolation mechanisms may be crossed, for example a snail may adapt from one ecological environment to another. The one barrier that cannot not be crossed in natural situations is the reproductive or genetic barrier.

posted by Marc Bernard Carmichael in Biology Eleven,Biology Eleven Notes and have No Comments

No comments

Leave a Reply

Your email address will not be published.