Download Notes: Chapter 26

Notes: Chapter 26
Origin of Life and Classification
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I. Introduction to the History of Life
A. Life on Earth originated between 3.5 and 4.0 billion years ago.
i. The planet Earth formed about 4.5 billion
years ago.
ii. The oldest known rocks are 3.8 billion years old and
were found in Greenland.
iii. The oldest fossils found so far are about 3.5
billion years old and were found in Australia. These fossils are
of bacteria and resemble certain bacteria still found today.
B. Prokaryotes dominate evolutionary history from 3.5 to 2.0 billion years ago.
i. The earliest organisms were Eukaryotic. This means they lacked membrane bound
organelles and nucleus.
ii. Two main groups evolved during this time, the bacteria and the archaea.
C. Oxygen began accumulating in the atmosphere about 2.7 billion years ago.
i. The early photosynthetic prokaryotes that generate oxygen
are called cyanobacteria.
ii. Most atmospheric oxygen comes from the
water - splitting step of photosynthesis.
iii. As photosynthesis first evolved, free oxygen dissolved into
the surrounding water until the bodies of water
became saturated.
iv. Excess oxygen reacted with iron to form iron oxide.
v. When the dissolved iron precipitated, additional oxygen
began to “gas out” and accumulate in the atmosphere.
vi. Oxygen destroyed many prokaryotes, but those species who
evolved could survive the new atmosphere. Oxygen in the atmosphere also opened up new niches for
species who could tolerate it.
D. Eukaryotic life began by 2.1 billion years ago.
i. Eukaryotic cells are generally larger and more complex than prokaryotic cells.
ii. The oldest eukaryotic fossils are about 2.2 billion years old.
iii. Two organelles that most likely developed during this time are mitochondrai and chloroplast.
E. Multicellualr eukaryoties evoleve by 1.2 billion years ago.
i. The decendants of single celled protests began to develop. Multicellular organisms such as
algae, plants, fungi and animals.
ii. Multicellular organisms usually developed from a single cell called a zygote.
iii. Sexular reproduction probably developed during this time. Its evolution advantage is
genetic variation.
F. Animal diversity exploded during the early Cambrian period
i. Great diversity of animals began to appear around 543 million years ago.
ii. Most major groups (phyla) of animals appeared during the first 20 million years of the Cambrian
period.
G. Plants, Fungi and animals colonized the land about 500 million years ago.
i. Plants most likely colonized the land first. They kept many adaptations of aquatic plants that
prevented dehydration.
ii. Plants transformed the landscape and created new niches for animals.
II. The Major Lineages of Life
A. The five-kingdom system reflected increased knowledge of life’s diversity.
i. Linnaeus first developed a two kingdom system: Plants and Animals.
ii. The five kingdoms appeared in 1969 and includes
a. Plantae
b. Fungi
c. Animalia
d. Protista
e. Monera
iii. Two types of cells were defined:
a. Prokaryotic – has a membrane bound
nucleus and membrane bound organelles such
as mitochondria, ribosomes, etc (Plantae,
Fungi, Animalia, and Protista)
b. Eukaryotic – lacks a membrane bound nucleus and membrane bound organelles.
(Monera)
iv. The plantae, fungi, and animalia kingdoms were developed around nutrition.
a. Plantae – autotrophic (photosynthetic)
b. Fungi – heterotrophic by absorption
c. Animalia – heterotrophic by ingestion
v. Protista became a “dumping ground” for all organisms that did fit into any of the other
eukaryotic kingdoms.
B. Arranging the diversity of life into the highest taxa is a work in progress.
i. There are many problems with the five kingdom classification scheme.
ii. Evidence for two distict lineages of prokaryotes has led to a three – domain system. The three
domains are bacteria, Archaea and Eukarya.
iii. Molecular data and cladistics have determined that kingdom Protista is not a
true group. Protista could be broken down into at least five new kingdoms.
iv. Current classification schemes are simply hypothesis’s that continue to be tested and
changed over time.