Species are a group of organisms that have
5–T HE N ATURE OF L IFE ON E ARTH common characteristics (and can interbreed).
5.1 D EFINING L IFE They are genetically distinct
o Genus (generic) Species (Specific): Homo
WHAT ARE THE GENERAL PROPERTIES OF LIFE ?
We focus our search on life that is similarWtHAT IS THE ROLE OF EVOLUTION IN DEFINING LIFE?
own. We do not look for silicon life because we
don’t have any examples on Earth. AN ANCIENT IDEA
Evolution means “change with time”
SIX KEY PROPERTIES
Order: Materials in Anaximander said life arose in water and evolved
into more complex forms.
living organisms always Aristotle said species are fixed and independent
exhibit some type of and do not evolve or go extinct.
order. For example,
molecules in living cells Lamarck suggested that fossils were related by
evolution. Life adapted by using some traits more
are not scattered and passing them onto kids. Like Arnold having
randomly about but
instead are arranged in super babies.
Fossils prove it occurred, Darwin proved HOW
patterns that make cell
structures. THE M ECHANISM FOR E VOLUTION
Reproduction: Living Charles Darwin described observations of living
organisms and showed how they supported that
organisms reproduce or are products of evolution does occur
reproduction Overproduction and competition for survival:
mules can not reproduce (horse/donkey) but are
still living organisms populations can make more offspring than
environment can support but can’t due to limited
viruses cannot reproduce by themselves but can resources. This leads to competition
infect other organisms and use them
prions cause other proteins to become abnormal Individual Variation: individuals are unique
and some have traits that are more competitive
Growth and Development: Living organisms unequal reproductive success: those with best
grow and develop directed by genetics
suited traits will survive.
Energy Utilization: Living organisms use enIt is this unequal reproductive success that is called
to create order, reproduce, and grow. natural selection. This explains how species change in
Without an input of energy, systems tend response to their environment – by favouring traits that
towards disorder (second law of improve adaptation
EVIDENCE FOR EVOLUTION BY NATURAL SELECTION
Reponse to the environment: Living organisms An ancestral pair of finches reached the
respond to environment Galapagos from the mainland and over time they
adapted to the different islands to become the
Evolution: Involves ability to reproduce and and different species.
He also discovered fossils of extinct organisms
respond to environment. Differences in
organismal traits mean that some has a survival that were related to modern species
advantage over others. Those traits become
dominant. He made two inferences: natural selection can
explain the differences between species, and can
also produce new species that replace old ones.
He also found evidence for evolution by looking
at artificial selection.
o For example, wild mustard can be
selected to make other vegetables.
o Natural selection also allows resistant
bacteria to become more common
THE MOLECULAR BASIS OF EVOLUTION
Evolution by natural selection means species that
have adaptations to their environment survive
and pass on hereditary traits to offspring.
The medium for natural selection is DNA.
W HAT IS LIFE?
Something that can reproduce and evolve
Darwin’s theory does not tell us how life started,
so we assume at one point, chemistry became
biology. EARTH LIFE IS CARBON BASED
5.2 C ELLS : THE BASIC UNIT OF LIFE
Life on Earth is made up of more
WHAT ARE LIVING CELLS ? than 20 elements
o C, O, H, N accounts for
All organisms are composed of cells and
surrounded by a membrane 96%
Some are single celled others are multicellular A cells structure and function is
due to carbon
All cells pass on their hereditary data through
DNA Why is carbon so important?
o It can bind to four
This led to the conclusion that all life on Earth atoms at a time
shares a common ancestor
o It can to itself in
o It can bind in various
o It can form double
WATER o It can form rings
Used by organisms – plants use it for o Not too strong, not too weak
Used as a solvent – transporting NON -CARBON BASED LIFE
mechanism Silicon is the only element besides carbon
Is a polar molecule due to slightly positive that can bind to 4 atoms
hydrogen and slightly negative oxygen Silicon has three strikes against it
o This makes it a great solvent o Bonds formed are weaker
o Does not form double bonds
Properties o Mixed with oxygen it is solid, immobile
1. Water is abundant 1000x more abundant yet carbon is basis of life
2. It is good at dissolving – can carry molecules It turns out carbon is common in the universe
3. High heat capacity and high vaporization WHATARETHEMOLECULARCOMPONENTS
energy – regulate temperature
4. High surface tension – keeps cells together OFCELLS?
5. Breaks down in UV light – produce ozone CARBOHYDRATES
6. Water floats when it is ice – insulated water
below for organisms Polymers of monosaccharide’s
7. Liquid for 100 degree range Used for energy storage