Lecture 10 Flashcards
in what year .. earliest cells identified prokaryotes found in stromatolites
3.5 billion years ago
in what year ..Homo sapiens
195,000 years ago
sequence of events ?
Prokaryotes → oxygen revolution → single-celled eukaryotes → way more oxygen →multicellular eukaryotes →Cambrian explosion→ colonization of land by plants and fungi→ colonization of land by animals → Homo sapiens
Fossils?
the remains or traces of ancient organisms left in sedimentary rock, or ice, sand or other places
what info do fossils give?
Fossils give you some information on where and when these organisms lived, as well as when there were extinctions or an arrival of a new species.
The richest source of fossils are ___, that get deposited into layers called __
sedimentary rocks
strata
The fossils found in the bottom stratum were formed __, then more rocks got deposited, covered these fossils, then more fossils were formed on top.
first
The fossils at the top are the __, while those at the bottom are the __.
youngest
oldest
How can the date of fossils be determined
The dates of fossils can be determined using carbon dating (if <50,000 years old).
How can the date of rocks be determined
The dates of the rocks that fossils are found in can be estimated using radioisotopes that are not found in living organisms, but are found in some rocks
Identify the organism that is thought to have caused the oxygen revolution.
Prokaryotes :
Cyanobacteria
what are Cyanobacteria
the first photosynthetic autotrophs to release oxygen into the atmosphere around 2.7 billion years ago. Even today, Cyanobacteria are the only living photosynthetic prokaryotes that generate oxygen.
anaerobes ?
an organism that grows without air, or requires oxygen-free conditions to live.
first eukaryotes appeared to be __ organisms that lived in __.
single-celled
water
The first eukaryotes are thought to have been __
Protists
Where did the eukaryotes come from?
Eukaryotes are hypothesized to have arisen from prokaryotes.
HOW did eukaryotes arise?
It has been proposed that some of the membranes around organelles were formed when the plasma membrane of a prokaryotic cell folded inwards. These infoldings resulted in the formation of an early endomembrane system
the endosymbiont theory ?
which proposes that eukaryotic mitochondria and chloroplasts evolved from a symbiotic relationship between two or more cells.
The bigger eukaryote ingests the smaller prokaryote.
The smaller prokaryote would then have become part of the larger eukaryotic cell and be passed on when the new eukaryotic cell divided.
The bigger eukaryote _____the smaller prokaryote.
ingests
Mitochondria have been hypothesized to have arisen when __
a eukaryote ingested an aerobic bacterium
chloroplasts would have arisen when __
a photosynthetic bacterium (cyanobacterium) was ingested by a cell that contained mitochondria.
The advantage of having mitochondria is __
the ability to do cellular respiration (produces more than 10x the amount of ATP compared to fermentation), which is possible now that the free-living cyanobacteria have delivered oxygen to the atmosphere.
Because all eukaryotic cells have mitochondria, but not all eukaryotes have chloroplasts, it is thought that __
mitochondria evolved before chloroplasts
prokaryotes have __ chromosomes
circular
Circular chromosome?
chromosome in bacteria, archaea, mitochondria, and chloroplasts, in the form of a molecule of circular DNA, unlike the linear chromosome of most eukaryotes.
__are the ancestors to plants, animals, and fungi
Protists
Cambrian explosion:
About 535 million years ago, the animal kingdom underwent a massive change, with large numbers of new animals formed (in water).
Fossil records suggest that prokaryotes were on land __ years ago, but __ , __, and __ didn’t arrive on land until about 500 million years ago.
~1 billion
plants, fungi, and animals
Just as Cyanobacteria released O2,___caused another large increase in the levels of O2.
the arrival of photosynthesizing eukaryotes, both in the water and on land
Ultraviolet radiation forms __ from __in the upper atmosphere so the presence of O2 allowed for the production of the __.
O3 (ozone)
O2
ozone layer
Ozone prevents much of the __ from reaching Earth, reducing the amount of __
UV
UV-induced mutagenesis (genetic mutations).
__ enabled organisms to live in surface waters and on land, since they were now somewhat protected from the UV rays.
the formation of the ozone layer
Earth experienced __ mass extinction events
5
Over __ of marine life and __ of terrestrial life went extinct during the Earth’s largest mass extinction
90%
70%
limitations to the use of fossils
- deciding when such an old (billions of years old) fossil is really a fossil, and not just an artefact made up of crystals or other irregularities in the sediment itself
the first cells were likely to be ____and that they arose in _-.
heterotrophic prokaryotes
water
the earth is about __ years old.
4.6 million
