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Lecture 3

BIOLOGY 1M03 Lecture Notes - Lecture 3: Cell Theory, Natural Selection, Robert HookePremium

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Jon Stone

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BIOLOGY 1M03 - Lecture 3 - The Tree of Life
Key Concepts of Life:
The main concept of life is that organisms are ‘alive’, meaning they display the
ability to grow, metabolize, reproduce, respond to the environment by processing
information, and, collectively as populations, evolve.
The cell theory, another concept of life, involves the idea that all organisms
comprise cells and that all cells derive from preexisting cells.
The theory of evolution by natural selection involves the idea that species change
through time because individuals with particular heritable traits survive and
produce offspring more effectively than do other individuals, continuing to pass
on those traits from generation to generation.
A phylogenetic tree is a diagram that may be interpreted as representing
evolutionary relationships, concluded from research, among species.
Phylogenics (translates into ‘tribe sources’) can be established by
analyzing similarities and differences in traits. Species sharing
distinctive traits are situated in close proximity on phylogenetic
Scientific Theories in Biology:
Biologists, and scientists in general, ask questions, generate hypotheses to
answer them, and design experiments or make observations that test the
predictions made by competing hypotheses, creating scientific theories.
Scientific theories are made of two components: patterns observed in the
natural world, and mechanisms or processes identified that produce
A hypothesis is a proposal; a prediction is something that can be
measured and must be correct if a hypothesis is valid.
Louis Pasteur, a French chemist and microbiologist, demonstrated
experimentally that cells arise from cells and not by spontaneous
Pasteur’s experimental setup was effective because the two
groups he involved differed in only the one factor being tested:
exposure to preexisting cells.
For his experiment, Pasteur simply placed nutrient broth in a
straight-necked flask with a nearby opening to the outside of the
glassware, exposing the living organisms within the broth to the
outside, and vice versa. He boiled the flasked, killing any living
cells, and preexisting cells from the outside simply made their way
in through the opening, and repopulated.
Pasteur then repeated the experiment, with only a swan-
necked flask with the opening stretching far from the broth.
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