Origin of (i) sex and (ii) multicellular organisms

Question 1

is origin of life Panspermia or simple organic chemistry on early Earth

Answer 1

-Most likely the latter occurring in the ‘primordial soup’
-Organic chemistry leads to prokaryote life via RNA World (with mutation combined with neo-Darwinian evolution leading to origin and refinement of metabolism).

Question 2

Rocks of suitable age contain three types of fossil evidence for prokaryote life, they are:

Answer 2

1) Fossil stromatolites- colonies of different types of prokaryote
2) Fossil microorganisms (2a silicified in cherts)
2) Fossil microorganisms (2b resistant cell walls called acritarchs preserved in siltstones)
3) Carbonaceous matter that can be identified chemically as the product of ancient life

Question 3

why were early signs of o2 being produced bad for prokaryotes

Answer 3

-only knew life and only evolved in anaerobic conditions

Question 4

what is the origin of eukaryotes coincident with

Answer 4

-the atmosphere becoming aerobic
-probably happens due to as series of symbiotic events including various prokaryotes

Question 5

by 950-850 Ma what do architarchs reach

Answer 5

-their zenith in terms of diversity and size
-From 850 Ma Acritarchs suffer a major wane during various extinction events

Question 6

whats the snowball/ slush ball earth

Answer 6

-mass glaciation which pretty much covered the whole earth- life survived through
-atmosphere changed from greenhouse- glacial
-glacial deposition from equator to whole planet- so much o2 in atmosphere, methane taken out
-froze the whole planet therefore
-The boulder clays representing the glaciations are bounded below by carbonates and above by cap carbonates.
-The carbonates below have exceptionally high C-isotope values. (Due to continental break up producing narrow seaways with enhance C burial. These reduced atmospheric CO2 leading to the glaciations.)
-Banded Iron Formations occur within the boulder clays–for the first time in 1.8 billion years iron accumulates in the oceans.
0The cap carbonates have exceptionally low C-isotope values. (Due to rapid accumulation and/or absence of organisms and/or a burst of methane that ended the glaciations.)

Question 7

what are the two extensive glaciations extending into equatorial latitudes that produce snowball/slushball Earth scenarios

Answer 7

-Cryogenian (635-720 Ma)
-Marinoan Ice Age (635-650 Ma), Sturtian Ice Age (660-720 Ma)

Question 8

whats mitosis

Answer 8

-Involved in natural cell division (asexual reproduction) in unicellular organisms and natural cell division in multicellular organisms

Question 9

whats meiosis

Answer 9

-Sexual reproduction in unicellular or multicellular organisms

Question 10

how do variation occur in asexually reproducing organisms

Answer 10

-mutations
-In sexually reproducing organisms variation is due to mutation, independent assortment and crossing over

Question 11

what are the Four main theories regarding why sex evolved

Answer 11

-1) A method of adapting to change by evolving faster
-2) A method of fending off disease/parasites
-3) A method of repairing genes
-4) Historical accident

Question 12

do primitive eukaryotes asexually or sexually reproduce

Answer 12

-asexually

Question 13

problems with sex

Answer 13

-women gets pregnant- biologically useless for 9 months, therefore male finds another woman
-incredibly expensive
-mutations can be passed on- good when beneficial but bad when not
-mutatiosn make population more diverse
-if one mutation occurs in asexually predicting things, then this is bad

Question 14

when did multicellularity evolve

Answer 14

-by 1000 Ma.
-It evolved several times independently in different biological groups (various protists, plants, animals and fungi).
-It probably evolved via experimentation with colony formation.
-It has the advantage of division of labour.