Mastering Biology RQ 19: Endosymbiosis and Eukaryote Evolution

The chloroplasts of all of the following are thought to be derived from ancestral red algae, except those of a. green algae. b. diatoms. c. dinoflagellates. d. brown algae. e. golden algae.

A

If it were possible to conduct sophisticated microscopic and chemical analyses of microfossils found in 3.2-billion-year-old stromatolites, then one should be surprised to observe evidence of which of the following within such microfossils? I. double-stranded DNA II. a nuclear envelope III. a nucleus IV. a nucleolus V. ribosomes a. III only b. II and IV c. II only d. II, III, and IV e. all five of these

B

Which of these observations gives the most support to the endosymbiotic theory for the origin of eukaryotic cells? a. the observation that some eukaryotic cells lack mitochondria b. the similarity in size between the cytosolic ribosomes of prokaryotes and the ribosomes within mitochondria and chloroplasts c. the existence of structural and molecular differences between the plasma membranes of prokaryotes and the internal membranes of mitochondria and chloroplasts d. the size disparity between most prokaryotic cells and most eukaryotic cells

B

Select the correct statement about photosynthesis by primary producers. a. Cyanobacteria carry out more of the world's photosynthesis than protists do. b. Photosynthetic protists and prokaryotes carry out the majority of the photosynthesis in aquatic communities. c. Land plants carry out over 80% of the world's photosynthesis.

B Scientists estimate that 30% of the world's photosynthesis is performed by aquatic protists. Photosynthetic prokaryotes contribute another 20%, and land plants are responsible for the remaining 50%. Read about the key roles that protists play in ecological communities.

According to the endosymbiotic theory of the origin of eukaryotic cells, how did mitochondria originate? a. when a protoeukaryote engaged in a symbiotic relationship with a protocell b. from infoldings of the plasma membrane, coupled with mutations of genes for proteins in energy-transfer reactions c. from engulfed, originally free-living proteobacteria d. from the nuclear envelope folding outward and forming mitochondrial membranes e. by secondary endosymbiosis

C

Which of the following was derived from an ancestral cyanobacterium? a. mitochondrion b. mitosome c. chloroplast d. hydrogenosome e. Two of the responses above are correct.

C

Which of the features below are found in all protist lineages? a. Organelles that arose by secondary endosymbiosis. b. Plastids c. Mitochondria

C Scientists used to think that some groups of protists lacked mitochondria, but they have since discovered that many of these protists have at least modified mitochondria. Read about the diplomonads and parabasalids.

Archaeplastids, which include red and green algae and land plants, are thought to have descended from a heterotrophic protist that engulfed a(n) _____. a. slime mold b. alpha proteobacterium c. cyanobacterium d. apicomplexan e. archaean extremophile

C Structural and molecular biological evidence supports the idea that endosymbiotic cyanobacteria gave rise to the chloroplasts found in red and green algae and land plants.

Which of the following statements supports the hypothesis of an endosymbiotic origin of mitochondria? a. Diplomonads have modified mitochondria called mitosomes. b. Some algae contain plastids surrounded by four membranes. c. Each mitochondrion has its own DNA molecule.

C The fact that mitochondria have their own DNA provides strong support for the hypothesis of an endosymbiotic origin of mitochondria.

The chloroplasts of land plants are thought to have been derived according to which evolutionary sequence? a. cyanobacteria → red algae → green algae → land plants b. cyanobacteria → green algae → fungi → land plants c. red algae → brown algae → green algae → land plants d. cyanobacteria → green algae → land plants

D

The earliest organisms were most likely _____. a. eukaryotic b. plants and fungi c. multicellular d. prokaryotic e. proto-cells

D Prokaryotes originated a few hundred million years after Earth's crust cooled and solidified.

Which of the following is true of secondary endosymbiosis? a. It is indicated by the presence of a double membrane surrounding the endosymbiont. b. An organism containing one endosymbiont engulfs another organism, and that organism becomes an endosymbiont. c. It is indicated by the presence of a nucleomorph. d. An organism containing an endosymbiont is engulfed by another organism and becomes an endosymbiont. e. It is indicated by the presence of a mixotroph.

D This is a description of secondary endosymbiosis. In many cases secondary endosymbionts are surrounded four membranes.

All protists are a. symbionts. b. mixotrophic. c. monophyletic. d. unicellular. e. eukaryotic.

E