Endosymbiotic theory Knowledge-Based Download PDF

Questions

1. 1.

   According to the endosymbiotic theory and phylogenetic analyses of gene sequences, which groups of prokaryotes share the closest common ancestry with mitochondria and chloroplasts, respectively?

   • A) Cyanobacteria and spirochetes
   • B) Alphaproteobacteria and cyanobacteria
   • C) Betaproteobacteria and actinobacteria
   • D) Methanogenic archaea and cyanobacteria
2. 2.

   According to the endosymbiotic theory, which statement correctly explains the origin of the double membrane surrounding mitochondria and chloroplasts?

   • A) Both the inner and outer membranes were synthesized de novo by the host cell's endoplasmic reticulum following the uptake of the endosymbiont.
   • B) The inner membrane derived from the plasma membrane of the engulfed bacterium, while the outer membrane derived from the host cell's endocytic vesicle.
   • C) The outer membrane originated from the peptidoglycan cell wall of the engulfed bacterium, while the inner membrane arose from the host cell's nuclear envelope.
   • D) The inner membrane formed through the invagination of the host cell's vacuolar membrane, while the outer membrane was secreted by bacterial genetic material.
3. 3.

   Which observation regarding the sensitivity of mitochondria and chloroplasts to pharmacological inhibitors provides evidence supporting the endosymbiotic theory?

   • A) Their protein synthesis is completely blocked by cycloheximide, which selectively inhibits eukaryotic cytosolic ribosomes.
   • B) Their translation cycles rely exclusively on host-supplied cytoplasmic transfer RNAs and nuclear ribosomal subunits.
   • C) Their translation is inhibited by antibacterial antibiotics like chloramphenicol rather than inhibitors of eukaryotic ribosomes.
   • D) Their polypeptide elongation is disrupted by antifungal agents that specifically bind eukaryotic elongation factor 2.
4. 4.

   According to the serial endosymbiotic theory, which observation best explains why the acquisition of mitochondria is thought to have preceded the evolution of chloroplasts?

   • A) Chloroplasts contain larger genomes with significantly more bacterial genes than mitochondria.
   • B) Nearly all eukaryotic lineages contain mitochondria or related derived organelles, whereas chloroplasts are found only in photosynthetic clades.
   • C) Mitochondria possess an inner membrane derived from the ancestral host cell, while chloroplast membranes are entirely bacterial.
   • D) Chloroplasts undergo independent binary fission, whereas mitochondrial division is completely controlled by host nuclear mitosis.
5. 5.

   According to the endosymbiotic theory, which feature of mitochondria and chloroplasts provides direct evidence that they originated from ancestral free-living prokaryotes?

   • A) The presence of a nuclear membrane enclosing their genetic material
   • B) The ability to synthesize linear chromosomes associated with core histone proteins
   • C) The presence of a single-layer phospholipid membrane derived from the host endoplasmic reticulum
   • D) The presence of circular DNA molecules and 70S ribosomes similar to those found in bacteria