Question 1

Which of the following best explains the origin of mitochondria in eukaryotic cells according to the endosymbiont theory?

Accepted Answer

Mitochondria originated from an aerobic bacterium engulfed by an ancestral cell, forming a symbiotic relationship.

Question 2

Which evidence supports the endosymbiotic origin of mitochondria and plastids?

Accepted Answer

Mitochondria and plastids have their own DNA, which is similar to bacterial chromosomes.

Question 3

Which sequence best describes the evolutionary steps leading to photosynthetic eukaryotes?

Accepted Answer

An ancestral anaerobic prokaryote engulfs a heterotrophic aerobic prokaryote; the descendant aerobic eukaryote then engulfs a photosynthetic prokaryote.

Question 4

Which organelles most likely arose from endosymbiosis?

Accepted Answer

Chloroplasts and mitochondria

Question 5

What feature of mitochondria and plastids supports their bacterial origin?

Accepted Answer

They have circular DNA lacking histones.

Question 6

Which of the following is thought to be the likely identity of the host cell that ultimately led to the origin of the eukaryotes?

Accepted Answer

A heterotrophic archaean

Question 7

Which of the following correctly describes an example of secondary endosymbiosis?

Accepted Answer

A red alga is ingested by a heterotrophic eukaryote.

Question 8

Which of the following is NOT a feature shared by mitochondria, plastids, and bacteria?

Accepted Answer

Presence of a nucleomorph

Question 9

The plastids of red algae and green algae have two membranes. What does this suggest about their evolutionary origin?

Accepted Answer

They evolved from cyanobacteria engulfed by a eukaryote.

Question 10

Which of the following best describes the serial endosymbiosis hypothesis?

Accepted Answer

Mitochondria arose first in eukaryotes, followed by plastids in certain lineages.

Question 11

Which of the following is a real-world example of secondary endosymbiosis?

Accepted Answer

A chlorarachniophyte containing a nucleomorph within its plastid.

Question 12

Which of the following features allowed early eukaryotes to have irregular forms and predatory behavior?

Accepted Answer

A cytoskeleton

Question 13

Which equation best represents the timeline for the appearance of eukaryotes in the fossil record?

Accepted Answer

$$t = 1.8 	ext{ BYA}$$

Question 14

Which of the following is a key difference between primary and secondary endosymbiosis?

Accepted Answer

Primary endosymbiosis involves a prokaryote engulfed by a eukaryote, while secondary endosymbiosis involves a eukaryote engulfed by another eukaryote.

Question 15

Which of the following supergroups includes organisms that evolved from early photosynthetic eukaryotes?

Accepted Answer

Archaeplastida

Question 16

Which of the following best explains why aerobic endosymbionts were beneficial to anaerobic host cells as oxygen increased in the atmosphere?

Accepted Answer

Aerobic endosymbionts allowed host cells to utilize oxygen for energy production via cellular respiration.

Question 17

Which of the following is NOT a novel biological feature that evolved during the early diversification of eukaryotes?

Accepted Answer

Binary fission

Question 18

Which of the following best describes the relationship between the host cell and the endosymbiont in the origin of mitochondria?

Accepted Answer

The host cell engulfed an aerobic bacterium, which became a permanent, beneficial resident.

Question 19

Which of the following best explains why mitochondria and plastids are considered 'combination' organisms?

Accepted Answer

They contain genes and cell characteristics derived from both archaea and bacteria.

The Origin and Diversification of Eukaryotes (Campbell Biology in Focus, Chapter 25)

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