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Chapter 1

BIOLOGY 1M03 Chapter Notes - Chapter 1: Capsaicin, Eukaryote, Estrous Cycle


Department
Biology
Course Code
BIOLOGY 1M03
Professor
Ben Evans
Chapter
1

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Chapter 1: Biology and the Tree of Life
The Cell Theory
Robert Hooke used a crude microscope to examine the structure of cork (bark tissue)
from an oak tree
In the cork, he observed small, pore-like compartments that were invisible to the naked
eye, which came to be called cells
Anton van Leeuwenhoek developed a much more powerful microscope and made the
first observations of single-celled organisms like Paramecium
Today, a cell is defined as a highly organized compartment that is bounded by a thin,
flexible structure called a plasma membrane and that contains concentrated chemicals
in an aqueous solution
The chemical reactions that sustain life take place inside cells
Where cells come from
o Most scientific theories have two components
The first describes a pattern in the natural world
The second identifies a mechanism or process that is responsible for
creating that pattern
o The complete cell theory is
All organisms are made of cells and all cells come from pre-existing cells
o At that time, most scientists believed in spontaneous generation, which was a
hypothesis (proposed explanation)
o The all-cells-from-cells hypothesis in contrast, maintained that cells do not spring
to life spontaneously, but are produced only when pre-existing cells grow and
divide
o Louis Pasteur set out to test the validity of the all-cells-from-cells hypothesis
o He created two treatment groups, a broth exposed to a source of pre-existing
cells and a broth that wasn’t
o The spontaneous generation hypothesis predicted that cells would appear in
both treatments while the other predicted that cells would appear in only the
treatment exposed to a source of pre-existing cells
o He used two glass flasks filled with the same amount of the same nutrient broth
o Both were boiled for the same amount of time to kill any existing organisms such
as bacteria or fungi
o However, one flask had a straight neck, while the other had a swan neck
o The straight neck flask was exposed to pre-existing cells after sterilization
(bacteria and fungi that cling to dust particles in the air)
They could drop into the nutrient broth because the neck of the flask was
straight
o In contrast, in the swan neck flask, water would condense in the crook of the
neck after the boiling treatment
o This water would trap any bacteria or fungi that entered on dust particles

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o The results showed that treatment exposed to pre-existing cells quickly filled
with bacteria and fungi
o This observation showed that the heat sterilization step had not altered the
nutrient broth’s capacity to support growth and because it supported the
hypothesis that growth started with pre-existing cells
o However, the treatment in the swan neck flask remained sterile
o The results showed that the all-cells-from-cells hypothesis was correct
Pasteur achieved this via an effective experimental setup
o The results had an important implication
If all cells come from pre-existing cells, it follows that all individuals in a
population of single-celled organisms are related by common ancestry
Similarly, in a multicellular individual, all of the cells present are
descended from pre-existing cells, tracing back to a fertilized egg
In this way, all of the cells in a multicellular organism are connected by
common ancestry
The Theory of Evolution by Natural Selection
Darwin and Wallace claimed that
o Species are related by common ancestry
o Characteristics of species can be modified from generation to generation
Evolution means that species are not independent and unchanging entities, but are
related to one another and can change through time
Natural selection explained how evolution occurs
Natural selection occurs whenever two conditions are met
o Individuals within a population vary in characteristics that are heritable, meaning
traits that can be passed on to offspring
A population is defined as a group of individuals of the same species
living in the same area at the same time
o In a particular environment, certain versions of these heritable traits help
individuals survive better or reproduce more than do other versions
If certain heritable traits lead to increased success in producing offspring, then those
traits become more common in the population over time
In this way, the population’s characteristics change as a result of natural selection acting
on individuals
Natural selection acts on individuals, but evolutionary change affects only populations
Ex. If tall wheat plants are easily blown down by wind, then in windy environments
shorter plants will tend to survive better and leave more offspring than tall plants do
Populations of wheat that grow windy environments tend to become shorter from
generation to generation, but in any given generation, none of the individual wheat
plants get taller or shorter as a result of natural selection
This short of change in characteristics of a population, over time, is evolution
Evolution occurs when heritable variation leads to differential success in reproduction
Fitness means the ability of an individual to survive and produce offspring
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