27.2 Eukaryotic Origins

Question 1

what do chloroplasts in plant cells closely resemble?

Answer 1

certain photosynthetic bacteria, specifically cyanobacteria

Question 2

symbiont

Answer 2

an organism that lives in closely evolved association with another species

Question 3

symbiosis

Answer 3

close interaction between species that live together, often interdependently

Question 4

endosymbiosis

Answer 4

a symbiosis in which one partner lives within the other

Question 5

based on Merezhkovsky’s hypothesis and Margulis findings, where did chloroplasts originate?

Answer 5

chloroplasts originated as symbiotic cyanobacteria that through time became permanently incorporated into their hosts

Question 6

what was the deciding evidence in support of chloroplasts’ being descendants of symbiotic cyanobacteria that lived within eukaryotic cells?

Answer 6

the DNA of chloroplasts is independent and different from nucleotides of the nuclei of photosynthetic eukaryotes but match with those of cyanobacteria

Question 7

eukaryotes were able to acquire photosynthesis because…

Answer 7

they could engulf and retain cyanobacterial cells

Question 8

what is a common symbiotic relationship in the eukaryotic domain?

Answer 8

symbiosis between a heterotrophic host and a photosynthetic partner

Question 9

mitochondria also originated as endosymbiotic bacteria from…

Answer 9

proteobacteria

Question 10

mitochondria/chloroplast genomes are greatly reduced compared to bacteria because:

Answer 10

genes from the original bacteria endosymbiont migrated to the nucleus

Question 11

what eukaryotic organisms don’t contain mitochondria?

Answer 11

single-celled eukaryotic organisms found in oxygen-free environments

Question 12

many eukaryotes that lack mitochondria contain small organelles called:

Answer 12

hydrogenosomes that generate ATP by anaerobic processes. hydrogenosomes are basically highly altered mitochondria adapted to life in oxygen-poor environments

Question 13

other anaerobic eukaryotes contain smaller organelles called:

Answer 13

mitoses that also appear to be remnant mitochondria; only has genes needed for assembling the clusters of iron and sulfur found in many proteins

Question 14

nuclear genes in Eukarya resemble those of Archaea because:

Answer 14

primoridal eukaryotic host cell was closely related to Archaea

Question 15

what are two hypotheses for the origin of the eukaryotic cell?

Answer 15

1. eukaryotic cells evolved from an ancestral archaeon and only later incorporated the proteobacterial cell that became a mitochondrion
2. eukaryotic cells evolved from a symbiosis between an archaeon and a proteobacterium. the proteobacterium became a mitochondrion.